No kitchen should be without this engaging, carefully researched and practical guide to the carbon in our food.

Prof Mike Berners-Lee

Author of How Bad are Bananas and There is no planet B

Did you know a latte is ten times worse for the climate than a cup of black coffee? Or that each calorie of beef requires 20 calories of feed? Or that an out-of-season tomato can have 80 times the climate impact of an in-season tomato? ‘Food and Climate Change Without the Hot Air’ provides a levelheaded, clear, and detailed picture of food emissions - a basic literacy we should all have in a time of accelerating climate consequence.

Peter Kalmus

NASA climate scientist and author of Being the Change: Live Well and Spark a Climate Revolution

This is a wonderful, fact-filled but readable book, full of clear explanations of the emissions associated with everything we eat, identifying what is important and what is negligible. I shall never look at spaghetti bolognese in the same way again.

Prof Sir David Spiegelhalter

Winton Professor of the Public Understanding of Risk at Faculty of Mathematics, University of Cambridge

Superb work. In ‘Food and Climate Change’ Sarah Bridle takes us on an eye-opening journey through the climate costs of our food and drink. From our buttered breakfast toast to teatime tikka masala this book lays bare the carbon footprints of the food choices we make every day. Succinct and well-researched, this book is a great resource for anyone who wants to know how to help tackle climate change with every meal.

Prof Dave Reay

Author of Climate-Smart Food

I have already used information and ideas from this book in helping a landowner develop a strategy for climate friendly food production, shaping a research project and deciding on a tasty dinner at my favourite Indian restaurant (approximately 1000g CO^2 equivalent and lower than the 3000g of a typical meal). ‘Food and Climate Change without the hot air’ will be an essential reference just as David Mackay’s companion volume guided many of us through the maze of information about energy.

David Baulcombe

Royal Society Research Professor, University of Cambridge

I’m rather glad, perhaps, that I hadn’t read Sarah Bridle’s book before dinner. It allows readers no refuge from the inescapable climatic consequences of their dietary desires because it quantifies them in such orderly and precise terms. It’s a marvel of synthesised research, clear explanation, and friendly wit.

Prof Philip Tabor

Former Director of the Bartlett School of Architecture, University College London

Sarah Bridle leads the reader through the climate impacts of our food, meal by meal. She uses the most up-to-date science and brings it to life in a personal, engaging and non-judgemental way.

Prof Pete Smith

Director of the Scottish Climate Change Centre of Expertise

Sarah Bridle has turned a page in our understanding of the impacts of our everyday eating habits with this ground-breaking, well-researched and accessible book. It will enable conscious decisions by individuals and industry concerned over the sustainability of our planet.

Prof David J Drewry

Non-Executive Director (Natural Science), UK Commission for UNESCO

Sarah Bridle provides information about the carbon footprint of foods many of us eat in an attractive, readable, well-researched and nicely-structured volume. I will be dipping into it regularly.

Prof Joanna Haigh

Former co-director of the Grantham Institute on Climate Change and the Environment, Imperial College London

…wonderful book - a fantastic contribution - just what is needed to start the very serious process of getting useful information to people so that they can make informed decisions about the emission associated with what they eat.

Prof Sir Ian Boyd

Former Government Chief Scientific Adviser, DEFRA and Professor of Biology, University of St Andrews

For people who want to eat sustainably Professor Bridle has the answers. The book takes this complicated topic and turns it into something readable, educational and fun.

James Hand

Co-Founder of Giki (a mobile app that helps you cut your environmental impact)

Bridle has given important information we should all know and understand about emissions and the food we waste, and included tips for how to reduce waste, which adds action to information.

Dr Liz Goodwin

World Resources Institute

This is a terrific book. It unpicks the connections between the food we eat and climate change in an engaging and straightforward manner with numerous notes to help you delve deeper. You will be amazed. Your preconceptions are often wrong.

Martyn Poliakoff

Research Professor in Chemistry, University of Nottingham

Sarah Bridle cuts through much of the confusion and complexity around the climate-change consequences of what we eat to provide a clear guide of how changes to diets can contribute to a more sustainable world.

Prof Sir Charles Godfray

Director of the Oxford Martin School, University of Oxford

Ever wondered whether beef produces over 100 times more carbon emissions than cabbage per gram? Then wonder no more as this book has the answer. An accessible approach to foot printing your meal to help you balance not just your diet but also your planetary impact!

Prof Aled Jones

Director of the Global Sustainability Institute, Anglia Ruskin University

How does the food we eat create climate change? This excellent, accessible handbook tells us; and guides us in personally tackling climate change through changing what we eat.

Prof Tim Benton

Director, Energy, Environment and Resources Programme, Chatham House

Sarah Bridle presents a crystal clear and very readable summary of how our meals through the day affect climate change. This should be an essential addition to all our cookery book shelves!

Dr John Ingram

Food Systems Programme Leader, Environmental Change Institute, University of Oxford

This book provides the information for students to make an educated decision about how to help turn around the climate crisis through food, free of political and personal baggage.

Jennie Hargreaves aka Mrs Physics

Scottish Institute of Physics, Physics Teacher of the year Award (2016)

I’ve been looking for ages for a guide as useful as this. This book provides a way to think about carbon emissions from food that is both clear and simple as well as providing the details and accuracy needed. The key points at the end of each chapter are really useful and will help many people to know how to make better decisions - without having to be absolutist.

Dr Julian Huppert

Former Member of Parliament for Cambridge and Director of the Intellectual Forum, Jesus College, University of Cambridge

Real food for thought! Sarah Bridle follows up the David MacKay’s pioneering approach to sustainability in an absorbing and thought-provoking analysis of cooking’s contribution to greenhouse gases. Very easy to follow and make your own judgements.

Prof Malcolm Longair

Emeritus Jacksonian Professor of Natural Philosophy, University of Cambridge

It’s all about quality ingredients beautifully prepared. And here you’ll be nourished by tasty hard facts and zesty stats, mellowed in a sauce of wit and clarity. A climate friendly kitchen essential.

Tom Heap

Rural Affairs Correspondent of BBC News, presenter of BBC Radio 4’s Costing the Earth and presenter on the BBC’s Countryfile and Panorama TV programmes

Have you ever wondered how you personally can help save the planet? Here are some answers!

Christian Holler

Professor at the Munich University of Applied Sciences and author of Erneuerbare Energien - ohne heiße Luft

Engaging and constructive -- this book puts climate facts on food choices into perspective and helps readers make climate-positive changes in the way they eat.

Baroness Jennifer Jones of Moulsecoomb

Green Party Life peer

If you want to understand how our food choices lead to carbon emissions, I thoroughly recommend this book. Using example meals, Bridle explains important but non-trivial issues such as intensive production versus grass fed cattle, the importantance of food waste, the impact of refrigeration and canning, and the nutrition in vegan food substitutes in a straightforward manner. Each chapter has useful tips and a ‘key points’ summary. Plus, for those of you (like me) who like to know more, there are more detailed notes and references. This book is an accessible overview and a handy reference all in one. It definitely gets a place on my shelf.

Nicola Terry

Energy consultant and Cambridge Sustainable Food volunteer

If you want to do the right thing for the planet but dont know how, this is the book for you. It is evidence-based but never preachy. More importantly it gives you hope and agency- changes to your diet will have a real and meaningful impact on the climate, and this book guides you which ones to choose.

Prof Mark Miodownik

Professor of Materials & Society, University College London

Thinking about what we eat is one of the most important things we can all do to reduce our carbon footprint. This book shows how it’s possible to make a big difference and enjoy a nutritious, healthy, balanced diet without having to be an eco-saint every single meal. If you enjoy your food but also care about the planet, as I do, then this book is for you.

Craig Bennett

Leading environmentalist, Chief Executive of The Wildlife Trusts and former Chief Executive of Friends of the Earth

Very accessible guide on how to eat more sustainably. Cuts through all the confusion to give clear figures and diagrams that stay with you.

Dave Darby

Founder of Lowimpact.org

Want to reduce your contributions to climate change? Sarah Bridle’s ‘Food and Climate Change without the hot air’ will help you do so one bite at a time. Her book examines the foods and beverages we eat from breakfast to dinner-- and traces how they affect the climate. If you care about food and climate change, buy this book!

Andrew F Smith

Culinary Historian

‘Food and Climate Change without the hot air’ is a breath of fresh air! Sarah Bridle provides a clear-eyed and exquisitely readable journey through our food and its impact on climate change and beyond. The book provides exactly the awareness and consciousness that each of us needs in our daily lives to make responsible decisions.

Prof Paul Anastas

Former Head of Research and Development for the US Environmental Protection Agency and the Director of Yale University’s Center for Green Chemistry and Green Engineering

This fascinating and important book deserves world-wide success. Sarah Bridle presents, engagingly and clearly, a vast amount of information that’s important not just for policymakers but for all of us who want to make a difference in our everyday lives.

Prof Sir Martin Rees

Baron Rees of Ludlow, former Astronomer Royal, Master of Trinity College, University of Cambridge and President of the Royal Society

Climate change is complex. Yet Sarah Bridle’s book elegantly illustrates the role that food choices and food waste play in this issue, and how simple steps can greatly reduce our impact.

Dr Tom Quested

Lead Analyst, the Waste & Resources Action Programme

Both astounding and frightening, this book lays out in simple terms that anyone can understand the remarkable environmental impact of our daily food choices.

Ken Albala

Professor of History, University of the Pacific

As an omnivore who loves his food, I loved this book. With a wealth of super-clear, attractive charts Bridle goes through a typical day’s meals, ever so gently highlighting the often-small tweaks we can make to produce meals that are as tasty as ever… yet far kinder to our planet.

David Bodanis

Author of E=mc^2: A Biography of the World’s Most Famous Equation and Einstein’s Greatest Mistake

This book is brilliant. Well-presented and understandable information gives both the detail and the big picture to show how our food and climate are linked, and how our dietary choices can make a real difference. The weight-for-weight comparisons are just what are needed. Forget calorie-counting; it is carbon-counting that really matters.

Dr Phil Williamson

Climate Change Scientist, University of East Anglia

Sarah Bridle has written an important book that is full of useful information and is easy to read. I’m already thinking differently about the food I eat.

Prof Jeff Forshaw

Professor of Physics, University of Manchester and author of Why Does E=mc^2?

What was once a mystery has now been made crystal clear: the decisions about how we produce and consume food are some of the most impactful humanity can make to solve the climate emergency. This book opens the mind to the realities of the embodied emissions in everything we eat – and waste – from farm to fork to landfill. An essential source for anyone working to save the planet.

Chad Frischmann

Vice President and Research Director, Project Drawdown

FOOD

and

CLIMATE

CHANGE

WITHOUT THE HOT AIR®

Change your diet:

the easiest way

to help save the planet

S L BRIDLE

In memory of David JC MacKay

“To have constructive conversations … one needs to take a calm look at the numbers.”

– David JC MacKay

Contents

Title Page

Dedication

Preface

1 Introduction

I Breakfast

2 Tea and coffee

3 Sugar

4 Milk

5 Bread and toast

6 A bowl of cereal

7 Eggs

8 Breakfast summary

II Lunch

9 A cheese sandwich

10 Ham, pork and bacon

11 Salad

12 Pizza

13 A baked potato, or fries

14 Beans and other legumes

15 Yogurt and cream

16 Lunch summary

III Snacks

17 A piece of fruit

18 Chocolate and sweets

19 Nuts

20 Potato crisps / chips

21 Soft drinks and juices

22 A piece of cake

23 Snacks summary

IV Evening meal

24 Spaghetti bolognese

25 Chicken curry tikka masala

26 Rice

27 Fish and chips

28 Veg

29 Beer or wine?

30 Dessert

31 Evening meal summary

V Looking ahead

32 Food emissions for a whole day

33 Leftovers and food waste

34 Health

35 Vegan and other climate-motivated diets

36 How can governments help?

37 Food as part of the solution

38 Making the change

Appendixes

A Climate change

B Impacts of climate change on food

C Food in the future

Bibliography

List of URLs and web links

References

Index

Acknowledgements

Copyright

Preface

In 2015, when my children started school, I wondered about the future: what the world will be like for them in 2050, when they are my age. Around the same time my former mentor and friend David MacKay was diagnosed with terminal cancer. David had brought great clarity to the discussion of greenhouse gas emissions, especially through his brilliant book Sustainable Energy – Without the hot air, which greatly influences this book. In his absence, I started to research climate change and to wonder how it might impact the future, and what we can do about it. I now divide my time between food and my other research field of astrophysics, as a Professor at the University of Manchester, UK.

I have immersed myself in the research literature on food and climate change to write the book I’d have liked to read at the beginning of my journey. As a practising physics researcher I bring a balanced synthesis of the academic literature on this topic: asking basic quantitative questions about where foods come from, how much emissions they cause, why, and what can be done about it. As an inquisitive eater I discuss what we citizens can do to reduce greenhouse gas emissions from food. But most of all I want you to benefit from the information in this book to help you figure out for yourself what you’re going to do to help the generations to come.

In all this, I am heavily influenced by David MacKay’s passion for empowering others to just get started working stuff out.

This book

This book doesn’t promote a particular diet or set of food choices. Instead, it sets out clearly the scientific consensus on how individual foods contribute to climate change, and illustrates this with some typical example food combinations. There are no recipes in this book, although it examines some simplified common recipes from the internet and calculates their greenhouse-gas emissions. By the end of the book you will be able to apply what you’ve learned to your own favourite meals and recipes.

Throughout we visualize greenhouse-gas emissions using vertical bars or “stacks”: the height of a stack indicates the number of grams of emissions. Each stack is drawn to the same scale, so you can use the heights of different stacks to compare the relative amounts of emissions from different foods and activities. This approach draws heavily on the energy stacks in David MacKay’s Sustainable Energy – Without the hot air. David’s motto was “numbers not adjectives”: instead of vague descriptions like “huge” or “lots”, we need to quantify impacts and compare them numerically to get a useful analysis.

The main body of each chapter presents the information about a specific food as simply as possible. However, the world often isn’t as straightforward as we might like, so detailed numbers, calculations, discussions and references are included in the endnotes at the end of each chapter. You can use the endnotes to explore topics in depth, and see exactly how each emission figure has been calculated. (Some readers might prefer to skip over the endnotes on first reading.)

This is a world book, rather than being specific to any one country. Individual countries may differ in some details – depending on their climate, energy sources, etc. – but the information is valid for the world as a whole.

Errata: the latest list of changes, corrections (and interesting additions) for this book are online, accessed via the book’s page at www.uit.co.uk/without-the-hot-air

You can also get details of the free ebook version of this book, via the book’s page at www.uit.co.uk/without-the-hot-air

Continue the conversation at #FACCWTHA on Twitter.

Chapter 1 Introduction

How much do you think the last meal you ate contributed to climate change? And which bits of it were the biggest culprits? Diets aimed at reducing environmental impact are becoming more popular, for example vegans avoid all animal products including meat, fish, cheese, milk and eggs. But does this really help, and anyway how much of a big deal is food compared to all the other contributions to climate change?

When I first learned about the impact of food on climate change I went vegan for a while. I put my jacket potato into the oven for two hours and waited around smugly with my can of beans, unpacking my suitcase after a transatlantic flight. I drove to the shop 3 km (1.86 miles) down the road just to buy some plant milk, and also probably picked up a pack of green beans flown in from another continent.

My efforts to help reduce climate change were based on little more than a gut feeling. What I really needed was detailed figures, so I could make informed decisions that would make a big difference, and that’s why I wrote this book – to get clear numbers that I could use, and share with everyone else.

Climate change

The overwhelming scientific consensus is that climate change is real, it is happening, and it needs to be addressed. There is a wealth of information available about climate change, so this book doesn’t repeat all that. There is just a short appendix at the end, summarizing the main facts (appendix “Climate change”).

However, we will address one issue that often confuses people: what’s the difference between climate change and global warming? Yes, greenhouse gases in the Earth’s atmosphere are trapping heat and cause the planet to warm up. (There’s more detail on greenhouse gases in the next section.) However, some parts of the globe are warming up faster than others. For example the continents warm up faster than the oceans. However, the world isn’t just getting warmer – the changing climate causes extreme weather events such as droughts, floods, and storms, sometimes affecting multiple continents (appendix “Climate change”).

So the “global” in “global warming” refers to the temperature change averaged across the whole the surface of the Earth. While it’s nice to focus on a single number, this hides a complexity that has serious consequences. Cloud, wind and rainfall patterns have an intricate dependence on variations in temperature from one geographical location to another.

This changing climate also affects food production (appendix “Impacts of climate change on food”); some farmers have already had to change what they grow. Looking ahead, crop yields and the numbers of fish caught at sea are expected to go down.

“The main way that most people will experience climate change is through the impact on food: the food they eat, the price they pay for it, and the availability and choice that they have”

– Tim Gore, Head of Policy, Advocacy and Research of Oxfam’s GROW Campaign

Greenhouse gases

We humans release a range of gases into the atmosphere. The most important of these that contribute to global warming are carbon dioxide, methane and nitrous oxide.1 The best known of these is carbon dioxide (CO_2), which is released by burning fossil fuels – in cars, aeroplanes, heating and to generate electricity.

When plants rot in a damp place they turn into methane, which is how natural gas (which is a “fossil fuel”) was made in the first place (appendix “Climate change”). In addition, about one twentieth of all the calories eaten by a cow are burped out again as methane (chapter 4). Because of the amount of food we’re producing to feed the world, and because we’re producing fossil fuels, the amount of methane in the atmosphere is increasing. When it first enters the atmosphere, 1 gram of methane causes more warming than 80 grams of carbon dioxide, but it only lasts for about 10 years before turning into carbon dioxide, so the total heat-trapping effect is equivalent to about 28 grams of carbon dioxide over a 100-year period. Have you ever inhaled laughing gas (another name for nitrous oxide)? I had nitrous oxide as a painkiller when I was giving birth – it made the pain seem less important, but I don’t remember laughing! One gram of nitrous oxide causes a similar global warming effect to about 270 grams of carbon dioxide.

The amount of nitrous oxide in the atmosphere is increasing because we’re feeding our crops with nitrogen fertilizers (box 2.1), and because nitrous oxide is released from animal manure (chapter 4).

For the rest of this book we will talk about “greenhouse-gas emissions” to refer to the combined effect of all the greenhouse gases. We will describe emissions in grams of carbon dioxide equivalent (written as “gCO_2e” in the scientific literature) which means the amount of carbon dioxide that would cause the same energy input as all the greenhouse gases combined together, averaged over a one hundred year period. Therefore

- 100 grams of carbon dioxide corresponds to 100 grams of greenhouse-gas emissions

- 4 grams of methane corresponds to 100 grams of greenhouse-gas emissions, and

- 0.4 grams of nitrous oxide corresponds to 100 grams of greenhouse-gas emissions.

Box 1.1: Grams, kilos and precise numbers

Throughout this book we will talk about the number of grams of food consumed, as well as the number of grams of emissions. This can be written out the long way e.g. “20 grams” or in a more compact way e.g. “20 g”. When the numbers get big we sometimes switch to using kilograms (or “kilos”, for short), where one kilogram (1 kg) is the same as 1000 grams (1000 g).

To make this book easier to use and more readable, it has to be specific about the amount of greenhouse-gas emissions from different types of food. To make it easier to use the numbers we have highlighted them throughout, like this:

1 g milk = 2 g emissions

However, the actual values will depend on the specific production systems used. For example, in the case of cows’ milk it will depend on what the cow is eating and how much milk it produces. In the case of plants it will depend on the soil type (which affects the amount of fertilizer needed) and weather (which affects yield for a given amount of fertilizer).

So there is no single number, only a range of numbers for different suppliers. But we have to start somewhere. My hope is that you will start to demand the exact information from your food suppliers, so that you can make informed choices and buy from the producers who are making advances in reducing their impact on the climate.

How much emissions?

So where are all these greenhouse gases coming from? Fig. 1.1 shows a map of the world showing total greenhouse-gas emissions (not just food-related) for each country. On average, each world citizen causes about 24 kilos of emissions per day, but this varies greatly from one country (and person) to the next. For example, an average US citizen causes over 50 kilos of emissions per day, whereas an average citizen of most African countries causes less than 2 kilos of emission per day.

Fig. 1.1: A map of the world showing the total greenhouse-gas emissions for each country, per person per day. We are extremely grateful to the Our World In Data project for making this figure. You can find the data for this plot on their website. (URL 2)

How much do you think food contributes to the total emissions? To work this out we need to add up all the greenhouse-gas emissions from all parts of the food chain. We have to include growing, clearing land, processing, manufacturing, packaging and transportation, as well as cooking the food at home and disposing of any waste. Overall, about a quarter of all global greenhouse-gas emissions come from food (Fig. 1.2). The amount of emissions from food varies from one country to the next, as does the total emissions. Food typically causes about a quarter to one third of the emissions.

Fig. 1.2: A quarter of all greenhouse-gas emissions come from food.

The amount of emissions varies greatly depending on which food is being eaten, and on the production method. For example, a steak causes more than 10 times the emissions of a portion of beans. Furthermore, the steak itself can cause 10 times the emissions again if the cow lives for 20 years instead of just 1 year (chapter 24). Fig. 1.3 shows the amount of greenhouse-gas emissions for different food categories, for the amounts of each type of food consumed in the UK. In the rest of this book we consider the emissions from producing each of these foods, and investigate some alternatives. But first we need to get a sense of scale.

Box 1.2: Giga/billions tons/tonnes

When we discuss large amounts of CO_2 we use metric tonnes. A metric tonne is 1,000 kg by definition, and an imperial ton is 1,016 kg, so you hardly ever have to worry about the difference – it’s less than 2%). One gigatonne (1 Gt) equals one billion tonnes (giga = billion, or one thousand million).

Food emissions in perspective

On average, each person in the world causes 6 kilos of emissions each day because of the food they eat. Just as for total emissions, the emissions from food vary significantly from one country to the next, reaching 13 kilos per person per day in the US (Fig. 1.4), which is 10 times the value for all emissions (including food) in some countries in Africa (Fig. 1.1).

What does 6 kilograms of emissions look like? Most people could pick up something weighing 6 kg, but you probably wouldn’t want to carry it around with you all day. Carbon dioxide, methane and nitrous oxide are transparent gases, and so are invisible to our eyes, perhaps making them feel mysterious and hard to imagine. We can visualize the amount of space taken up by 6 kilos of carbon dioxide – it corresponds to the volume of a small car.

Is this a problem? We combine numbers from IPCC Special Report: Global Warming of 1.5°C (IPCC, 2018), chapter 3, to make a crude estimate of the total emissions budget including both CO_2 and non-CO_2 emissions.

Fig. 1.3: UK average daily greenhouse-gas emissions per person per day from food, showing a breakdown into different types of food.

1. A CO_2 emissions budget of 420 Gt (i.e. 420 billion tonnes) is given by the latest scientific reports.

2. We subtract 100 Gt to account for Earth system feedbacks, which include melting permafrost and methane emissions from wetlands, that are exacerbated by climate change. Research is ongoing to improve the accuracy of this estimate.

3. We add 320 Gt to allow for non-CO_2 emissions including methane and nitrous oxide. The size of the non-CO_2 budget depends on how much carbon dioxide we emit, and when, because some of the most important non-CO_2 emissions have a much shorter lifetime than CO_2 (especially methane). For example, the sooner we reach 1.5°C, the smaller the non-CO_2 budget will be, because over shorter timescales methane has a bigger impact on warming than CO_2.

Fig. 1.4: The total daily greenhouse-gas emissions from food for the average person for the world, the US and China.

Adding up these contributions gives 640 GtCO_2e. This might sound like a lot of room for manoeuvre but we will use up the whole 1.5°C budget before 2030 if food continues to make up one quarter of all emissions, even if the average food emissions per year were to remain unchanged and the population didn’t rise. Even in the impossible scenario where there are zero emissions from everything else, the emissions from food alone would exceed this limit in 38 years, i.e. by 2056. (In fact average food emissions per person, total emissions per person, and the world population are all projected to increase – see appendix “Food in the future”.)

The world needs to reduce emissions by stopping burning fossil fuels, and switching to using clean energy. But we still have to eat, and food causes greenhouse-gas emissions. So how much is OK? The latest conclusion of world experts is that we can limit global warming to 1.5°C if we can halve all emissions by 2030. Looking beyond 2030, the experts conclude we need to reduce our emissions much more drastically by 2050, by 80% or more.

Throughout this book, we use 3 kg of food emissions (per person per day) as a yardstick, based on halving global average food emissions from changes in which foods we choose to eat. In tandem with this we also need to reduce emissions from the food production process, keep population numbers under control, and ensure that gains arising from spared land are put to work for the purpose of removing greenhouse gases from the atmosphere.

Food emissions yardstick = 3 kg CO_2e per person per day

In short, the answer to the question we asked earlier (“Is this a problem?”) is “yes”: we need to significantly reduce emissions from food and other activities, especially in countries that are already well above the global average. This book focuses on emissions from food, but to evaluate my post-flight hunch about a vegan jacket potato we need to compare food emissions with those from non-food activities.

Non-food emissions

A single transatlantic round-trip flight causes about 3,000 kilos of emissions per person.

20,000 km as an air passenger = 3,000,000 g emissions

Whether or not this is significant for global warming depends on how often you go, and how typical you are of the world population. If you go once every year, then we can share out the emissions over 365 days to calculate the emissions per day. This works out as about 9 kilos of emissions a day – about 50% more than an average day of food; Figs. 1.5 and 1.6 compare food and non-food emissions.

Fig. 1.5: Greenhouse-gas emissions showing non-food activities.

Left: A return transatlantic flight (10,000 km [6214 miles]) divided across 365 days (55 km).

Centre left: Driving a car 20 km (12 miles) return (40 km).

Centre right: Travelling by train 20 km (12 miles) return (40 km).

Right: Global average emissions from food per person per day.

Emissions from driving a car depend on the size of the car and whether it burns fossil fuels or uses electricity generated from “clean energy” (carbon-neutral sources including wind and solar). Driving my small fossil-fuelled car for 40 kilometres (24 miles) every day would cause about 6 kilos of emissions a day, which is less than the emissions from one transatlantic flight every year, and similar to the global average daily food emissions.

40 km in a fossil-fuelled car = 6,200 g emissions

How much would it help to travel by train instead? Travelling 40 km by train causes about 1,100 g of emissions, which is about five times better than the value for driving a car the same distance.

Fig. 1.6: Greenhouse-gas emissions showing non-food activities.

Left: An electric heater on for 6 hours (360 minutes at 2 kW).

Centre left: Heating water by 40°C for a bath.

Centre right: Heating water by 40°C for a shower.

Right: A light on for 6 hours, using a 13 W LED bulb (2 minutes at 2 kW).

40 km by train = 1,100 g emissions

How about emissions from heating or cooking? Again, this all depends on where the energy comes from. Throughout this book we assume a typical global mixture of electricity coming from fossil fuels and from clean energy, of roughly 0.5 kgCO_2e / kWh which means that if we put a 2 kW heater (or a 2 kW air conditioner) on for 6 hours a day then it causes about 6 kilos of emissions – similar to the emissions from average food choices.

2 kW of electricity on for 1 minute = 16 g emissions

Depending on your oven, switching it on for two hours causes about 2.5 kilos of emissions (box 12.1).

Recommendations on how to help climate change often include turning off all the lights. It’s something we can all do easily, and it feels productive. But how much does it help? Running an old-fashioned (incandescent or halogen 100 W) bulb for 6 hours a day uses 0.6 kWh of electricity and so causes 300 gCO_2e, whereas a modern LED bulb (13 W) causes less than 40 gCO_2e.

1 LED light on for 6 hours = 40 g emissions

Compared to the heater or the car journey, this is not a big deal. I should lighten up on my light-police duties and focus on the bigger things.

Heating water for an average bath takes about 5 kWh of energy, which corresponds to about 1.5 kilos of emissions, or for a quick shower the value is around 0.5 kilos of emissions, depending on how long you spend in there, and how much water comes out of your shower head.

1 litre of water warmed by 40°C = 14 g emissions

So we can already start making some informed comments on my jacket-potato-fuelled vegan smugness. I was making more than one transatlantic flight a year, and so this would have been the biggest contributor to my impact on climate change (more than 9 kilos a day). Putting the oven on for two hours caused more than twice the emissions of my trip to the shops, and a lot less than my flight habit. We will find out how the potato, beans, green beans, milk and other individual food emissions add up as we go through the book (chapters 13, 14, 28 and 4).

Key points

- About a quarter of all greenhouse-gas emissions come from food.

- On average each person in the world causes 6 kilos of emissions every day because of the food they eat.

- By 2030 we need to halve our emissions, which would correspond to the average person causing 3 kilos of emissions every day from food.

- One transatlantic round-trip flight every year causes about 9 kilos of emissions per person per day.

- Driving a small family car 40 kilometres (24 miles) causes about 6 kilos of emissions.

- Putting the oven on for two hours causes about 2.5 kilos of emissions.

Notes

What I really needed was detailed figures, so I could make informed decisions that would make a big difference, and that’s why I wrote this book – to get clear numbers that I could use, and share with everyone else. I highly recommend the excellent popular book that discusses the carbon footprints of all sorts of food and non-food emissions by Mike Berners-Lee; How Bad are Bananas?: The Carbon Footprint of Everything (Berners-Lee, 2010), and the more recent book by the same author There Is No Planet B: A Handbook for the Make or Break Years (Berners-Lee, 2019) which has an extensive discussion of food. For an entertaining and accurate description of the issues I recommend A Greedy Man in a Hungry World: How (almost) everything you thought you knew about food is wrong by Jay Rayner (Rayner, 2013) and for more details on a subset of the foods covered in this book as well as more information about future impacts of climate change, I recommend the well-researched book Climate-Smart Food by Dave Reay (Reay, 2019) which is free online. The major feats of political and scientific consensus building from the Intergovernmental Panel on Climate Change (URL 1) are well worth reading. You may also be interested to read the compelling EAT-Lancet report, which summarises the scientific consensus on healthy diets that are good for climate change (Willett, 2019), early influential reports in this area Beddington (2011) and Audsley and Williamson (2010), and a case study based on the UK in P. Allen et al. (2019). The endnotes of this book are full of references to the academic literature, a subset of which is available for free to anyone with an internet connection.

The most important of these for climate change are carbon dioxide, methane and nitrous oxide. The man-made gases causing the most warming are, in order of impact: carbon dioxide, methane, chlorofluorocarbons / hydrochlorofluorocarbons followed by nitrous oxide. However, because of the restrictions to protect the ozone layer, there is little current injection of chlorofluorocarbons / hydrochlorofluorocarbons so we don’t discuss them further (see details in figure 8.6 of Myhre et al. 2013). Water vapour is also an important greenhouse gas, but has its own feedback mechanisms for removal (rain), so I don’t discuss it more in this book, except to use the radiative forcing correction for aviation (box 17.4).

When it first enters the atmosphere, 1 gram of methane causes more warming than 80 grams of carbon dioxide, but it only lasts for about 10 years before turning into carbon dioxide, so the total heat-trapping effect is equivalent to about 28 grams of carbon dioxide over a 100-year period. Averaging over a 20-year period, methane traps more heat than 83 times as much carbon dioxide. However, because methane is destroyed over a 10-year period (and carbon dioxide stays around for more than 100 years) methane is “only” 28 times more potent than carbon dioxide when averaged over 100 years. (Values from table 8.7 of Myhre et al. 2013). These numbers refer to the amount of extra energy trapped under the blanket of the atmosphere (“radiative forcing” in the academic literature), which depends on the amount of each greenhouse gas in the atmosphere, as described in this book. This differs from the amount of global warming for two reasons (i) global warming refers to the mean surface temperature of the Earth, and currently the ocean depths are cooler than the mean surface temperature due to the time it takes for the extra heat to permeate, so some of the extra energy causes deep-sea warming even if emissions are low enough to keep the surface temperature constant (ii) the increased atmospheric temperature causes more heat to be radiated into space. Both of these effects mean that the relationship between the amount of radiative forcing and global (surface temperature) warming depends on both the amount of greenhouse gases in the atmosphere and how these are changing with time. For more details see Cain et al. (2019).

One gram of nitrous oxide causes a similar global warming effect to about 270 grams of carbon dioxide. The exact value depends on whether feedback is taken into account between the increased temperature causing additional release of the gas in question (“climate-carbon feedback”). Averaging over a 100 year time period nitrous oxide is 265 times more potent than carbon dioxide (for a given weight) if climate-carbon feedbacks are not taken into account (see table 8.7 of Myhre et al. 2013). Taking into account climate-carbon feedbacks this same reference recommends using relative warming effect of 298.

greenhouse-gas emissions from different types of food. In the main text we talk about grams of emissions, or give the number of grams of emissions for a particular weight of food. In the endnotes we use the same notation as in the scientific literature, so you can more easily find the details in the references given. For example, in the main text we might write “1 g milk = 2 g emissions”, and in an endnote we would write that milk causes 2 kgCO_2e / kg. We could equally well write that milk causes 2 gCO_2e / g, since the grams or kilograms cancel out. Furthermore, in the endnotes we give the exact values from the literature, whereas in the main text these are rounded to avoid giving the impression that these numbers are known to great accuracy – see the discussion about the range of values in the main text.

a map of the world showing total greenhouse-gas emissions (not just food-related) for each country. This map is the amount of emissions produced in each country (production-based emissions), as opposed to the amount of emissions each country is responsible for (consumption-based emissions). International trade makes these two numbers different, so a country might produce few emissions but be responsible for much larger emissions because they import high-emissions products from overseas, thus “exporting” their emissions. For a discussion of the importance of consumption-based emissions accounting see e.g. Larkin et al. (2012). Unfortunately consumption-based emissions values are not available, however you can view consumption-based emissions values for just carbon dioxide here (URL 2).

about a quarter of all global greenhouse-gas emissions come from food Perhaps surprisingly, this fraction is the about same in countries like the US and China, even though the total amount of emissions is very different in each country. According to Bajželj et al. (2013) (table S19), an average person in the U.S. causes about 65 kilos of emissions each day, whereas an average person in China causes nearly three times less (25 kilos a day), which is similar to the global average of 22 kilos of emissions a day. The exact number depends on how much of the food system is included. For example, Bajželj et al. (2013) (whose results are reproduced in figure 10.1 of Edenhofer et al. 2014) include energy used for cooking, and land clearance for agriculture, as well as emissions on farm and packaging. Springmann, Godfray, et al. (2016) give a value of 1.15 tCO_2e per person per year (calculated from their value of 7.6 Gt per year for 2005/7 and a population of 6.6 billion in 2006), which corresponds to 3.2 kg per person per day, i.e. half the value shown in the main text. They use emissions data from Tilman and Clark (2014) which do not include the impacts of land clearance and extend only from “cradle to farm gate” i.e. they do not include transport, processing, packaging or cooking.

the amount of greenhouse-gas emissions for different food categories, for the amounts of each type of food consumed in the UK. Calculated from the National Diet and Nutrition Survey Year 6 (URL 3) grouping the “FoodCategory” values into broader groupings and matching the “FoodNumber” values with Intake24 (URL 4) greenhouse-gas emissions estimates for each food by the Rowett Institute.

each person in the world causes 6 kilos of emissions each day because of the food they eat. Dividing the 2.2 tonnes CO_2e / person / year from Bajželj et al. (2013) out over 365 days of the year and converting from tonnes to kg gives 6 kg / person / day. Springmann, Godfray, et al. (2016) give a value of 1.15 tCO_2e per person per year (calculated from their value of 7.6 Gt per year for 2005/7 and a population of 6.6 billion in 2006), which corresponds to 3.2 kg per person per day, i.e. half the value used in the main text. They use emissions data from Tilman and Clark (2014) which do not include the impacts of land clearance and extend only from “cradle to farm gate” i.e. they do not include transport, processing, packaging or cooking. Poore and Nemecek (2018) give a value of 13.7 GtCO_2e per year for the world in 2010, which converts to a value of 5.4 kgCO_2e per person per day. Including food waste adds 2.05 GtCO_2e per year for the world in 2010, which brings the total to 6.2 kgCO_2e per person per day, in agreement with the number we use in the main text.

the emissions from food vary significantly from one country to the next, reaching 13 kilos per person per day in the US (Fig. 1.4), See Bajželj et al. (2013).

We can visualize the amount of space taken up by 6 kilos of carbon dioxide – it corresponds to the volume of a small car. The density of CO_2 is 1.98 kg / m^3 at standard temperature and pressure. Therefore 6 kilos of emissions corresponds to 6 kg / (1.98 kg / m^3) = 3 m^3.

A CO_2 emissions budget of 420 Gt (i.e. 420 billion tonnes) is given by the latest scientific reports. See the 67th percentile for 1.5°C warming from table 2.2 of IPCC (2018).

subtract 100 Gt to account for Earth system feedbacks, From IPCC (2018) - who note that this number has an uncertainty range of about 250 Gt.

Adding up these contributions gives 640 GtCO_2e. This approach is approximate due to a lack of established studies. It would be much better to add up the amount of each greenhouse gas separately and propagate these values into warming, or to calculate separate budgets, as proposed in Rogelj et al. (2019).

we will use up the whole 1.5°C budget before 2030 if food continues to make up one quarter of all emissions, even if the average food emissions per year were to remain unchanged and the population didn’t rise. 6 kg / year / person × 365 days / year × 7.7 billion people / (1000 billion kg / Gt) = 16.8 Gt / year. Sharing out the 640 Gt gives 38 years. 38 years after 2018 is 2056. 38 years × one quarter = 9.5 years. 2018 + 9.5 = 2027.5.

The latest conclusion of world experts is that we can limit global warming to 1.5°C if we can halve all emissions by 2030. See the table on page 14 of the “Summary for Policy Makers” in IPCC (2018). The line for “Kyoto-GHG emissions in 2030” gives values of -50%, -49% and -35% for scenarios P1, P2 and P3 respectively, and an interquartile range for no/limited overshoot scenarios of -51 to -39%.

Looking beyond 2030, the experts conclude we need to reduce our emissions much more drastically by 2050, by 80% or more. The table on page 14 of the “Summary for Policy Makers” in IPCC (2018) gives values of -82, -89 and -78 % in 2050 for scenarios P1, P2 and P3 respectively, and an interquartile range for no/limited overshoot scenarios of -93 to -81%.

A single transatlantic round-trip flight causes about 3,000 kilos of emissions per person. The UK Government greenhouse-gas reporting conversion factors document 2018 (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2018) gives 0.16 kgCO_2e / passenger / km (i.e. 160 gCO_2e / passenger / km) for long-haul flights to/from the UK in economy class (including the radiative forcing factor of 1.9 to account for the higher impact of emissions at altitude, see their paragraph 8.37 – but note that this factor is uncertain). I’m assuming the transatlantic round-trip is 20,000 km, which therefore causes 3,200 kg of emissions, which is rounded to 3,000 kg in the main text. See more discussion of the energy required for transportation in MacKay (2009). Interestingly, the emissions per km are about the same as for driving a car, although note that short-haul flights will cause more emissions per kilometre than the long-haul flights considered here, because the energy-intensive take off will be a larger fraction of the total energy.

Driving my small fossil-fuelled car for 40 kilometres (24 miles) every day would cause about 6 kilos of emissions a day, The UK Driver and Vehicle Licensing Agency website (URL 5). says our small family car causes 155 gCO_2e / km.

Travelling 40 km by train causes about 1,100 g of emissions, We use a value of 6 kWh per 100 person-km from MacKay (2009) for the Japan rail system. For a 40 km trip this corresponds to 2.4 kWh (40 person-km / 100 × 6 kWh per 100 person-km = 2.4 kWh). Converting this into emissions using an electricity conversion factor of 0.475 kgCO_2e / kWh (see next endnote) gives 2.4 kWh × 0.475 kgCO_2e / kWh = 1.14 kgCO_2e, which we round to 1.1 kg in the main text.

Throughout this book we assume a typical global mixture of electricity coming from fossil fuels and from clean energy, of roughly 0.5 kgCO_2e / kWh We use a value for the global energy mix in 2018 from URL 6 of 475 gCO_2e / kWh. We can convert this to gCO_2e per minute if we know the power uptake of our appliance, e.g. 2 kWh corresponds to 15.8 gCO_2e each minute (475 gCO_2e / kWh × 2 kW / 60 minutes/h). This number varies from one country to the next and is decreasing as fossil fuels are replaced by clean energy. The UK electricity mix in 2018 caused 300 gCO_2e / kWh according to the Committee on Climate Change (UK Committee on Climate Change, 2018). For a more detailed discussion of energy from electricity versus chemical heat from fossil fuels see MacKay (2009).

if we put a 2 kW heater (or a 2 kW air conditioner) on for 6 hours a day then it causes about 6 kilos of emissions 0.475 kgCO_2e / kWh × 2 kW × 6 h = 5.7 kgCO_2e.

Depending on your oven, switching it on for two hours causes about 2.5 kilos of emissions (box 12.1). 15 minutes of warm up time, plus 120 minutes, at an average power of 2.4kW causes 2.4 kW × 135 minutes / (60 minutes / hour) × 0.475 kgCO_2 / kWh = 2.56 kgCO_2e.

Heating water for an average bath takes about 5 kWh of energy, See MacKay (2009) for a calculation for a 150 cm × 50 cm × 15 cm depth bath (110 litres), heating the water up by 40°C. Warming 1 litre of water by 40°C causes 4200 Joules / litre / °C × 40°C / 3600000 Joules / kWh × 0.3 kgCO_2e / kWh × 1000 g / kg = 14 gCO_2e. Natural gas causes 190 gCO_2 / kWh if all the energy is captured. For simplicity here we use an inefficiency of 50% in capturing this energy in your bathwater, which gives a conversion factor of 0.3 kgCO_2 / kWh, which is the same value as if you had used electricity instead.

for a quick shower the value is around 0.5 kilos of emissions, We use 30 litres of water, following MacKay (2009), which gives 420 g emissions, which is rounded to 400 in the main text because the exact value depends on your personal circumstances.

1 This is the only footnote in the book because we have endnotes instead. For example, you can find an endnote relating to the text “The most important of these that contribute to global warming are carbon dioxide, methane and nitrous oxide.” in the notes beginning on page 10. In the text, links to the endnotes are highlighted.

Part I: Breakfast

What did you have for breakfast today? A snatched cup of coffee or tea on your way out the door, or a leisurely piece of toast with a boiled egg? Or maybe a quick bowl of cereal?

Where do these foods come from, and why do they contribute to climate change? And are there more climate-friendly alternatives?

Chapters

Chapter 2: Tea and coffee

Chapter 3: Sugar

Chapter 4: Milk

Chapter 5: Bread and toast

Chapter 6: A bowl of cereal

Chapter 7: Eggs

Chapter 8: Breakfast summary

Chapter 2 Tea and coffee

Fig. 2.1: What’s the climate impact of your mug of tea? (URL 7)

Good morning! How about heating some water for a cup of tea or coffee, and maybe stretching out or checking the weather while you wait for the water to boil?

Tea

As you drop the teabag into your cup, think about its journey from tea plants far away, and the hard-working people picking out the top shoots of the tea plant, like in the advertisements.

The good news is that transporting a teaspoon (2 grams) of tea half way across the world by boat causes very little greenhouse-gas emissions compared to most other things you’re likely to eat today (we cover transport emissions in chapter 17, but don’t worry about that for now).

What about boiling the water? Burning natural gas to heat a pan, or using electricity generated from burning coal or natural gas, unlocks carbon dioxide taken up by plants millions of years ago, and releases it back into the atmosphere, which causes global warming.

Fig. 2.2 shows the amount of greenhouse-gas emissions caused by making one cup of black tea assuming that, like many people, you boil twice as much water as you really need.

Fig. 2.2: Emissions for a cup of black tea: a teabag (2 g); boiling half a litre of water (1.5 minutes at 2 kW).

Boiling the water causes more emissions than the teabag itself, but even so the total is still small compared to our reference value of 3 kg per day per person (chapter 1).

1 g teabag = 3 g emissions

Coffee

Do you prefer coffee? Coffee is made from the seeds of the coffea plant, which are often referred to as “beans”. To grow well, the coffea plants are tended, watered and fertilized (box 2.1). The coffee cherry fruits take most of a year to ripen, and then the seeds have to be extracted from the fruit (Fig. 2.3), then roasted and ground.

Fig. 2.3: A squashed coffee cherry alongside the seed that came out of it. This seed is dried and becomes the coffee “bean”. (URL 8)

Box 2.1: Fertilizer emissions

Most nitrogen fertilizer is made from the nitrogen freely available in the air we breathe, so how can it contribute to global warming? Firstly, to produce the fertilizer, nitrogen from the air has to be heated to about 500°C and compressed to a pressure that would crush even a submarine. This takes a lot of energy – usually produced by burning fossil fuels.

The most common fertilizer is ammonium nitrate, a white crystalline powder that looks like salt or sugar. This ammonium nitrate is spread over the soil and much of it is absorbed by the roots of the plants.

Furthermore, about one percent of the applied nitrogen is absorbed by microbes in the soil and turned into nitrous oxide. Nitrous oxide is an extremely potent greenhouse gas (see chapter 1), and so even this tiny amount produces about as much global warming as the fossil fuels used to produce the fertilizer.

For dried coffee, the emissions from the fertilizer cause about one third of the total emissions; processing the bean from plant to cup and packaging contribute most of the remainder.

1 g instant coffee powder = 17 g emissions

For a typical cup of coffee, the instant coffee emissions are similar to those from boiling the water. Even so, the amount of emissions from a single cup (Fig. 2.4), are small compared to our reference value of 3 kg per day per person.

Fig. 2.4: Emissions for a cup of black coffee: a teaspoon of instant coffee (2 g); boiling half a litre of water (1.5 minutes at 2 kW).

Take-out drinks

Coffee shops have conveniently sprung up on street corners all over the world, helping us get a quick fix of caffeine on the go. They provide a new social space and often a comfy place to access the internet. However, many of these drinks are taken away in disposable cups. This generates waste that often goes to landfill, but how bad is the cardboard for climate change?

Cardboard is made by processing wood from trees, which remove carbon dioxide from the atmosphere and turn it into wood. So if we’re planting extra trees especially to supply the cardboard factory, we are actively removing greenhouse gases from the air. That sounds like good news for the climate, but it depends on two crucial questions: (i) is the cardboard from trees that were planted especially for the purpose, or is its production driving deforestation and (ii) how is the cardboard disposed of at the end of its life?

- If the cardboard is composted with good access to oxygen, it decomposes back into carbon dioxide, thus returns to the air the greenhouse gases absorbed by the tree. In this case the emissions are just those from generating the energy to process the wood into cardboard, which is roughly equal to the weight of the cardboard.

1 g cardboard, composted = 1 g emissions

- However, if the cardboard is sent to landfill, it is likely to rot into methane, so the total emissions are larger, rising to twice the weight of the cardboard.

1 g cardboard, landfilled = 2 g emissions

In practice, most disposable coffee cups are lined with a thin layer of plastic, and so need specialist recycling facilities that aren’t widely available. Therefore they mostly end up in landfill and rot into methane. The cup emissions are then about the same as those from boiling the water (Fig. 2.5), but still cause lower emissions than their contents.

Fig. 2.5: Emissions for a cup of black coffee in a cardboard cup: a teaspoon of instant coffee (2 g); boiling half a litre of water (1.5 minutes at 2 kW); a cardboard cup (10 g).

While it’s true that lots of small contributions can add up to a big contribution, we’ll see later on there are bigger things to focus on first. So it turns out I’m not making a significant dent in my daily food emissions by whipping out my reusable cup at the coffee shop, especially if I take milk (discussed shortly).

Key points

- Teabags contribute less to global warming than boiling the water to make the tea.

- Coffee causes more greenhouse-gas emissions than tea because of the fertilizer needed to produce a good crop of coffee cherry fruits and the greater energy needed for processing.

- The greenhouse-gas emissions from making one cup of black tea or coffee are smaller than most other things you’re likely to eat today.

Notes

the teabag Tea causes a total of 12.08 kgCO_2e / kg of dry tea, according to Azapagic et al. (2016), which includes 9.20 kgCO_2e / kg dry tea from boiling the water. Since we account for the water heating separately, the value we use here is the difference between these two numbers, i.e. 2.88 kgCO_2e / kg dry tea, which covers the raw materials, production, storage and transport, of which packaging is the largest contributor (1.46 kgCO_2e / kg dry tea), followed by transport and then production (for which nitrogen fertilizer is the largest contributor). See also Doublet and Jungbluth (2010). and Cichorowski et al. (2015).

the emissions from the fertilizer cause about one third of the total emissions; processing the bean from plant to cup and packaging contribute most of the remainder. Using 33 grams of emissions per cup of coffee from Humbert et al. (2009) (using their value for spray-dried coffee, and ignoring use phase emissions as these are added separately here), and taking into account that 2 grams of spray-dried coffee is used per cup, gives 17 kgCO_2e / kg instant coffee granules. You can read about filtered and capsule coffee in Humbert et al. (2009), which cause higher emissions because they use more coffee beans. 7 grams out of 33 grams of CO_2e are caused by cultivation, which is dominated by fertilizer use.

is the cardboard from trees that were planted especially for the purpose, or is its production driving deforestation The numbers for cardboard emissions assume the trees have been especially planted to produce cardboard, otherwise they would be higher.

If the cardboard is composted with good access to oxygen, it decomposes back into carbon dioxide, thus returns to the air the greenhouse gases absorbed by the tree. In this case the emissions are just those from generating the energy to process the wood into cardboard, which is roughly equal to the weight of the cardboard. Eriksson et al. (2010) give a value of 0.964 kgCO_2e / kg for production and transport of cartons (their table 1). See also the UK Government conversion factors 2019 (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2019) which gives a similar value of 0.84 kgCO_2e / kg for “Paper and board: board” (842.58 kgCO_2e / tonne) for primary material-production plus an additional 0.01 kgCO_2e / kg for composting (10.02 kgCO_2e / tonne), bringing their total to 0.85 kgCO_2e.

if the cardboard is sent to landfill, it is likely to rot into methane, so the total emissions are larger, rising to twice the weight of the cardboard. In addition to the primary material production emissions, the landfill adds a further 1.0 kgCO_2e / kg (1041 kgCO_2e / tonne) according to the UK Government conversion factors 2019 (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2019), bringing the total to 1.964 kgCO_2e / kg cardboard sent to landfill (though note this number depends heavily on the management of the landfill site e.g. see the detailed discussion in Arnold and Yang (2005)). A final (unlikely) disposal option would be to hoard the cardboard at home for decades or, much better, turn the cardboard into something useful, like building materials. This helps to reduce climate change by removing carbon dioxide from the atmosphere for the period of time until it is finally composted. Ultimately it might be disposed of carefully and turned into compost, but in the intervening decades some global cooling would have happened because there was less carbon dioxide in the atmosphere.

cup emissions are then about the same as those from boiling the water For a cardboard cup weighing 10 grams, we need to multiply the cup weight by the emissions factor of 2 referenced in chapter 2 for cardboard to landfill, which gives 20 gCO_2e per cup. See also the detailed discussion of this topic in Harst and Potting (2013), including their figure 2 which compares a range of cup materials and recycling options which span a range from less than 10 gCO_2e per cup to 100 gCO_2e per cup. There is a nice analysis in CarbonClear (2012) who compare ceramic (re-usable) cups with paper and polystyrene disposable cups, concluding that if the re-usable cups are used 1000 times then they are better than the disposable paper cups (though note this depends on the amount of hot water used to wash the cups). See also Almeida et al. (2018) and Martin et al. (2018).

Chapter 3 Sugar

Fig. 3.1: A sugar beet plant in a field. You can see the fat root which is crushed to extract its sweet juice. (URL 9)

Do you take sugar? Most sugar comes from either sugar beet or sugar cane. Either way, sweet juice is extracted from the plant and heated up to concentrate the sugar.

Sugar beet is a small leafy plant with a fat root like a carrot or beetroot (Fig. 3.1). It originated in Europe and grows well in temperate climates. After crushing the root to extract its sugary juices, the water has to be evaporated off to leave the sugar crystals behind; it is this heating that causes most of the greenhouse-gas emissions at the farm.

Fig. 3.2: Some cut sugar canes. If you look closely you can just see white dots on the cut stalk where sugar crystals are starting to form from the leaking sugary sap. (URL 10)

Fig. 3.3: Emissions for a cup of black tea with sugar: a teabag (2 g); boiling half a litre of water (1.5 minutes at 2 kW); a teaspoon of sugar (4 g).

Sugar cane, by contrast, only grows well in warmer climates, producing a more concentrated sugary liquid in its long stems (Fig. 3.2). Because the juice is more sugary in the first place, it takes less energy to evaporate off the water to turn it into sugar. On the other hand, the sugar has to be transported a longer distance to reach people living in cooler countries. In addition, sugar cane tends to be grown in countries that are expanding their food production by cutting down forests (chapter 7).

Overall the emissions are higher for sugar cane than sugar beet, but for the kind of quantity you’re likely to put in your tea, it isn’t a big deal either way (Fig. 3.3).

1 g sugar = 3 g emissions

We’ll add milk in the next chapter.

Key points

- Sugar can be made from either sugar beet or sugar cane.

- The main ways sugar contributes to global warming are (i) heating the sugary juices to crystallize the sugar (ii) transporting the sugar across the world (iii) deforestation to clear land for growing sugar cane.

- Given the kinds of quantities you’re likely to be eating, sugar isn’t a major contributor to emissions.

Notes

it is this heating that causes most of the greenhouse-gas emissions at the farm. See Klenk et al. (2012).

it takes less energy to evaporate off the water to turn it into sugar. However, innovative farmers can reduce these fossil fuel emissions further by capturing the energy made by burning the leftovers from extracting the sugar from the crop.

Overall the emissions are higher for sugar cane than sugar beet, but for the kind of quantity you’re likely to put in your tea, it isn’t a big deal either way The average of the global value for sugar cane (3.2 kgCO_2e / kg) and sugar beet (1.8 kgCO_2e / kg) from Poore and Nemecek (2018) gives 2.5 kgCO_2e / kg, used for the figures in this book. See also lower values e.g. 0.32 kgCO_2e / kg in Seabra et al. (2011) and 0.38 kgCO_2e / kg in URL 11. The range in values reflects the different assumptions about transportation, and on whether deforestation has occurred to grow the crop, and whether or not energy is captured from burning the co-products (leftovers from crushing the cane or beet), thus reducing fossil fuel emissions.

Chapter 4 Milk

Fig. 4.1: A glass of milk a day? (URL 12)

Most people in the UK drink their tea with milk, typically adding just over one tablespoon (20 ml) to each cup. Consumed in various ways, cows’ milk is a major source of nutrients in many countries.

Are you concerned about all the plastic milk cartons? In fact, when it comes to greenhouse-gas emissions, the plastic isn’t a big deal compared to the milk itself. Even if we bought all our milk in small plastic bottles, the emissions from producing the plastic would be dwarfed by emissions from the cows themselves.

Fig. 4.2: A Friesian cow grazing happily. (URL 13)

Rumination

Fig. 4.2 shows a beautiful scene of a cow in a field, munching contentedly on grass. You can almost hear the snuffling, ripping sound as the cow chomps. I’m transported back to childhood walks through the fields near our house, lifting my feet up through the long grass and dodging cow poo.

How do cows contribute to climate change? Tabloid newspaper headlines warn about methane from cow farts, but in fact most methane comes out of their mouths as burps. About one twentieth of all the calories eaten by a cow comes back out of their mouths as methane, a potent greenhouse gas (chapter 1; Fig. 4.3).

Fig. 4.3: About 5% of the calories eaten by a cow are burped out of their mouths as methane, a powerful greenhouse gas. (Adapted from URL 14).

Cows have evolved a complicated stomach (Fig. 4.4) to help them digest the most common plant on the planet, grass. Their stomachs have four compartments, the first and biggest of which is called the “rumen”. This is home to bacteria which produce methane, in a process called “enteric fermentation”. Animals that digest food in this way, including sheep, goats, deer, moose and giraffes, are called “ruminants”.

Most animals produce much less methane than ruminants. Horses, rabbits, elephants and other “hindgut fermenters” digest grass differently – in a chamber that comes after the small intestine (although rabbits do eat their own poo in an effort to extract even more grassy goodness).

Fig. 4.4: A cow’s stomach. (URL 15)

Exactly how much methane are we talking about? A typical dairy cow eats over 70,000 kCal a day – about the same intake as 30 humans (although a cow weighs less than 10 humans). To be fair, the cow is churning out milk at an average rate of 16 litres a day, but at the same time it’s burping out over 7 kilos of emissions each day. (But please don’t try this at home!)

We can already estimate the emissions from milk by sharing out the 7 kilos of emissions across the 16 litres of milk produced. A more accurate calculation takes into account the methane burped by the cow during the two years before it reached milk-bearing age. Since cows are then slaughtered for beef at around the age of 4, then this roughly doubles the milk emissions, although the emissions can then be shared out between the milk and the beef.

In addition to the cow burps, we have to add in the impact from cow poo. Depending on how it’s stored and distributed on the fields as fertilizer, cow manure produces both methane and nitrous oxide and adds about 50% to the total milk emissions. (Cow pats in fields produce less methane than cow slurry stored in a building, because the oxygen in the air allows the cow pats to rot down into carbon dioxide instead of methane. So maybe I shouldn’t have been complaining about all the cow poo in the fields on my childhood country walks.)

1 g milk = 2 g emissions

Overall, cows’ milk causes about twice its own weight in greenhouse-gas emissions, but this number can vary by more than 50% depending on how the cows are raised. For example, if the cows produce less milk each day then the emissions will be higher.

Fig. 4.5: Emissions for a cup of tea with milk and sugar: a teabag (2 g); boiling half a litre of water (1.5 minutes at 2 kW); a teaspoon of sugar (4 g); a large tablespoon of milk (20 g); a one litre plastic milk carton weighing 53 g, shared between 50 cups of tea (1 g).

Milk in tea and coffee

We can now add up the total emissions caused by a cup of tea with milk: we find that half of the emissions come from the milk (Fig. 4.5). For white coffee, the emissions from a splash of milk (20 ml) are slightly more than those from a teaspoon of coffee granules (Fig. 4.6, left). However we can be reassured that our morning brew is still a small fraction of the 3,000 g discussed in chapter 1, assuming we’re being reasonably careful with the milk and water.

However, if you’re drinking ten cups a day, and being a bit generous with the milk or leaving a lot of water in the kettle, you might want to think more carefully, not least due to the amount of caffeine! (Ten cups of white tea causes over 25% of the reference 3 kg daily food emissions.) However, you can bring the emissions from your drink of choice to relatively insignificant levels by only boiling the water you need, and switching to black tea (Fig. 4.6, centre).

How about a latte or a cappuccino? Popular coffee shops serve half-litre cups of latte, made from a shot of espresso topped up with milk. The emissions from making a latte are more than ten times those from a regular cup of coffee, almost entirely because of the large amount of milk (Fig. 4.6, right). The milk emissions alone are more than 1 kilo, and the total latte emissions are use up nearly half of the 3 kilo food emissions budget for a whole day of food, as discussed in chapter 1. How can you reduce emissions?

How could milk emissions be reduced? Plant-based milk alternatives

have become popular: soya, almond, coconut, rice, oat, cashew, macadamia, hemp… light, no added sugar, organic, fresh, long-life… the range is overwhelming. (We discuss almond milk in more detail in chapter 19.) But, as usual for plants, the emissions mostly depend on the amount of nitrogen fertilizer applied to the growing plant, on the amount of fossil fuels used in processing, and on the transport, packaging and refrigeration. These latter stages are usually as important as the choice of plant. Overall the emissions from producing plant-based milks are usually found to be less than half of those from dairy milk.

1 g plant milk = 0.8 g emissions

The amount of methane produced by a cow is halved if the cow eats higher-quality feed, more like that given to pigs or chickens (mostly wheat and soy) instead of grass (page 25), however the production of soy is currently driving deforestation which tends to cancel out this benefit (chapter 7). There is research into reducing methane emissions from cows by adding special ingredients to their feed and genetically modifying their gut microbes, as well as breeding better cows. One feed additive has been shown to reduce methane emissions by 30% if it is given to the cow regularly. Putting these developments together with improvements in manure handling could potentially halve the climate impact of milk and beef.

In chapter 9, we discuss the feasibility of milking animals other than cows. Alternatively, new products are coming out which use milk proteins produced in a laboratory, using genetically modified cousins of yeast.

Key points

- Cows’ milk contributes to climate change mainly because of the cow’s emissions.

- Cows burp about 5% of their calories back out into the air as methane, a powerful greenhouse gas.

- Adding a generous tablespoon (20 ml) of milk to your tea or coffee causes more emissions than boiling the water or producing the tea or coffee itself.

- The large amount of milk in a latte pushes the emissions to nearly half a daily food emissions budget of 3 kilos.

- Plant milks cause less than half the emissions of dairy milk.

Fig. 4.6:

Left: Emissions for a cup of coffee with milk and sugar: a teaspoon of instant coffee (2 g); boiling half a litre of water (1.5 minutes at 2 kW); a teaspoon of sugar (4 g); a large tablespoon of milk (20 g); a one litre plastic milk carton weighing 53 g, shared between 50 cups of coffee (1 g).

Centre: Emissions for a cup of black tea boiling minimal water: teabag (2 g); boiling the right amount (200 ml) of water (0.6 minutes at 2 kW).

Right: Emissions for a latte: coffee (we assume 4 g of instant coffee for this calculation but the result would be slightly higher if using non-instant, see Humbert et al. (2009)); heating the milk (2.5 minutes at 2 kW); a teaspoon of sugar (4 g); milk (500 g); a one litre plastic milk carton weighing 53 g, shared between 50 cups of coffee (13 g); cardboard cup (10 g).

Notes

typically adding just over one tablespoon (20 ml) to each cup. Analyzing the data from the UK National Diet and Nutrition Survey years 5 and 6 (Hemmings, 2016), there is a peak in consumed milk quantity at around 20 grams. I’m guessing this is people putting milk in their tea and coffee. One tablespoon of milk is about 15 grams, so people are using just over one tablespoon of milk in each cup of tea.

Even if we bought all our milk in small plastic bottles, the emissions from producing the plastic would be dwarfed by emissions from the cows themselves. My plastic carton from a small (1 pint) bottle of milk weighed 20 grams. Using the emissions factor for plastic (box 21.1) of 3.0 kgCO_2e / kg plastic, this means 60 grams of CO_2e per plastic bottle. The milk is responsible for about 2.2 kgCO_2e / kg, therefore about 1,100 gCO_2e for 1 pint (~500 g) of milk. The plastic from the bottle is therefore 5% of the emissions. The emissions will be smaller (per pint of milk) if you buy bigger bottles and the packaging becomes even less significant.

About one twentieth of all the calories eaten by a cow comes back out of their mouths as methane, a potent greenhouse gas This varies with the diet of the cow, from 6.5% for grass-fed to 3% for a more digestible diet e.g. grains and soy (Dong et al., 2017).

A typical dairy cow eats over 70,000 kCal a day Calculated using the methodology of Dong et al. (2017) using a milk rate of 6,000 litres / year (see their table 10.11; see also 5,380 in O’Brien et al. (2014)) as an input to their equation 10.16, and assuming grass-fed cows to determine the feed digestibility.

but at the same time it’s burping out over 7 kilos of emissions each day. Calculate the number of kCal of methane by multiplying 70,000 kCal by 0.05 to account for the 5% of calories turned into methane. Then we divide by the energy density of methane (13,000 kCal / kg) to turn this into the weight of methane produced by the cow each day (0.26 kg). Since a given weight of methane causes a lot more warming than the same weight of carbon dioxide, we need to multiply by the global-warming potential of methane (chapter 1) of 28 to get the weight of emissions (7.4 kg). We can then convert this into a number of balloons following the method in chapter 1 (292 balloons).

the emissions can then be shared out between the milk and the beef. This type of allocation is discussed more in box 9.1. See O’Brien et al. (2014) for more allocation details specific to milk.

Overall, cows’ milk causes about twice its own weight in greenhouse-gas emissions, but this number can vary by more than 50% depending on how the cows are raised. Poore and Nemecek (2018) find a value of 2.2 kgCO_2e / kg milk for Europe, which is used for the figures in this book. Note that this is lower than the global average (3.2 kgCO_2e / kg milk) and slightly lower than the value for the US (2.5 kgCO_2e / kg).

on the amount of fossil fuels used in processing, and on the transport, packaging and refrigeration. These latter stages are usually as important as the choice of plant. For Oatly, the farm stage makes up about half of the plant milk emissions, with the rest coming from processing, transport and packaging (URL 16).

the emissions from producing plant-based milks are usually found to be less than half of those from dairy milk. Values are given by Poore and Nemecek (2018) for milk alternatives made from soy (1.0 kgCO_2e / kg), almond (0.7 kgCO_2e / kg), oat (0.8 kgCO_2e / kg) and rice (1.2 kgCO_2e / kg). See also much earlier studies especially “Tesco Product Carbon Footprint Summary” (2012, accessed 2018). However, these should be superseded by reliable (ideally independent) estimates produced for individual companies. Oatly gives a value of 0.44 kgCO_2e / kg on their website (URL 16). For the calculation in chapter 6 we use a value of 0.8 kgCO_2e / kg. Note that all these values already include packaging.

reducing methane emissions from cows by adding special ingredients to their feed and genetically modifying their gut microbes, as well as breeding better cows. One feed additive has been shown to reduce methane emissions by 30% if it is given to the cow regularly. Putting these developments together with improvements in manure handling could potentially halve the climate impact of milk and beef. The 3NOP feed additive (Hristov et al., 2015) blocks the final step of methane production and was found to reduce emissions by 30%. See academic reviews on the topic of reducing cow emissions Grossi et al. (2018) and Haque (2018) or this more accessible overview of the research by the BBC: URL 17.

Alternatively, new products are coming out which use milk proteins produced in a laboratory, using genetically modified cousins of yeast. For example from the company Perfect Day (URL 18).

Chapter 5 Bread and toast

Fig. 5.1:

Top left: Marmite on toast. Love it or hate it? (URL 19)

Top right: Making bread in an orphanage in Tanzania. (URL 20)

Bottom left: A close-up of a head of wheat. (URL 21)

Bottom right: Rolls fresh from the oven. (URL 22)

Hot buttered toast is a comforting meal on its own, and even better with a simple spread on top. My favourite is Marmite (yeast extract) on toast, served with the butter just starting to melt (Fig. 5.1, upper).

We only really need four ingredients to make bread: flour, water, salt and yeast. Squash them together until the dough becomes smooth and stretchy (Fig. 5.1, upper middle). Leave the dough to rise, i.e. give the yeast time to produce bubbles of carbon dioxide, making the bread lighter and softer. Then bake it in the oven.

So how does bread contribute to climate change? To produce the flour needed for two slices (80 g) of bread, a farmer needs to grow about 20 wheat plants in an area of land about the size of a large dinner plate. So if I eat two slices of bread a day, there is an area about half the size of a small classroom permanently in cultivation to keep me in bread.

Fertilizer is spread on the wheat fields to make sure they yield big, protein-rich grains (Fig. 5.1, lower middle), and about one teaspoon of fertilizer is used to grow the flour for two slices of bread (box 2.1).

1 g flour = 0.8 g emissions

Overall, bread causes roughly its own weight in emissions, the biggest single component of which comes from producing and applying fertilizer.

1 g bread = 0.8 g emissions

They say you should bake bread when prospective purchasers view your house, because the smell makes people want to buy (it worked the one time I tried it!). Perhaps it’s the ultimate sign of domestic bliss, that you have the time and energy to bake a loaf. However, if you put your oven on while the bread proves for one hour, and only use it to bake a single loaf, then you more than triple the emissions of your bread ingredients.

Luckily, most bread is baked in factories (Fig. 5.1, lower), which are about 3 times more efficient as baking one loaf at a time, so the baking only contributes about one fifth of the total bread emissions. People often ask about the emissions from the plastic bag the bread arrives in, but it turns out the plastic bread bag emissions are tiny compared to the other ingredients.

Box 5.1: Shocking statistics: country-sized emissions

In this book we consider emissions per person per day, because that relates directly to the decisions we make every day as individuals. However, some people quote values for a whole country for a whole year, which easily gives a number that sounds shocking.

If everyone in the UK eats two slices of bread every day, the total annual country emissions in tonnes

= daily emissions per person in grams × population × number of days in a year  ÷ number of grams in one tonne

= 80 × 66,000,000 × 365 ÷ 1, 000, 000

~ 2, 000, 000.

So UK bread is responsible for about two million tonnes of emissions a year, which makes it sound really bad! As well as considering numbers per person per day, it’s also helpful to compare with other numbers to work out whether or not we should really feel shocked.

Fig. 5.2: Two slices of toast in a toaster. (URL 23)

Let’s compare the 60 g of emissions for two slices of bread with those for other daily food items and activities. For example, drinking one glass of milk (250 ml) causes nearly 10 times the emissions of the two slices of bread (chapter 4), as does driving a car 4 kilometres (2.5 miles) (chapter 1).

Fig. 5.3: Emissions for two slices of toast: two slices of bread (80 g); toasting the bread (3.6 minutes at 2 kW).

Do you like your bread toasted? One newspaper claims that 3.6 minutes is the perfect toasting time. The required electricity produces about as much global warming as producing the bread (Fig. 5.3).

But who eats dry toast on its own? Making butter results in similar greenhouse-gas emissions to cheese (chapter 9). The milk is concentrated down, raising the emissions by about four times, to around 8 times its own weight in emissions.

1 g butter = 8 g emissions

With one teaspoon (5 g) of butter per slice of toast, you’ve nearly doubled the carbon footprint of your toast. By contrast, vegetable spread causes about five times lower emissions than butter, so switching to a vegetable spread is the easiest way to reduce emissions (compare Fig. 5.4 left and centre), and is more important than foregoing the toasting.

1 g vegetable spread = 1.5 g emissions

How about some jam or jelly on that? The emissions depend on whether you’re trying to emulate TV chef Mary Berry by making your own, perhaps bubbling up a cauldron on the hob while sweating from the wasted heat (I’ve been there!). Just as for baking bread, industrially produced jam is more efficient. But unless you like it very thickly spread, the jam emissions are less than those from producing the bread.

1 g jam = 3 g emissions

Perhaps Paddington Bear wasn’t as decadent as we thought!

You can more than halve your jam on toast emissions by replacing butter with vegetable spread and foregoing the toasting, or using a clean energy source to run the toaster (Fig. 5.4).

Fig. 5.4:

Left: Emissions for two slices of toast with butter and jam: two slices of bread (80 g); toasting the bread (3.6 minutes at 2 kW); two teaspoons of butter (10 g); two teaspoons of jam (10 g).

Centre: Emissions for two slices of toast with spread and jam: two slices of bread (80 g); toasting the bread (3.6 minutes at 2 kW); two teaspoons of vegetable spread (10 g); two teaspoons of jam (10 g).

Right: Emissions for two slices of bread with spread and jam: two slices of bread (80 g); two teaspoons of butter (10 g); two teaspoons of jam (10 g).

Key points

- For a piece of toast with jam, about 40% of the climate-impact comes from the hidden melted ingredient: butter.

- Switching from toast to bread (and butter to vegetable spread) can reduce emissions further, bringing the total emissions down to less than half of the original buttery toast.

Notes

To produce the flour needed for two slices (80 g) of bread, a farmer needs to grow about 20 wheat plants in an area of land about the size of a large dinner plate. Goucher et al. (2017) state 0.000072 hectares per loaf, which converts to 720 cm^2 for two slices of bread, which corresponds to a circle of diameter 30 cm. This corresponds to 22 wheat plants, assuming a planting density of 300 plants per square metre (which is the middle of the range considered in Li et al. (2016)).

two slices of bread a day, there is an area about half the size of a small classroom permanently in cultivation to keep me in bread. For an annual harvest we need 720 cm^2 × 365 days / 10000 m^2 / cm^2 = 26 m^2, which corresponds to a square room 5 metres by 5 metres.

flour Goucher et al. (2017) calculate 0.42 kgCO_2e for 0.52 kg of flour (see their figures S5 and S2 respectively), which corresponds to 0.8 kgCO_2e / kg flour.

bread causes roughly its own weight in emissions, the biggest single component of which comes from producing and applying fertilizer. The value used for the figures is 0.75 kgCO_2e / kg bread which comes from Goucher et al. (2017) who find 0.6 kgCO_2e for an 800 g loaf. This means that two slices (80 g) of bread cause about 60 g of emissions. According to this study, about half of the emissions are caused by producing and applying the fertilizer; the next largest component is baking the bread, which causes about 30% of the emissions. See also Espinoza-Orias et al. (2011) who find 0.97 kgCO_2e / kg bread.

if you put your oven on while the bread proves for one hour, and only use it to bake a single loaf, then you more than triple the emissions of your bread ingredients. In this case the oven would be on for 90 minutes. Using the value in chapter 12.1 this causes 1700 grams of emissions for an 800 gram loaf, so adds 2.1 kgCO_2e / kg bread. The emissions from just the ingredients are 80% of 0.75 kgCO_2e / kg based on Goucher et al. (2017) i.e. 0.6 kgCO_2e / kg. Putting these together means that the home-baked loaf causes 2.7 kgCO_2e / kg, which is 3.6 times the emissions of the the mass-produced loaf.

the baking only contributes about one fifth of the total bread emissions. See Goucher et al. (2017).

the plastic bread bag emissions are tiny compared to the other ingredients. I weighed a plastic bread bag and it was about 5 grams, which causes 15 grams of greenhouse-gas emissions (gCO_2e) (see box 21.1), assuming there is no recycling. Remember that there is one bag for a whole loaf, so per slice the emissions are less than 1 gram from the plastic, which is tiny compared to the fertilizer and baking.

In this book we consider emissions per person per day, because that relates directly to the decisions we make every day as individuals. This follows the popular approach taken in MacKay (2009) in the context of energy use.

One newspaper claims that 3.6 minutes is the perfect toasting time. The UK’s Daily Mail says the perfect toast takes 3.6 minutes (URL 24).

The required electricity produces about as much global warming as producing the bread (Fig. 5.3). Assuming the toaster draws 2 kW, the toasting time of 3.6 minutes corresponds to 0.12 kWh, which is about 55 g of emissions using 0.3 kgCO_2e / kWh (chapter 1).

Making butter results in similar greenhouse-gas emissions to cheese (chapter 9). The milk is concentrated down, raising the emissions by about four times, to around 8 times its own weight in emissions. The value of 8.3 kgCO_2e / kg is an average of values from Vergé et al. (2013) (7.3 kgCO_2e / kg), Sheane et al. (2011) (8.9 kgCO_2e / kg), Nilsson et al. (2010) (4.8/0.5 kgCO_2e / kg for UK butter) and Finnegan et al. (2018) (9.7 kgCO_2e / kg).

vegetable spread The value of 1.4 kgCO_2e / kg for vegetable spread (margarine) is an average of the values for the UK (1.1 kgCO_2e / kg), Denmark (1.32 kgCO_2e / kg) and France (1.66 kgCO_2e / kg) from Nilsson et al. (2010).

the jam emissions are less than those from producing the bread. The emissions value is 3.2 kgCO_2e / kg from “The greenhouse gas footprint of Booths” (2012) for jam, marmalade and honey.

Chapter 6 A bowl of cereal

Fig. 6.1: A bowl of cereal. (URL 25)

As a child I loved choosing between an array of those tiny individual boxes of cereal (probably because they included the sugary and chocolatey ones I wasn’t usually allowed to eat). In the supermarket the range of cereal options stretches out along the shelves with different shapes, sizes, coatings and even fillings.

Despite this huge range of cereals, most are made from corn, rice or wheat. The greenhouse-gas emissions for the cereal itself are about three times the dry weight of cereal, and depend mostly on the type of grain and the amount of processing required to puff, extrude or otherwise create your preferred shape.

1 g cereal = 3 g emissions

However, adding milk usually makes these different options pale into insignificance (see more information on milk in chapter 4). For a typical bowl of cereal the majority of the half kilo of emissions come from the milk (Fig. 6.3).

Fig. 6.2: Emissions for a bowl of cereal: cereal (30 g); milk (200 g).

For a lot of people the simplest way to reduce “cereal” emissions is to pour on less milk, especially if you often find a lot left at the end of the bowl. Or, at the risk of sounding like an annoying parent, please would you at least drink up the leftover milk, instead of pouring it down the sink (for a discussion of food waste, see chapter 33).

Fig. 6.3: Emissions for cereal with plant milk: cereal (30 g); plant milk (200 g).

We saw in chapter 4 that plant milks cause less than half the emissions of cows’ milk. Since most of the cereal emissions come from the milk, then this switch more than halves the cereal breakfast emissions (Fig. 6.2).

Key points

- For a typical bowl of cereal, the greenhouse-gas emissions from the milk are much bigger than the emissions from the cereal itself.

- Make sure not to waste the milk at the end of the bowl!

- Switching to plant milk more than halves your cereal emissions.

Notes

The greenhouse-gas emissions for the cereal itself are about three times the dry weight of cereal, and depend mostly on the type of grain and the amount of processing required to puff, extrude or otherwise create your preferred shape. Jeswani et al. (2015) figure 7 gives 2.64 kgCO_2e / kg, which is used for the figures in this book. See also “Tesco Product Carbon Footprint Summary” (2012, accessed 2018) who give 95 gCO_2e for a 30 g serving of cornflakes, which is 3.2 kgCO_2e / kg.

Chapter 7 Eggs

Fig. 7.1: A soft boiled egg. (URL 26)

Boiled, poached, scrambled or fried: eggs transform from a gloopy liquid into a wobbly solid that tastes satisfying on its own, or even better with a little salt. Or perhaps you like to whisk them up with cream and stir them into soft folds in a buttery scramble?

Packed with all the nutrients needed to make a baby chicken, an egg is a culmination of a hen’s hard work pecking for its food. Chickens don’t burp significant amounts of methane (do chickens even burp?), but their biggest contribution to global warming is still associated with their front end: the production of chicken feed is the most important source of egg greenhouse-gas emissions at the farm.

Chicken feed

An average egg-laying chicken is fed mostly on wheat, with some soy added for extra protein. As discussed in the bread chapter (chapter 5), the main climate impact of wheat comes from making and applying fertilizer.

However, growing soy raises an important additional issue. Most soy varieties need a long hot summer to produce a good crop. Global soy production has been doubling approximately every 10 years, driven by its use in animal feed. The biggest producers of soy are Brazil and Argentina, where agricultural expansion is mostly into rainforest, often to grow soy.

Even though most of the chicken feed is wheat, soy contributes similar emissions to the wheat because forest is cut down to grow soy, and cutting down forest is bad news for the climate.

There are many problems with cutting down forest, not least the destruction of the habitat of endangered animals and plants. However, this book is about climate change so we’ll focus exclusively on how deforestation affects greenhouse gases.

When forest is converted into agricultural land, the carbon stored in the trees and shrubs is mostly returned to the air as carbon dioxide (along with some carbon from the soil). This happens quickly if the forest is burnt, or over several years if the plants are left to rot. The amount of emissions released depends on how much vegetation there is in the deforested area.

To produce each egg, a chicken must eat about three times the weight of an egg. We also have to add in other contributions to global warming including feed production for the young chicken before it starts to lay eggs, and emissions from chicken manure, as well as transport and storage. Overall each egg is responsible for about 5 times its own weight in greenhouse-gas emissions.

1 g egg = 5 g emissions

Cooking eggs

Cookery writer Delia Smith recommends boiling an egg for 6 minutes. Even for a single boiled egg the cooking emissions are small compared to the emissions from producing the egg (Fig. 7.2, left).

There is much debate about whether or not to add milk when scrambling an egg. Jamie Oliver recommends adding only a knob of butter, the size of which is also a matter of debate. Using 25 grams of butter increases the emissions from a two-egg scramble by 30%. Some recipes recommend adding a few tablespoons of cream as well, which can push the total emissions over 1 kilo – three times as much as the emissions from a single boiled egg (Fig. 7.2, centre).

Fig. 7.2:

Left: Emissions for one boiled egg: one egg (60 g); boiling the egg (6 minutes at 2 kW).

Centre: Emissions for scrambled eggs: two eggs (120 g); cooking the eggs (10 minutes at 2 kW); a knob of butter (25 g); cream (50 g).

Right: Emissions for two fried eggs: two eggs (120 g); frying the eggs (10 minutes at 2 kW); two teaspoons of vegetable oil (10 g).

How can you reduce emissions?

Combining a smaller number of eggs with a lower-emissions food like toast reduces the total carbon footprint of your breakfast. Alternatively, skipping the dairy and replacing with vegetable oil reduces emissions by one third, compared to the dairy-heavy scramble (compare Fig. 7.2 centre and right).

The chicken feed can be sourced from land that has not been recently deforested. This helps if the total demand for soy is no longer increasing, otherwise it just pushes the problem elsewhere. Alternative chicken feeds can also be used: for example, duckweed is a highly nutritious food that can even be grown in deserts, given the right enclosed conditions.

Some companies are researching their holy grail of plant-based low-carbon egg substitutes, and several options are on the market. Few if any of these plant-based alternatives are going to give you the perfect omelette yet, let alone a soft-boiled egg. But they can work well as a substitute in baking or in a pancake.

Meanwhile the bizarre discovery of aquafaba has spread around the world, making it into the dictionary in 2018. This liquid leftover from cooking chickpeas can act like egg whites by trapping small air bubbles and solidifying around them during cooking. Aquafaba meringues and mayonnaise can taste great, if combined with other ingredients (though probably not when combined with each other!). Maybe the recently-found properties of chickpea liquid points to other discoveries yet to be made for lower-carbon food alternatives.

Key points

- The most significant way eggs contribute to climate change is through production of chicken feed.

- The biggest reason chicken feed contributes to climate change is through the destruction of forest to produce soy.

- A dairy-heavy scrambled egg causes 40% of a 3 kilo daily food emissions budget, and three times the emissions of a single boiled egg.

Notes

An average egg-laying chicken is fed mostly on wheat, with some soy added for extra protein. See Leinonen et al. (2011b).

Global soy production has been doubling approximately every 10 years, driven by its use in animal feed. The biggest producers of soy are Brazil and Argentina, where agricultural expansion is mostly into rainforest, often to grow soy. See figures C1 and C2 and surrounding discussion in MacLeod et al. (2013) and T. C. Ponsioen and T. J. Blonk (2012).

soy contributes similar emissions to the wheat because forest is cut down to grow soy, Table 5 of Leinonen et al. (2013) states that 41.9 % of emissions are due to wheat and 34.1 % of emissions are due to soy, even though 60 to 70 % of the feed is wheat (depending on life stage, see their table A1) and 10 to 15 % is soy.

The amount of emissions released depends on how much vegetation there is in the deforested area. Numbers have been estimated for different types of forest in different countries e.g. table 4.7 of Aalde et al. (2006), based on exploration and counting the number of trees of different sizes (Malhi et al., 2004). See the bottom two rows of table 3 of T. C. Ponsioen and T. J. Blonk (2012), which give about 10 tonnes of CO_2e per hectare from land-use change.

To produce each egg, a chicken must eat about three times the weight of an egg. Chickens eat 0.130 kilograms of feed per bird per day (free range value from Table 1 of Leinonen et al. 2011a). During the laying phase they lay 0.75 eggs a day (calculated from 293 eggs in 56 weeks given in table 1 of Leinonen et al. 2011b) i.e. 0.75 × 0.057 kg egg / bird / day so 0.130 / (0.75 × 0.057) kg feed / kg egg = 3.04 kg feed / kg egg.

Overall each egg is responsible for about 5 times its own weight in greenhouse-gas emissions. The world average for eggs from Poore and Nemecek (2018) is 4.7 kgCO_2e / kg, which is in between the value for Europe (5.1 kgCO_2e / kg) and North America (3.7 kgCO_2e / kg).

Alternative chicken feeds can also be used: for example, duckweed is a highly nutritious food that can even be grown in deserts, given the right enclosed conditions. For more information see Leinonen and Kyriazakis (2016).

Few if any of these plant-based alternatives are going to give you the perfect omelette yet, let alone a soft-boiled egg. Amazingly, fake eggs are a problem for food fraud, because it is possible to make cheap realistic-looking egg shells (see the fascinating popular book Sorting the beef from the bull (Evershed and Temple, 2016)).

Chapter 8 Breakfast summary

Having looked at all these breakfast options, let’s see how they compare with each other in terms of greenhouse-gas emissions, and how a typical breakfast compares with more decadent or frugal options.

Typical-emissions breakfast

To make a typical breakfast, let’s add up the emissions from a cup of coffee and a bowl of cereal. This comes to just over half a kilo of greenhouse-gas emissions in total, about 20% of a 3 kilo daily food emissions budget (Fig. 8.1, left). Most of this is caused by the bowl of cereal, most of which comes from the milk (chapter 6).

Higher-emissions breakfast

If you’re eating out you might be tempted by a latte or a hot chocolate, some toast and some creamy scrambled eggs. (We’ve deliberately picked some of the higher-emissions options here, to see how much difference it makes.) This really starts to add up, to nearly 4 times the emissions of the more typical breakfast (compare Fig. 8.1 centre and left). It blows most of a daily budget of 3 kilos of emissions, even though we’ve only had breakfast so far. Most of the emissions are from the dairy products, even though the egg is the most prominent item on the menu.

Is this a fair comparison? Maybe not, because you get so much more nutrition from the higher-emissions breakfast than the typical-emissions breakfast. If you’re planning a big healthy lunch and dinner then the typical-emissions breakfast will be fine. On the other hand, if the rest of the day is going to be hectic and low on nutrients then the higher-emissions breakfast might be just the ticket to keep you healthy.

At the end of the book we’ll add up the emissions from a typical-emissions breakfast, a typical-emissions lunch, some typical-emissions snacks and a typical-emissions dinner (chapter 32). We’ll try to pick out some options that complement each other and meet our daily nutritional requirements. It will be a fairer comparison when the whole day of food is considered.

Fig. 8.1: Comparison of breakfast options.

Left: Emissions for a typical-emissions breakfast: a white coffee; bowl of cereal.

Centre: Emissions for a higher-emissions breakfast: a latte; scrambled eggs.

Right: Emissions for a lower-emissions breakfast: a cup of black tea, boiling minimal water; bread (4 slices).

Lower-emissions breakfast

Could you make a lower-emissions breakfast from the options on the menu? How about going really frugal by having black tea with bread and jam? You could be careful to only boil just enough water for the tea, and use vegetable spread instead of butter. This would reduce the emissions by over five times, compared to the typical-emissions breakfast. To avoid being hungry at the end of the day, let’s double up the amount of bread in this lower-emissions option from two to four slices (and correspondingly increase the amount of spreads). This still keeps emissions down at nearly one third those the typical breakfast, and one tenth those of the higher-emissions breakfast (Fig. 8.1, right).

Key points

- For a typical breakfast of coffee and cereal, the milk causes most of the emissions.

- A higher-emissions option with a latte, scrambled eggs and buttered toast causes nearly four times more emissions, more than half of which comes from the dairy products.

- Going frugal with bread and black tea reduces emissions by nearly 3 times compared to the typical breakfast, or 10 times compared to the higher-emissions breakfast.

Part II: Lunch

What do you normally do for lunch? Head to a canteen, eat a sandwich at your desk, or whip up a fresh meal at home? In this part, we’re going to consider a few standard western lunch options.

A cheese and ham sandwich seems simple enough, but involves turning milk into cheese, and raising animals to eat. Salads can contain a huge range of ingredients, but for simplicity we’ll focus on the challenges of growing tomatoes and lettuce. We then put the tomatoes together with bread, cheese and a few toppings to make a pizza.

Next on the menu is a baked potato, with beans and cheese. As well as being a popular baked potato topping, beans are a type of legume – a highly nutritious plant-based option and an important component of animal feed. We round off our lunch with a milk-based dessert.

Chapters

Chapter 9: A cheese sandwich

Chapter 10: Ham, pork and bacon

Chapter 11: Salad

Chapter 12: Pizza

Chapter 13: A baked potato, or fries

Chapter 14: Beans and other legumes

Chapter 15: Yogurt and cream

Chapter 16: Lunch summary

Chapter 9 A cheese sandwich

We can take the bread and butter discussed in the breakfast section, and just add some slices of cheese to make a tasty sandwich.

Making cheese

Fig. 9.1: Cutting the curds to release the whey. (URL 27)

To make cheese, warm some milk to body temperature (or you could freshly milk a cow), add rennet and leave it to solidify. The result wobbles like a fragile jelly. Cheese makers cut these curds to release the liquid whey, keeping just the semi-solid curds to turn into cheese (Fig. 9.1).

I put in a photo of some curds in one bowl, and the whey in another, to emphasize the big difference in quantity. There is about 10 times as much watery whey as there is cheese curds, so it takes approximately 10 kilos of milk to make 1 kilo of cheese.

The whey contains milk proteins, along with many vitamins and minerals. It’s used in various products including baby formula milk, and is also fed to calves. Recently, whey proteins have become popular in body-building drinks.

Milk storage

Fig. 9.2: In cheese-making, milk is separated into plentiful whey (large bowl) and meagre curds (small bowl). The curds are then pressed to make cheese. It takes about 10 kilograms of milk to make 1 kilogram of cheese. (URL 28)

The curds can be eaten straight away as a soft cheese. Or to make a tangy hard cheese extra ingredients are needed – for example yogurt cultures, acid and salt. The curds are pressed, dried and matured at carefully controlled temperature and humidity – sometimes for years for the strongest cheeses.

It’s more difficult to produce milk in the winter than in the summer. By the time autumn comes around, a calf would be getting most of its nutrition from solid food and the mother cow would stop producing milk, unless milked regularly. Even in modern dairies it’s usual to give the cows a break from producing milk before they give birth again in spring. The gaps can be staggered to provide a continuous supply of milk, but cheese is an important way to store up many of the nutritional benefits of a milk supply that doesn’t match up with demand.

Fig. 9.3: Cheeses being matured in carefully controlled conditions. (URL 29)

Cheesy emissions

Most of the climate impact of cheese production comes from the burps of the dairy cow. We should share out the emissions between the end products (cheese and whey, see box 9.1), and add in the contribution from processing the cheese.

Box 9.1: Emissions from co-products

When calculating the emissions from a process that produces more than one product, we have to share out the emissions between the outputs to avoid double counting. How should we divide the emissions up? The most common approach is to use the economic value, or cost, of each product. This means that the most sought-after products are allocated the largest share of the emissions.

It also means that when we have an unwanted byproduct, such as the liquid left over from draining chickpeas (aquafaba, see chapter 7), we would assign this item zero emissions. This is also relevant for some by-products of the meat industry, for example the pigs’ blood used to make black pudding. More generally, we can reduce greenhouse-gas emissions if we use every edible part of the food production process, and therefore help to avoid food waste (chapter 33).

Taking everything into consideration, cheese turns out to be responsible for producing about 16 times its own weight in greenhouse-gas emissions.

1 g cheese = 16 g emissions

We can now build up our cheese sandwich from two slices of bread (80 g), a smear (10 g) of butter and two slices (50 g) of cheese (Fig. 9.4, left). Most of the greenhouse-gas emissions come from the cheese. Only a small fraction comes from the bread, even though it provides about half the calories, and a slightly larger amount comes from the butter. The total emissions add up to nearly a kilo of greenhouse gases, or one third of a daily food emissions budget of 3 kilos.

Fig. 9.4:

Left: Emissions for a cheese sandwich: two slices of bread (80 g); two teaspoons of butter (10 g); two medium slices of cheese (50 g).

Centre: Emissions for a cheese sandwich (1 thin cheese slice): two slices of bread (80 g); two teaspoons of vegetable spread (10 g); one thin slice of cheese (20 g); two teaspoons of relish (20 g).

Right: Emissions for a peanut butter and jam sandwich: two slices of bread (80 g); two teaspoons of peanut butter (20 g); one teaspoon of jam (10 g).

How can you reduce emissions?

Can you reduce the cheese sandwich emissions? The simplest option is to use less cheese, for example by using one thin 20 g slice of cheese instead of two standard 25 g slices. Maybe some relish or mustard could fill the gap? Even a generous 25 g portion of relish is unlikely to have a big impact on emissions.

1 g relish = 3 g emissions

By reducing the amount of cheese and replacing the butter with vegetable spread, the emissions are halved (Fig. 9.4, centre). You lose out on some of the nutrition from the cheese and butter, but much of this can be restored by using wholemeal instead of white bread. As an added bonus, switching to wholemeal bread doubles your fibre intake, which will keep you feeling fuller for longer and, for most people, it will also improve gut health (see chapter 34).

Cheese from other animals

How about making cheese from the milk of animals other than cows? The most common alternatives are sheep, goats and buffalo. Unfortunately, from the point of view of greenhousegas emissions, these are similar to cows: they are all ruminants, with the same methane-producing rumen compartment in their stomachs.

It is said that Cleopatra bathed in the milk of over 700 donkeys every day, and its health benefits are widely claimed. Horses and donkeys have both been farmed for their milk and, because they are not ruminants, the greenhouse-gas emissions could be lower than those for cows (depending on how much milk they can produce). However, I’m not going to place my bets on a future rise in the popularity of horse cheese.

Vegan “cheese”

“It is important to combat false claims. Our products must be designated correctly: the terms of #cheese or #steak will be reserved for products of animal origin” – tweeted by French MP Jean-Baptiste Moreau

Some people say cheese made from anything other than animals’ milk should not be called cheese. Nevertheless there are a number of plant-based cheese alternatives you can make or buy, and this chapter would not be complete without considering them. To avoid being sued, we refer to them as vegan “cheese”.

I’d be more enthusiastic about the vegan “cheese” option if I hadn’t been disappointed by the taste and texture so many times. But maybe this is just a problem with the brands I’ve tried so far. I am an optimist and I want to know how this switch would affect emissions.

Standard shop-bought vegan “cheese” is usually made from oil, starch and water. Putting together these ingredients brings the emissions of a standard vegan “cheese” down to around one tenth of that of cows’ cheese, allowing for processing and refrigeration.

1 g oil-based vegan cheese = 1.4 g emissions

If, in addition, you replace the butter with vegetable spread then the “cheese” sandwich stack now looks quite different: the total emissions are six times lower than the standard cheese sandwich (compare Fig. 9.5 with Fig. 9.4, left).

The main ingredients of the majority of vegan “cheeses” (oil and starch) are derived from plants using processes which remove most of the vitamins and minerals. This means that standard vegan “cheeses” lack many of the nutritional benefits of regular cheese. Part of this can be made up by switching to wholemeal bread, and some vegan “cheeses” are fortified with nutrients that can’t easily be made up by the bread, including calcium and vitamins A, B12 and D. Some people eat cheese to get their protein fix, but standard vegan “cheese” usually contains little or no protein, unless protein has been specifically added to the formulation.

Fig. 9.5: Emissions for a vegan “cheese” sandwich: two slices of bread (80 g); two teaspoons of vegetable spread (10 g); two slices of vegan “cheese” (50 g).

Search for vegan “cheese” recipes on the internet and you will find bold claims of tastiness, yet almost none are made from the starch and oil used in most shop-bought vegan “cheese”. Some are based on tofu, but most are made from nuts (chapter 19). The total emissions will be slightly higher than those of standard oil- and starch-based vegan “cheese” (and the price is much higher), but as a food it is much more nutritious, and causes about 6 times lower emissions than regular cheese, depending on the processing and water content.

Other alternatives

If you don’t feel like whipping up a batch of vegan nut “cheese” at home, you can have a similar emissions footprint and nutritional profile by using nut or seed butter (chapter 19). Readily available options include peanut butter and almond butter (but watch out for added salt and sugar, and nut allergies).

My favourite is peanut butter with orange marmalade for a bit of tang to cut through the thick nut butter. Jam is also popular. The peanut butter (chapter 19) and jam (chapter 5) emissions come to about the same as the low values for the vegan “cheese” sandwich (Fig. 9.4, right).

Alternatively, any improvements in emissions from milk production (discussed in chapter 6) will translate into lower cheese emissions.

Of course, many other sandwich fillings exist, and that’s without even considering the non-sandwich lunchbox options. In the next chapter we consider replacing a slice of cheese with some ham.

Key points

- It takes about 10 kilos of milk to make 1 kilo of cheese, so cheese is a relatively high-impact food.

- A cheese sandwich causes nearly 1 kilo of emissions, which is one third of a daily food emissions budget of 3 kilos.

- This means that switching out some cheese for a low-impact alternative, like relish, halves the total sandwich emissions, particularly if butter is also replaced by vegetable spread.

- Cheese alternatives are usually much more climate-friendly than cheese, but often lack nutrition.

- Switching a cheese sandwich for a nut butter sandwich reduces emissions by five times.

Notes

add rennet Rennet occurs naturally in the stomachs of cows and other ruminants. This cheese-making combination of warm milk and rennet is not as surprising as it might seem at first sight, because cows’ stomachs were historically used as handy waterproof containers. Fill up an empty cow stomach with warm milk straight from a cow and leave it until the morning, and you’ve got curds and whey. Even more fascinating is that the rennet exists in the young cow’s stomach precisely because it curdles the mother’s milk. This slows down the passage of milk through the calf’s digestive system and allows more nutrients to be extracted. These days most cheese in the US and UK is vegetarian, because it’s made using artificial rennet. The artificial rennet is made using a black mould found on onions; this has been genetically modified to produce the rennet enzyme in carefully controlled laboratory conditions. The result is then purified to remove all traces of the mould, so the final rennet doesn’t contain any GM material.

The most common approach is to use the economic value, or cost, of each product. This means that the most sought-after products are allocated the largest share of the emissions. Alternative approaches include sharing the emissions out according to the weight of the product, or the weight of the solids in the product. For example, to share the emissions between cream and skimmed milk (chapter 15), the weight of dried milk is used, rather than the weight of the milk, because most of the milk is water.

cheese turns out to be responsible for producing about 16 times its own weight in greenhouse-gas emissions. The value used here is for European cheese of 16 kgCO_2e / kg cheese from Poore and Nemecek (2018), which is similar to the value for the US (15 kgCO_2e / kg), although note that this is much lower than the global average (24 kgCO_2e / kg) due to varying milk production practices.

Even a generous 25 g portion of relish is unlikely to have a big impact on emissions. Due to a lack of available information on emissions from relishes, the value here is an average of the value of Frankowska et al. (2019a) for UK pickled onions (2.4 kgCO_2e / kg) and the value for jam (see chapter 5), which gives 2.8 kgCO_2e / kg.

“It is important to combat false claims. Our products must be designated correctly: the terms of #cheese or #steak will be reserved for products of animal origin” Tweeted by French MP Jean-Baptiste Moreau, as reported in the Guardian (URL 30).

emissions of a standard vegan “cheese” down to around one tenth of that of cows’ cheese, allowing for processing and refrigeration. This uses the estimate of 1.43 kgCO_2e / kg for vegan “cheese” by Frankowska (private communication) based on retailer information on ingredients, and adding a margin for processing using the cheese processing figure from Frankowska (2019) (0.79 kgCO_2e / kg), and adding 0.3 kgCO_2e / kg for retail following Poore and Nemecek (2018) for cheese.

The total emissions will be slightly higher than those of standard oil- and starch-based vegan “cheese” (and the price is much higher), but as a food it is much more nutritious, and causes about 6 times lower emissions than regular cheese, depending on the processing and water content. Later, in our afternoon snack (chapter 19) we will find that nuts are responsible for about 3.2 grams of emissions per gram of nut, although this varies widely depending mostly on how the land was used before it came into nut production (since nut production is on the increase). The recipes mostly call for the nuts to be pre-soaked in water, before being blitzed and combined with other ingredients, typically including salt, garlic and lemon juice. For a nut “cheese” made of 50% nuts, the nuts contribute about 1.6 grams of emissions per gram of nut “cheese”. To this add 1.1 gram of emissions for processing and retail combined (see previous endnote), giving total emissions for nut “cheese” of less than three times its own weight. Replacing the dairy cheese with a nut-based vegan “cheese” still reduces the sandwich emissions by more than four times.

Chapter 10 Ham, pork and bacon

Fig. 10.1: Sliced ham. (URL 31)

How about replacing some, or all, of the cheese in your sandwich with ham? Ham is such an easy sandwich filling – you don’t even have to get out a knife!

Where does ham come from anyway? Wikipedia says it comes from the leg of a pig, but in Fig. 10.2 it’s more like the pig’s bottom, which sounds less appetizing, although it still tastes great to me.

Piglets

Fig. 10.2: Map of a pig showing where different cuts of meat are taken from. (URL 32)

A one-year-old female pig usually has about 11 piglets at once, and may give birth to 11 more just 5 months later. She typically gives birth to about 50 piglets in total before being slaughtered for bacon herself at 2 or 3 years of age.

A piglet eats nearly twice as many calories as an average human each day, so there is some justification to the phrase “to pig out”. And pigs do put on weight fast: a piglet is born weighing less than a human baby, and grows to weigh more than the average adult human in just 5 months, when it is slaughtered for about 70 kilos of pork meat.

On western commercial farms the piglets mostly eat grains like wheat, beans like soy, and some leftovers from human food production. This includes “seed cake”, which sounds like it would be tasty with a cup of tea, but in fact is the squashed remains of seeds after pressing out vegetable oil. For every 7 calories eaten by the pigs, about 1 goes into pork and the other 6 end up in manure.

Fig. 10.3: Piglets. (URL 33)

Animal wee and poo

We do need to talk about all that manure. An archetypal cow lives outside in pasture doing their business all over the field (chapter 4). At first glance this sounds bad for climate change, but the alternative is worse…

Farmed pigs typically live indoors and their manure is collected and stored in a big “slurry pit”, to be spread on the fields at a later date. When I used to walk to school as a kid, there was one day of the year when there was an awful smell – the day the winter pig manure got spread on the fields to feed the crops. I don’t think I would have liked it much if the muck spreading had happened more frequently, but that would actually have been better for the environment.

Fig. 10.4: Some pigs looking content. (URL 34)

Manure is a combination of both wee and poo – the wee is important because it contains much of the valuable nitrogen. Because wet pig manure can’t rot down using oxygen from the air, it instead makes methane, a powerful greenhouse gas (chapter 1). The amount of methane released by manure depends on the temperature and the length of time it is kept for – the longer it is kept in wet and warm conditions, the more methane is produced.

Box 10.1: Animal efficiency / inefficiency

Many animals eat several times as many calories as they provide to us in the form of meat.

- For every calorie we get from chicken, 3 have to be eaten by the animal (chapter 25).

- For every calorie we get from ham or pork, 7 have to be eaten by the pig (see above).

- For every calorie we get from beef, 50 have to be eaten by the cow (chapter 24).

One nutritional benefit of this apparent inefficiency is that the animals concentrate the nutrients from the plants, so meat has a higher concentration of some nutrients than plants. In fact the nutrient profile of meat is extremely well matched to what we need to grow strong muscles. (This is neither a coincidence or grand design – it’s simply because we too are animals and are mostly made of meat!)

However, with a large population on a limited planet demanding increasing amounts of animal products, this inefficiency is now driving deforestation which is bad news for the climate (see chapters 7 and 37).

As a result of this inefficiency, you will notice a trend emerging, that the even the lowest-emissions animal products generally cause more climate change than plant-based products.

A piece of ham causes about 11 times its own weight in emissions, depending mostly on how the farm is managed.

1 g ham = 11 g emissions

Growing food for pigs causes about half of this total, manure is responsible for about a quarter, and the other quarter is mostly energy, including the processing from pig into ham.

The more the pork is processed (for example dry-cured ham or bacon) the higher the emissions. However, if the pork product uses less popular parts of the animal that would otherwise be unused (e.g. black pudding or sausages) then the emissions are lower (see box 9.1).

Fig. 10.5: A high-quality ham sandwich, which is a lot more photogenic than the plain white bread ham and cheese sandwich we’re mainly discussing here. (URL 35)

Cheese and ham toastie emissions

Ham emissions are therefore usually lower than those caused by cheese (which is typically responsible for 16 times its own weight in emissions – see chapter 9). In a ham sandwich containing two slices of ham (50 g), most of the emissions are caused by the ham (Fig. 10.6, left). If you replace the ham with cheese, the greenhouse-gas emissions will increase by about 40% (compare Fig. 10.6 left and centre). We’ll settle on one slice of each for now (Fig. 10.6, right).

Fig. 10.6:

Left: Emissions for a ham sandwich: two slices of bread (80 g); two teaspoons of butter (10 g); two slices of ham (50 g).

Centre: Cheese sandwich (duplicated from chapter 9 for ease of comparison).

Right: Emissions for a cheese and ham sandwich: two slices of bread (80 g); two teaspoons of butter (10 g); one slice of cheese (25 g); one slice of ham (25 g).

Would you like the sandwich toasted? With melting cheese in the middle and crunchy cheese bits oozing out of the sides? Go on… put the grill on for 10 minutes, so it heats up and gets the cheese really gooey. This adds about 20 per cent to the emissions, so it’s better to focus on reducing the amount of cheese and ham in the sandwich, rather than feeling too virtuous by forsaking the toasting.

How can you reduce emissions?

What about ham alternatives? Switching from ham to beef steak more than triples the total sandwich emissions (Fig. 10.7, centre; see steak details in chapter 24). A single steak sandwich containing 50 grams of beef blows most of a 3 kg daily food emissions budget. On the other hand, switching from ham to chicken reduces the climate-impact by about a third, if you’re also prepared to use vegetable spread instead of butter (compare Fig. 10.7 left and right; see chicken details in chapter 25).

Ham emissions can be reduced further by feeding pigs on more leftovers from processing human food, or other novel feed sources (chapter 7), and their manure can be spread on the fields more frequently, or the methane collected to use as fuel. However, it would be hard to make ham that has lower emissions than chicken, because pigs are less efficient at converting feed calories into meat calories (box 10.1).

Fig. 10.7:

Left: Greenhouse-gas emissions for a ham sandwich (duplicated from Fig. 10.6 for ease of comparison.

Centre: Emissions for a steak sandwich: two slices of bread (80 g); two teaspoons of butter (10 g); two slices of steak (50 g).

Right: Emissions for a chicken sandwich: two slices of bread (80 g); two teaspoons of vegetable spread (10 g); two slices of chicken (50 g).

Lab protein

For medical purposes, animal cells are routinely grown in small petri dishes in laboratories. The dish is kept warm and nutrients are added to keep the cells happy and growing. So why not grow our food that way too? Less energy wasted on being an animal is good news for the climate, and there may be welfare benefits.

As an innovation enthusiast I’m excited at the idea of producing meat without the need to grow a whole animal, but I realize not everyone is going to be so enthusiastic. And for all my technophilia, how would I really feel when it came time to put the lab burger into my mouth? Is it safe? What are the ethics here? Would you eat it?

Academic studies of consumer reactions to the concept have recorded disgust, and concern about the impact on farming and eating traditions, with less than half of consumers prepared even to try lab meat.

However, the idea of growing protein in a laboratory is not new. Mycoprotein is a naturally occurring close relative of mushrooms and is sold commercially in Quorn. The greenhouse-gas missions of making mycoprotein arise mostly from growing it in a warm nutrient bath. On top of that, for the sliced Quorn used in sandwiches, we have to add on the processing from mycoprotein into Quorn slices, which triples the emissions.

1 g Quorn pieces = 1 g emissions

1 g Quorn slices = 3 g emissions

Overall the fresh sliced Quorn emissions are still less than half those for ham or chicken – so this provides another low-carbon option for our sandwich, without waiting around for tasty lab meat to become widely available (Fig. 10.8).

Fig. 10.8: Emissions for a Quorn sandwich: two slices of bread (80 g); two teaspoons of vegetable spread (10 g); two Quorn slices (50 g).

Of course you can just eat plants directly! In the next chapter we consider a bowl of salad, which can also be used as a sandwich filling.

Key points

- Ham and pork contribute to climate change mostly because of emissions from pig feed and manure.

- Ham and cheese cause similarly large amounts of emissions, so the exact proportions of ham and cheese in the sandwich aren’t as important as reducing the total amount.

- A steak sandwich causes triple the emissions of a ham sandwich, and uses up most of a daily food emissions budget of 3 kilos.

- Switching to mycoprotein can more than halve the sandwich emissions, to one tenth of a daily food emissions budget of 3 kilos.

Notes

She typically gives birth to about 50 piglets in total before being slaughtered for bacon herself at 2 or 3 years of age. The number of litters per sow per year is 2.3 and the number of piglets is 11.2 pigs weaned per litter, taken from the UK 2018 AHDB Pig Pocketbook (AHDB, 2018a). From the same source, the average pig replacement rate is 51.6%, so the sow phase is nearly 2 years – which allows time for 4 or 5 litters (44 to 55 piglets in total). A single sow gives birth to so many piglets that she contributes just under 10% of the total pig emissions (assuming the emissions are proportional to the number of pig years) since she is alive for 2.5 years and the 50 piglets are alive for 0.5 years (2.5 / (2.5 + 50*0.5) * 100 = 9%). There is typically 1 male pig for 20 or more female pigs (Roese and Taylor, 2006) so the emissions from the boar are less than 1% of the total (approximately 9%/20). This means that when we calculate the greenhouse-gas emissions of ham the thing we need to consider most carefully is the emissions from the piglets as they grow up.

grows to weigh more than the average adult human in just 5 months, when it is slaughtered for about 70 kilos of pork meat. According to the UK 2018 AHDB Pig Pocketbook (AHDB, 2018a) the average number of days in the herd was 146 in the UK in 2017, which is 4.8 months. The average weight of pigs produced is 109.9 kg. To convert this into the weight of pork meat we use the lean meat percentage of 61.1 from the AHDB Pork Yearbook 2017 (AHDB, 2017), which gives 67 kg of lean meat per pig (rounded up to 70 kg in the main text for simplicity).

piglets mostly eat grains like wheat, beans like soy, and some leftovers from human food production. e.g. see Table 3.1 of Kool et al. (2009).

For every 7 calories eaten by the pigs, about 1 goes into pork and the other 6 end up in manure. Growing pigs eat 3872 kCal a day, calculated from 16.2 MJ/day given in Table A1.10 of Kool et al. (2009). The pigs are fed for 146 days, and so consume 3872 kCal/day × 146 days = 565,312 kCal in total. 67 kilograms of lean meat is produced from one pig. Pork has about 120 kCal per 100 g (1200 kCal / kg), so a whole pig provides 67 × 1200 kCal = 80,400 kCal for human consumption. Therefore we eat 80,400 / 565,312 × 100 = 14% of the calories consumed by the pig, or one in seven.

the wee is important because it contains much of the valuable nitrogen. In humans most of the valuable nitrogen is in the urine rather than the faeces (Rose et al., 2015). It’s a running joke on my favourite gardening show that panellist Bob Flowerdew pees on his compost heap – urine is a great fertilizer once diluted or composted. In pigs the fraction is lower, but still usually more than 50% (Jørgensen et al., 2013).

The amount of methane released by manure depends on the temperature and the length of time it is kept for – the longer it is kept in wet and warm conditions, the more methane is produced. Because the UK doesn’t get very hot, an annual manure spread leads to only about one fifth of the maximum methane being released. Kool et al. (2009) use a methane conversion factor (MCF) of 20% for England).

ham causes about 11 times its own weight in emissions, depending mostly on how the farm is managed. This is based on the value of 10.7 kgCO_2e / kg from Noya et al. (2016) which specifically studied ham, though see also values in Poore and Nemecek (2018) of 10 kgCO_2e / kg for pork from Europe and 12 kgCO_2e / kg for the global average.

The more the pork is processed (for example dry-cured ham or bacon) the higher the emissions. Noya et al. (2016) calculate emissions of 12.7 kgCO_2e / kg for dry-cured ham.

Less energy wasted on being an animal is good news for the climate, and there may be welfare benefits. The main contributions to lab meat emissions are from the nutrients provided to the growing cells, and the heat required to warm the system up to body temperature. The feed conversion ratio is thought to be better than two, which is better even than for chicken meat, which is good news for fertilizer-related emissions and use of land (Tuomisto and Mattos, 2010).

less than half of consumers prepared even to try lab meat. According to Siegrist et al. (2018).

the fresh sliced Quorn emissions are still less than half those for ham or chicken The comprehensive book Sustainable Protein Sources (Nadathur et al., 2016) contains a chapter contributed by employees of Quorn Foods which describes the process and emissions. The Quorn webpage (URL 116) gives carbon footprints from a 2019 study accredited by the Carbon Trust: the mycoprotein itself causes 0.8 kgCO_2e / kg, whereas Quorn Pieces cause 1.3 kgCO_2e / kg up to the point of sale and Quorn Vegan Ham-free Slices cause 3.2 kgCO_2e / kg. The Quorn sandwich calculation uses the Quorn Slices value and the Quorn tikka masala (chapter 25) uses the Quorn Pieces value.

Chapter 11 Salad

Fig. 11.1: Tomato salad. (URL 36)

How about some refreshing salad to go with all that melty cheese and ham? Perhaps some tomatoes or lettuce mixed with a little oil and vinegar?

Tomatoes

Most tomatoes grow in open fields and are given fertilizer and water to produce a heavy crop. We eat some of those fresh, and preserve the rest to use later, for example in sauces.

Fertilizer dominates the greenhouse-gas emissions on the farm, just as for most vegetables (box 2.1). Depending on the weather, they may also need water pumped to the fields to keep the plants happy, which contributes to the emissions if the pumps are powered by fossil fuels. However, even adding this in, the total tomato emissions are still small for in-season field-grown tomato emissions, at one sixth of their own weight (although out-of-season tomatoes are a different matter, as we shall see next).

1 g local, in season, field-grown tomatoes = 0.16 g emissions

How about chopping up your tomatoes and taking them to another level by drizzling on some oil and vinegar, and maybe a pinch of salt (Fig. 11.1)? (Salt causes negligible emissions, so is not shown in the stacks.) The salad dressing causes more emissions than the tomatoes themselves, but the total is still less than 2% of a daily food emissions budget of 3 kilos (Fig. 11.3, left).

Fig. 11.2: Tomatoes growing on their vines. (URL 37)

You prefer cherry tomatoes (Fig. 11.2)? I do, and my kids can finish off a bumper pack in one sitting! What a great way to eat more veg! So I was disappointed to learn that most cherry tomatoes are grown in heated greenhouses or plastic constructions called polytunnels. Natural gas (fossil fuel) is burned to keep the plants warm and to produce carbon dioxide for the plants to breathe. Electricity is used to circulate water, nutrients and air.

The emissions from a heated greenhouse totally depend on the outside temperature and on how well insulated the greenhouse is (i.e. the thickness of the glass or plastic, and the quality of the draught exclusion). Commercial heated-greenhouse tomato farms can produce over 10 kilos of carbon dioxide for every kilo of tomatoes (Fig. 11.3, centre), which is right up there with the ham (chapter 10) and chicken (chapter 25).

Fig. 11.3:

Left: Emissions for a tomato salad (in season): a local in-season tomato (50 g); two teaspoons of vegetable oil (10 g); a teaspoon of vinegar (5 g).

Centre: The same salad but using tomatoes grown in a heated greenhouse, without any additional measures such as combined heat and power.

Right: Emissions for a lettuce salad (by truck 400 km [250 miles]): a portion of lettuce (50 g); transport 400 km [250 miles] by truck; two teaspoons of vegetable oil (10 g); a teaspoon of vinegar (5 g).

1 g tomatoes grown in a heated greenhouse = 13 g emissions

The small tomato salad now causes over 20% of a 3 kilo budget for total daily food emissions.

A number of improvements have been made by the most advanced growers, most significantly by using waste heat and carbon dioxide from fossil-fuelled power stations instead of burning fossil fuels just for the tomatoes. In this case we have to share out the greenhouse-gas emissions between the electricity produced by the power station and the fresh produce (box 9.1). This can reduce the out-of-season tomato emissions significantly. Savvy growers also store the excess daytime warmth from the sun and pump sun-warmed water back through the greenhouses at night time to even out the temperature.

Fig. 11.4: Vertical farming. Image thanks to LettUsGrow (URL 39).

Lettuce

Lettuce, spinach and herbs are increasingly grown using a new technology called vertical farming: plants are illuminated by artificial lights, which means they can be grown indoors and stacked up high, layer after layer. This might sound extremely inefficient, but the colour of the lights can be tuned to match the needs of the plants, thereby saving electricity and giving the grow rooms an eerie pink glow (Fig. 11.4).

The indoor vertical farms can be kept warm more easily than greenhouses and polytunnels, thus reducing the need for heating. Vertical farms usually avoid using soil, which means that fertilizers cannot escape or be turned into nitrous oxide by soil microbes. Finally, vertical farms can produce a lot of food in a very limited land area, and can be situated close to the consumer, for example in basements of city buildings. Vertical farming is currently only economically viable for high-value crops such as salads and herbs, and isn’t expected to produce anywhere near enough food to replace soil-based farming, but it is (literally) a growing industry and may be coming soon to a building near you.

Salads like lettuce, peppers (capsicum) and cucumbers have to be kept in refrigerators or else they rot quickly, whereas tomatoes taste best if they aren’t chilled. This is partly why the emissions from lettuce are higher than those for seasonal tomatoes (compare Fig. 11.3 left and right).

1 g lettuce = 1.5 g emissions

Other than that, the emissions of lettuce depend crucially on how it is grown: whether it is grown outdoors, in a heated greenhouse (leading to emissions like the tomato in Fig. 11.3, centre) or in a vertical farm powered by clean energy.

Box 11.1: Supermarket fridges

I get excited about the quality of a supermarket when I walk through an array of tasty-looking fresh fruit and vegetables, perhaps while subconsciously inhaling the smell of fresh bread piped over from the bakery. But unfortunately there is a cost to the climate of having the most fragile foods out on display. Refrigerators use a significant fraction of the electricity used by the whole supermarket and the refrigerant fluid used to cool the fridge has historically been a powerful greenhouse gas.

The greenhouse-gas emissions of an item of food therefore depend on whether it is kept refrigerated, or frozen, for how long, and how much room it takes up (which determines how many can fit in the fridge or freezer). It has been calculated that supermarket fridges can add around 1 kilo of emissions for every kilo of product, with roughly equal contributions from electricity consumption and refrigerant leakage.

Winter salad

We’re being told to eat more fruit and vegetables, so what are the most climate-friendly options? You can enjoy local tomatoes in season without worrying about emissions. In the middle of winter you can still get plenty of tomatoey goodness by eating them preserved (e.g. tinned tomatoes, passata or tomato puree), which can be made from field-grown tomatoes picked in season.

Many winter vegetables can also be eaten raw in salads, including carrot, parsnip, turnip and cabbage. These have much lower emissions than a winter tomato. We’ll come back to these at dinner (chapter 28).

Key points

- Local, in-season, field grown tomatoes are a very low-emissions food.

- Salad grown in heated greenhouses can cause emissions comparable with chicken and ham, but this can be significantly reduced with heating technology.

- Keeping salad items (e.g. lettuce) in supermarket chiller cabinets can add roughly their own weight in emissions compared with those that don’t (e.g. tomatoes).

Notes

the total tomato emissions are still small for in-season field-grown tomato emissions, at one sixth of their own weight (although out-of-season tomatoes are a different matter, as we shall see next). Field-grown tomatoes in Italy cause 0.16 kgCO_2e / kg according to Frankowska et al. (2019a). Note that this is 78 times lower than the UK value (which includes heating greenhouses). See also Payen et al. (2015).

oil Assuming a 50% mix of sunflower and rapeseed oil gives a global average of 3.7 kgCO_2e / kg from Poore and Nemecek (2018).

vinegar, Due to a lack of studies, this uses the wine value (chapter 29).

Salt causes negligible emissions, so is not shown in the stacks. Salt causes about 0.2 kgCO_2e / kg salt accordingly to “CCaLC PVC Manual (V2.0)” (2011). Half a teaspoon of salt weighs about 3 grams, so it causes less than 1 gram of emissions, which is tiny compared to all the other items.

Commercial heated-greenhouse tomato farms can produce over 10 kilos of carbon dioxide for every kilo of tomatoes Frankowska et al. (2019a) find 12.52 kgCO_2e / kg tomatoes for the UK taking into account heating greenhouses.

Savvy growers also store the excess daytime warmth from the sun and pump sun-warmed water back through the greenhouses at night time to even out the temperature. These ideas are taken from the webpage of the tomato growers APS Group (URL 38). See chapter 21 of MacKay (2009) for comments on combined heat and power, and some ways smart heat storage can be taken to another level using heat pumps.

tomatoes taste best if they aren’t chilled. See Zhang et al. (2016).

emissions from lettuce Figure S44 of Frankowska et al. (2019a) gives a value of 1.45 kgCO_2e / kg lettuce for UK production.

Refrigerators use a significant fraction of the electricity used by the whole supermarket “In UK supermarkets, more than 70% of the energy consumed is electricity of which between 30% and 60% is used to drive the refrigeration equipment in the store.” – Greenhouse Gas Impacts of Food Retailing: Report for Defra (2008).

It has been calculated that supermarket fridges can add around 1 kilo of emissions for every kilo of product, with roughly equal contributions from electricity consumption and refrigerant leakage. This was calculated for strawberries in Table 5.2 of Greenhouse Gas Impacts of Food Retailing: Report for Defra (2008). This assumes the supermarket is using electricity almost entirely from fossil fuels (0.537 kgCO_2e / kWh) and the refrigerant (R-404A) is 3860 times more potent than carbon dioxide as a greenhouse gas. This number would be reduced depending on the fraction of clean energy in the electricity mix, and using modern refrigerants such as carbon dioxide. However, the lower density of lettuce (compared to strawberries) would significantly increase emissions (e.g. see Table 11 of Frankowska et al. 2019a).

preserved (e.g. tinned tomatoes, A value of 1.8 kgCO_2e / kg comes from figure S26 of Frankowska et al. (2019a) for canned tomato, using 92% of 1.95 (to exclude the cooking and waste emissions which are covered separately in chapter 33).

passata Figure S26 of Frankowska et al. (2019a) gives a value of 2.04 kgCO_2e / kg for bottled tomato, using 88% of 2.32 (to exclude the household cooking and waste emissions).

tomato puree Figure S26 of Frankowska et al. (2019a) shows a value of 4.6 kgCO_2e / kg, after excluding waste emissions.

Chapter 12 Pizza

Fig. 12.1: A pepperoni pizza with plenty of cheese. (URL 113)

Who doesn’t like pizza (Fig. 12.1)? It’s the safest bet to serve at a kids’ play date these days. In terms of ingredients though, it isn’t very different from the cheese sandwich we already discussed (chapter 9). The main difference in ingredients is the tomato sauce which, as we just saw, is not going to contribute much to greenhouse-gas emissions because it can be made from in-season field-grown tomatoes and stored at room temperature. The total emissions for a pizza can approach 1.5 kilos, or half of a budget of 3 kilos for daily food emissions (Fig. 12.2, left). Of this 1.5 kilos, nearly 1 kilo comes from the cheese.

Meaty feast?

What about a ham or pepperoni pizza, or a meat feast with several meat and sausage toppings? Pepperoni can be made from pork or beef, or some combination. As we discovered in chapter 10, meats from pigs have comparable emissions to cheese, weight-for-weight. So it doesn’t make much difference if you swap out some cheese for ham (compare Fig. 12.2 centre and left).

Other meaty options include beef pepperoni or ground beef, for which the emissions depend significantly on the quality of the beef (chapter 24). In the extreme case of using high quality steak as a pizza topping, the pizza emissions are increased to nearly 2 kilos – about 30% more than the ham pizza (Fig. 12.2, right).

Oven use

Unlike a sandwich, a pizza is best served crispy and hot. The oven is pre-heated to a high temperature, and the pizza goes on the top shelf until the cheese just starts to bubble. Depending on your oven and energy supplier, the cooking may be the next biggest contributor to emissions after the toppings (Fig. 12.2).

Fig. 12.2: Emissions from different choices of pizza topping, assuming the pizza is cooked for 10 minutes for one person.

Left: Emissions for a cheese and tomato pizza: a pizza base (210 g); tomato puree (30 g); cheese (60 g); putting the oven on for 10 minutes, plus warm-up time (25 minutes at 2 kW).

Centre: The same as the cheese and tomato pizza, but replacing half the cheese with ham.

Right: The same as the cheese and tomato pizza, but replacing the 60 g cheese with 20 g cheese, 20 g ham and 20 g steak.

Box 12.1: Oven emissions

The emissions from cooking depend mostly on how long you have the appliance on for. Which do you think impacts the climate more i) putting the oven on for one hour or ii) putting the grill on for 10 minutes? Just by comparing the two durations you can already correctly guess that the oven is going to use more electricity.

For appliances that stay on for a long time, we also have to factor in leakage of the heat. I don’t know how efficient your own oven is, but you can find out if you watch the little temperature indicator light: when the light is on, the oven is using electricity to heat itself up, but when the light is off the oven is at the right temperature and not using electricity.

A really well-insulated oven would heat up to the required temperature and then stay there without needing extra power (so long as you don’t go opening the door to check on the pizza…) but realistically some heat is going to escape into your kitchen, which means that the power will have to switch on again.

If you needed the kitchen to be warmed up anyway, and if you turn the heating down to compensate for the heat generated by the oven, then the energy used to heat the oven has been compensated for. Also, if you’re cooking for several people at once, then the cooking emissions per person reduce proportionately.

How can you reduce emissions?

How can you still enjoy the crunchy tastiness of a pizza without blowing half a daily food emissions budget of 3 kilos in one go?

- Halving the amount of cheese reduces the emissions by 30%. Or, if you cook for two people at once, and if you can cope with using just a sprinkling of cheese, you halve your pizza emissions (Fig. 12.3, centre).

- Switching to vegan cheese makes the biggest single difference.

- Or you might want to switch in some vegetables – I like sweetcorn because it adds back in a lighter colour to compensate for the missing cheese, and a sprinkling of ground almonds feels a bit like Parmesan (for more details on nuts see chapter 19).

1 g sweetcorn = 2 g emissions

If you’re also cooking for a family of four then you’ve just reduced your pizza emissions by 70% (Fig. 12.3, right), down to less than half a kilo per pizza.

I’ll be honest though that, in my experience, without any of the gooeyness of melted cows’ cheese, the toppings do tend to fall off. You might want to warn people to keep that pizza slice level – or maybe those artificial lab milk proteins will come to the rescue (chapter 6)?

Fig. 12.3:

Left: The cheese and tomato pizza from Fig. 12.2 (left), reproduced for ease of comparison.

Centre: Emissions for a cheese and tomato pizza (one third cheese): a pizza base (210 g); tomato puree (30 g); cheese (20 g); putting the oven on for 10 minutes, plus warm-up time, shared between two people (13 minutes at 2 kW).

Right: Emissions for a vegan “cheese” and sweetcorn pizza: a pizza base (210 g); tomato puree (30 g); vegan “cheese” (25 g); putting the oven on for 10 minutes, plus warm-up time, shared between four people (6 minutes at 2 kW); sweetcorn (30 g); ground almonds (10 g).

Key points

- For a typical cheesy and/or meaty pizza, the topping is responsible for most of the emissions, so reducing the amount of cheese and meat on the top is the single most effective way to reduce the climate impact.

- Using alternative toppings, such as vegetables, and cooking for four people at once, can make the pizza a low-emissions meal, and three times better for the climate than a traditional pizza.

Notes

but realistically some heat is going to escape into your kitchen, which means that the power will have to switch on again. The calculations here assume your oven draws 2 kW of power while it warms up for 15 minutes, and is then on at an average of 2 kW for the rest of the cooking time too. In practice the emissions will depend not only on your oven but also on the temperature you’re cooking at: the hotter the cooking temperature, the more heat will flow into your kitchen.

sweetcorn An emissions value of 1.9 kgCO_2e / kg comes from figure S58 of Frankowska et al. (2019a) for frozen UK sweetcorn, taking the first 82% of 2.27 kgCO_2e / kg to avoid double-counting cooking (household) and waste.

Chapter 13 A baked potato, or fries

Fig. 13.1: Baked potato with beans and cheese. (URL 40)

I do like a baked potato, with baked beans and cheese and lots of butter. Fig. 13.1 shows a really greasy-looking serving in a polystyrene tray – a classic British lunch – as yummy as it is squeaky (Fig. 13.1).

Growing potatoes

Have you ever grown your own potatoes? I couldn’t see what the excitement was about until I gave in last year and bought a special potato bag for the patio. The potatoes sprouted, I didn’t get around to earthing them up, they dried out and wilted between the rains and got mostly eaten by enormous black slugs. Eventually the leaves looked so yellow I thought I should move them at least out of view. I have to admit to a great sense of satisfaction and amazement – and excitement from the kids – at searching through the compost and finding all the small potatoes that grew, despite my neglect.

Fig. 13.2: Potato plants in a field. (URL 41)

Commercial potatoes grow in the ground with fertilizers, but even a large potato isn’t going to make much of an impact on your daily food emissions, until you start factoring in the cooking and accompaniments.

1 g potato = 0.6 g emissions

Fig. 13.3: Potatoes as they are dug up. (URL 42)

Cooking potatoes

What could be an easier meal than sticking a potato in the oven and forgetting about it for an hour or two? My oven has usually been on for at least 2 hours by the time I’ve pre-heated it, remembered to put the potatoes in, and remembered to take them out. If you’re cooking for one, then the oven alone causes over 2 kilos of emissions (see also chapter 1 and box 12.1). A generous helping of cheese and some butter brings the total emissions up to over 3 kilos per portion (Fig. 13.4, left), using up a daily food emissions budget of 3 kilos.

But this is lunchtime – perhaps you’re at a work canteen where there are lots of potatoes and other food in the oven, so the cooking emissions per potato would be very small. Or, if you’re cooking for two and prepared to halve the amount of cheese, and replace butter with vegetable spread, you can halve the emissions (Fig. 13.4, centre).

Fig. 13.4: Comparison of some different baked potato choices.

Left: Emissions for an oven-baked potato with generous cheese and butter: one potato (250 g); a large tablespoon of butter (20 g); two slices of cheese (50 g); putting the oven on for 2 hours, plus warm-up time (135 minutes at 2 kW).

Centre: Emissions for an oven-baked potato with modest cheese and veg spread: one potato (250 g); a large tablespoon of vegetable spread (20 g); one slice of cheese (25 g); putting the oven on for 2 hours, plus warm-up time, divided between 2 people (67.5 minutes at 2 kW).

Right: Emissions for a microwaved potato with relish: a potato (250 g); a large tablespoon of vegetable spread (20 g); two teaspoons of relish (20 g); microwave oven (8 minutes at 1.2 kW).

Maybe you’re being quick at home and cooking your potato in the microwave oven? I’m not a big fan of this method, but the internet says it takes about 8 minutes per potato. Assuming the microwave is on full power for that time, the cooking produces nearly 30 times less greenhouse-gas emissions per potato than baking in the oven for two hours (see box 12.1).

If you want to go ultra-low-emissions then you can also replace the cheese with a lower-emissions alternative, like chutney or relish (Fig. 13.4, right; see also chapter 9). This produces the lowest-emissions hot meal in the book, at less than 400 grams of emissions.

Chips or french fries

Chopping up the potato before putting it in the oven, for example to make small roast potatoes, potato wedges or chips, reduces the cooking time, but the climate impact depends a lot on how they are processed and cooked.

The lowest-emissions chip or potato wedge would be made from hand-chopped potatoes, cooked in a modest amount of oil on a large scale. When cooking for one person for 30 minutes, the oven causes most of the emissions (Fig. 13.5, left). On the other hand, if cooking for four people at once then the oven emissions are nearly as small as those from the potato (Fig. 13.5, centre) – this is even lower than the microwaved jacket potato emissions.

However, taking into account the processing of potatoes all the way to frozen oven chips can increase emissions to 3 times the weight of the chips (Fig. 13.5, right).

1 g chips = 3 g emissions

Fig. 13.5: Emissions for potato wedges and chips.

Left: Emissions for potato wedges (homemade): potato (150 g); vegetable oil (5 g); putting the oven on for 30 minutes, plus warm-up time (45 minutes at 2 kW).

Centre: Same as left but cooking for four people at once so the oven emissions are divided by four.

Right: Emissions for chips: oven chips (150 g); putting the oven on for 30 minutes, plus warm-up time, shared between 2 people (22.5 minutes at 2 kW).

Key points

- The emissions from a simple potato are small compared to those from dairy toppings or heating an oven using fossil fuels.

- Adding in cheese and butter, and cooking for one, brings the baked potato emissions to over 3.2 kilos, which is greater than our daily food emissions budget of 3 kilos.

- You can halve the emissions by going easy on the cheese, replacing butter with vegetable spread, and cooking two potatoes at once.

- Cooking in the microwave oven and replacing cheese with relish turns the baked potato into a very low-emissions meal, causing nearly 0.3 kilos per portion, which is one tenth of a 3 kilo food emissions budget per day.

- Chopping up potatoes before putting them in the oven reduces the cooking time, and therefore the emissions. Using home-chopped potatoes instead of processed shaped potatoes saves energy.

Fig. 13.6: I love potatoes! (URL 43)

Notes

but even a large potato isn’t going to make much of an impact on your daily food emissions, 0.6 kgCO_2e / kg of raw potato is taken from Frankowska et al. (2019a) (figure S.52) who give a value of 1.2 kgCO_2e / kg of which household/cooking and waste contribute 50% so are subtracted to avoid double counting. See also 0.5 kgCO_2e / kg from Poore and Nemecek (2018).

hand-chopped potatoes, cooked in a modest amount of oil on a large scale. This doesn’t mention peeling the potatoes, because keeping the skin on helps reduce emissions because there is less waste (chapter 33). Eating the skin is also healthier because it contains more of some nutrients (including fibre) than the potato flesh.

taking into account the processing of potatoes all the way to frozen oven chips can increase emissions to 3 times the weight of the chips Frankowska et al. (2019a) find a value of 3.9 kgCO_2e / kg for frozen chips prepared in the oven at home of which 14% is household/cooking and waste, which we discuss separately, giving 3.4 kgCO_2e / kg. Alternatively T. Ponsioen and H. Blonk (2011) find a value of 2.0 kgCO_2e / kg. The figures in this book use an average of these two numbers. Ultimately the value will depend greatly on the type of energy (fossil or clean) used in the manufacturing).

Chapter 14 Beans and other legumes

Fig. 14.1: Soya bean pods on the plant. (URL 44)

Reach for a tin of beans from the store cupboard or pantry and you have a nutritious meal in your hand – if you’re desperate the beans can even be eaten cold, straight from the can. (I have done this.) The beans have been transformed from their green beginnings, when they grew like peas in a pod (Fig. 14.1).

In this chapter we focus on mature beans and other legumes that have been left on the plant to grow fat and ready to sprout into a new generation of plants whenever they get enough water to start swelling and growing. These include soya beans, the beans used to make baked beans, haricot beans (Fig. 14.2), and their close relatives lentils and chick peas.

Fig. 14.2: Haricot beans (also known as navy beans, so-called not because of their colour, but because they are so nutritious they are fed to the US Navy). (URL 45)

Legumes and nitrogen

In terms of greenhouse gases, beans and other legumes are almost magical: they work with bacteria in their roots to take nitrogen from the air and convert it into a form that the bean plant can use. This reduces the amount of fertilizer needed by the plants and, if the roots are left in the ground, they even reduce the amount of fertilizer needed by the next crop. This means that alternating or mixing other crops with legumes helps to cut greenhouse-gas emissions.

Cooked beans

The beans themselves cause less than their own cooked weight in emissions,

1 g beans, cooked weight (excluding cooking) = 0.63 g emissions

so the big question is how much energy is used to cook them. Dried beans need a lot of cooking, and the boiling time varies significantly between different types. The amount of energy required also depends on whether you cook the beans in a sealed pressure cooker or in ordinary saucepan that allows lots of water to evaporate.

Two different bean-cooking calculations illustrate the wide variation in energy use. On the one hand, cooking for one person using an open pan for 40 minutes is very inefficient, and causes higher than half a kilo of emissions (Fig. 14.3, left): the cooking causes much more emissions than the beans themselves. On the other hand, you can be much more efficient by cooking four portions at once using a pressure cooker for 20 minutes (Fig. 14.3, centre). Now the cooking emissions are similar to those from the beans, and the total is only one quarter of the emissions of the inefficiently cooked beans.

Fig. 14.3: Comparison of some different ways of cooking beans.

Left: An extremely inefficient example of boiling up an open pan for 40 minutes to cook 45 g of dried beans into 125 g of cooked beans.

Centre: A much more efficient case in which the same quantity of beans are cooked for 20 minutes (for example in a pressure cooker) and the cooking emissions are shared between four people (5 minutes of 2 kW electricity per person).

Right: Emissions for canned beans re-heated: the same quantity of beans (125 g cooked beans, or half a drained can); a 50 g steel can, shared between 2 people (25 g); cooking in a microwave oven (3 minutes at 1.2 kW).

How do home home-cooked beans compare with ready cooked beans in a tin can? I put in a diagram showing the emissions from canned beans, showing separately the contribution from the steel packaging, and reheating the beans in a microwave for three minutes (Fig. 14.3, right).

1 g beans, tinned = 1.8 g emissions

The total emissions are nearly double those of the efficiently cooked beans, but less than half those of the inefficiently cooked beans.

Box 14.1: Tin cans

A typical 400 g-capacity tin can is made from about 50 g of steel. For typical recycling rates and energy mix, steel causes about twice its own weight in emissions.

1 g steel = 2 g emissions

If we don’t recycle then this number increases, but if we eat communally then it goes down – since caterers use bigger containers, the relative contribution from the steel tin becomes smaller.

Most of the tin-can emissions are caused by energy to run the steel plant, which can be reduced if sufficient renewable energy is used. The canning process itself also uses energy, mostly to heat the food.

The calculations here assume 100% fossil fuels are used to run the steel-processing plant and the canning process.

Canned beans often come with a tomato sauce, which makes little difference to the emissions.

1 g baked beans = 2 g emissions

We can serve the baked beans on toast with vegetable spread to make one of my favourite dinners (Fig. 14.4). This is the second-lowest hot meal, after the baked potato with relish (chapter 13).

Fig. 14.4: Emissions for beans on toast: two slices of bread (80 g); toasting (3.6 minutes at 2 kW); two teaspoons of vegetable spread (10 g); a 400 g can of baked beans, shared between 4 people (100 g); a 50 g steel can, shared between 4 people (12.5 g); microwave oven (3 minutes at 1.2 kW).

Alternatively, we can add the beans on to our baked-potato lunch. Adding beans to the cheesy oven-baked potato makes little difference to the total (Fig. 14.5, left), whereas the plain microwaved potato had such low emissions in the first place that the beans nearly double the emissions, but the result is still a low climate impact meal (Fig. 14.5, right), and packs in a good deal of nutrition from both the beans and potato.

Fig. 14.5: Comparison of some different choices for potato and beans. Left: Rich, oven-baked: a potato (250 g); tbsp butter (20 g); two slices of cheese (50 g); oven 15 mins warm-up + 2 hours (at 2.4 kW).

Centre: Microwaved, with relish: a potato (250 g); tbsp vegetable spread (20 g); two tsp relish (20 g); microwave oven (8 mins at 1.2 kW).

Right: Microwaved, with beans: a potato (250 g); tbsp vegetable spread (20 g); two tsp relish (20 g); microwave oven (8 minutes at 1.2 kW); 400 g can of baked beans, shared between 4 people (100 g); 50 g steel can, shared between 4 people (12.5 g); microwave (3 mins at 1.2 kW).

Key points

- A portion of beans cooked efficiently at home causes very low greenhouse-gas emissions.

- Beans from a tin can cause about twice their own weight in emissions, if fossil fuels are used to do the canning.

- Adding beans makes very little difference to the large emissions from an oven-baked potato cooked for one person with added butter and cheese.

- Adding a portion of tinned beans more than doubles the tiny emissions of a microwaved potato, but it still makes a very low-emissions healthy meal, causing just over half a kilo of emissions.

Box 14.2: Personal emissions

When I give public talks about emissions from beans, there’s usually someone bold enough to ask about the greenhouse-gas emissions from farts. Here I’m going to refer to human flatulence as “personal emissions” to spare readers’ blushes. Often the questioner is concerned that switching from beef to beans is simply moving the cow methane problem elsewhere, i.e. into personal emissions.

Some personal emissions do contain methane, but academic research finds that this is not connected with the amount of beans or other legumes in the diet. Even for the people who do produce methane, the daily output is still a tiny fraction (1%) of the amount of methane produced by cows to make a large steak. However, an increase in the amount of dietary fibre (e.g. from beans) is linked to increased amounts of personal emissions, and improved health (chapter 34).

Notes

The beans have been transformed from their green beginnings, when they grew like peas in a pod (Fig. 14.1). Young soya beans can be eaten lightly steamed with salt, and are better known as edamame beans – they are more like the green beans discussed in chapter 28.

if the roots are left in the ground, they even reduce the amount of fertilizer needed by the next crop. For example see fertilizer application recommendations in Kissel and Harris (n.d.).

The beans themselves cause less than their own cooked weight in emissions, The global average for beans and pulses from Poore and Nemecek (2018) is 1.8 kgCO_2e / kg dry beans. To convert this into the cooked weight of beans (described in the text) we use a value of 100 g of cooked pulses from 35 g dry pulses (from table 4.21 of Durlinger et al. (2017), which gives 0.63 kgCO_2e / kg rehydrated beans (1.8 kgCO_2e / kg × 35 g/100 g).

emissions from canned beans, showing separately the contribution from the steel packaging, and reheating the beans in a microwave for three minutes Taking an average of UK (1.6 kgCO_2e / kg after subtracting the can) and imported (1.7 kgCO_2e / kg) beans, values from Frankowska et al. (2019a) for beans in a can. To subtract the can we use the emissions for steel of 1.68 kgCO_2e / kg, a steel weight of 50 g for 250 g of beans from a 400 g can after draining: 1.68 kgCO_2e / kg steel × 50 g steel / 250 g beans = 0.3 kgCO_2e / kg for the can.

steel causes about twice its own weight in emissions. The value from “CCaLC PVC Manual (V2.0)” (2011) for recycled tinplate (steel) is 1.68 kgCO_2e / kg (62% recycled) and 2.7 kgCO_2e / kg for virgin (not recycled) tinplate. To learn more about the energy needed to make materials, see Sustainable Materials – Without the Hot Air: Making Buildings, Vehicles and Products Efficiently and with Less New Material (Allwood and Cullen, 2015).

Canned beans often come with a tomato sauce, which makes little difference to the emissions. The value of 2.0 kgCO_2e / kg is taken from Frankowska et al. (2019a) for baked beans in a can (including canning and tomato sauce), averaging the values for UK (1.6 kgCO_2e / kg after subtracting 0.2 kgCO_2e / kg for the can) and imported beans (2.3 kgCO_2e / kg after subtracting the can).

Some personal emissions do contain methane, but academic research finds that this is not connected with the amount of beans or other legumes in the diet. Even for the people who do produce methane, the daily output is still a tiny fraction (1%) of the amount of methane produced by cows to make a large steak. For the sake of science, 16 people agreed to have a tube inserted into their rectums (bottoms) to collect gas (Suarez et al., 1997). They had to eat 200 grams of beans the previous day, to make sure there would be enough material to study. They each passed gas between 3 and 9 times in the 4-hour hour period of the study, producing between 100 ml and 1000 ml of gas. Most of the gas was hydrogen, carbon dioxide and nitrogen, and only 5 of these people produced any significant amount of methane, on average about 100 ml each. By contrast, a cow and calf produce 0.4 kg or 400 litres of methane a day for 700 g of steak (chapter 24). This means that production of a large (8 oz or 226g) steak causes 130 litres of methane to be released into the atmosphere, which is 1000 times the daily amount for people who produce a lot of methane in their personal emissions.

Chapter 15 Yogurt and cream

Fig. 15.1: A pot of yogurt. (URL 46)

To round off lunch, how about a yogurt (Fig. 15.1)? In this chapter we also consider cream, which you might like as a topping on fruit (chapter 17) or dessert (chapter 30), or as a cookery ingredient (chapters 7, 22 and 25).

Yogurt

A mesmerizing array of yogurt options stretches along the supermarket aisles – from light to extra creamy, to fruit layers and crunchy corners. By definition though, they are all mostly made of milk. Special bacteria feed off the lactose (milk sugar) and produce lactic acid, which changes the shape of the milk proteins and causes the milk to get thicker.

Fig. 15.2: Emissions for a pot of yogurt: yogurt (150 g); plastic pot (10 g).

Unlike cheese, nothing is strained off when making most types of yogurt, so the emissions from yogurt are similar to those from milk, causing twice their own weight in emissions.

1 g yogurt = 2 g emissions

What about the plastic pot? For research purposes I’ve just eaten a large (150 g) yogurt and weighed the pot – 10 g – which means the pot causes only about one tenth of the total emissions (Fig. 15.2; see box 21.1 for more details on plastic emissions).

Fig. 15.3: Emissions for cream (two tablespoons): cream (30 g).

Cream

Nowadays, most western milk is processed (homogenized) to mix together the cream and the milk, but in the olden days (well, when I was growing up!), the milk gradually separated into cream at the top of the bottle, and milk at the bottom. These days, whole milk is separated commercially into skimmed milk and cream, and turned into a full spectrum of products from double cream and single cream at one end, through to whole milk, semi-skimmed milk and skimmed (nonfat) milk at the other extreme.

This means that the greenhouse-gas emissions for cream depend on the emissions of the original full-fat milk, and on how you share out the full-fat milk emissions between the cream and the skimmed milk. If cream were unpopular and considered a by-product of the skimmed milk industry then we could treat it like a free by-product (box 9.1). But in reality both cream and skimmed milk are popular, and cream has been attributed about five times its own weight in emissions.

1 g cream = 5 g emissions

It’s unusual to eat cream as a stand-alone dessert, but cream can appear in ingredients lists in larger quantities and ends up making a significant difference to the emissions of some foods, despite being relatively hidden from view; for example, in this book we consider scrambled egg (chapter 7), a black forest cake (chapter 22) and chicken tikka masala (chapter 25). At the end of the evening meal we will drizzle two tablespoons of cream (Fig. 15.3) over a slice of apple pie (chapter 30), which adds about 150 g of emissions.

Alternative puddings include super-healthy fruit, or less-than-healthy cake (with added cream), both discussed in the next Part on snacks.

Key points

- Yogurt emissions come mostly from the production of the milk.

- Since yogurt is simply milk thickened by the action of good bacteria, it has lower emissions than products that are concentrated down from milk, such as cheese, cream and butter.

- Cream emissions are a few times higher than those for milk, depending on how they are shared with its skimmed-milk co-product.

Notes

the emissions from yogurt are similar to those from milk, causing twice their own weight in emissions. A value of 1.8 kgCO_2e / kg is from Frankowska (2019) for packaged yogurt in cold storage at the retailer and consumer, after subtracting packaging.

cream has been attributed about five times its own weight in emissions. 4.9 kgCO_2e / kg cream is an average of values from Finnegan et al. (2018) (5.06 kgCO_2e / kg), Djekic et al. (2014) (4 kgCO_2e / kg) and Sheane et al. (2011) (5.6 kgCO_2e / kg).

Chapter 16 Lunch summary

At the risk of comparing apples and oranges (though we will literally do that in the next Part!), we now compare the greenhouse-gas emissions of the various lunch options.

Lunch has illustrated that there is often a big range of emissions for a single type of food, depending on the ingredients, their seasonality and the method of preparation. For example, the simple sandwich emissions vary by more than ten times depending on whether it contains beef or peanut butter (compare Figs. 10.7 centre and 9.4 right). Emissions also change by more than ten times depending on whether salad is grown locally and seasonally, or in a heated greenhouse (chapter 11). And baked potato emissions are significantly reduced by using the microwave instead of the main oven, and reducing the amount of cheese. In Fig. 16.1 we compare typical-, high-, and low-emissions lunches.

Typical-emissions lunch

A ham sandwich with a lettuce salad and a yogurt comes to about a kilo of emissions (Fig. 16.1, left), which is one third of a 3 kilo daily food emissions budget. The biggest single ingredient is the ham, followed closely by the yogurt.

Higher-emissions lunch

For a higher-emissions alternative, we’ll take the oven-baked potato dripping with butter and generous cheese (cooking for one), and add to this a tomato salad, produced from a dedicated heated greenhouse, plus the same yogurt we had for the typical-emissions lunch. This quadruples the total lunch emissions to 3 kilos, more than half of which come from the cheesy baked potato, cooked for one person, followed by the hothouse tomatoes (Fig. 16.1, center). In this one meal, we’ve already blown a daily emissions budget of 3 kilos.

Fig. 16.1: Comparison of some different lunch choices.

Left: Emissions for a typical-emissions lunch: ham sandwich; lettuce salad; a pot of yogurt.

Centre: Emissions for a higher-emissions lunch: an oven baked potato with butter and cheese; a tomato salad, from tomatoes grown in a heated greenhouse; a yogurt.

Right: Emissions for a lower-emissions lunch: a microwaved potato with relish and beans; a local seasonal salad.

Lower-emissions lunch

You can reduce the typical lunch emissions by 40% by eating a microwaved baked potato with beans, eating an in-season salad (Fig. 16.1, right), and postponing a treat until snack time, discussed next.

Key points

- The typical-emissions lunch options cause about one kilo of emissions, which makes up one third of a daily 3 kilo food emissions budget.

- The higher-emissions option is four times as bad (for the climate) as the typical-emissions lunch, mostly due to the energy to power the oven, the cheese, and heating a greenhouse to grow tomatoes out-of-season.

- You can halve lunch emissions by skipping dessert, eating a microwaved potato with beans and eating a seasonal salad.

Part III: Snacks

Lets face it, snacks are a temptation at any time of day. They’re usually ready to eat, and provide pleasant sensations such as crunchiness, saltiness or sweetness.

In this Part we’ll consider fruit first, and compare the impact of different transport options. Will the emissions story of chocolate leave a bitter taste, or are there simple fixes that can keep it as a daily not-so-guilty pleasure? Nuts are sometimes hailed as great substitutes for animal products, increasingly in some milk alternatives, but are they really better for climate change? Crisps (potato chips) are my favourite snack, but what level of emissions am I causing? Soft drinks raise the topic of emissions from different sorts of packaging. Finally, baking a cake allows us to play with combining some of the ingredients discussed so far.

Chapters

Chapter 17: A piece of fruit

Chapter 18: Chocolate and sweets

Chapter 19: Nuts

Chapter 20: Potato crisps / chips

Chapter 21: Soft drinks and juices

Chapter 22: A piece of cake

Chapter 23: Snacks summary

Chapter 17 A piece of fruit

Fig. 17.1: Which fruit do you think is responsible for the most greenhouse-gas emissions? (URL 47)

Fruit, the archetypal healthy snack, has evolved especially to be attractive to animals like ourselves (Fig. 17.1). Here we focus on the widely eaten fruits: apples, oranges, bananas and strawberries.

Apples

I was brought up on the mantra “an apple a day keeps the doctor away”. This was partly fuelled by visits to the local fruit farm where I would be encouraged by the owner to take a fresh, new-season apple from the big crate, and eat it right there in the shop. I was thrilled when the first house we bought had a garden complete with apple trees (Fig. 17.2). By autumn we had a lot more than one apple a day, and tens of blackbirds would fly in to eat the fallen fruit that still lay on the ground as the snow arrived.

Fig. 17.2: Apples on a tree. (URL 48)

In contrast to our back garden, commercial apple orchards do a lot of pruning, thinning and picking. Hydraulic ladders make the work less precarious but this and other mechanization make up about half of the greenhouse-gas emissions at the farm. To get the best apple crop, extra nitrogen is applied as fertilizer, which causes most of the rest of the emissions from the farming stage. Cold storage of the apples to eat out of season doubles their emissions, but the impact of an apple is still relatively low.

1 g local seasonal apples = 0.4 g emissions

Even if you eat two apples a day, you still only spend 3% of a daily food emissions budget of 3 kg.

A typical (100 g) apple racks up a minuscule 5 grams of emissions when transported across a small country – just one thousandth of a typical day of food emissions (Fig. 17.3, left). This is not something to worry about! But how can you keep the doctor away in the spring, when apples are out of season? UK shops are full of apples from New Zealand, on the other side of the world – the highest possible food miles away.

Box 17.1: Transporting food by truck

Within a country, usually food is transported by road in a big truck. As an example, consider a journey of 400 km across the UK, from the ‘garden of England’ in Kent to my local supermarket in Manchester. If the truck is powered by fossil fuels, and has a typical packing density of food, the trucking emissions are about one twentieth of the weight of the product being transported.

1 g transported 400 km by truck = 0.05 g emissions

Fig. 17.3:

Left: Emissions for an apple, trucked across the UK (400 km): an apple (100 g); transport 400 km by truck.

Centre: Emissions for an apple, shipped across the world (20,000 km): an apple (100 g); transport 20,000 km by boat.

Right: Emissions for an apple, from the local farm shop: an apple (100 g); transport 30 km by car, shared between 60 apples (0.5 km).

Box 17.2: Shipping food by sea

Emissions from ships vary significantly depending on the ship size and type of fuel. As a rule of thumb, transporting food by boat to the other side of the world (20,000 km, e.g. from New Zealand to the UK) causes about one quarter of its own weight in emissions.

1 g transported 20,000 km by boat = 0.3 g emissions

For a shorter journey, for example around a continent, the emissions are correspondingly lower. For example, for a typical distance (3,000 km, e.g. from Spain to the UK), the sea-freight emissions are about one twentieth of the weight of the food being transported, which is the same as trucking across a small country.

1 g transported 3,000 km by boat = 0.04 g emissions

An apple on a journey from one side of the world to the other is responsible for 26 grams of emissions due to transportation (Fig. 17.3, centre). Perhaps surprisingly, shipping apples from the other side of the world turns out to be only five times worse than driving the fruit across a small country. An alternative to shipping from overseas is storing locally grown fruit: apples can keep for months in properly controlled conditions (this is already factored into the apple emissions used here).

How about driving to the local fruit farm? My last drive there and back took at least 30 minutes. Maybe we bought a crate of apples to keep us going for a couple of weeks. But even if we bought 50 apples, this trip caused 3 times the emissions per apple compared with shipping from New Zealand. Local isn’t always better. They were the best apples I ever tasted though. And maybe it was the merry banter with the owners of the farm that sparked my curiosity about food production and led me to write this book?

Visiting local farms and talking to local farmers at markets are fantastic when they help us to appreciate where our food comes from. However, making a dedicated extra excursion every week in a fossil-fuelled car would do more harm than good to the climate. In contrast, vegetable and fruit box deliveries can be a great way to reduce transport emissions and support your local farm, because the delivery trip emissions are shared out across many customers.

Fig. 17.4: Oranges growing in an orange grove. (URL 49)

Oranges

Like apples, oranges grow on trees, but orange are sensitive to cold temperatures and need a lot of sunshine. Despite not being well suited to the UK, oranges have become associated with the British, because the Navy fed them to sailors on long sea journeys to avoid scurvy. And it turns out that the ability of oranges to keep well on a long journey is critical to their relatively low impact on the climate.

Emissions from growing the oranges are similar to those for growing apples, but they do not need to be kept so cold to store them between seasons.

1 g oranges = 0.3 g emissions

The emissions are still extremely low, though, and the same transportation issues apply as for apples: oranges are fine sitting on a ship for a couple of months, which is enough time to ship them across the world. Shipping across a single continent causes about 4 grams of emissions, which is smaller than the emissions from growing the fruit (Fig. 17.5, left).

Bananas

Bananas come in their own easily removable skin as packaging, and don’t even need much chewing (they would be a very lazy healthy snack if I didn’t end up with a forgotten squashed brown banana at the bottom of my bag most of the times I’m organized enough to take one to work). To transport bananas across the world they need to be carried in protective boxes to stop them getting squashed, which adds to their total emissions, and is a much bigger issue than the thin plastic bag we often see as a consumer.

Fig. 17.5:

Left: Emissions for an orange, shipped across a continent (3000 km): an orange (100 g); transport 3,000 km by boat.

Centre: Emissions for a banana, shipped across the world (20,000 km): a banana (100 g); transport 20,000 km by boat.

Right: Emissions for strawberries (by air): a bowl of strawberries (80 g); transport 5,000 km by air.

Bananas are usually grown in even hotter countries than oranges, so often require longer voyages to reach us. Overall the emissions caused by a banana are 70% of their own weight, of which less than half comes from transport by sea (Fig. 17.5, right).

1 g banana, transported by boat = 0.7 g emissions

This is about twice the emissions caused by an orange or a local apple, but one banana (100 g) still causes only about 2% of a daily food emissions budget of 3,000 g.

Soft fruits

For me, summer isn’t complete without gorging on a bowl of strawberries (Fig. 17.6). Ideally I would also fit in a trip to a pick-your-own fruit farm, bringing back childhood memories of hunching over and searching for the perfectly ripe fruits among the straw, and hiding the evidence from “testing” a few sample fruits to make sure they were OK.

Fig. 17.6: A delicious bowl of strawberries – but did they fly over to you? (URL 50)

Nowadays commercial strawberries are grown more like cherry tomatoes (chapter 11): away from the soil, watered with fertilizer and usually protected by glass or plastic; they cause about twice their own weight in emissions if grown locally and in-season. The emissions for raspberries are similar.

1 g strawberries = 2 g emissions

1 g raspberries = 2 g emissions

We can enjoy eating plenty when the fruit is in-season in our hemisphere, but what about the food miles travelled by a strawberry in the winter?

The wonders of world trade mean that in our winter we can eat strawberries grown in the summer of the opposite hemisphere, which makes a kind of sense, until you factor in the transportation by air. Bringing food by air causes 100 times the emissions of bringing the food the same distance by ship, and flying over a portion (80 g) of strawberries adds more than 0.5 kilos of emissions to the serving, using up one sixth of a 3 kg daily food emissions budget.

Box 17.3: Perishable produce

“Perishable” food deteriorates quickly after being harvested, if not preserved somehow, for example by freezing or canning. Examples of perishable fruits and vegetables include strawberries, raspberries, blueberries, green beans, lettuce and cucumber. By contrast, “non-perishable” foods like oranges and bananas can be shipped across the world and stay fresh in the hold of a temperature-controlled container ship. Perishable foods need to be consumed shortly after they have been harvested and must be air-freighted if they are to remain fresh over a long journey.

Box 17.4: Flying food

A lot of fresh produce is carried in the hold of passenger planes (one reason why budget airlines charge us a fortune for hold luggage, especially when we bring it along at the last minute). Transporting food 5,000 km from another continent (e.g. Africa to the UK) causes 8 times the weight of the food in emissions, once we factor in the extra impact of burning fossil fuels at altitude where they cause more warming.

1 g transported 5,000 km by air = 8 g emissions

This puts air-freighted fruit and veg in the same climate-impact category as lower impact animal products like chicken.

Key points

- Enjoy local fruits when in season.

- Enjoy seaworthy (non-perishable) fruits, like apples, oranges and bananas, at any time of the year.

- Cut back on soft (perishable) fruits, like strawberries, when they are out of season.

Notes

Hydraulic ladders make the work less precarious but this and other mechanization make up about half of the greenhouse-gas emissions at the farm. See Fig 5 and 7 of Milà i Canals et al. (2006).

the impact of an apple is still relatively low. Commercial apples cause about 0.35 kgCO_2e / kg apple, based on Frankowska et al., 2019b, figure S15 which gives 0.5 kgCO_2e / kg apple including 18% waste (subtracted for now but discussed in chapter 33) and 13% for transport (subtracted for now and added back in later). Most of the remainder is divided equally between on-farm emissions and storage.

trucking emissions are about one twentieth of the weight of the product being transported. Based on values for transportation from the UK government transport reporting factors document (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2018) For a diesel refrigerated heavy goods vehicle (HGV) with an average load, this gives 0.13 kgCO_2e / tonne / km. Therefore for a load of 1 kilo travelling 400 km, the emissions are 0.13 kgCO_2e / tonne / km × 1 kg × 400 km / (1,000 kg / tonne) = 0.05 kgCO_2e.

transporting food by boat to the other side of the world (20,000 km, e.g. from New Zealand to the UK) causes about one quarter of its own weight in emissions. The value for refrigerated boat cargo used for UK government reporting (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2018) is 0.01308 kgCO_2e / tonne / km. Converting this into kgCO_2e for a 20,000 km trip for 1 kilo of food means multiplying by 20,000 km and dividing by 1000 kg / tonne, which gives 0.26 kgCO_2e / kg.

for a typical distance (3,000 km, e.g. from Spain to the UK), the sea-freight emissions are about one twentieth of the weight of the food being transported, Modifying the previous calculation from 20,000 km to 3,000 km gives 0.04 kgCO_2e / kg of produce.

even if we bought 50 apples, this trip caused 3 times the emissions per apple compared with shipping from New Zealand. A 30 kilometre round trip in a typical small family car causes nearly 5 kilos of emissions (30 × 155 gCO_2e / km; see chapter 1). Sharing this out between 50 apples works out to be nearly 100 grams of emissions per apple.

Emissions from growing the oranges are similar to those for growing apples, but they do not need to be kept so cold to store them between seasons. Poore and Nemecek (2018) give a value of 0.4 kgCO_2e / kg. Subtract the value of 0.09 kgCO_2e / kg which they added to account for the transport, as this is added back on in the calculations in this book for consistency across different types of food, giving a value of 0.31 kgCO_2e / kg for the figures. This is similar to the value of 0.27 from Frankowska et al. (2019b) without transport, retail and waste (although note that Frankowska et al. 2019b have a value of 1.27 kgCO_2e / kg including retail, which would be most relevant for oranges sold in chiller cabinets).

To transport bananas across the world they need to be carried in protective boxes to stop them getting squashed, which adds to their total emissions, and is a much bigger issue than the thin plastic bag we often see as a consumer. See Iriarte et al. (2014).

the emissions caused by a banana This uses 0.43 kgCO_2e / kg banana, taking the value from Frankowska et al. (2019b) which gives 1.3 kgCO_2e / kg of which 67% is transport and waste, which is discussed later. See also Svanes et al. (2011) and Iriarte et al. (2014) which give similar values.

strawberries are grown more like cherry tomatoes (chapter 11): away from the soil, watered with fertilizer and usually protected by glass or plastic; they cause about twice their own weight in emissions if grown locally and in-season. 2.1 kgCO_2e / kg comes from Frankowska et al. (2019b), which gives 2.23 kgCO_2e / kg for fresh UK strawberries, of which 94% is before the household/waste stage (which we discuss separately in this book).

raspberries Fresh UK raspberries from figure S34 of Frankowska et al. (2019b) cause 2.2 kgCO_2e / kg. Subtract off 6% to remove the household and waste components which gives 2.1 kgCO_2e / kg. Note that more than one third of this is “retail” mostly due to fridges (box 11.1).

Transporting food 5,000 km from another continent (e.g. Africa to the UK) causes 8 times the weight of the food in emissions, once we factor in the extra impact of burning fossil fuels at altitude where they cause more warming. The UK Government reporting factors document (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2018) gives 0.8 kgCO_2e / tonne / km for long-haul dedicated-cargo flights (table 34), to which we apply the radiative forcing factor of 1.9 to account for the higher impact of emissions at altitude (see paragraph 8.37 – but note that this factor is uncertain – previous advice was to use a factor of 2.7 (UK Government Department for Business, Energy & Industrial Strategy (DEFRA), 2016)) To get the number for 1 kilogram of food transported 5,000 km we have to multiply by 5,000 and divide by 1,000 kg / tonne, which gives 7.6 kgCO_2e / kg.

Chapter 18 Chocolate and sweets

Fig. 18.1: Cocoa pods growing on a cacao tree. (URL 51)

These days it’s often hard to get out of a shop without being tempted by rows and rows of sweets and chocolates. These are popular snacks: on average in the UK we each eat the equivalent of about one small chocolate bar every day.

Chocolate comes from cocoa trees, grown in tropical climates and producing large pods directly on their branches (Fig. 18.1). Each tree makes about 20 of these fruits, which contain the cocoa seeds (Fig. 18.2), which have to be removed from their pods and dried to produce cocoa “beans” (Fig. 18.3), ready for roasting, milling and pressing into cocoa butter, liquor and powder.

Fig. 18.2: A cocoa pod showing the beans in white pulp. (URL 52)

The emissions from cocoa products depend greatly on whether forests have been cut down to grow the trees (chapter 7). Considering a stable cocoa plantation, the emissions are about 3 times the weight of the cocoa, mostly due to fertilizing and watering the cocoa trees, their relatively low yields, and the energy needed to process the beans.

1 g cocoa = 3 g emissions

How does this stack up when we consider a realistic portion size and include the other ingredients in chocolate? Dark chocolate is often made with 70% cocoa carefully mixed with sugar. A small (25 g) bar of this chocolate causes about 100 grams of emissions (Fig. 18.4, left), which is just 3% of a daily food emissions budget of 3,000 g.

Fig. 18.3: Cocoa beans alongside cocoa pods. (URL 53)

Chocolate often contains less than half this amount of cocoa, with added milk and sugar. Does this reduce the carbon footprint? As highlighted on some chocolate bars, the weight of milk in a bar of chocolate can actually be greater than the weight of the chocolate bar (which is possible because the milk is concentrated into powder before being added to the cocoa).

1 g milk powder = 9 g emissions

Reducing the amount of cocoa reduces the emissions, but this is more than made up by the addition of the milk powder, which pushes the chocolate bar emissions up by 30% relative to the dark chocolate (compare Fig. 18.4 centre and left).

Fig. 18.4:

Left: Emissions for dark chocolate (25 g bar): cocoa (17.5 g); sugar (7.5 g); processing.

Centre: Emissions for milk chocolate (25 g bar): cocoa (6 g); sugar (12.5 g); processing; powdered milk (6 g).

Right: Emissions for sweets (25 g bag): sugar (25 g); processing.

Finally we consider sweets (candies), which are basically all sugar. Just as for cocoa, the emissions depend mostly on whether forest has been cut down to clear land for agriculture, but are lower than those for the dark chocolate (Fig. 18.4, right).

I would enjoy the challenge of eating enough chocolate to make a significant impact on my daily food emissions. However, a large (100 g) bar of milk chocolate contains one quarter of my daily calorie intake, and causes half a kilo of emissions, or one sixth of a daily budget of 3 kilos of emissions caused by food. Furthermore, by increasing demand for products that grow in equatorial regions we drive deforestation. In any case, I think if I ate this much chocolate every day I would have bigger concerns about my health than about the environment.

Key points

- A small bag or bar of chocolate causes about 3% of a budget of 3 kilos of emissions from food, so probably isn’t the main thing for most people to cut back on when trying to reduce emissions.

- Sweets (candies) usually cause less emissions than chocolate but don’t provide any nutrients.

- Switching from dark to milk chocolate increases emissions by 30%.

Notes

one small chocolate bar every day. In the UK we eat 7.9 kg / person / year (Konstantas et al., 2018), which is 7900 grams / 365 days a year = 21.6 grams per day. A small chocolate bar usually weighs 25 grams.

roasting, milling and pressing into cocoa butter, liquor and powder. For details of all the processes and how they contribute to emissions, see Recanati et al. (2018) and Myhre et al. (2013).

The emissions from cocoa products depend greatly on whether forests have been cut down to grow the trees (chapter 7). Considering a stable cocoa plantation, the emissions are about 3 times the weight of the cocoa, mostly due to fertilizing and watering the cocoa trees, their relatively low yields, and the energy needed to process the beans. An average of values from (i) Recanati et al. (2018) who give 2.63 kgCO_2e / kg (ii) Ntiamoah and Afrane (2009) who give 3.56 kgCO_2e / kg. See also Konstantas et al. (2018) whose values for manufactured chocolate we use for manufacturing emissions. However, note the extremely wide range for different cocoa production estimates in Poore and Nemecek (2018), which range from negative values where cacao trees have been newly planted thus capturing carbon dioxide, through to values of around 200 kgCO_2e / kg where deforestation has occurred to plant cacao.

A small (25 g) bar of this chocolate causes about 100 grams of emissions Each of the examples in this chapter, allows 1 kgCO_2e / kg of final product for processing emissions, based on figure 2 of Miah et al. (2018).

the weight of milk in a bar of chocolate can actually be greater than the weight of the chocolate bar It takes 7.69 kilograms of milk to produce 1 kilogram of milk powder, and a typical milk chocolate recipe is 24.5% milk powder, according to Konstantas et al. (2018). The emissions of 8.7 kgCO_2e / kg for milk powder are taken from Frankowska (2019) though note that this does not include the additional emissions from drying the milk, so is an underestimate.

Chapter 19 Nuts

Fig. 19.1: Almonds as they grow on trees, inside their hulls. (URL 54).

Most plants create their offspring by making seeds. The seeds can often stay alive outside the plant until conditions are right to spring into life, perhaps as the weather starts to warm up, or when enough rain falls. Just like a chicken’s egg, the seed contains all the nutrients needed for the first stages of growth of the next generation, making them very nutritious for us to eat. Some types of seed have a hard outer shell and are referred to as nuts.

How many different types of nut have you tried? Peanuts are a popular snack, often salted and roasted. Classier alternatives includes almonds, cashews or Brazil nuts. Peanut butter is a popular sandwich filling, especially when paired with jam or jelly (chapter 9). Nowadays nut milk alternatives, particularly almond and cashew, are gaining popularity as an alternative to cows’ milk. In this chapter we focus on emissions from almonds and peanuts because they are the two most popular and best studied nuts.

Almonds

Have you ever eaten a juicy ripe peach or apricot, and then fiddled with the stone at the centre, wondering what lies inside the intricate lacy carpentry of the stone? On prizing it apart you might find a small almond-like seed inside. Peach and apricot seeds are bitter and poisonous because they contain cyanide.

Fig. 19.2: Almond kernels after being taken out of their hulls and shells. (URL 55).

Almond trees are closely related to peaches and apricots, and we call their seeds almonds. (Wild or “bitter” almonds are also poisonous, but you can enjoy regular sweet almonds without worrying.)

As with most crops, the greenhouse-gas emissions are mostly from fertilizer (box 2.1). The amount of almonds harvested from a tree can vary significantly (by 5 times) depending on the amount of fertilizer available, as well as other factors including the weather and the soil quality. Also, depending on where the almonds are grown, they may need to be watered – if fossil fuels are used to power pumps to bring the water up from under the ground then this can contribute about one third of all the almond greenhouse-gas emissions (and cause other environmental problems). Overall, typical commercial almonds cause about twice their own weight in emissions.

1 g almonds = 2 g emissions

Almond milk

How does the climate impact of almond milk compare with that of cows’ milk? We have to take into account the emissions from producing almonds, as well as processing them into almond milk, and the packaging, transportation and refrigeration.

To be really be climate-friendly, should we make our own almond milk at home, to keep the transport emissions as low as possible? Just soak some almonds overnight in water, then whizz them up in a blender and strain the result. Anyone who makes their own almond milk sees the large amount of leftovers in the strainer. It takes about 50 grams of almonds to make one (250 ml) cup of almond milk at home, of which more than two thirds gets left over as pulp.

Apparently you can use the pulp for smoothies, or dry it out and use it as a handy gluten-free flour for baking. But how many people really do this, and how much mush goes into the bin and causes methane at the landfill site (chapter 33)? Industrial production lines can get a lot more milk out of their almonds than I can from squeezing my tea towel full of almond mush. And if the factories aren’t already turning the residue into cakes and puddings, they will at least be using it as animal feed.

In terms of reducing greenhouse-gas emissions, it makes sense to make your own almond milk only if you use the pulp as well. If you put the oven on especially to dry out the pulp then this might blow all the emissions you’ve saved from avoiding dairy milk. And, if you’re making almond milk to put into a smoothie, then you can reduce emissions and get some extra fibre by instead adding ground almonds and water and skipping the straining (if you don’t mind a slightly grainy texture).

Returning to the commercial almond milk calculation, and assuming only 25 grams of nuts are needed to make one cup, the almond milk raw ingredient (almonds) cause 10 times less emissions than dairy milk. Transportation, packaging and storage in supermarket fridges (box 11.1) adds to both the almond and cows’ milk total emissions. However because the almond emissions are so small, the other contributions are likely to make up most of the total almond-milk emissions, which often makes estimates of non-dairy milk emissions “only” two times better than cows’ milk (chapter 6).

Fig. 19.3: Peanuts in their shells. (URL 56)

Peanuts

Did you know that peanuts are more closely related to peas and beans than to almonds? As a type of legume, they can extract nitrogen from the air via microbes, and therefore don’t need so much fertilizer (chapter 14). Unlike peas and beans, they push their seed pods under the ground, leading to their other name, “groundnuts”. The pods are pulled up and dried, giving the brittle outer shell of the peanuts, inside which live about two peanuts inside their papery brown coats (Fig. 19.3).

Just like almonds, the amount of peanuts produced in a field can vary greatly (by about 10 times) depending on the ground type, climate, crop variety, cultivation methods, irrigation and the crop rotation scheme. As with other legumes, even though peanuts can get some nitrogen fertilizer from the air, they usually have nitrogen fertilizer applied to the soil to increase the yield further (chapter 14). On average, peanut emissions come out slightly higher than those for almonds, causing about 3 times their own weight in emissions.

1 g peanuts = 3 g emissions

Peanut butter is essentially just blended roasted peanuts. Some health food shops whizz them while you wait, putting in peanuts at the top and squirting out peanut butter at the bottom. You can even do it yourself in a food processor, if you don’t mind some messy washing up. Being turned into butter increases the peanut emissions to about four times the weight of the spread.

1 g peanut butter = 4 g emissions

Fig. 19.4: Emissions for mixed nuts: peanuts (15 g); almonds (15 g).

Mixed nuts

To conclude this chapter, consider a tasty and nutritious snack of mixed nuts: a handful (30 g) containing equal quantities of almonds and peanuts. This portion causes 80 grams of emissions (Fig. 19.4), which is less than 3% of a budget of 3,000 g of emissions from food per day, but packs a punch in terms of nutrition.

Key points

- Nuts and seeds are literally the plant-based alternative to eggs and as a result they are very nutritious.

- On average, nuts cause 2-3 times their weight in greenhouse-gas emissions, although there is a wide variation in the values depending on the type and growing conditions.

- The almond raw ingredient in almond milk causes very little emissions compared to dairy milk, but taking everything else into consideration nut milks cause less than half the climate-impact of dairy milk (chapter 4).

Notes

Page

you can enjoy regular sweet almonds without worrying. The wild bitter almond contains cyanide and can be fatal. Bitter almonds yield about 6.2 mg of cyanide per almond, whereas the standard sweet almond contains 100 times less, bringing it well below toxic levels. For more information see Chaouali et al. (2013).

amount of almonds harvested from a tree can vary significantly (by 5 times) depending on the amount of fertilizer available, as well as other factors including the weather and the soil quality. Almond yields vary from 1 to 5 tonnes per hectare, see Nemecek et al. (2012).

typical commercial almonds cause about twice their own weight in emissions. The value of 2.1 kgCO_2e / kg is based on Bartzas et al. (2017) who give a value for shelled almonds. This is consistent with the individual numbers for almonds calculated by Poore and Nemecek (2018) but note there is a very large range, from negative numbers (where almond trees are reducing greenhouse-gas emissions relative to the previous use of the land) to larger numbers.

the almond milk raw ingredient (almonds) cause 10 times less emissions than dairy milk. Depending on the brand, a glass (250 ml) of almond milk alternative can contain 5% almonds, which is 12.5 grams of almonds (1 ml weighs about 1 g). Here we assume that half the almonds are wasted as pulp, so 25 grams of almonds will be needed to make the drink. (If the “milking” process were less efficient then more almonds would be needed, which would reduce the difference between the almond milk ingredients and cows’ milk.) For almonds that cause 2.1 times their own weight in emissions, 25 grams of nuts will cause 53 grams of emissions. Compare this to 250 grams of dairy milk, which causes about 550 grams of emissions (chapter 4). On the other hand, many brands contain more like 2.5% almonds, which increases the difference between almond milk and cows’ milk.

amount of peanuts produced in a field can vary greatly (by about 10 times) Peanut yields vary between 0.5 and 4 tonnes per hectare, according to Nemecek et al. (2012)

On average, peanut emissions come out slightly higher than those for almonds, causing about 3 times their own weight in emissions. Value of 3.2 kgCO_2e / kg taken from Poore and Nemecek (2018) for groundnuts (peanuts) global average.

Being turned into butter increases the peanut emissions to about four times the weight of the spread. The value for processing of the peanut butter is 0.238 kgCO_2e / kg from McCarty et al. (2014). We add this to the value for peanuts from earlier to get 4.2 kgCO_2e / kg for peanut butter.

Chapter 20 Potato crisps / chips

Fig. 20.1: Some crunchy crisps. (URL 57)

In this chapter we focus on thin slices of potato, fried in oil and sprinkled with salt and maybe some other flavourings (Fig. 20.1), known as potato chips in the US, and as crisps in the UK. Crunchy, salty and very moreish, I felt compelled to precede writing this chapter by munching though a packet. I will refer to them as “crisps” to avoid confusion, because in the UK “chips” means thick-cut fried potatoes.

We already covered the carbon footprint of potatoes in chapter 13 and used oil and salt in the context of salad (chapter 11). Overall, crisps cause about twice their own weight in emissions (Fig. 20.2).

1 g crisps = 2 g emissions

The potato and oil cause about half of the total; the remainder comes from processing, cooking and packaging.

Fig. 20.2: Emissions for a packet of crisps (25 g).

Since crisps are very light, even if I eat two small (25 g) packets a day, they still cause less than 5% of a 3 kg daily food emissions budget. Anyone eating significantly more than two packets a day probably has bigger health issues to consider from all the salt and oil.

What about flavoured crisps, particularly the meaty ones? Many meaty crisps are suitable for vegetarians, because they often contain the classic seasonings used on meat, but without any actual meat, which is likely to be good for their carbon footprint.

But what about crisps containing meat, cheese or even (new to me) egg? We learned at lunchtime that ham and cheese have a comparable carbon footprint, so we’ll focus on cheese. Cheesy crisps contain up to about 10% cheese, which less than doubles the crisp emissions. In other words, crisps still make up only a small fraction of the average daily food emissions, even for a relatively cheesy crisp.

Key points

- A packet of crisps causes about twice its own weight in emissions.

- A small packet of crisps causes less than 5% of a daily food emissions budget of 3 kg.

- For most people, cutting down on crisps isn’t going to be the best place to start reducing their food emissions.

- Meaty and cheesy crisps don’t usually contain enough meat or cheese to change these conclusions.

Notes

crisps cause about twice their own weight in emissions We use a value of 2.15 kgCO_2e / kg from Nilsson et al. (2011) which is consistent with the Carbon Trust Walkers Crisps analysis in 2009 (no longer available) and roughly consistent with Frankowska et al. (2019a) if a the current clean energy mix (chapter 1) is used for the processing and storage (which dominate the emissions in this calculation which assumes 100% fossil fuels for electricity generation and finds a value of 4.4 kgCO_2e / kg).

Cheesy crisps contain up to about 10% cheese, which less than doubles the crisp emissions. Since cheese causes about 16 times its weight in emissions, 10% cheese adds 1.6 kgCO_2e / kg to the crisps, taking their total emissions factor to 3.6 kgCO_2e / kg, which is less than twice the original value of 2 kgCO_2e / kg.

Chapter 21 Soft drinks and juices

Fig. 21.1: Fizzy drink. (URL 58)

The hiss of a can of fizzy drink opened on a hot summer’s day might evoke a Pavlovian dribble – will we be tempted to drink more of these refreshing beverages in a warmer world (Fig. 21.1)? And, if so, will we accelerate climate change further with the release of lots of little bubbles of carbon dioxide?!

Fizzy drinks

Each small (0.5 litre) bottle of soft drink causes less than half its own weight in emissions. However, only a tiny part of that is caused by the gas that makes it sparkle.

The other ingredients cause few emissions, since the main ingredient is water, followed by sugar (chapter 3). Refrigerators in shops cause about a quarter of the total climate impact of a store-bought cold drink (box 11.1). It turns out that nearly half of the greenhouse-gas emissions come from the plastic bottle (Fig. 21.2, left).

1 g fizzy drink on tap = 0.2 g emissions

From a climate change perspective, would it be better to instead buy a drink in a glass bottle, or in a can?

Fig. 21.2:

Left: Emissions for a soft drink in a plastic bottle: a soft drink (500 g); a plastic bottle (27 g).

Right: Emissions for water in a 500 ml plastic bottle: bottled water, including manufacturing and transport (500 g); a plastic bottle (27 g).

Centre: Emissions for orange juice in a plastic bottle: orange juice (200 g); a plastic bottle (10.8 g).

Box 21.1: Plastic and glass bottles, and drinks cans

Plastic is usually made from fossil fuels. This association might automatically suggest it is therefore bad for the climate, but in this case the fossil fuels are converted into plastic, not into greenhouse gases. The main cause of plastic-bottle emissions is the energy needed to turn the fossil fuels into plastic, including separating out the important components of the fossil fuel and joining these pieces together into long molecular chains.

The manufacturing processes cause emissions of about 3 times the weight of the final plastic container, so you can weigh any plastic food packaging and multiply by 3 to get the emissions likely to be caused by the packaging.

1 g plastic = 3 g emissions

However, if the bottle is made entirely from recycled material then the emissions are significantly reduced, to less than the weight of the container.

1 g recycled plastic = 0.8 g emissions

Glass causes about half its own weight in emissions, which is much lower than for plastic. But the fragile nature of glass means that the bottles have to be much thicker and heavier than very light and thin plastic bottles.

1 g glass = 0.6 g emissions

This more than cancels out the benefits of the lower emissions factor, making glass bottles have almost twice the climate impact of plastic.

What is your drinks can made of? If you have a magnet handy (maybe stuck to the fridge?) you can tell whether it is made of steel or aluminium. If the magnet sticks to the can, then it’s made of steel (box 14.1), and you can also rest assured that the magnetic properties of the steel will allow your drinks can to be automatically picked out of the rubbish from the recycling bin, to be used again.

If your magnet doesn’t stick, the can is made of aluminium, which causes 6 times its weight in emissions, for typical recycling rates.

1 g aluminium = 6 g emissions

This is nearly four times the value for steel (box 14.1), and twice the value for the same weight of plastic.

However, aluminium cans weigh less than plastic bottles, so which wins? The higher emissions factor for aluminium cancels out the difference in weight, making the can packaging emissions about the same as for the slightly bigger plastic bottle.

So, overall, plastic is usually the lowest-emissions choice, followed closely by aluminium cans, and glass bottles cause the most emissions. However, this depends a lot on the mix of fossil fuels used for manufacturing, as well as the fraction of recycled materials used. And there are other environmental issues you may want to consider beyond the climate, such as microplastics pollution, and the future journey of your packaging after it leaves your house: will it be recycled into new packaging, burned in place of fossil fuels, or go to landfill?

Bottled water

Because of the health impact of these sugary drinks, you might choose bottled water instead. However, from an emissions perspective, switching to bottled water from a supermarket chiller cabinet doesn’t help as much as you might think, because the packaging, refrigeration, manufacture and waste disposal still have to be accounted for (Fig. 21.2, centre). For maximum climate brownie points, carry a refillable water bottle and top it up at public water fountains or by asking for a refill in drinking establishments. (Tap water causes negligible emissions once the infrastructure is in place.)

1 g tap water = 0.001 g emissions

Orange juice

Fruit juice (Fig. 21.3) provides a healthy dose of vitamins and minerals, but it isn’t as healthy as eating the fruit itself because the chewy part of the fruit has been removed, depriving you of dietary fibre. Juice is so easy to drink that we can consume the juice of several fruits in a single glass: for example, it takes nearly three oranges to make a 200 ml serving of pure juice. This can provide a significant fraction of our recommended daily maximum intake of sugar, and the fruit emissions also start to add up.

Fig. 21.3: Fresh orange juice. (URL 59).

To calculate the total greenhouse-gas emissions, we have to include the emissions from growing the fruit (chapter 17), as well as the processing, packaging, transport and refrigeration, which brings the orange juice emissions to approximately twice its own weight (Fig. 21.2, right).

1 g orange juice = 2 g emissions

The emissions from a single packaged drink are around 10% of a daily food emissions budget of 3 kilos but, although it might not look much in your home recycling bin, it is estimated that nearly half of all food packaging in the UK is drinks packaging, and the numbers can add up if you have several packaged drinks each day.

Key points

- The carbon dioxide in drinks isn’t a major contributor to climate change.

- For a small drinks bottle, the packaging causes nearly half the emissions.

- The ultra-low-emissions option is to carry around your own cup or bottle and refill it from water fountains and catering outlets.

Notes

Each small (0.5 litre) bottle of soft drink causes less than half its own weight in emissions. However, only a tiny part of that is caused by the gas that makes it sparkle. This uses the values from Amienyo et al. (2013), see in particular their Figure 5, which shows the contributions from the separate processes. Subtract their number for the packaging (174 gCO_2e / litre) and group all the other contributions together (388-174 gCO_2e / litre), for the 0.5 litre PET bottle. Regarding the bubbles in the drink, the amount of carbon dioxide fizz is 0.6% the weight of the drink (Amienyo et al. 2013 Table 1), so a 0.5 litre bottle contains 3 grams of carbon dioxide, which is less than 2% of the total emissions caused by the drink and its packaging (388 gCO_2e / litre * 0.5 litres = 194 gCO_2e).

Refrigerators in shops cause about a quarter of the total climate impact of a store-bought cold drink From Amienyo et al. (2013) Fig. 5, 95 / 388 = 0.25.

nearly half of the greenhouse-gas emissions come from the plastic bottle (Fig. 21.2, left). In the figures, the packaging emissions are shown as the upper boxes, and the lower boxes include all the other contributions to emissions, such as refrigeration, ingredients, manufacturing and transport.

emissions of about 3 times the weight of the final plastic container, This means that we can estimate the emissions of any container just by weighing it and multiplying up the number of grams by 3. The value 3.0 kgCO_2e / kg plastic comes from v3.1 of Ecoinvent (Frischknecht and Jungbluth, 2007) for virgin (i.e. non-recycled) polyethylene terephthalate. See also Boustead (2005) who give a value of 3.4 kgCO_2e / kg.

However, if the bottle is made entirely from recycled material then the emissions are significantly reduced, to less than the weight of the container. From the written evidence submitted by the British Plastics Federation and PlasticsEurope to the UK House of Commons Environmental Audit Committee “it takes 75% less energy to make a plastic bottle from recycled material than when using virgin materials” (British Plastics Federation and PlasticsEurope, 2017). Doing the calculation (1-0.75) × 3.0 gives 0.75 kgCO_2e / kg for recycled plastic.

Glass causes about half its own weight in emissions, For 85% recycled glass CCalc2 (“CCaLC PVC Manual (V2.0)” 2011) gives 0.62 kgCO_2e / kg glass.

aluminium, which causes 6 times its weight in emissions, for typical recycling rates. The value from CCalc2 (“CCaLC PVC Manual (V2.0)” 2011) for aluminium is 5.94 kgCO_2e / kg aluminium for 48% recycled aluminium. For virgin (not recycled) aluminium the value is 10.5 kgCO_2e / kg aluminium.

The higher emissions factor for aluminium cancels out the difference in weight, making the can packaging emissions about the same as for the slightly bigger plastic bottle. A typical empty 330 ml-capacity aluminium drinks can weighs about 14 grams, which is about half the weight of an empty 500 ml plastic bottle. The emissions factor of plastic is half that of aluminium so the two effects cancel out. Though note that you get a bit more to drink in a 500 ml plastic bottle than a 330 ml drinks can.

from an emissions perspective, switching to bottled water from a supermarket chiller cabinet doesn’t help as much as you might think, because the packaging, refrigeration, manufacture and waste disposal still have to be accounted for This assumes the manufacturing, transport and retail (refrigeration) stages are the same for the fizzy drink and bottled water, and then uses the values from Amienyo et al. (2013) for the fizzy drink, minus the packaging (listed separately) and the ingredients (i.e. 388 - 174 - 40 = 174 gCO_2e / litre), which gives 0.17 kgCO_2e / kg for water in a bottle. (Packaging emissions are added separately later.)

carry a refillable water bottle and top it up at public water fountains or by asking for a refill in drinking establishments. It took me a while to figure out, but carrying an empty water bottle is still useful, and much lighter than carrying a full one – you can fill it up next to a tap and then drink it straight away!

(Tap water causes negligible emissions once the infrastructure is in place.) Tap water from conventional drinking water treatments (scenario 1 of Garfi et al. 2016) causes emissions of about 0.5 kgCO_2e / m3 of water. 1 m3 of water weighs 1,000 kg, so this corresponds to 0.0005 kgCO_2e / kg of water, the lowest emissions ratio in this book by a large margin. We round this to 0.001 kgCO_2e / kg in the main text due to a lack of studies.

it takes nearly three oranges to make a 200 ml serving of pure juice. Based on numbers from Dwivedi et al. (2012).

orange juice emissions to approximately twice its own weight From Frankowska et al. (2019b) for orange juice, which gives 2.0 kgCO_2e / kg including complete lifecycle (which includes 10% from packaging). Since packaging is shown separately in this book, the value used for the juice alone is 1.8 kgCO_2e / kg.

nearly half of all food packaging in the UK is drinks packaging, Amienyo et al. (2013) state that 40% of all food packaging comes from drinks in the UK.

Chapter 22 A piece of cake

Fig. 22.1: A Victoria sponge cake. (URL 60)

A piece of cake is the ultimate snack-time indulgence, perfect with tea or coffee (chapter 2). We’ve worked hard to understand the carbon footprints of enough different ingredients so we can now get baking!

We start with a classic sponge cake containing just four ingredients: eggs, flour, sugar and butter. While it’s baking, let’s make a batch of butter icing, by mixing together butter and icing sugar; when the cake is cooled we slice it in half, and slather on the icing and some jam.

Fig. 22.2:

Left: Emissions for sponge cake with butter icing and jam: 4 eggs, shared between 10 slices (20 g); sugar (22.5 g); flour (22.5 g); butter (22.5 g); jam (6 g); butter (for icing) (7.5 g); sugar (for icing) (17.5 g); putting the oven on for 35 minutes, plus warm-up time, shared between 10 slices (5 minutes at 2 kW).

Centre: The same ingredients as the left panel replacing butter with vegetable spread in both the cake and the icing.

Right: Emissions for Black Forest chocolate cake: 6 eggs, shared between 10 slices (30 g); sugar (15 g); flour (5 g); cocoa powder (5 g); cherries (40 g); cream (75 g); putting the oven on for 1 hour, plus warm-up time, shared between 10 slices (7.5 minutes at 2 kW).

How big is a slice of cake? (How long is a piece of string?) We’ll divide our cakes into ten pieces, as recommended in standard recipes. We will also restrain ourselves from eating more than one slice, because this already provides about 500 kCal – one fifth of the recommended daily calorie intake. We can now add up the emissions from all the individual ingredients. Each slice clocks up about half a kilo of emissions, about half of which comes from the butter (Fig. 22.2, left).

Many recipes specify vegetable spread, or margarine, instead of butter, so we can safely make this switch – as long as the tub says the dairy-free spread is suitable for baking. This one change reduces the cake impact by 40% (Fig. 22.2, middle).

Alternatively you could go large on your waistline and your emissions by making a really creamy cake. For example, a whole Black Forest chocolate cake contains about 750 ml of cream (Fig. 22.3), as well as jammy stewed fruit. One slice has more than twice the emissions of the dairy-free sponge (compare Fig. 22.2, right and centre).

Fig. 22.3: A slice of melt-in-the-mouth creamy Black Forest cake? (URL 61)

How climate-friendly could you make the cake? Most of the main ingredients are low-impact foods: flour, sugar and vegetable spread. With care you can make an entirely vegan cake by replacing egg with one of the growing number of alternatives such as aquafaba (chapter 7). The oven emissions can also be reduced by cooking several cakes at once, or by buying from someone else who made a batch.

Key points

- A piece of cake causes 0.6 kilos of emissions, which is one fifth of a daily food emissions budget of 3 kilos.

- The climate impact can be reduced to 10% of a 3 kilo daily food emissions budget by switching to a dairy-free butter alternative, or having a smaller piece of cake!

- A very creamy cake (e.g. Black Forest cake) causes 0.8 kilos of emissions per slice, which is one quarter of a budget of 3 kilos from food per day.

- You can reduce cake emissions further by batch cooking, and replacing the eggs to make an entirely vegan cake.

Notes

a classic sponge cake containing just four ingredients: eggs, flour, sugar and butter. This calculation uses 4 eggs, 225 g sugar, 225 g flour and 225 g butter for the cake …

slather on the icing and some jam. … with 75 g of butter and 175 g of sugar for the icing, plus 60 g of jam.

because this already provides about 500 kCal Using standard values of 143, 394, 352, 748 and 238 kCal per 100 g for egg, sugar, flour, butter and jam respectively, and eggs weighing 50 g each. Note that cooking doesn’t affect the total calories, unless you leave a lot in the mixing bowl and on the mixing spoon (and, let’s face it, this can happen because licking it off while no-one’s looking is the best bit of baking!). So we can divide approximately 4000 kCal between the 10 pieces to get the total kCal per slice.

jammy stewed fruit. Using the emissions value for jam due to a lack of literature on stewed cherries (see chapter 5).

Chapter 23 Snacks summary

We’ve considered a range of popular snacks that can be enjoyed as part of a meal, or scattered throughout the day.

Typical-emissions snacks

Fig. 23.1 (left) shows a typical day’s collection of snacks: an apple, a banana, some milk chocolate and a packet of crisps. The emissions are relatively modest at about 300 grams, which corresponds to 10% of a 3,000 g daily food emissions budget (chapter 1).

Fig. 23.1:

Left: Emissions for typical-emissions snacks: an apple; a banana; milk chocolate; crisps.

Centre: Emissions for higher-emissions snacks: black forest chocolate cake; strawberries (by air); a soft drink.

Right: Emissions for lower-emissions snacks: mixed nuts; two oranges; dark chocolate.

Higher-emissions snacks

Air-freighted fruit and creamy cakes are in a different (high-emissions) league to the other snacks. Totting up the totals from a handful of air-freighted berries, a creamy cake and a bottle of juice comes to over 1.5 kilos of greenhouse gases (Fig. 23.1, centre) which is more than half of a daily food emissions budget of 3 kg.

Lower-emissions snacks

Sticking to healthy wholefood options like nuts and non-perishable fruit (box 17.3) works out well for the climate. Fig. 23.1 (right) shows a stack for mixed nuts, two oranges and a small bar of dark chocolate. The result is a little lower than for the typical-emissions snacks, but also healthier for replacing crisps with nuts.

Key points

- Fruit is both a healthy and low-impact snack, if it is nonperishable, or in season …

- … but air-freighted fruit adds a quarter of a daily food emissions budget of 3 kg.

- Snacks containing cream or butter can have relatively large emissions too.

- Nuts and seeds are both healthy and low-emissions.

Part IV: Evening Meal

This is the last Part of the book devoted to the climate change impact of individual foods, before we take stock and consider some broader issues later on.

Our dinner menu includes some of the biggest emissions contributions, getting our teeth into beef and chicken. We recall some issues from breakfast when we add milk and eggs. Then we consider one of the most widely eaten foods, which also makes a surprise appearance on the list of higher-emissions plant-based foods – rice.

We dive into two very different ways to bring fish to the table, before comparing different vegetables and their preparation methods. Wine and beer round out the main course, followed by a session in the kitchen combining ingredients from earlier, to make apple pie and chocolate mousse.

Chapters

Chapter 24: Spaghetti bolognese

Chapter 25: Chicken curry tikka masala

Chapter 26: Rice

Chapter 27: Fish and chips

Chapter 28: Veg

Chapter 29: Beer or wine?

Chapter 30: Dessert

Chapter 31: Evening meal summary

Chapter 24 Spaghetti bolognese

Fig. 24.1: A bowl of spaghetti bolognese, with a generous sprinkling of cheese. (URL 63)

Spaghetti bolognese can be a student staple containing just pasta, beef and tomato sauce, or it can be taken to sophisticated heights by using fresh pasta with homemade sauce including sun-dried tomatoes and red wine (Fig. 24). We already discussed tomato sauce over lunch (chapters 11, 12), and most pasta is just a processed form of wheat, so it’s time to address the elephant (or cow) in the room: beef.

Just as for the milk emissions (chapter 4), beef contributes to global warming mostly because cows burp methane and their manure decomposes into methane and releases nitrous oxide. This means that the climate impact of a piece of beef depends on how many days the cow has lived, how much it eats, and how much meat it can be slaughtered for.

We first consider “prime” beef herds, in which cows are raised for producing beef and do not produce milk for human consumption. This differs from a dairy herd (discussed later in this chapter), where the cow is milked and is then slaughtered for beef; we can share out the cow emissions between the beef and the milk.

Prime beef

A mother cow usually has a new calf every year, and that calf is fattened for about one year itself before being slaughtered for about 250 kilograms of beef meat (about four times the weight of a human). On average a calf eats over 40,000 kCal each day to grow big and strong, and we have to also take into account a similar number of calories eaten each day by the mother cow. In total the calf and mother cow eat about thirty times the average calorie intake of one human each day.

As discussed at breakfast (chapter 4), about 5% of the calories consumed by a cow are turned into methane. In the case of the beef cow and calf, this would create about half their own body volume of methane each day. However, the greater potency of methane as a greenhouse gas means that this amount of methane causes the same warming effect as a weight of 10 kg of carbon dioxide (chapter 4).

Each day the calf grows nearly 700 grams (24 oz) of extra flesh that can become beef meat, which would be enough for three large (8 oz) steaks. This means that just from the methane burps alone, beef causes 14 times its own weight in emissions. It also means that only about 2% of the calories eaten by the cow make it through to our stomachs; this is the least efficient of all the animal products considered in this book (box 10.1). However, we should note that pasture-fed cows are creating a nutritious food that we can eat from the most abundant yet effectively inedible-to-humans food source on the planet (grass).

Fig. 24.2: A juicy steak. (URL 64)

Where do all the other calories go, if not into the beef? Most of the calories come out of the other end of the cow, as manure. This is a good fertilizer for crops, if transported to the right place. Unfortunately it can also decompose into methane, if left without sufficient oxygen to help it decompose into carbon dioxide. While the manure is an excellent fertilizer because it contains a lot of nitrogen, this nitrogen causes nitrous oxide emissions whether or not the manure is being used to grow crops. The exact emissions depend on how dry the manure pile is, and how it is spread, but manure helps bring the total emissions for beef to around 46 times the weight of the portion.

1 g steak = 46 g emissions

However, there is a huge range in the way beef is produced across the world. To take an extreme example, a calf can live for 20 years instead of just the 1 year we assumed in the above calculation. If the only purpose of keeping that calf was to produce beef, then the steak emissions from that animal would be 10 times higher than for the calf that lived to the age of 1, i.e. the emissions will be 200 times the weight of the beef!

Cows are sometimes fed a more protein-rich diet including soy. This reduces the amount of methane burped by the cow (chapter 4), but requires more land to grow the soy, which can cause deforestation (chapter 7). If forest is cleared to create grassland then this is even worse.

Given all the variability it seems rash to provide a single number for beef in this book. However, for the sake of comparison with other foods, I use one number (beef causes 46 times its own weight in emissions) which corresponds to a relatively efficient beef production system, bearing in mind that this is at the low (better) end of the range for beef.

Fig. 24.3: Emissions for a fried steak: 8 ounces of steak (227 g); a teaspoon of vegetable oil (5 g); frying (5 minutes at 2 kW).

A meaty digression: steak

We can now calculate the global warming impact of the highest-emissions regularly eaten meal: a large steak (Fig. 24.2). A 225 g (8 oz) steak causes about 10 kilos of greenhouse-gas emissions (Fig. 24.3), which is three times larger than a budget of 3 kg of emissions for a whole day. If everyone in the world ate such a large steak every day then the steaks alone would use up the remaining 1.5°C carbon budget before 2040 (chapter 1).

Here are some other comparisons. Eating one large steak is equivalent to driving a fossil-fuelled car about 70 kilometres (40 miles), which is a relatively short daily commute to work in many countries. Alternatively, taking one transatlantic flight every year is equivalent to eating one large steak a day. So we should think twice about ordering a steak on a regular basis, but at the same time look at our non-food emissions.

Spaghetti bolognese emissions

Now we’re ready to make spaghetti bolognese. Every cook has their own special recipe, but the details are unlikely to make a big difference to global warming because almost all the greenhouse-gas emissions come from the beef (Fig. 24.4, left). The main issue is how much beef each person eats; a moderately sized portion causes over 6 kilos of emissions, which is twice a daily food emissions budget of 3 kg, just from this one dish. This is more than twice the emissions of all the non-ruminant meals considered in this book, is exceeded only by the steak and is similar to the lamb tikka masala (in the next chapter).

Lower impact beef

The climate impact of efficiently produced prime beef has roughly equal contributions from the calf and the mother. But what if the mother cow were also producing milk during most of her one year gap between calving, and if we slaughtered the mother for beef at the end of her milk-producing life?

Furthermore, male dairy calves aren’t needed for milk production and so are often killed young (producing a negligible amount of meat). Fattening them up for meat instead would produce a lower-emissions piece of beef, which can be as much as 2 times better for the climate than prime beef.

In fact, about half of all beef already comes from dairy cows. This can significantly reduce the environmental footprint of beef, by 2 or more times, depending on whether the male calves are fattened and how the emissions are allocated between the milk and beef (box 9.1).

Based on the current quantities of meat from dairy herds, we would have to roughly halve our beef consumption to remove the demand for dedicated prime-beef herds. To support dairy beef and encourage the most efficient practices, we also need more information on the meat we are buying, at very least we need the packet to tell us what kind of herd the meat comes from!

Fig. 24.4:

Left: Emissions for spag bol: prime mince (125 g); a small onion, shared between 4 people (25 g); carrot (25 g); two cans of tomatoes, shared between 4 people (200 g); two steel cans, shared between 4 people (25 g); vegetable oil (1 g); frying for 30 minutes, shared between 4 people (7.5 minutes at 2 kW); spaghetti (230 g); boiling the spaghetti for 15 minutes, shared between 4 people (4 minutes at 2 kW).

Centre: Switching the beef for the same weight of chicken.

Right: Switching the beef for the same weight of cooked lentils.

Beef alternatives

How about using a different meat in the spaghetti bolognese? Lamb is delicious but it has about the same emissions as beef, because sheep have similar stomachs to cows (chapters 4 and 6).

1 g lamb = 43 g emissions

Pork causes fewer emissions than beef (chapter 10), but chicken is lower still (chapter 25). A chicken spaghetti bolognese causes three times lower emissions than a prime beef spaghetti bolognese (compare Fig. 24.4 centre with Fig. 24.4 left). Switching to beans or lentils (chapter 14) halves the emissions again, to 1 kilo per person, (Fig. 24.4, right).

Key points

- A piece of efficiently produced beef causes 15 times its own weight in emissions from cow burps alone, which is already higher than the values for pork and chicken. The longer the cow lives, the higher this number is.

- Prime beef (even when efficiently produced) causes the highest emissions of any commonly consumed food at over 40 times its own weight in emissions; for example it causes 5 times the emissions of the same weight of chicken.

- An 8 oz steak causes 10 kilos of emissions, which alone is three times over budget compared to the value of 3 kilos of food emissions discussed in chapter 1.

- A portion of prime-beef spaghetti bolognese causes 6 kilos of emissions, depending on the amount of beef used.

- Eating beef from dairy cows instead of prime beef reduces the climate impact by 2 or more times, because the emissions are shared between the meat and milk.

- Replacing beef mince with chicken reduces the spaghetti bolognese emissions by more than 3 times, to below 2 kilos of emissions for each portion.

- Replacing the beef with lentils reduces emissions by 7 times, to 1 kilo of emissions per portion.

Notes

most pasta is just a processed form of wheat, An average of values from Recchia et al. (2019) (1.71 and 1.76 kgCO_2e / kg dry spaghetti) modified to account for hydration during cooking (62% of cooked spaghetti is water according to (URL 62), which brings the value to 0.66 kgCO_2e / kg hydrated spaghetti. Note that this number does not include cooking, which is added separately.

calf is fattened for about one year itself before being slaughtered for about 250 kilograms of beef meat (about four times the weight of a human). Steer average dressed carcass weight (after removing gut, skin, etc.) was 372.4 kg for August 2019 in the UK, from Defra (2019) which can be converted into a bone-free meat content of 260 kg, using the ratio of carcass weight to bone free meat from Clune et al. (2017). This number will vary from one farm and country to another so it is rounded to 250 kg in the main text.

a calf eats over 40,000 kCal each day to grow big and strong, and we have to also take into account a similar number of calories eaten each day by the mother cow. This is calculated using the equations in chapter 10 of Dong et al. (2017, hereafter IPCC2006), in particular their equation 10.16 and preceding equations, using default values from GLEAM (GLEAM Global Livestock Environmental Assessment Model 2017) of 34 kg birth weight and 511 kg for the mother cow, and a final weight of 511 kg for the calf when it is slaughtered at 1 year old. The feed is assumed to be grass, with a digestibility of 60% taken from table 10.2 of IPCC06 for “Pasture fed animals” and a crude protein percentage of 12 from Beauchemin et al. (2010) for pasture. Energy requirements are taken from table 10.4 of IPCC06 for Cattle/Buffalo (cows), from Table 10.5 of IPCC06 for activity levels in a feeding situation for Pasture, and the mother cow is assumed to be pregnant for 9 months of the year, causing an increase in feed requirement of 10% (Table 10.7 IPCC06).

In total the calf and mother cow eat about thirty times the average calorie intake of one human each day. Note that the mother cow and calf consume fewer calories per day than a dairy cow because they are not producing as much milk.

In the case of the beef cow and calf, this would create about half their own body volume of methane each day. 5% of calories being turned into methane means that 80,000 kCal (total eaten by the calf and cow each day) produces 4000 kCal of methane, which weighs 300 grams (given the energy content of methane of 13,300 kCal / kg). The density of methane is 0.717 kg m–3, so this corresponds to a volume of 300 g / 1000 g/ kg / 0.717 kg m–3 = 0.4 m–3, which is the volume of a small cow.

Each day the calf grows nearly 700 grams (24 oz) of extra flesh that can become beef meat, 250 kilograms of meat produced during 365 days corresponds to 684 grams of meat a day.

just from the methane burps alone, beef causes 14 times its own weight in emissions. 10 kg of emissions / 700 g beef = 10 kgCO_2e / 0.7 kg beef = 14 kgCO_2e / kg.

only about 2% of the calories eaten by the cow make it through to our stomachs; Compare the number of calories eaten by cows with the number of calories we get from beef. Beef typically provides about 200 kCal per 100 grams (check the supermarket label of your favourite cut of meat). So the calf provides us with an extra 1,400 kCal each day it grows a bit fatter. This is about 2% of the 80,000 kCal of food required by the cow and calf.

total emissions for beef to around 46 times the weight of the portion. Using a value of 46 kgCO_2e / kg beef for Europe prime beef from Poore and Nemecek (2018), which is lower than the value for the US of 54 kgCO_2e / kg beef from the same reference. However, the global average (mean) is 100 kgCO_2e / kg beef, because some countries have much higher emissions. For more explanation of the details of the calculation see GLEAM Global Livestock Environmental Assessment Model (2017) and Beauchemin et al. (2010), as well as examining the range of values compiled in the open access full spreadsheet of details from Poore and Nemecek (2018).

the steak emissions from that animal would be 10 times higher than for the calf that lived to the age of 1, i.e. the emissions will be 200 times the weight of the beef! Our calculation accounted for a calf and a cow being alive for one year, i.e. 2 years of burping. For the calf that lives to age 20, we need to account for 21 years of burping (20 years for the calf, and 1 year for the original mother cow). For simplicity we round 21 divided by 2 down to 10.

If everyone in the world ate such a large steak every day then the steaks alone would use up the remaining 1.5°C carbon budget before 2040 (chapter 1). 10 kg / person / day corresponds to 7.7 people * 365 days / year * 10 kg / person / day / 1,000,000,000,000 Gt / kg = 28 Gt / year. Therefore sharing out 640 Gt over the years gives 640 Gt / (28 Gt / year) = 23 years from the 2018 report date i.e. 2041, which is rounded to 2040 in the main text to avoid giving the impression this number is known to an accuracy of 1 year (the number 640 Gt depends on our understanding of warming triggered by warming (Earth system feedbacks) and depends on the time profile of future emissions see chapter 1).

The main issue is how much beef each person eats; This calculation assumes a 500 g packet of mince shared between four people.

slaughtered the mother for beef at the end of her milk-producing life? Prime-beef cows have been bred for the quality and quantity of their meat, and the beef from dairy cows isn’t usually considered to be as delicious. Whether this is really true depends on the breed of cow and the quality of life of the dairy cow. But note that if the dairy cow has a luxury retirement after milking has ended, then she is also burping out methane which will increase the emissions of the dairy beef.

male dairy calves aren’t needed for milk production and so are often killed young (producing a negligible amount of meat). Fattening them up for meat instead would produce a lower-emissions piece of beef, which can be as much as 2 times better for the climate than prime beef. If the male dairy calves live for 1 year and if they grow at the same rate and burp the same amount of methane as the prime beef calves, then their beef emissions are about half those of the prime beef. This is because we no longer have to account for the emissions of the mother cow, assuming these are attributed to the milk and the beef from the old dairy cow.

about half of all beef already comes from dairy cows. This can significantly reduce the environmental footprint of beef, by 2 or more times, The average dairy beef value for the US from Poore and Nemecek (2018) is just 10 kgCO_2e / kg beef because of the way emissions are allocated across the beef and milk, whereas the value for Europe is close to that for non-dairy beef at 38 kgCO_2e / kg. This makes putting a single number on dairy beef very difficult – it all depends on the farming practice, as discussed in the text. Globally just under half of all beef comes from dairy herds (26.8 million tonnes of beef come from dairy herds and 34.6 from beef herds), but in Europe the figure rises to 80% of all beef coming from dairy herds (Gerber et al., 2013).

Lamb is delicious but it has about the same emissions as beef, Poore and Nemecek (2018) find a value of 43 kgCO_2e / kg lamb for Europe, which is similar to the global value of 40 kgCO_2e / kg (using the value for mutton and goat meat). Note that transportation by ship across from the other side of the world causes far fewer emissions than the sheep themselves (see especially figure 2 of Ledgard et al. 2011). See chapter 17 for more information on transport emissions.

Chapter 25 Chicken curry tikka masala

Fig. 25.1: A bowl of chicken tikka masala with rice. (URL 65).

Chicken is the most popular meat in both the US and the UK, and consumption is rising steadily. In this chapter we focus on chicken tikka masala, which is now described as a British national dish (allegedly invented in Scotland when a customer demanded sauce in their chicken curry).

However, a wide range of sauces are available to turn pieces of chicken into a quick and nutritious meal, and most of this chapter is relevant to any chicken dish. We consider the emissions from chicken farming and then get cooking.

Raising chickens

Whereas egg-laying chickens live for about one year, “broiler” chickens grown especially for their meat typically live for just a few weeks. Standard broilers grow from about 40 grams at birth, to around 2 kg in just six weeks. Over the festive season I think I could probably eat enough to put on this much weight (2 kilos, or 4 lb), but these chicks are increasing their body weight by 50 times! Most incredible is that they do this while only eating less than twice their final body weight in food.

What are these chickens eating? Typically, more than half of their food is a grain such as wheat, a quarter is soya beans, and the rest includes seeds, oil and fish. These are the same foods eaten by the egg-laying chickens (chapter 7), but the amount of protein-rich soy is nearly doubled for the broilers, to build them up big and meaty.

Most of the on-farm greenhouse-gas emissions from chicken meat comes from producing food for them to eat – more than half of which comes from producing soya beans, because the increasing global demand for soy leads to deforestation (chapter 7). There are also some smaller emissions from heating the sheds and from the chicken manure. Additionally taking into account packaging, transport and refrigeration, chicken meat causes about 9 times its own weight in greenhouse-gas emissions.

Chickens are relatively efficient at turning animal feed into meat: about 3 grams of chicken feed are eaten by the chicken for every gram of chicken meat (this takes into account that the final body weight contains inedible parts like bones and intestines). This makes chickens over 10 times as effective as cows at turning food into meat. Even so, our appetite for poultry means that more than 3 chickens need to be fattening all the time to keep one Brit in chicken, and more than 4 per US citizen.

1 g chicken = 9 g emissions

Added ingredients

Chicken tikka masala recipes vary wildly, but many people fry chicken in butter with onions, garlic and spices and then simmer with tomatoes and cream. The environmental impact comes mostly from the chicken (Fig. 25.2, left). The cream and butter cause about a quarter of the emissions, followed by the tomatoes. Even though the spices are the most important sensory ingredient, they hardly make any difference to the total emissions because we add only a few grams at most.

1 g spices = 1 g emissions

Fig. 25.2: Greenhouse-gas emissions estimates for chicken-tikka masala options:

Left: Emissions for chicken tikka masala: two tablespoons of butter, shared between 4 people (7.5 g); an onion, shared between 4 (42.5 g); two cloves of garlic, between 4 (5 g); spices (5 g); passata (100 g); cream (50 g); chicken (125 g); frying for 10 minutes, shared between 4 (2.5 minutes at 2 kW); simmering for 1 hour, shared between 4 people (15 minutes at 2 kW).

Centre: The same as the left panel, but using half the amount of chicken (62.5 g).

Right: The same as the centre panel, but switching butter to vegetable oil (7.5 g) and switching cream to 12.5 g of nut butter.

Can you tweak the recipe to reduce the emissions? Would your guests notice if you halved the amount of chicken from 125 grams per portion to 63 grams (Fig. 25.2, centre)? This reduces the emissions by 30%, from approaching 2 kilos to less than 1.5 kilos per portion. Using yogurt (chapter 15) instead of double cream reduces the total emissions further. Alternatively replace the cream with nuts (chapter 19) and the butter with vegetable oil, reducing the halved chicken tikka masala emissions by nearly a further 20% (compare Fig. 25.2 centre and right).

Organic chicken

Does switching to organic chicken reduce the emissions even further? Organic chickens are raised more slowly than standard chickens and so consume more food, which increases their emissions. However if the organic feed comes from mature agricultural land instead of deforested land, this helps to reduce emissions attributed to the organic chicken (although it doesn’t help reduce the global demand for soy, which is causing deforestation). Overall, in the limited number of studies done so far, the emissions of organic chicken are higher those for standard chicken.

Box 25.1: Organic food

People often ask whether going organic helps reduce the impact of food on climate change. It turns out that the answer depends on the specific food being considered.

Organic food is grown according to strict sets of rules. These include tight restriction on the use of chemicals, which can increase the amount of wildlife on the farm (i.e. increase biodiversity) and increase the amount of micronutrients in the food.

In organic crop agriculture, synthetic fertilizers are replaced by animal manures, which reduces the amount of energy needed to make the fertilizers (box 2.1). However, manure is less finely matched to the needs of the plants, so more fertilizer is needed, which releases more nitrous oxide. Furthermore, for some crops, yields are lower, so organic agriculture generally requires more land, which can contribute to deforestation and thus decreasing biodiversity.

Overall, the various effects tend to cancel each other out, and on average there isn’t a big difference in greenhouse-gas emissions between organic and non-organic foods.

Chicken-less tikka masala

Let’s replace the chicken with something else and see how that changes things. My favourite curry meat is lamb, slow-cooked and infusing its delicious flavour through the sauce. Unfortunately this is bad news for emissions, and it causes 6 kilos of emissions per portion, which is double a 3 kg food emissions budget for a whole day. Even halving the quantity of lamb causes nearly twice the emissions of the original chicken tikka dish. I’ll keep that for special occasions then!

Fig. 25.3: Greenhouse-gas emissions estimates for chicken alternatives:

Left: The same ingredients as in Fig. 25.2 (left) but replacing the chicken with the same weight of lamb.

Centre: The same ingredients as in Fig. 25.2 (right) but replacing the lamb with the same weight of Quorn pieces.

Right: The same ingredients as the centre panel above, but replacing the Quorn with the same weight of rehydrated chickpeas.

You can reduce the emissions further by switching to Quorn (chapter 10), or even chickpeas (chapter 14). Efficient cooking of the chickpeas and using the dairy-free sauce keeps the emissions below 0.6 kilos – three times lower than the original chicken dish (compare Fig. 25.3 right and Fig. 25.2 left), and one fifth of a daily food emissions budget of 3 kg. Chickpea tikka masala anyone? Go on, it’s only three letters different from chicken tikka masala! Could it become the next British national dish?

Key points

- About half the chicken emissions come from growing crops to feed to chickens, much of which is from deforestation to produce soy.

- Chicken causes about 9 times its weight in emissions, which is the lowest of the commonly consumed land-animal meats.

- A chicken tikka masala portion causes nearly 2 kilos of emissions, with more than half of the emissions coming from the chicken.

- Replacing chicken with lamb increases the tikka masala emissions by three times, to 6 kilos, which is twice the 3 kg food emissions budget for a whole day discussed in chapter 1.

- Replacing chicken with chickpeas, and dairy with plant products in the sauce, reduces emissions to less than 0.6 kilos per portion.

Notes

Chicken is the most popular meat in both the US and the UK, and consumption is rising steadily. The word “popular” here refers to the amount eaten. In 1960 Americans ate about 35 pounds per capita per year. By 2017 they ate about 85 pounds. Furthermore, in the 1960s in the US, chicken was half as popular as beef or pork, but by 2017 it was twice as popular as either. This information comes from URL 66; UK statistics can be found in the UK Poultry Pocketbook 2018 (AHDB, 2018b).

chicken tikka masala, which is now described as a British national dish (allegedly invented in Scotland when a customer demanded sauce in their chicken curry). “Chicken Tikka Masala is now a true British national dish” declared the British Foreign Secretary Robin Cook in 2001.

Standard broilers grow from about 40 grams at birth, to around 2 kg in just six weeks. See Table 1 of Leinonen et al. (2011a).

while only eating less than twice their final body weight in food. 3.36 kilograms of food for a final bodyweight of 1.95 kilograms from Table 1 of Leinonen et al.’s broilers paper (Leinonen et al., 2011a).

more than half of their food is a grain such as wheat, a quarter is soya beans, and the rest includes seeds, oil and fish. See Leinonen et al. (2011a) Table A3. Chicken feed also contains limestone rock, which is needed for making eggshells. Chickens are also given vitamins, minerals and artificial proteins, which helps to reduce the need for more emissions-intensive foods such as more fish and soya beans.

Additionally taking into account packaging, transport and refrigeration, chicken meat causes about 9 times its own weight in greenhouse-gas emissions. This number (8.7 kgCO_2e / kg chicken) is the Europe value from Poore and Nemecek (2018). This number is similar to their world average value (9.9 kgCO_2e / kg chicken), but nearly double their value for the US (4.9 kgCO_2e / kg). For details of how the calculation is done, see Leinonen et al. (2011a) and GLEAM Global Livestock Environmental Assessment Model (2017).

about 3 grams of chicken feed are eaten by the chicken for every gram of chicken meat (this takes into account that the final body weight contains inedible parts like bones and intestines). This makes chickens over 10 times as effective as cows at turning food into meat. This takes into account that the amount of chicken meat is less than the final weight of a chicken, because the bones and other inedible parts have to be removed. Using a live-weight to bone-free meat ratio of 0.54, taken from Clune et al. (2017) Table 1. The amount of meat from one standard chicken is therefore 1.95 kg × 0.54 = 1.05 kg. The ratio of feed weight to meat weight is then 3.36 kg / 1.05 kg = 3.19. (Clune et al., 2017) Compare this with beef (chapter 24) where about 2% of calories eaten by the cow are turned into beef i.e. 50 grams of food is eaten by the cow for each gram of beef.

more than 3 chickens need to be fattening all the time to keep one Brit in chicken, and more than 4 per US citizen. First let’s work out the amount of chicken eaten per person per day in each country. According to the UK Poultry Pocketbook 2018 (table 6.1 of AHDB 2018b for 2017), the average Brit eats 36.3 kilograms of poultry per year, which is 99.4 grams per person per day. Only 90% of poultry is chicken though (see table 3.2 of the same reference, which assumes that the UK consumption fraction of chicken is the same as the UK production fraction), therefore the average person in the UK eats 88 grams of chicken meat a day. The average US person eats 92.2 lb of chicken per year (URL 66), which corresponds to 115 g per day. To work out the number of fattening chickens per person, we need to know the lifetime of a chicken and the amount of meat each chicken produces. The standard chicken lifetime is 39 days from Leinonen et al. (2011a), and the amount of meat per chicken is 1.05 kg, so the number of chickens per person is 88 g / day / person × 39 days / (1.05 kg / chicken × 1000 g / kg) = 3.27 chickens per person. The US calculation gives 4.3 chickens per person.

onions, Taking the pre-household stages for UK fresh onions from Frankowska et al. (2019a) (their figure S46) gives 0.18 kgCO_2e / kg.

garlic A value of 0.36 kgCO_2e / kg garlic is used for the figures in this book, based on values of 0.39 kgCO_2e / kg, 0.248 kgCO_2e / kg and 0.43 kgCO_2e / kg taken from Moudrý jr. et al. (2015) and Khoshnevisan and Rafiee (2013).

The environmental impact comes mostly from the chicken See also the detailed studies by the World Wide Fund for Nature Schreiber (2018) and the Defra (2012) which analysed chicken tikka masala with a slightly different recipe and numbers, but with a lot of similarities.

Even though the spices are the most important sensory ingredient, they hardly make any difference to the total emissions because we add only a few grams at most. Audsley and Williamson (2010) table 13 state 0.87 kgCO_2e / kg for spices. This is rounded to 1 in the main text because there are very few studies.

Organic chickens are raised more slowly than standard chickens and so consume more food, which increases their emissions. Table 1 of Leinonen et al. (2011a) has standard chickens living to 39 days and organic chickens living to 73 days, so nearly twice as long. The total feed is 5.75 kg compared to 3.36 kg i.e. 70% more feed. The final weight is slightly higher, at 2.17 kg, but the feed conversion ratio is still worse, at 5.75 / (0.54 × 2.17) = 4.9, compared to 3.2 for standard chicken farming.

the emissions of organic chicken are higher those for standard chicken. 19% higher in Leinonen et al. (2011a) and 33% higher in Williams et al. (2006), which are the two studies cited for poultry in the Clarke and Tilman (2017) comparative study of organic vs non-organic.

organic agriculture generally requires more land, See figure 1 of Clarke and Tilman (2017).

Overall, the various effects tend to cancel each other out, and on average there isn’t a big difference in greenhouse-gas emissions between organic and non-organic foods. For more details, read Clarke and Tilman (2017).

Chapter 26 Rice

Fig. 26.1:

Top left: A bowl of rice. (URL 67)

Top right: Rice grains forming on the plant. (URL 68)

Bottom left: Rice seedlings emerging in a flooded field. (URL 69)

Bottom right: Traditional paddy fields, with tiers of flooded fields down the side of a slope. (URL 70)

A curry is traditionally served with rice, the staple food of over half the people in the world (Fig. 26.1, top). Fig. 26.1 (upper middle) shows the seed heads on the rice plant, with the grains developing. It looks a bit like wheat, with the long grassy leaves and slightly drooping elongated seed heads, and with many seeds on each stalk. The ripened seeds must be thrashed off the stalk, and hulled to remove the outer husk.

But, unlike wheat, most rice is grown submerged in 5-10 centimetres of water (Fig. 26.1, lower middle), sometimes on lush green hillsides terraced to create submerged paddy fields (Fig. 26.1, bottom). Why go to all this trouble? Most crops can’t thrive with their roots in stationary water, but rice is different. Rice growers can save themselves a lot of work by growing the rice in conditions where the usual weeds will die off.

Unfortunately this waterlogging is bad news for the climate, because fertile soil usually contains the remains of living things, such as decaying plants or manure. The complex carbon molecules that make up living things decompose into either carbon dioxide or methane; underwater there is little oxygen and so bacteria turn the organic matter into methane.

Taking this and other factors into account, dry rice causes over 4 times its own weight in emissions, but if we take into account the absorbed water, this reduces to 2 times its own weight in emissions for cooked rice, so a (200 g) bowl causes nearly half a kilo of greenhouse gases, once we include the energy used in cooking (Fig. 26.2).

1 g cooked weight of rice = 2 g emissions

And humans eat a lot of rice – averaged across the world, we all eat two portions of rice a day. Growing rice causes about 10% of global methane emissions, and 2% of all global warming.

However, in a personal context, eating one (200 g) portion of rice causes one sixth of a daily food emissions budget of 3 kg, and the same emissions as driving a fossil-fuelled car for 3 kilometres (2 miles).

Fig. 26.2: Emissions for rice: rice, plus enough water (200 g); boiling the rice for 20 minutes, shared between 4 people (5 minutes at 2 kW).

Adding a portion of rice to your chicken tikka masala from the previous chapter adds about 25% to the total greenhouse-gas emissions (Fig. 26.3, left), whereas for the ultra-low-emissions chickpea tikka masala, the rice portion nearly doubles the emissions (Fig. 26.3, centre).

How can you reduce emissions?

Given rice is so integral to many food cultures, is there a way to grow rice that causes lower emissions? The amount of methane depends on the length of time the paddy fields are flooded, and the amount of organic matter in the soil. These can both be reduced. In fact, rice can be grown on dry land just like wheat and other grains, and this is common practice in some countries; the main disadvantage is the increased burden of weeding or applying herbicides and pesticides.

Fig. 26.3: Emissions stacks comparing alternatives to chicken tikka masala with rice.

Left: Emissions for chicken tikka masala with rice: chicken tikka masala; a portion of rice.

Centre: Emissions for chickpea tikka masala with rice: chickpea tikka masala; a portion of rice.

Right: Emissions for chickpea tikka masala with bread: chickpea tikka masala; bread.

Growing rice without flooding might be practical on commercial farms with suitable land, but what about the many small farms where growing rice is a way of life? Emissions can be more than halved if the fields are kept flooded for the minimum time outside the growing season and by allowing the fields to dry out multiple times while the rice is growing. The way fertilizer is applied can also make a big difference; for example, applying fertilizer significantly before the waterlogging further reduces emissions.

Furthermore, new varieties of rice are being developed that produce higher yields for a given area, and that exude less nutrients into the soil to feed the microbes. The bottom line is that rice emissions can be reduced significantly by suitable growing.

What alternatives are there to rice? Wheat-based alternatives include bread, and a naan bread goes nicely with curry. Or couscous (usually made from wheat) brings a similar grainy comfort.

Switching from conventional rice to bread reduces the emissions of the chickpea tikka masala meal by nearly one third (compare Fig. 26.3 centre and right). Switching to low-emissions rice reduces emissions by a similar amount, but at the moment this is not an option for most people because the emissions information is not available.

Key points

- Rice is traditionally grown in flooded fields, which cause about 2% of all greenhouse-gas emissions.

- A portion of rice still causes less emissions than lower-impact animal products.

- Switching from rice to bread or low-impact rice reduces the emissions by nearly four times.

Notes

dry rice causes over 4 times its own weight in emissions, but if we take into account the absorbed water, this reduces to 2 times its own weight in emissions for cooked rice, The global average is 4.5 kgCO_2e / kg of dry rice. This is divided by a hydration factor of 2.25 to account for the change in weight on cooking, to give 2.0 kgCO_2e / kg of cooked rice. Note that the cooking emissions are not included in this number as they are added separately.

Growing rice causes about 10% of global methane emissions, and 2% of all global warming. Rice paddies cause 0.9 GtCO_2e compared to a total of 9.3 GtCO_2e for methane and 50.6 GtCO_2e in total in 2010 from Bajželj et al. (2013) figure 2.

The amount of methane depends on the length of time the paddy fields are flooded, and the amount of organic matter in the soil. See chapter 5 of Lasco et al. (2006) especially section 5.5, equation 5.2 and related equations.

Emissions can be more than halved if the fields are kept flooded for the minimum time outside the growing season and by allowing the fields to dry out multiple times while the rice is growing. Lasco et al. (2006) Table 5.12 gives scaling factors for intermittent flooding of 0.52 and 0.60 compared to continuous flooding during the growing season. Table 5.13 of the same reference gives scaling factors of 0.68 to 1.9 depending on whether the fields are flooded in the non-growing season. Taking these two factors together can produce a greater than 50% reduction in emissions (0.52 * 0.68 = 0.35).

new varieties of rice are being developed that produce higher yields for a given area, and that exude less nutrients into the soil to feed the microbes. Adding a gene to rice was found to produce more rice and less methane in Su et al. (2015).

Chapter 27 Fish and chips

Fig. 27.1: Fish and chips. (URL 71)

It was a childhood treat to visit the fish ’n’ chip shop and come out with steaming bundles of food, ripping through the paper to pull out fat, greasy vinegar-soaked chips. Then shovelling in crunchy pieces of fish and biting through to the soft flakes inside. Shouldn’t eating fish be low on emissions – the fish were already there in the sea after all?

Wild food

In fact, more generally, might eating from the wild be a good route to reducing food emissions? Eating wild ruminants like deer or moose would cut their large methane emissions. Some people in Australia advocate eating kangaroo that have been culled for other reasons.

Leaving aside ethical issues with killing wild animals, and taking a human-centric view for now, it turns out that the amount of wild food just doesn’t come close to the quantity of food demanded for the current human population. While our ancestors may have lived by rivers and the sea, happily eating fish without depleting their annual numbers, over-fishing has been a problem in recent decades. For fishing to be sustainable into the long-term future, the amount of fish being caught has to be balanced by enough new fish being born and surviving long enough to reproduce.

Fishing emissions

So, if we take only a little fish from the sea, what emissions is your fish and chips responsible for? A ship has to go to sea, haul in the fish and refrigerate or freeze the catch to keep it fresh. The fuel burnt to power these activities, and the leakage of refrigerant (box 11.1), causes the greenhouse-gas emissions of deep-sea-caught fish (e.g. cod) to be about 5 times the weight of the fish.

1 g cod = 5 g emissions

Fig. 27.2: Emissions for battered cod: cod (250 g); flour (30 g); milk (60 g); egg (12.5 g); vegetable oil (20 g); putting the fryer on for 30 minutes, shared between 4 people (7.5 minutes at 2 kW).

This is lower than chicken, and only slightly higher than eggs, which are the lowest nutritionally-dense animal-based food considered so far (excluding milk, cream and yogurt). However, it is higher than all the plant-based ingredients considered in this book (with the exception of hothoused tomatoes, air-freighted fruit and vegetables and coffee granules, the latter of which isn’t likely to become a staple foodstuff).

For both the fish and the chips, portion sizes vary wildly from one chip shop to the next, but using a typical portion size, the total fish ’n’ chip emissions is over 1.5 kilos, mostly from the fish (Fig. 27.4 left), and has the largest climate-impact of any of the non-ruminant dishes in this book (closely followed by chicken tikka masala and a steak pizza).

Why is it so high, when the fish causes relatively low emissions per kilo? Simply because we’ve used a large portion of fish, weighing 250 grams: this is twice the weight of meat used in the chicken tikka masala, and the fish itself causes most of the battered fish emissions (Fig. 27.2). Adding the emissions from a portion of chips takes the large fish ’n’ chips emissions over 2 kilos, using up most of a 3 kg emissions budget for a whole day (Fig. 27.4, left).

How can this be reduced? I think the anticipation of the vinegar and salt makes me greedy to have a large portion, whereas often I’d be equally happy with half the quantity of fish, which would reduce emissions for the whole meal by about half a kilo (Fig. 27.4, centre). I might want to add some lower-impact foods to compensate though, maybe some extra chips, or some old-fashioned protein from classic mushy peas (produced in a similar way to beans, discussed in chapter 14).

Fig. 27.3: Salmon farming in Norway, using floating cages. (URL 73)

Fish farming

An increasing proportion of the fish we eat is from fish farms. These fish farms can be entirely inland, for example in an artificial pond, or they can be in a caged part of the sea or river (Fig. 27.3). Most salmon is now farmed.

The emissions per gram of farmed fish are higher than for wild fish, and more similar to chicken (which is a relatively low-impact meat).

1 g salmon = 8 g emissions

Just as for chicken, about half of the carbon footprint comes from producing the fish food, which is mostly fishmeal and fish oil, as well as seed cake (chapter 10), soy and wheat (chapter 25).

Fig. 27.4:

Left: Emissions for fish ’n’ chips: battered cod; fried chips.

Centre: The same ingredients as the left panel but using 125 g of cod instead of 250 g.

Right: Emissions for fish pie: salmon (100 g); butter (15 g); potato (100 g); milk (100 g); boiling the potatoes for 15 minutes, shared between two people (7.5 minutes at 2 kW); putting the oven on for 40 minutes, plus warm-up time, shared between 2 people (28 minutes at 2 kW).

Fish pie

Fig. 27.4 (right) shows the emissions for a fish pie. The total emissions are about one quarter less than for the large fish and chips (Fig. 27.4 left), mostly because we used much less fish. Even so, nearly half the total emissions come from the fish, with the cooking causing a quarter of the emissions, and the dairy products making up most of the rest.

Reducing the amount of salmon and replacing it with some vegetables or beans is therefore the easiest way to reduce emissions. The fishy footprint also depends on the type of fish, since some fish are easier to catch than others. For example, small fish such as herring cause about half the emissions of the more commonly eaten large fish like cod, mostly because the nets do not need to be cast as deeply, which reduces the fuel needed to run the ship.

If we could lower the emissions of the farmed fish food, then this could significantly reduce the salmon emissions. Developments in new animal feeds have the potential to significantly decrease this, as discussed at breakfast in the context of eggs (chapter 7).

Given most of the sea-caught fishing emissions come from fuel on boats, how about a nice family fishing trip to the local lake or river? If the only purpose of your trip is to catch dinner for two, then your fossil-fuelled car emissions will be worse than those of the fishing vessels if you drive more than 15 kilometres (10 miles) each way.

Key points

- Caught-fish emissions are between chicken and eggs, in terms of emissions per kilo of fish, which puts them at the low end of animal-based foods and higher than all the plant-based foods (other than out-of-season perishable fruit and veg).

- Just as for chicken, farmed-fish emissions arise largely from producing the fish food, and the emissions per kilo are similar to those for chicken.

- The easiest way to reduce emissions is to reduce the quantity of fish, and perhaps bulk out with vegetables or pulses.

Notes

the greenhouse-gas emissions of deep-sea-caught fish (e.g. cod) to be about 5 times the weight of the fish. The most recent review and calculations for sea-caught fish was done by Buchspies et al. (2011), who find 5.3 kgCO_2e / kg cod (their figure 4.3). See also the earlier review by Winther et al. (2009) which gives more details on the shipping emissions.

portion sizes vary wildly from one chip shop to the next, but using a typical portion size, A newspaper report (URL 72) says “Currently a medium portion of cod varies from 93 g to 562 g and a medium portion of chips varies from 100 g to 797 g.” so the calculation assumes 250 g of fish.

the total fish ’n’ chip emissions is over 1.5 kilos, mostly from the fish (Fig. 27.4 left), Per portion using 250 g cod, 30 g flour, 60 g milk, 14 of an egg, and 20 g oil. See also Schreiber (2018) who examine a fish and chips meal, among others.

The emissions per gram of farmed fish are higher than for wild fish, and more similar to chicken (which is a relatively low-impact meat). Averaging the values for salmon from Poore and Nemecek (2018) (which is all for farmed fish), which gives 8 kgCO_2e / kg salmon. See also Buchspies et al. (2011); Ziegler et al. (2012), who find 6.6 kgCO_2e / kg salmon.

Just as for chicken, about half of the carbon footprint comes from producing the fish food, which is mostly fishmeal and fish oil, as well as seed cake (chapter 10), soy and wheat (chapter 25). Figure 4.3 of Buchspies et al. (2011) shows that nearly 4 kgCO_2e / kg salmon is due to the fish feed. Table 4.11 of the same reference shows the non-fish components of fish feed used in that study.

small fish such as herring cause about half the emissions of the more commonly eaten large fish like cod, mostly because the nets do not need to be cast as deeply, which reduces the fuel needed to run the ship. Buchspies et al. (2011) calculated a value for tinned herring (their figure 4.3), but removing the tin can (packaging emission) and replacing it with the fresh fish overheads (packaging, storage and distribution) from as cod (and using no oil) would give a value of 2 kgCO_2e / kg herring. See also figure 2 of Winther et al. (2009).

If the only purpose of your trip is to catch dinner for two, then your fossil-fuelled car emissions will be worse than those of the fishing vessels if you drive more than 15 kilometres (10 miles) each way. Emissions from 500 g of fish (to make a large fish and chips for two people) are about 8 × 500 g = 4 kg. Driving 30 kilometres causes 155 gCO_2e / km × 30 km = 4,650 g for a mediumsized family car. If the fishing location is 15 kilometres away, you drive 30 kilometres for the round trip.

Chapter 28 Veg

Fig. 28.1: Some tasty-looking carrots, including a cute couple that wouldn’t normally make it to the supermarket shelves. (URL 74)

We’re told to eat more vegetables to improve our health, but will this also be better for the climate? The answer is affected mostly by the method of transportation, the cooking time and the additional ingredients.

Carrots

You can watch carrots growing on your own windowsill by putting a seed down the side of a clear plastic cup of soil. The orange root is visible through the side of the container, but it takes a frustratingly long time to grow into a sizeable snack! Alternatively, cut the top off a carrot from the shop and put it in a saucer of water on the windowsill and wait for edible green shoots to sprout out of the top. (Clean your windowsill first though, and make sure there is plenty of ventilation to avoid mould.)

Carrots need fertilizer to grow well, although they don’t need much because they are good at extracting the nitrogen from the soil and can produce a heavy crop in a small area. Carrots are doing a beefed-up version of what nature intended: storing up energy in the roots to tide the plant through the winter and allow strong growth in the spring, ahead of producing seeds in the second year. Because the fertilizer emissions are so low, the storage, sorting, packing and transportation cause most of the carrot climate impact, but the total is still small.

1 g carrots = 0.6 g emissions

Carrots are a common ingredient in many soups and stews, along with onions and celery, and are also served boiled on their own, with or without melting butter. Depending on how big the carrots are (which affects the cooking time) and on the amount of butter added, the carrot itself is only one third of the total climate impact of cooked, buttered carrots (Fig. 28.2, left). This can be reduced by using vegetable spread instead of butter, or reduced to a tiny amount (less than 1% of average daily emissions) by eating the carrot raw (Fig. 28.2, centre).

Fig. 28.2: Carrots three ways:

Left: Emissions for buttered carrots: carrots (80 g); a teaspoon of butter (5 g); boiling the carrots, shared between two people (7.5 minutes at 2 kW).

Centre: Emissions for a raw carrot: a raw carrot (80 g).

Right: Emissions for oven roast root veg (cooking for 2): root vegetables (80 g); a teaspoon of oil (5 g); putting the oven on for 45 minutes, plus warm-up time, shared between two people (30 minutes at 2 kW).

Oven baking is a popular way to make vegetables taste great with very little effort. Other root vegetables have similar impacts to carrots, and also taste good roasted in the oven. Try beetroot, turnip, parsnip, sweet potato or swede (rutabaga). These have low emissions when raw, but if you cook for two people, and cook nothing else at the same time, the oven baking is the biggest contribution to the emissions (Fig. 28.2, right).

However, if you only cook the veg as an extra when cooking something else, then you can attribute the oven emissions to the other food and you get the veg roasted “for free”. Root vegetables can be washed and chopped a couple of days in advance and left in the fridge until the oven is on for something else, and then when cooked they can be put back in the fridge ready to be added to any meal, or as a fridge-raid snack.

Fig. 28.3: A bowl of green beans. (URL 75)

Green-vegetable emissions

Would you like some green vegetables with your meal? Green beans are popular and easy to cook. Opinions are divided on whether to steam them lightly (retaining their vibrant green colour and crunch) or whether to cook them for longer (leading to a softer, greyer texture).

Like carrots, green beans are strong growers, and fix nitrogen on their roots like the other beans in their family (chapter 14). More than half their contribution to climate change comes from being stored at the supermarket in open-fronted fridges that chill the aisle as well as the produce (box 11.1).

1 g french/green beans = 0.8 g emissions

However, even with supermarket refrigeration, seasonal green beans have very little impact on climate change, especially if cooked al dente in the microwave (Fig. 28.4, left). The total emissions are less than 5% of a daily emissions budget of 3 kg.

However, do you know when green beans are in season in your area? (I had to look it up.) The rest of the year they are imported, often from another continent by air, which causes similar emissions per kilo to the lowest-impact animal products (Fig. 28.4, centre).

Even if you add a teaspoon of butter and boil them for 10 minutes, the air transport still dominates the climate impact, and a single portion of beans causes nearly 0.8 kilos of emissions, or a quarter of a daily food emissions budget of 3 kg.

1 g beans, french/green, by air = 8 g emissions

Fig. 28.4:

Left: Emissions for green beans with spread: green beans (80 g); a teaspoon of vegetable spread (5 g); microwave oven (3 minutes at 1.2 kW).

Centre: Emissions for green beans (by air) with butter: green beans (80 g); transport 5,000 km by air; a teaspoon of butter (5 g); boiling for 10 minutes, shared between two people (5 minutes at 2 kW).

Right: Emissions for fried cabbage: cabbage (80 g); a teaspoon of vegetable oil (5 g); frying for 10 minutes, shared between two people (5 minutes at 2 kW).

So what can you eat when green beans are out of season? Unfortunately it turns out that a lot of other vegetables are also out of season at the same time!

Cabbage is the archetypal go-to year-round vegetable of our grandparents.

1 g cabbage = 0.4 g emissions

I remember many school dinners of cabbage boiled to a mushy grey. Nowadays I love cabbage fried in oil with cumin seeds. It tastes so good, it could be a different vegetable. Frying makes up half the emissions, but the numbers are still low – you could eat 6 portions before you match the climate impact of air-freighted green beans (Fig. 28.4, right).

Before the days of global food transportation, the over-abundance of food at harvest-time had to be turned into supplies that would last the winter, using a range of preservation methods. We still benefit from the commercial versions of many of these preservation methods today, including drying, pickling, canning/bottling and cool or cold storage. Freezing works really well for a lot of vegetables, especially if they are to be used in a soup or stew.

To get even lower emissions, how about eating the green leaves of root vegetables? Baby beetroot greens are a popular addition in posh salad mixes (look out for the red stems and earthy taste). Mature beetroot leaves, turnip leaves, and even the leaves of carrots are extremely nutritious. They can be eaten raw, or quickly fried up with garlic and oil, and maybe some mustard or cumin seeds.

Box 28.1: Frozen food

Emissions from frozen food add up because the produce has to be prepared, is often blanched (which heats it up) and then cooled down again to the freezer temperature. It’s often transported at this cold temperature, then kept in supermarket freezers, and then kept in your freezer at home. Finally, unless it’s ice-cream, you have to heat the food up from frozen before you eat it.

How do the emissions from frozen food compare with their refrigerated counterparts? To work this out we have to compare with the emissions from running a refrigerated chiller cabinet, and the increased amount of food waste that arises because of the shorter shelf life and fluctuating demand for refrigerated products. Taking all this into account, frozen vegetables cause more emissions than fresh, adding roughly the weight of the vegetables again in emissions.

Frozen food emissions can be reduced further by using clean energy to freeze and transport the food, and to run the freezers in the supermarkets and in your house, as well as using the latest refrigerants (box 11.1).

Key points

- Seasonal vegetables have a very low impact on the environment.

- Emissions from cooking are often the same or greater than those from the vegetables themselves.

- If the vegetables are air-freighted then this contributes 8 times the weight of the food in extra emissions, putting air-freighted veg into the same emissions category as animal products.

Notes

the storage, sorting, packing and transportation cause most of the carrot climate impact, but the total is still small. Figure S34 of Frankowska et al. (2019a) gives 1.12 kgCO_2e / kg for carrots, of which about 56% is the stages before household/cooking and waste. Including only these stages gives 0.63 kgCO_2e / kg. Note that about half of this value is for storage, so will depend on the length of time the carrots are stored for. See also the value of 0.4 kgCO_2e / kg from Poore and Nemecek (2018) for root vegetables.

Other root vegetables have similar impacts to carrots, and also taste good roasted in the oven. See the “Root Vegetables” references in Poore and Nemecek (2018) which include parsnip, celeriac and swede.

More than half their contribution to climate change comes from being stored at the supermarket Information is from figure S24 of Frankowska et al. (2019a) who find a value of 1.1 kgCO_2e / kg. The figures in this book use a value of 0.84 kgCO_2e / kg to avoid double-counting of cooking (household) and waste. Of this value, 0.64 kgCO_2e / kg comes from retail (e.g. open-fronted refrigerators).

Cabbage is the archetypal go-to year-round vegetable of our grandparents. Emissions are about half the weight of the raw cabbage. The figures use a value of 0.44 kgCO_2e / kg taken from figure S32 of Frankowska et al. (2019a) which gives 0.61 kgCO_2e / kg for UK fresh cabbage, of which 72% is pre-household.

drying, pickling, canning/bottling and cool or cold storage. See Frankowska et al. (2019a) for a wide range of storage methods for different vegetables.

Taking all this into account, frozen vegetables cause more emissions than fresh, adding roughly the weight of the vegetables again in emissions. The average difference between fresh and frozen emissions is 0.85 kgCO_2e / kg, calculated from Frankowska et al. (2019a) for all UK vegetables with both fresh and frozen values. However, there is a wide range from 0.2 to 1.3 kgCO_2e / kg depending on whether the item is stored at ambient temperature when fresh (e.g. onions) and how much processing is needed in freezing.

Chapter 29 Beer or wine?

Fig. 29.1: Red wine or white? (URL 76)

How about a drink with dinner? Do you prefer beer or wine, or maybe a bottle of water? Which do you think has the biggest impact on climate change?

For beer and wine we need to take into account the nitrogen fertilizer used to grow the barley or grapes. These main ingredients are fermented with much smaller quantities of other ingredients (such as hops, for beer).

Transportation varies hugely depending on your preferred tipple, but can be a major contributor.

Cans and bottles

Just as for soft drinks (chapter 21), packaging is an important contribution to the total impact. Fig. 29.3 shows the total emissions from a can of beer, a bottle of beer and a medium (175 ml) glass of wine poured from a regular wine bottle.

1 g beer on tap = 1 g emissions

1 g wine on tap = 1 g emissions

The results are surprisingly similar for the canned and bottled beer, given that the serving sizes are different. The reduced emissions from the lower amount of beer in the bottle are cancelled out by the increased emissions from the bottle itself: the beer bottle causes over a quarter of the emissions.

Fig. 29.2: A cold beer to stave off global warming? (URL 77)

The emissions for the glass of wine are about half those for the can or bottle of beer, but again this depends greatly on where the wine has been transported from (and note that the quantity of wine in a glass is less than half the quantity of beer in a can).

One way to reduce the climate impact is to make sure we recycle cans and bottles, and to drink from bigger containers. Drinking beer on tap saves greatly on packaging emissions, but should we then add in the electricity necessary to run the pub? One study did this and found that heating and lighting the pub doubled the beer emissions.

Fig. 29.3:

Left: Emissions for beer (in a can): beer (440 g); an aluminium can (9 g).

Centre: Emissions for beer (in a bottle): beer (330 g); a glass bottle (210 g).

Right: Emissions for a glass of wine: wine (175 g); a 750 ml-capacity glass bottle shared between 4.3 servings (98 g).

Fancy glass-bottled water is commonly provided by restaurants. If you’re thirsty and drink a whole bottle of water, then it causes emissions similar to those for a single glass of wine. This because the emissions saved by drinking water instead of wine are cancelled out by drinking a larger quantity of water.

Potable tap water is better than other drinks, as far as climate change is concerned, because its production causes very little greenhouse-gas emissions and it requires no packaging or transportation, since the pipe network is already in place (chapter 21). Restaurants can increase their green credentials (if not directly increasing their profits) by refilling carafes with tap water instead.

At what price luxuries?

Do drinks other than tap water offer enough psychological benefits to justify their consequences for the climate? Or perhaps we should ask ourselves how these drinks compare with other luxuries? One can of beer causes emissions similar to those from 30 cups of black tea (chapter 2), four cups of white coffee (chapter 4), a piece of cake (chapter 22) or driving one mile in a fossil-fuelled car (chapter 1).

Most of us can cut our emissions significantly before we need to give up all our luxuries. However, these numbers can help you to weigh up the benefits against the climate impact, and to really appreciate the luxuries you choose to keep.

Key points

- The impact on climate change is similar for a can of beer, a bottle of beer, or two glasses of wine, so pick your favourite!

- One beer causes half a kilo of emissions, which is one sixth of a 3 kg budget for daily food emissions.

- For wine in a glass bottle, the packaging causes about a quarter of the emissions, so it helps to drink (the same size serving!) from a large container or, even better, from a tap.

Notes

Transportation varies hugely depending on your preferred tipple, but can be a major contributor. See Garnett (2007) where Figs 21, 24, 25 show transport at 10-20% of emissions.

beer A value of 1.0 kgCO_2e / kg of beer is from the global average for beer from Poore and Nemecek (2018) of 1.2 kgCO_2e / kg, subtracting a rough average of 0.2 kgCO_2e / kg for packaging. See also figure 3 of Amienyo and Azapagic (2016) which have a value of 0.34 kgCO_2e / kg for beer not including packaging.

wine Using a value of 1.0 kgCO_2e / kg, taken from the global average from Poore and Nemecek (2018) of 1.8, after subtracting their value of 0.8 for the packaging which we add on separately. See also the references cited in Garnett (2007) including only growing/viticulture and wine making contributions. Aranda et al. (2005) gives (205 + 189) / 750 = 0.525 kgCO_2e / kg of wine, and Fullana et al. (2005) gives (491.51 + 20.87) / 750 = 0.683 kgCO_2e / kg wine, so a value of (0.525 + 0.683) / 2 = 0.604 on average.

given that the serving sizes are different. Typical can and bottle sizes mean that the amount of beer in the bottle (330 ml) is a bit smaller than the amount in the can (440 ml).

heating and lighting the pub doubled the beer emissions. See figure 21 of Garnett (2007).

a whole bottle of water, then it causes emissions similar to those for a single glass of wine. This because the emissions saved by drinking water instead of wine are cancelled out by drinking a larger quantity of water. A medium glass of wine is about a quarter of a 750 ml bottle. For a glass of wine, the glass bottle causes about a quarter of the emissions. Obviously drinking a whole bottle of wine causes other problems.

Chapter 30 Dessert

Fig. 30.1: Apple pie. (URL 114)

Do you have a dessert after dinner? Perhaps it’s time for a treat at the end of a long day, or a bribe to convince children to eat their main course? In this chapter we’ll get creative with some of the ingredients already covered in other chapters, focusing on two popular desserts: apple pie and chocolate mousse.

Apple pie

Apple pie is a classic pudding, at its best made by a kindly grandparent and decorated with pastry shapes of leaves and fruit (Fig. 30.1). It’s an American staple, and has similar ingredients to the traditional British crumble and the US cobbler. Apples are baked under a crust of buttery pastry, and the finished pie is often topped with cream or ice cream.

Which ingredient do you think causes the most greenhouse-gas emissions? Fig. 30.2 (left) shows the total emissions for a classic apple pie recipe shared between four people, baked in the oven for an hour, and drizzled with a teaspoon of cream. The result for one portion is over half a kilo, and one fifth of a 3 kg daily food emissions budget.

Of all the ingredients, butter causes the highest emissions: the butter and cream cause 40% of the total. The apple itself isn’t a big deal, causing about 10% of the total. (We could ask whether the apple was a windfall from the back garden, or transported by ship from another hemisphere, but this turns out to be a minor issue – see chapter 17.)

What if you bake an apple pie for one person? It’s unlikely that anyone would make an apple pie at home for one person, but shops sell individual pies, for reheating at home. If you use the oven just for reheating this dessert, and add a generous helping of cream, you nearly triple the emissions.

From TV baking shows I understand that the type of fat, and how it is handled, can make a big difference to the quality of pastry. I’m not going to give an opinion on that here, but note that switching from butter to vegetable spread can make a significant difference to the greenhouse gases caused by an apple pie. Making this substitution and cooking for 8 instead of 4 nearly halves emissions from the standard apple pie recipe we first considered. Many people have been cooking with margarine or other vegetable spreads for years, illustrating nicely that it’s not always necessary to switch to novel ingredients to make a significant difference to emissions. The single teaspoon of cream makes very little difference to the total, so it isn’t necessary to go completely vegan either (assuming you’re going to put the rest of the tub of cream to good use…).

Fig. 30.2:

Left: Emissions for apple pie and cream: apple (125 g); sugar (19 g); flour (37.5 g); butter (19 g); putting the oven on for 1 hour, plus warm-up time, shared between 4 people (19 minutes at 2 kW); a teaspoon of cream (5 g).

Centre: The same ingredients as the left panel, but all the cooking emissions are attributed to one portion (75 minutes at 2 kW), and more cream is added (two tablespoons of cream, 30 g).

Right: The same ingredients as the left panel but replacing butter with the same weight of vegetable spread, and sharing the cooking emissions between 8 people instead of 4 people (9 minutes at 2 kW, per portion).

Fig. 30.3: Chocolate mousse. (URL 115)

Chocolate mousse

Let’s have some decadent chocolate mousse to end the day: creamy yet airy, with the bitter chocolate flavour coming through the sugar (Fig. 30.3). The simplest chocolate mousse recipes contain no cream at all, just eggs, with their whites whisked up until light and smooth before folding in the chocolate and sugar.

The result is quite rich, so the mousse is often served in small pots. And, since a lot of it is air, the environmental impact is nowhere near as bad as you might think considering how decadent it seems (Fig. 30.4, left), dialling up about 0.25 kg of emissions. Most of the impact comes from the egg.

However, the toppings can really add up. How about some raspberries air-freighted from another continent (chapter 17), and whipped cream? You more than quadruple the emissions this way, to over 1 kilo per person (compare Fig. 30.4 centre)!

We discussed egg alternatives in chapter 7: if you have some leftover chickpea water (aquafaba) from boiling chickpeas, or draining a can, you can whisk this up just like egg white. I tried this and it does take quite a lot longer than whisking egg whites, so I’ve taken care to add on the electricity for the whisking (although it actually makes little difference to the total).

Fig. 30.4: A trio of chocolate mousse options:

Left: Emissions for a chocolate mousse: cocoa powder (15 g); sugar (15 g); three eggs, shared between 4 people (37.5 g); whisking for 5 minutes, shared between 4 people (1 minute at 2 kW).

Centre: Emissions for a chocolate mousse with cream and raspberries (by air): a chocolate mousse; cream; raspberries by air.

Right: The same ingredients as the left panel, but replacing the egg white with aquafaba and whisking for 10 minutes instead of 5 minutes.

If you were otherwise going to throw out the aquafaba, then you can count it as zero emissions (box 9.1). It will be quite a while before the production of chickpeas is driven by the demand for aquafaba so it’s shown as zero in the stack for now. With this substitution, the standard chocolate mousse emissions are halved (compare Fig. 30.4 right and left) to less than 5% of a daily food emissions budget of 3 kilos. Now most of the emissions come from the cocoa (without which it wouldn’t really be a chocolate mousse!).

Key points

- The most important ingredients, e.g. apples, are not always the biggest contributors to climate change.

- Hidden butter can have two or three times the impact of the main ingredient, but is easily replaced with vegetable spread.

- Putting the oven on to reheat one portion of apple pie causes more emissions than the butter- and cream-laden pie itself.

- Watch out for adding toppings of perishable out-of-season fruit.

Notes

a classic apple pie recipe shared between four people, 500 g apple, 75 g sugar, 150 g flour and 75 g butter.

The simplest chocolate mousse recipes contain no cream at all, Just three ingredients, serving four people: 60 g cocoa, 60 g icing sugar and 3 eggs.

Chapter 31 Evening meal summary

How do these different dinner options compare side by side? We’ll combine them to make three different meals – typical-emissions, then high- and then low-emissions evening meals, which are compared in Fig. 31.1.

Typical-emissions dinner

One possible typical-emissions dinner includes chicken tikka masala with rice, with a beer, followed by apple pie and cream (Fig. 31.1, left). This comes to over 3 kilos of emissions, of which 1 kilo is caused by the chicken. This uses up the entirety of a 3 kg budget for food greenhouse emissions for a whole day, in one meal.

Higher-emissions dinner

Of all the single food items considered in this book, the highest emissions item is the 8 oz steak, which causes 10 kilos of emissions from just the one item. If everyone in the world ate a steak every day, and caused no other emissions from other food or any other activities including transport or heating, the steaks alone would blow the 1.5°C carbon budget by 2040 (chapter 24).

For a higher-emissions dinner, to a steak add fries, air-freighted green beans, a glass of wine and the chocolate mousse topped with cream and air-freighted raspberries (Fig. 31.1, centre). It does sound delicious.

Even in this extravagant pile, the steak still causes most of the damage, with the air-freighting coming in second, although quite far behind. Overall this is 4 times worse for climate change than the typical-emissions dinner, and this one meal causes 4 times a daily food emissions budget of 3 kg.

Fig. 31.1: Stacking up the emissions from different dinner options discussed in this Part.

Lower-emissions dinner

What happens if you choose the lowest-emissions options from the chicken and dessert chapters (chapters 25 and 30) and get frugal by drinking only tap water? Chickpea tikka masala with bread, followed by aquafaba chocolate mousse, comes in at less than 1 kilo of emissions (Fig. 31.1, right). This is more than three times lower than the typical-emissions dinner, mostly due to cutting back on the chicken, rice and beer, and replacing with chickpeas, bread and tap water. Unlike the typical-and higher-emissions dinner options, the lower-emissions dinner allows room for other meals in a daily food emissions budget of 3 kilos.

The next chapter combines these dinner choices together with those from the other meals to see how they contribute to a whole day of food.

Key points

- The typical-emissions dinner causes about 3 kilos of emissions, more than half of which comes from the chicken tikka masala.

- An 8oz steak dominates all other menu items in the higher-emissions dinner, which causes more than 4 times the emissions of the typical-emissions dinner.

- The lower-emissions dinner replaces chicken with chickpeas and makes use of the chickpea cooking liquid to make a chocolate mousse. The emissions are 4 times lower than those for the typical-emissions dinner, and 16 times lower than those for the higher-emissions dinner.

Part V: Looking ahead

In this final Part of the book, we bring everything together, and look at the bigger picture from several different perspectives. We combine all our food choices, to work out the total emissions from a whole day of food, and consider the emissions impact of food waste.

The main point of this book is comparing the emissions of different foods rather than pitting different diets against each other (e.g. veganism versus vegetarianism). We look at the health implications of making long-term major changes to your diet, and consider the relative green credentials of different popular diets.

Most of this book has been about changes that you as an individual can make. However, suppliers and governments also have a role to play.

Finally, we discuss whether food in all its aspects could be an important part of the solution to climate change, and the options that changing our food habits could open up.

Chapters

Chapter 32: Food emissions for a whole day

Chapter 33: Leftovers and food waste

Chapter 34: Health

Chapter 35: Vegan and other climate-motivated diets

Chapter 36: How can governments help?

Chapter 37: Food as part of the solution

Chapter 38: Making the change

Chapter 32 Food emissions for a whole day

So far we have stacked up the emissions for three different choices for each meal. Now we can add up all the “typical-emissions” choices for all the meals and see the total for a whole day. We will compare it to the totals from the “higher-emissions” and “lower-emissions” choices.

Typical-emissions day

The total of all the “typical-emissions” choices for breakfast, lunch, snacks and dinner comes to more than 5 kilos of green-house gases (Fig. 32.1, left). This is about the same as the global average for a day of food (chapter 1) once waste is taken into account (chapter 33), and is significantly above a daily food emissions budget of 3 kg (chapter 1).

The biggest single items within this stack are the chicken used in the chicken tikka masala, and the ham in the lunchtime sandwich. Between them they cause over one fifth of the total. Dairy products appear throughout the day: especially milk in cereal at breakfast, yogurt at lunch, and cream in the sauce of the chicken tikka masala; taken together they add up to over 1 kilo of emissions, or about 20% of the total. The other biggest items are the rice and beer, which cause about 10% each.

From a nutritional perspective, the typical-emissions food choices meet most of the standard daily health requirements, with the exception of fibre and vitamin D, which are often deficient in average western diets (see discussion in chapter 34).

Higher-emissions day

The total for the “higher-emissions” choices is 20 kilos, which is 4 times the “typical-emissions” total (Fig. 32.1, centre). Half of this comes from one single food item: the 8 oz steak for dinner. There are also more dairy products than in the “typical-emissions” day – the milk-based latte at breakfast, and cheese in the lunch sandwich. Taken together the dairy items alone cause over 3 kilos of emissions, with the largest contributions from milk in the latte and cheese on the potato. And air-freighted fruit and vegetables added about 1.5 kilos of emissions.

Fig. 32.1: Whole-day emissions. (The steak contribution is so high we’ve had to truncate it; the inset shows the true ratio of the options.)

The higher-emissions food choices provide more than we need of most of the nutritional requirements, including nearly 3 times the recommended daily intake of protein. The only exception is that the higher-emissions choices provide less than half the recommended daily intake of fibre, which is a common feature of western diets. This decadent option also provides 50% more calories than we need.

Lower-emissions day

With our “lower-emissions” choices (Fig. 32.1, right), we’ve reduced emissions by 10 times compared to the “higher-emissions” day, and more than halved the climate impact compared to the “typical-emissions” day. The total comes to under 2 kilos of emissions, which fits comfortably within the 3 kg daily food emissions budget discussed in chapter 1.

But are these lower-emissions food choices good for our bodies? The whole day of food provides 20% more protein than our bodies require and, unlike the typical and higher-emissions choices, meets the recommended daily intake of fibre. Just as for the typical-emissions choices, and a typical western diet, the lower-emissions options do not provide enough vitamin D. Vitamin B12 can only be found in animal products, or in plant-based products that have extra vitamin B12 added, so the lower-emissions options need to be complemented with a vitamin B12 supplement (see chapter 34). The lower-emissions options are a little low on selenium and vitamin B2, which could be fixed by eating a Brazil nut and consuming B2-fortified dairy alternatives.

Key points

- Meat products are the single largest emissions food items in the typical and higher-emissions days of food.

- Meat is closely followed by dairy items.

- Air-freight of perishable fruits and vegetables can cause similar emissions to a whole lower-emissions day of food on its own.

- It is possible to reduce food emissions to fit comfortably within a 3 kg daily budget without resorting to novel foods, and you can probably use the information in this book to be much more creative than I have been!

Notes

the typical-emissions food choices meet most of the standard daily health requirements, with the exception of fibre and vitamin D, The typical-emissions day of food contains 10.5 grams of fibre, which is 35% of the recommended daily intake (calculated using nutrition information from the National Diet and Nutrition Survey (NDNS) year 6 Hemmings 2016). It contains 2.3 micrograms of vitamin D, which is 23% of the recommended daily amount.

the higher-emissions choices provide less than half the recommended daily intake of fibre, which is a common feature of western diets. The higher-emissions day of food contains 12 grams of fibre, which is 40% of the recommended daily intake of 30 grams. The UK average is about 60% of the recommended daily intake (URL 78).

meets the recommended daily intake of fibre. The lower-emissions day of food provides 95% of the recommended daily intake of fibre if you eat white bread, or 130% if white bread is replaced by wholemeal bread.

The lower-emissions options are a little low on selenium and vitamin B2, which could be fixed by eating a Brazil nut and consuming B2-fortified dairy alternatives. This option meets the other dietary requirements of vitamins and minerals, with the exception of selenium and vitamin B2, only providing about half the recommended daily levels, using the nutrition data from the National Diet and Nutrition Survey UK Year 6. However, note that there is considerable variation in selenium levels even for a single type of food depending on the soil it is grown in. According to the standard nutrition information, a single Brazil nut provides the recommended daily intake of selenium, but no emissions data was available for Brazil nuts so they are not included in chapter 19. Since the lower-emissions day of food is supposed to be an example rather than a prescription for healthy living, and selenium deficiency is rare, we don’t discuss this further here. The daily requirement of Vitamin B2 is provided by dairy products in the average UK diet (NDNS year 6 Hemmings 2016, own calculation) but is also provided by fortified breakfast cereals and rice. Again vitamin B2 deficiency is rare, and can be addressed with vitamin supplements.

Chapter 33 Leftovers and food waste

Fig. 33.1: Happily, misshapen fruit and veg are not the biggest food waste problem. (URL 80)

Do you often have leftovers as a snack, raiding the fridge when you get home, or on the way up to bed? To me, leftovers rarely look as attractive as a new crunchy packet of crisps, but maybe that says a lot about my cooking, or my addiction to crisps! It turns out that reducing food waste can be as important as switching foods when it comes to combating climate change, but not for the reason most people expect.

Binning food

Globally, about one third of food is lost or wasted. Our first thought might be to sigh at the supermarkets or lawmakers for setting their standards too high and throwing away perfectly edible (and sometimes amusingly) wonky veg (Figs. 33.1 and 33.2). But the embarrassing fact is that in western countries, more than half of wasted food is caused by us, the citizens.

Fig. 33.2: The most wasted foods are vegetables and salads, but not because they are misshapen. (URL 81)

We might expect catering outlets, for example canteens and restaurants, to contribute to food waste because they have to over-cater in case of unexpected high demand yet, of all the wasted food, only 10% occurs here. By contrast about 70% of the wasted food is discarded in people’s homes, when we scrape food off our plates into the bin, or throw out unopened packets. On average, each UK citizen wastes over 200 grams of food each day, almost literally throwing 60 pennies in the bin.

What sorts of food are we throwing away? Researchers were so keen to find out that they went through people’s rubbish bins to find and identify rotting leftovers. (Don’t worry, they got permission from the residents first and the bins were all anonymized, so they aren’t out there right now tutting over your most recent guilty food oversight.) They found that the most wasted foods are vegetables and salads, followed by drinks and bread.

Isn’t this just stuff like orange peel or teabags? Actually no. So far this chapter included only food that was intended to be eaten. If we were to include those other sorts of inedible food waste then all the numbers would be about 50% larger.

Fig. 33.3: What to do with all that stalk? (URL 82)

Needless to say, the exact definition of “edible” and “inedible” food waste depends on culture and personality. We all know of someone who eats the whole apple – peel, core and all. It turns out they are going above (and perhaps beyond) the call of duty when it comes to reducing greenhouse-gas emissions.

I’m not advocating everyone starts eating apple cores. However, the statistics on “inedible” food waste do mean that buying pre-prepared vegetables is not as extravagant as it might seem. I love my veg box, but it’s surprising how much waste is produced as I carve off the outer leaves of a cauliflower and snap off the Brussels sprouts from their thick stalk. While I sometimes find this therapeutic, it is actually wasteful, because when these operations are carried out at scale, the waste can often be put to better use than compost: often “inedible” food waste is fed directly to animals. Some of the less digestible foods can be fed to insects, which are then fed to animals as a high protein food. This is important because it can help reduce the amount of crops grown for animal feed.

Fig. 33.4: A poster attempting to shame people into not wasting food, from the US government in World War II. Image credit: the United States National Archives and Records Administration. (URL 83)

With an increasing awareness of the importance of reducing food waste, there are some exciting new projects to re-purpose the less popular parts of fresh foods into new food. For example, fashionable and healthy cauliflower rice can be made from cauliflower stalks (Fig. 33.3), ugly and undersized fruit and veg are made into juices, and the bread-ends left by the sandwich industry are being made into beer.

Emissions from wasted food

Why is it so important to reduce food waste? When I was growing up I was told to finish the food on my plate because there were starving children who would have been glad to eat my leftovers. For climate change, we are clearly wasting resources by producing food that is then wasted. But there is another problem that can be an even bigger contributor to emissions, depending on the type of food.

Most wasted food goes into the bin, which goes to rubbish dumps, or landfill as they are now more correctly known. Landfill sites smell of rotting food – I’ve learned to close my car window when I see lots of seagulls circling overhead because I’m probably approaching a rubbish dump. Because all the rubbish is piled up, not much air can reach the buried food waste. As discussed in the rice chapter (chapter 26), rotting stuff without enough oxygen makes methane, which is a powerful greenhouse gas.

Fig. 33.5: If food waste ends up in landfill it adds about one kilo of emissions per person, per day.

Including the waste in our homes, and in catering outlets, and the “inedible” food waste, as well as processing and manufacturing that happens after food leaves the farm, each of us is responsible for about one kilo per day of greenhouse-gas emissions from food waste.

1 g food waste = 3 g emissions

This is about the same as one extra cheese and ham toastie! Fig. 33.5 includes this in the emissions stack for a typical day of food, to illustrate that it adds about 20% to the total food emissions for the “typical-emissions” day of food, bringing the total close to the 6 kilo global average daily food emissions discussed in chapter 1.

Tips for reducing food waste at home

Are you now wondering how you can reduce your food waste, or are you like a lot of people who think they don’t waste food when they actually do? It’s just not a big part of our day like, say, eating. We don’t think “OK, what food am I going to waste today?”. It happens when we’re tired and looking for something to eat and have to move something mouldy out of the way to find something tasty, or when we’re hastily clearing up after the kids at the end of a meal.

It also turns out that we can’t exclusively blame it all on a different generation. A UK survey found that all ages wasted a significant amount of food, although millennials wasted 50% more than people over retirement age. It’s a long time since the World Wars, when it was socially unacceptable to waste food in the UK.

I’m sure you have lots of thoughts about how other people waste food – I do! So probably the first painful step towards reducing food waste is to try to spot when we’re the ones doing it. We can try to notice what sorts of food we regularly throw away. Milk at the bottom of bowls of cereal? Bread crusts? Unopened liquified bags of salad discovered too late at the bottom of the fridge? Meals that are past their use-by-date?

Box 33.1: Top tips for reducing food waste

- Make a habit of storing leftovers and reheating them as a bonus snack the next day.

- Check whether old food is still safe to eat or simply of a lower quality which can be eaten in a different way (for example by toasting old bread).

- Plan your food before going shopping, so you only buy food you expect to use.

- Measure out the amount of products like rice or pasta before cooking, so you don’t make too much.

- If you buy extra of a product on special offer, remember to buy less of something else to compensate.

Governments have big incentives to cut food waste, not least because it contributes to their greenhouse-gas emissions quotas. Several governments provide helpful guidelines on how to cut food waste, so you can find more ideas on their websites.

Key points

- Globally, about one third of food is wasted. In western cultures more than half of that food waste is caused by individuals at home.

- Wasted food that goes into rubbish bins turns into methane at landfill sites. Because methane is a much more potent gas than carbon dioxide, this typically causes over 1 kilo of emissions per person per day.

- Most people think they don’t waste food even though they do. Try to spot yourself wasting food over the coming days.

- Check out some tips for reducing waste (box 33.1).

Notes

Globally, about one third of food is lost or wasted. Our first thought might be to sigh at the supermarkets or lawmakers for setting their standards too high and throwing away perfectly edible (and sometimes amusingly) wonky veg (Figs. 33.1 and 33.2). But the embarrassing fact is that in western countries, more than half of wasted food is caused by us, the citizens. Take a look at the graphic in the following reference, which shows the food waste from different parts of the food chain, for each continent separately (URL 79). In North America and Oceana, and in Europe, the fraction lost in the “consumption” phase is over 50%.

We might expect catering outlets, for example canteens and restaurants, to contribute to food waste because they have to over-cater in case of unexpected high demand yet, of all the wasted food, only 10% occurs here. By contrast about 70% of the wasted food is discarded in people’s homes, when we scrape food off our plates into the bin, or throw out unopened packets. These figures are for the UK, from section 1 of the UK Waste and Resources Action Programme report (Waste Resources Action Plan (WRAP) UK 2019b, especially their figure 2).

On average, each UK citizen wastes over 200 grams of food each day, almost literally throwing 60 pennies in the bin. See section 2.2.1 of Waste Resources Action Plan (WRAP) UK (2019a), which says the amount of wasted food that could have been eaten was 5 million tonnes, worth approximately 15 billion for the whole UK in 2015. Sharing this out across people and days gives 209 grams per person per day and 63 pence per person per day.

the most wasted foods are vegetables and salads, followed by drinks and bread. See Waste Resources Action Plan (WRAP) UK (2019b) who state 28% of fresh vegetables and salad are wasted, followed by 15% of drinks, followed by 11% of bakery items.

If we were to include those other sorts of inedible food waste then all the numbers would be about 50% larger. See Table 3 of Waste Resources Action Plan (WRAP) UK (2019b), which shows 427 g per person per day (156 kg per person per year) of post-farm food waste (food plus inedible parts) versus 293 g per person per day (107 kg per person per year) of post farm-gate food waste (food only).

the exact definition of “edible” and “inedible” food waste depends on culture and personality. There is no worldwide agreement on the definition of “inedible” food waste. Inedible food waste includes skin, bones, meat or fish carcasses, inedible peelings, banana skins, other fruit peels, fruit pits, teabags and eggshells.

With an increasing awareness of the importance of reducing food waste, there are some exciting new projects Did you ever search through the packets on a supermarket shelf, to find one that has a later sell-by date? I certainly have. This “date-picking” is a significant cause of waste at the supermarket. It has been suggested that packets could gradually change price as their sell-by date approaches, depending on demand. Some airlines already use this tactic with plane ticket pricing to maximise their profit and reduce the “waste” of flying under-filled aircraft. This is probably a fair way to price foods and reduce waste, although I’m a little in trepidation of adding any more things to consider when choosing which packet to put in my basket.

Including the waste in our homes, and in catering outlets, and the “inedible” food waste, as well as processing and manufacturing that happens after food leaves the farm, each of us is responsible for about one kilo per day of greenhouse-gas emissions from food waste. WRAP reports that 10 million tonnes of food caused 25 million tonnes of emissions (Waste Resources Action Plan (WRAP) UK, 2019b).

A UK survey found that all ages wasted a significant amount of food, although millennials wasted 50% more than people over retirement age. See figure 10 of Quested and Luzecka (2014) which found 1950 grams of food waste per week when survey respondents were aged 18-34, and 1250 grams of food waste per week when respondents were over 65 (these numbers are controlled for household size).

Check whether old food is still safe to eat or simply of a lower quality which can be eaten in a different way (for example by toasting old bread). The UK rules are that food past its “use-by” date is not safe to eat, but food past its “best-before” date is safe but of a lower quality so you can taste it to see if you think it’s OK or not. For example see the UK guidance to food producers here: URL 84

If you buy extra of a product on special offer, remember to buy less of something else to compensate. This list was compiled based on the WRAP report quantifying how different behaviours correlate with reduced food waste (see table 3 of Quested and Luzecka 2014).

Several governments provide helpful guidelines on how to cut food waste, so you can find more ideas on their websites. For lots more great ideas check out these lists: URL 85 and URL 86.

Chapter 34 Health

Changing what you eat might be easy compared to insulating our house, or changing how you get to work. But it’s also close to your heart, both metaphorically and literally. What you eat directly affects your health, and making a major change needs to be done with care. Do seek medical advice before making a big long-term change to your diet.

Cutting back versus switching

You don’t need me to tell you that continuing to eat as normal, but abstaining from high-emissions foods, would leave you hungry at the end of the day. If you just eat more sugar to make up the calories then you’re likely to be short on the vitamins and minerals which are plentiful in some of the highest emissions foods, such as meat.

Many people find abstaining completely from particular types of food to be challenging and undesirable. It may also be unnecessary if we can make enough changes to the majority of our food intake. As a result, most official advice recommends significantly reducing your intake of red meat (rather than needing to cut it out completely) while significantly increasing your intake of fruit and vegetables.

Many people worry about getting enough protein when cutting back on meat. Fig. 34.1 shows the emissions for a range of different protein-rich foods, per gram of protein. There are four clusters in the chart:

- “Very high-emissions proteins” ruminant meat (lamb and beef) is at the top, causing over 10 times the emissions of the “low-emissions protein” at the bottom of the chart.

- Milk, cheese and pig meat form a “high-emissions protein” group, each causing less than half the emissions of the “very high-emissions proteins”.

- The “medium-emissions protein” group, which includes eggs, farmed fish (salmon), chicken, and tinned beans, halves emissions yet again.

- At the bottom the two “low-emissions proteins” each cause half the emissions of the “medium-emissions proteins”. The “low-emissions protein” group contains beans and nuts.

Caught fish (cod) is intermediate between the “medium-emissions protein” and the “low-emissions protein” groups. However, note that in practice all these values depend on decisions made throughout the food production process, particularly around deforestation for feed (especially for eggs, chicken and salmon) and the amount of fossil versus clean energy used for processing and cooking (especially for beans and Quorn).

Fig. 34.1: Greenhouse-gas emissions for a quantity of food that provides the same amount of protein as a 150 g chicken breast (45 grams of protein), for some high-protein foods.

Many governments issue dietary guidelines, indicating the vitamins and minerals, and how much of them, that you need to get from your food. (In the US these are published by the Department of Health & Human Services, in the UK by the National Health Service.) For example, UK guidelines state that children under the age of 4 should take vitamin D tablets during the winter, when our bodies can’t naturally synthesize vitamin D from the weak sunlight – and that’s before making any climate-motivated diet changes. If you eat no animal products at all, you will likely need to take a vitamin B12 supplement to stay healthy. Normal quantities of vitamin tablets cause less than 1% of the average daily emissions from food.

1 g vitamin tablets = 10 g emissions

Dietary guidelines

Have you ever looked at your government’s dietary guidelines? And if so, did you try to work out whether you are following them? I hadn’t until I started researching this book. But they are there, and a lot of research goes into them. In practice we eat twice as much red meat as in the guidelines and eat 25% less fruit and vegetables.

What would happen to greenhouse-gas emissions if everyone followed the guidelines? It turns out that emissions would be reduced by 25%. So one quarter of our emissions from food come about just because we aren’t eating the healthy government-recommended diet. Why are the emissions so different? The 25% reduction in emissions comes almost entirely from the reduced red-meat consumption in the healthy diet.

We need to change our diets anyway

Would following the dietary guidelines improve our health? The government guidelines limit red-meat consumption because there’s an increased risk of bowel cancer when people eat more than the recommendation. The recommended daily limit corresponds to about two sausages, three rashers of bacon, three slices of ham, or one third of an 8 oz steak.

Another major result of not following the guidelines is that western diets contain a lot less fibre than would be healthy. This is largely because the healthiest, most fibrous part of grains is removed when making white bread or white rice. But it’s also because we don’t eat nearly enough fruit and vegetables. Eating more fibre can reduce our risk of heart disease, stroke and type II diabetes, as well as bowel cancer.

Health-wise, the most dangerous single way in which we are flouting the recommendations is in the amount of sugar we consume. This is causing a massive rise in obesity. In 2015/16 nearly 4 out of every 10 people in the US were obese, and the rates of obesity are rising at an alarming rate across the globe. Obesity causes a range of problems including heart disease, stroke, type II diabetes and some cancers.

Not only is this bad news for the people involved, but it is also hugely problematic for governments who need to find money for treatment. Estimates suggest that obesity costs economies billions of pounds a year, which includes the health-care costs and missed working days. Even though obesity is not a problem for climate change, it is relevant because it means that governments are extremely motivated to change our diets.

Key points

- We are what we eat, so making changes to our diet needs serious consideration and medical advice.

- Following government dietary guidelines would make a significant reduction to food greenhouse-gas emissions, mostly because they recommend a lot less red meat than people actually eat on average.

- Worldwide our diets are becoming increasingly unhealthy. Dietary change is needed irrespective of climate change.

Notes

most official advice recommends significantly reducing your intake of red meat (rather than needing to cut it out completely) while significantly increasing your intake of fruit and vegetables. For example Willett (2019).

beans Using the “efficient” cooking time for 4 people, from chapter 14, to try to make a fair comparison with low-emissions foods that can be eaten raw.

UK guidelines state that children under the age of 4 should take vitamin D tablets during the winter, For more information see URL 87.

vitamin tablets cause less than 1% of the average daily emissions from food. Audsley and Williamson (2010) set the emissions for vitamin supplements to the value for lysine production, which we take as 7.7 kgCO_2e / kg from CCalC2 (“CCaLC PVC Manual (V2.0)” 2011) (from their “sugar cane 1”). We round this to 10 kgCO_2e / kg in the main text due to a lack of studies.

we eat twice as much red meat as in the guidelines and eat 25% less fruit and vegetables. See Springmann, Godfray, et al. (2016).

It turns out that emissions would be reduced by 25%. Springmann, Godfray, et al. (2016) table S9 gives a value of 0.89 tCO_2e per person per year, which we compare to their 2005/7 value of 1.15 tCO_2e per person per year (calculated from their value of 7.6 Gt per year for 2005/7 and a population of 6.6 billion in 2006); the ratio is 0.89 / 1.15 = 0.77 i.e. their healthy global diet causes 77% of the emissions of the global average diet in 2006.

The 25% reduction in emissions comes almost entirely from the reduced red-meat consumption in the healthy diet. See the HDG bars in Fig 1B of Springmann, Godfray, et al. (2016).

there’s an increased risk of bowel cancer when people eat more than the recommendation. For example see the UK National Health Service website (URL 88).

But it’s also because we don’t eat nearly enough fruit and vegetables. Eating more fibre can reduce our risk of heart disease, stroke and type II diabetes, as well as bowel cancer. For more information see (URL 89). See also the fantastic popular book by James Wong (10-a-Day the Easy Way: Fuss-free Recipes & Simple Science to Transform your Health, Wong 2019) for links to the scientific studies and loads of great ideas about how to sneak more fruit and veg into your diet

In 2015/16 nearly 4 out of every 10 people in the US were obese, See Hales et al. (2017).

the rates of obesity are rising at an alarming rate across the globe. NCD Risk Factor Collaboration (NCD-RisC) (2016).

obesity costs economies billions of pounds a year, which includes the health-care costs and missed working days. For example the cost to the UK National Health Service is estimated at £6.1 billion, and the cost to wider society is estimated at £27 billion for 2014/15 (URL 90).

Chapter 35 Vegan and other climate-motivated diets

It’s convenient to have a name for a set of dietary choices, for example “vegetarianism”. It makes it easier to communicate preferences, or spot suitable dishes when ordering food, or when choosing what to buy or cook. In this chapter we discuss a few popular diet choices, and then speculate on how low our food emissions could be if we designed a diet especially for the climate.

In every chapter where we found a high-emissions food, we found simple lower-emissions alternatives which are already available in most shops. Not all of these might be to your taste, or be convenient for your lifestyle at the present time, but they do show you can eat in a climate-friendly way without switching to a strict or specialist diet.

However, because detailed emissions information about each food hasn’t been readily available, people concerned about food and climate change often think specific strict diets are necessary, so let’s look at the evidence.

Mediterranean diet

There are many definitions of the Mediterranean diet, but most are high in plant-based foods and low on red meat. The Mediterranean diet has been investigated in many research studies and is linked with better health, including heart health. Research has shown that the Mediterranean diet has similar emissions to the global average diet and so would cause a significant reduction for countries with the highest emissions. For example, the US diet causes over twice the emissions of the global average diet (chapter 1), so switching to the Mediterranean diet would more than halve emissions.

Vegetarianism

Vegetarians usually exclude all parts of formerly-living creatures from their diets and don’t eat meat, fish or other sea creatures. Their impact on emissions depends on what they eat instead of meat. For example, cheese has higher emissions than chicken or fish so a chicken-eater who otherwise eats a vegetarian diet would actually make their emissions worse by replacing chicken with cheese. However, estimates suggest that vegetarian diets produce only 60% of the emissions of a global average diet.

Fig. 35.1: Fried crickets for lunch anyone? (URL 91)

Veganism

How about cutting out all animal products, and going vegan? Being vegan usually involves avoiding any food that comes from animals, so it excludes eggs, milk, cheese and other dairy products, on top of the restrictions of a vegetarian diet.

We might expect a vegan diet to be good for reducing greenhouse-gas emissions because dairy products are some of the highest impact protein sources (Fig. 34.1). Research has found that existing vegan diets cause only 50% of the emissions of the global average diet, and therefore less than 25% of the average US diet.

However, just as for the vegetarian diet, vegans can cause more emissions than omnivores, depending on their food choices e.g. by eating air-freighted fruit and vegetables, cooking single portions in the oven, and sending food waste to landfill (including the inedible waste from preparing vegetables at home).

Fig. 35.2: Some cochineal insects on a cactus plant. You’ve probably already eaten an extract made from them. (URL 92)

Insectivore

Insects have been touted as a possible animal-based food of the future because they are very effective at turning crops into edible protein. This might not be the future you’ve been dreaming of, but some cultures already eat plenty of insects as a delicacy. Fig. 35.1 shows some particularly tasty-looking crickets at a marketplace.

You might already be eating insects without realizing it. Have you ever eaten a pink marshmallow? A popular natural pink food colouring comes from grinding up cochineal insects (Fig. 35.2). And, unless you’re washing your fruit and vegetables extremely carefully, you’re probably getting a bit of extra nutrition from tiny creatures living in their nooks and crannies.

Some farmers now grow insects on a commercial scale – you might have seen some on sale in the shops. Popular choices include meal worms, crickets and locusts. People often describe the freeze-dried versions as nutty, or like crisped rice or popcorn. Before you rush in, if you have a seafood allergy you might also be allergic to insects, since they have the same substance in their hard shells. In case you don’t fancy eating insects whole, you can also buy insect flour for baking, or buy them ready-made into cricket pasta, or a high protein energy bar.

Some exciting new enterprises are farming insects, feeding them on food that would otherwise go to waste, or on by-products of food production, such as leftovers from brewing beer. The insect meal is then fed to animals such as farmed fish or chicken, to reduce the need to grow crops which currently make up about half of their climate-impact.

Designing a climate-friendly diet

Could we design an ultra-low-emissions diet, and if so, what would it look like? Some researchers have devised the lowest possible emissions diet that still meets our nutritional requirements. It involves a lot of high fibre breakfast cereal with no milk, and a lot of seeds, peas and onions. It reduces emissions to 10% of the original value! However, the researchers note that this diet is unrealistic, and go on to investigate less extreme diets.

Some companies are already producing meal-replacement shakes they claim contain all the nutrition you need. By picking the ingredients from the lowest-emissions foods out there, and supplementing with vitamins and minerals produced for vitamin tablets, it should be possible to design very low-emissions foods.

What if an ultra-low-emissions diet looks like grey goop, as suggested by some science fiction stories? Will we one day consider it a luxury, or even a socially shameful act, to eat anything else? I’d rather figure out how to reduce emissions in some less drastic way before we reach that stage.

Key points

- For most of us, there is no need to follow a rigorous new diet to significantly reduce the impact our food on climate change.

- Mediterranean diets have been found to have similar emissions to the global average diet. (In contrast, the diets of some countries, e.g. the US, cause more than twice the emissions of the global average diet (see chapter 1).)

- On average, vegetarianism roughly reduces emissions to 60% of the emissions of the global average diet.

- Average vegan diets reduce emissions to 50% of the global average diet.

- The lowest-emissions diets can cause up to 10 times less emissions than an average diet, but might not be acceptable to our tastes.

Notes

Mediterranean diet has similar emissions to the global average diet Tilman and Clark (2014) calculate emissions from a global average diet (in 2009) and compare it with a Mediterranean diet and find that the Mediterranean diet causes about 5% less emissions than the global average diet.

vegetarian diets produce only 60% of the emissions of a global average diet. Tilman and Clark (2014) find a vegetarian diet causes 57% of the emissions of the global average diet in 2009 (using the left panel of their figure 4 which shows 189 kgCO_2e-Ceq per person per year for the vegetarian diet compared to 332 kgCO_2e-Ceq per person per year for the 2009 average diet; 189 / 332 = 0.57). Springmann, Godfray, et al. (2016) table S9 gives a value of 0.46 tCO_2e per person per year for a vegetarian diet, which we compare to their 2005/7 value of 1.15 tCO_2e per person per year for a global average diet (calculated from their value of 7.6 Gt per year for 2005/7 and a population of 6.6 billion in 2006); this is (0.89 - 0.46)/(0.89 - 0.37)*100% = 83% of the way towards their value for a vegan diet of 0.37 tCO_2e per person per year. In the following footnote, we conclude that a vegan diet causes a 50% reduction compared to the global average diet. Combining these two results we estimate that the vegetarian diet causes about 59% of the emissions relative to the global average diet (100 - 50 * 83 / 100). Springmann, Godfray, et al. (2016) attribute the biggest reduction to red meat (in the context of a change from the projected 2050 diet and the vegetarian diet). These are rounded to a value of 60% in the main text.

Research has found that existing vegan diets cause only 50% of the emissions of the global average diet, and therefore less than 25% of the average US diet. For their “No Animal Products” scenario, Poore and Nemecek (2018) give a value of 7.04 GtCO_2e per year for the world, which converts to a value of 2.78 kgCO_2e per person per day. This is a reduction of (5.41 - 2.78) = 3.56 kgCO_2e per person per day. They find that the amount of food waste was almost unchanged from the current (~2010) diet, so their value including food waste is (7.04+2.05)/6.993/365 × 1000 = 3.56 kgCO_2e per person per day i.e. the emissions are halved in their “No Animal Products” scenario, relative to their value of 6.2 kgCO_2e per person per day in their “Current (~2010) Diet”. See their Fig S14 for more details. This is similar to the value found in Blake (2014), who state a 43% reduction in food emissions on eliminating animal products. For comparison, Springmann, Godfray, et al. (2016) table S9 gives a value of 0.34 tCO_2e per person per year for the vegan diet, which we compare to their 2005/7 value of 1.15 tCO_2e per person per year. The ratio is 0.34 / 1.15 = 0.32, i.e. their vegan diet causes only 32% of the emissions of the global average diet in 2006. For consistency with the other numbers in this book, we use the Poore and Nemecek (2018) value in the main text, which includes land use change and post-farmgate emissions (see chapter 1).

Insects have been touted as a possible animal-based food of the future because they are very effective at turning crops into edible protein. Table 6 of Oonincx et al. (2011) presents values as low as 0.001 kgCO_2e / kg for the farming part of the insect production phase, however, this does not include the rest of the supply chain which will depend particularly on the feed source and energy used for processing.

some cultures already eat plenty of insects as a delicacy. If you’re intrigued then take a look at the book Insects: An Edible Field Guide by Stefan Gates (Gates, 2017) which devises imaginative recipes for common insects, including woodlouse cocktail (replace prawns with cleaned-up woodlice in a prawn cocktail recipe) and stir-fried earthworms. (I haven’t tried them yet…!)

leftovers from brewing beer. From the Entocycle website (URL 93).

Some researchers have devised the lowest possible emissions diet that still meets our nutritional requirements. It involves a lot of high fibre breakfast cereal with no milk, and a lot of seeds, peas and onions. It reduces emissions to 10% of the original value! However, the researchers note that this diet is unrealistic, and go on to investigate less extreme diets. See Macdiarmid et al. (2012). See also Reynolds et al. (2019) which more than halves emissions and takes affordability into account.

Chapter 36 How can governments help?

So far we’ve discussed changes that we as individual consumers can make to reduce the impact of food on climate change. This chapter asks whether we need some more coordinated effort, for example by governments. What can governments do to help, and how can we as citizens help governments to help us?

Consumers and producers need incentives

There are lots of different types of change that food producers can make to reduce emissions. Some changes will improve profits, for example by using less fertilizer or energy. Others don’t; for example spreading muck more often costs more money. Reducing the amount of water used in rice production might be risky for the farmer unless supported by good technical advice. Improving the welfare of animals to reduce disease and losses might cost more initially, but can save money and reduce emissions in the longer term.

Can we expect food producers to reduce emissions on their own? Is it even reasonable to expect the majority of farmers, growers and businesses to know which changes would help? Even if they do know, then how can they be appropriately rewarded for making improvements?

As citizens we might want to have a meat-free day, and try a new plant-based meal. But it takes time to investigate the options, and we take a risk by trying something new; Maybe at first we don’t like the taste of the new foods, and it might take weeks to find good options, or for our preferences to change. We’re going to some personal effort to try to reduce climate change for future generations, but what if our neighbour is still tucking into their daily steak? Most people are going to need more than a warm fuzzy feeling to reward their efforts to help.

We and future generations will pay a price for actions that degrade the environment – for eating foods that cause the largest greenhouse-gas emissions. It’s unrealistic to expect the majority of people, including food producers and individuals, to change their choices at the scale and speed needed, without incentives and help. Governments have a role to play here.

Food labelling

I hope that soon there will be no need for this book. If food producers and suppliers label their products with accurate emissions data you’ll be able to create your own emissions stacks yourself.

This book uses typical or average numbers for each type of food, but in reality there is a huge variation in climate impact depending on many decisions made by farmers, growers, manufacturers and suppliers. (If this book showed every value for all possible circumstances it would not only be huge, but unreadably over-complex too.)

As a consumer we can’t often tell whether a piece of beef is from a dairy herd or a prime beef herd (chapter 24), or whether a piece of fruit came by boat or by plane (chapter 17). We also don’t usually know whether a tomato was produced in a heated greenhouse (chapter 11) or whether the chickens were fed on soy from sustainable sources (chapter 25). Only if we have accurate and comprehensive labelling can we make properly informed choices about which food to buy.

Around 2008 some companies worked out the emissions from their products and put them on their packets. One major UK supermarket made a plan to provide emissions estimates across their product range. Some hoped that this would become the norm. In practice though, it took a lot of work to do these calculations at that time, and it wasn’t clear that the public really wanted the information enough to make the effort worthwhile.

I confess that if in 2008 I had noticed that my bag of crisps caused 85 grams of emissions then I wouldn’t have had a clue what to make of it. Is that number good or bad? And compared to what? This book addresses this carbon literacy problem, and shows why emissions labelling would be very useful.

Emissions calculations have moved on a long way in the past decade, with many software packages available to help. Is now the time for emissions labelling to become mainstream? Would you be more likely to buy a product that has a carbon footprint figure printed on the packet?

We need mandatory standardized emissions-labelling to give consumers the data they need, and ensure that responsible producers who label are not at a commercial disadvantage to those who would otherwise not label. Then food producers have a good reason to examine where their emissions are coming from, and reap some benefit for making improvements, even if it’s just a lower number on a packet. And producers who have already gone to great lengths to do the right thing will be easier to recognize. Look out for certified emissions calculation schemes in your country, because this will help improve the quality of the numbers that get provided.

Would a number on a packet realistically influence your shopping habits, even with your new-found carbon literacy? There is already plenty of information on the packet that it is too easy to ignore, although researchers have demonstrated that traffic light systems can influence behaviour. What’s surprising is that even if we as consumers don’t look at the labels it can still make a difference. For example, although there is some debate about whether people really understand what the traffic light nutrition labels mean, they can still have a big effect, because food producers don’t want a red label on their packets, and make the recipes healthier to avoid getting a red traffic light.

How do we get to the point where we have mandatory labelling? We citizens have a big role to play in showing our support for environmental labelling by choosing foods that state their emissions values, and also by campaigning. That shows the food suppliers and governments how much we want it. It might take a while to standardize the labelling calculations, but at the moment any labelling is a step in the right direction.

Changing diets is difficult

Unfortunately, the ongoing struggle to address obesity also illustrates a major problem. It’s very difficult for governments to change what we eat. We get through our busy lives relying on habits developed over a lifetime and, for many people, choosing what to eat is just one of those ingrained habits. However, switching one or two of the most emissions-expensive ingredients you eat each day to more climate-friendly alternatives is probably easier than avoiding your favourite sweet treat.

At the time of writing, most government dietary guidelines do not take into account planetary as well as human health, and this requires a concerted collaboration between environment and nutrition experts.

There is a burgeoning market in vegan recipes and products, as well as an increased awareness of the need to reduce the quantity of meat in dishes, but more remains to be done. Most well-meaning climate-friendly food products and recipes are not yet based on facts about emissions, and the foods most easily available are usually not the climate-friendly options. While individual actions can work well for a subset of dedicated people, most of us could use some help.

Taxes

“I don’t think we should be in the business of prescribing to people how they should run their diets… Who would I be to sit there advising people in the country coming home after a hard day of work to not have steak and chips?”

– Claire Perry, UK Minister of State for Energy and Clean Growth in 2018

No-one wants to be told they must (or must not) do something, especially when we’re told it’s for our own good. Compulsory car seat belt laws were initially opposed, for libertarian and other reasons. However, with time the public has accepted that wearing seatbelts saves injuries and lives, and the laws are no longer so controversial. Restrictions on smoking and taxes on cigarettes were extremely unpopular when they were first introduced, but people now realize the dangers of smoking People seem to accept that smoking doesn’t affect just the smoker: passive smoking is harmful to others. It is argued that if someone makes a lifestyle choice that costs other people money, then that person should have to contribute to the cost of dealing with the consequences.

So what about taxing food that’s bad for our health?

In 2016 the UK announced a “sugar tax” on drinks with very high sugar content, in spite of industry opposition. However, by 2018 when the tax came into effect, many manufacturers had already reduced the sugar content to avoid the taxes. Consumers don’t seem to mind the change, which almost certainly helped reduce obesity.

Plastic bags used to be given out for free at shop checkouts so people could carry their shopping home, and advertise the store around town. So many were thrown away that seeing a disused shopping bag blowing down the street or floating in a river was commonplace. Many countries have now banned or imposed a charge on plastic bags. In the UK a charge was brought in in 2014, which led to an 80% reduction in the number of plastic bags over the following four years.

So while we don’t want the government restricting our liberties unnecessarily, initially unpopular “nanny” legislation can become widely accepted and make a significant difference.

Taxes on meat have been proposed to account for the environmental and health burdens of high meat consumption. Should meat be taxed for environmental reasons? Is this fair on the producers of low-emissions meat? What about non-meat high-emissions products? For example, we saw that cheese typically has higher emissions than chicken (chapter 25). A tax based on the emissions of each food item would reward producers for reducing emissions, because the cost of their product would decrease, making it more likely to be bought.

One possible problem with emissions labelling is that it neglects other problems, and so could make some of them worse – for example water use, air pollution or animal and human welfare. Ideally we would have labels for the other impacts too, and have a way to combine them into a single tax which might vary from one country to the next.

Implementing this comprehensive solution will take several years but we can’t wait that long. Some impacts, such as land or water use, involve a lot of the same numbers and calculations as the greenhouse-gas emissions, so it might make sense to include them at the same time. Other more complex environmental risks, such as biodiversity, may be overshadowed by climate change anyway if we don’t do something about emissions soon. So this shouldn’t hold us back from trying to sort out emissions taxes on food.

Changing subsidies

Many countries give money to farmers to help them produce the food their country needs. These subsidies can help protect farmers from changes in weather from one year to the next, as well as changes in demand. In addition to government payments in many countries, supermarkets also subsidize the price of milk in their stores to tempt people into their shop.

Reducing the subsidies for the most emissions-intensive foods is an alternative to taxes. This increases the price of these foods, encouraging consumers to make more climate-friendly choices.

However, such changes have to be done very carefully to help farmers through a difficult transition phase. For example, it just isn’t realistic for a beef or dairy farmer to suddenly switch to farming vegetables. We also need a transition plan that respects the dedication of farmers over many decades during which we, and governments, asked for more and more of their products.

Food fairness

An increase in the price of your weekly shop might not be a big issue for you if you have enough money to buy a book like this one. But a new food tax can end up taking money away from people who are already struggling to feed their families.

The success or failure of new taxes often depends on how the government uses the extra money, and on whether the benefits are seen to outweigh the economic disruption. The UK sugary drinks tax has been used to support extra sports in schools, thereby addressing the childhood obesity problem from two different directions at the same time. However, Denmark’s tax on saturated fat was scrapped after a year because it was considered bad for the economy.

The money from a food-emissions tax could be used to subsidize healthy lower-emissions foods including vegetables, or used to help provide healthy food to people with less money.

How can we get governments to change?

In a democracy, governments have to listen to the voters or they won’t win the next election. Unfortunately, climate change is happening over a longer timescale than the gap between elections. In the run-up to the election, voters are often swayed by promises on short-term issues like extra money in their pockets.

It might seem unrealistic to expect governments to prioritize climate change until it’s too late. I’m optimistic citizens can make governments make a difference on food. We vote every time we make a choice about which food to buy. Retailers, food producers and governments can see the statistics.

I am writing this book because I believe ordinary citizens have the greatest power to change the food system. A number of individual choices by a small number of people will make a small difference in the short term. But we can make these choices now – without waiting for government legislation or producer changes, and our actions now will be amplified by the reactions of supermarkets and governments when they see that enough people want them to make changes that affect everyone.

Beyond this, individual governments also need to work with each other to help incentivize uncooperative countries or manage the truly international nature of the food system. For example, cutting down forest to make way for agricultural land is a major problem for climate change (chapter 7). Satellite images can help with monitoring, but international agreements have to be made and acted upon too, in a way that takes into account the historical deforestation of now-wealthy nations.

Key points

- Buying foods labelled with their emissions encourages food producers to calculate and share information about the emissions caused by their foods.

- The rise in obesity shows that it is incredibly difficult for individuals and governments to change what we eat, even with excellent dietary guidelines.

- We need to demand the changes we want from producers and government, for example mandatory emissions labelling, reduced subsidies for the highest-impact foods, or emissions taxes on food.

- Without waiting for anyone, we can vote with our stomachs every meal time, choosing low-emissions options based on the emissions information already available.

Notes

in reality there is a huge variation in climate impact depending on many decisions made by farmers, growers, manufacturers and suppliers. See the ranges in figure 1 of Poore and Nemecek (2018). For example, the range for prime steak spans from 25 kgCO_2e to 75 kgCO_2e for 100 g of steak protein steak.

Only if we have accurate and comprehensive labelling can we make properly informed choices about which food to buy. Joseph Poore makes a very readable and coherent case for labelling foods with their environmental impact in The Guardian (URL 94), pointing out the significant impact of mandatory labelling on the efficiencies of fridges and freezers, and the freedom of choice provided to producers and consumers in a metric-based system.

One major UK supermarket made a plan to provide emissions estimates across their product range. Tesco supermarket produced a landmark document providing emissions estimates for over 500 food items (“Tesco Product Carbon Footprint Summary” 2012, accessed 2018).

bag of crisps caused 85 grams of emissions For more details see URL 95.

Look out for certified emissions calculation schemes in your country, For example the Carbon Trust in the UK (URL 96).

researchers have demonstrated that traffic light systems can influence behaviour. Study participants were found to be more influenced by avoiding red traffic lights than being attracted to green lights (Scarborough et al., 2015).

food producers don’t want a red label on their packets, and make the recipes healthier to avoid getting a red traffic light. The Canadian Health Check programme was examined to assess its impact on levels of salt, and found that manufacturers reformulated their products to meet the criteria (Dummer, 2012).

many manufacturers had already reduced the sugar content to avoid the taxes. HM Treasury report “Soft Drinks Industry Levy comes into effect”. (URL 97)

In the UK a charge was brought in in 2014, which led to an 80% reduction in the number of plastic bags over the following four years. Defra (2018).

Taxes on meat have been proposed to account for the environmental and health burdens of high meat consumption. Wellesley and Froggatt (2015) considered the potential of meat taxes, among other interventions, and Springmann, Mason-D’Croz, et al. (2016) looked at the economic impact of meat taxes based on the potential health benefits.

Ideally we would have labels for the other impacts too, and have a way to combine them into a single tax which might vary from one country to the next. As suggested by Joseph Poore, Cambridge Climate Lecture Series 2019 (URL 98).

Denmark’s tax on saturated fat was scrapped after a year because it was considered bad for the economy. “The fat tax and the extension of the chocolate tax – the so called sugar tax – has been criticised for increasing prices for consumers, increasing companies’ administrative costs, and putting Danish jobs at risk.” – Danish health ministry, as reported in Stafford (2012).

Chapter 37 Food as part of the solution

What if everyone changed what they ate, to reduce their greenhouse-gas emissions from food? If everyone managed to halve their food emissions, it would reduce global greenhouse-gas emissions by over 10%. Somehow though, we need to make total emissions zero by 2050. Are we ever going to get there?

Emissions from heating, cars, planes and other non-food activities are not the subject of this book – often they require much bigger lifestyle changes than switching which shelf to pick food from, or they require governments to change in an internationally coordinated way. But the good news is that a major shift in diets can actually reduce climate change by much more than 10%, depending on what is done with the land that would otherwise have been used for farming. Since over one third of the Earth’s land area is currently used for food production, repurposing farmland is a big deal (Fig. 37.1).

Fig. 37.1: 37% of Earth’s ice- and desert-free land is used for food production.

Freeing up land by moving towards plant-based foods

Animal products cause more emissions than most plant-based products, and animals also use more land. This is not a coincidence – it’s due to the inefficiencies of producing food via animals. For example, even the relatively efficient chicken has to eat three calories for every one calorie we get from eating the meat (chapter 25). Globally, over 4 in every 5 farmed fields are used to grow food for animals. Despite this, less than one in every five calories we eat comes from animal products.

Animal products: 80% of land → 20% of calories.

Plant products: 20% of land → 80% of calories

Therefore plant products are 16 times more land-efficient.

This means that if we reduce the amount of animal products in our diets, then we free up a lot of land that can be used for other things.

If we were to stop eating animal products entirely then we would reduce the amount of land needed for food production by 75%, thus freeing up three quarters of the agricultural land on the planet. Such a radical shift would dramatically change the landscape and countryside; the rolling green hillsides I grew up with in the UK would become a thing of the past. We would have to confront not only our cultural attachments to meat and the livelihoods of farmers, but also our national identities, as defined by our landscapes. If we shift to lower emissions foods we can then use this freed-up land to help reduce global warming further. Currently several of the potential solutions to climate change are limited by the amount of land available. However, with the land freed up by shifting towards plant-based foods, we can implement three very different types of large-scale climate-change projects:

1. forests

2. solar power

3. bioenergy with carbon capture and storage.

1. Forests

There is one tried and tested solution to climate change, that has been tested at scale many times over, even before humans came into existence – trees! Trees take in carbon dioxide and store it both in their wood and underground in their roots and in the soil. Forests already remove about a quarter of all the greenhouse-gas emissions produced by humans. Forests also protect against some of the impacts of climate change: they reduce air pollution and absorb rainwater thus reducing flooding.

If we spare land from food production and turn it into forest, we can help to suck carbon dioxide out of the atmosphere. If we stopped eating animal products entirely and let the land change into natural forest, shrub or grassland, this would remove about 3 kilos of emissions per person per day. This number can then be equal to, or ideally greater than, the total emissions caused by the food production itself.

2. Solar power

Solar panels are now a common sight on the roofs of buildings, but to produce a significant fraction of the world’s power requirements would also need solar farms, in which large areas of land are covered in panels or mirrors to harness the energy from the sun.

Unlike forests, solar farms can be situated in areas not currently suited to plants, such as deserts. However, for countries with a large fraction of arable land (e.g. the UK), solar energy collection competes with food production. In these cases, a shift towards plant-based diets would provide land that could be used to provide renewable energy such as solar power.

3. Bioenergy with carbon capture and storage

If we grow plants (“biofuels”) and then burn them in cars and power stations, we can burn less of the fossil fuels which cause global warming. The plants take in carbon dioxide as they grow, and mostly turn back into carbon dioxide when they are burned to make energy. Therefore the biofuels temporarily help reduce greenhouse gas levels by taking in carbon dioxide, and can be used in place of fossil fuels to reduce emissions. However, since the plants don’t live for very long, they don’t actively reduce the total amount of greenhouse gases. Also, if nitrogen fertilizer is used to increase the growth of the biofuel crops then they will contribute to global warming (box 2.1).

Most climate projections which meet the 1.5°C target assume that someone will invent and deploy new ways to suck carbon dioxide out of the atmosphere in the second half of this century. The most discussed of these is called Bioenergy with Carbon Capture and Storage, or BECCS for short. In BECCS, we grow biofuels, that are then burnt in power stations, and the carbon dioxide they produce is captured. This captured carbon dioxide is then trapped underground, for example in old fossil-fuel mines. If we could carry out BECCS on a large area of land, for example the size of Europe, over 50 years, we could reduce global warming by more than 1°C.

Unfortunately, we have never tested the full BECCS process on anything like this scale so whether or not this would really work remains uncertain, and it is very risky to rely on it.

We need to find a way to reward regions and countries that preserve – and especially increase – their forest cover, and that implement emissions-reduction technologies at the scale needed. In 1987 we banned the production of chemicals that were causing the hole in the ozone layer, and the hole is on course to close up again this century. What if we were to implement emissions-reductions at unprecedented speed and scale? We might keep the temperature rise below 1.5°C, or ideally reduce it back down towards pre-industrial temperatures. We could find ourselves with the luxury problem of needing international agreement on exactly what temperature the planet should be. I don’t envy future politicians that job though, given that it’s hard enough for two humans to agree on the temperature for a bedroom!

Key points

- The foods that produce the most greenhouse-gas emissions also often require the most land.

- Therefore, switching to lower-emissions foods frees up land that we can put to good use in helping to reduce climate change.

- Forests are extremely good at taking carbon dioxide out of the air and locking it up in trunks, branches, roots and the soil.

- By switching agricultural land to climate-improving uses such as forest, we can turn our current food system into a part of the solution to climate change.

Notes

If everyone managed to halve their food emissions, it would reduce global greenhouse-gas emissions by over 10%. This is simply because food causes about a quarter of all greenhouse-gas emissions (chapter 1), so halving this reduces total emissions by 12.5%.

Fig. 37.1 43% of the ice- and desert-free land is used for agriculture, of which 87% is used for food and the rest is used or allocated for other purposes including biofuels, textiles, wool and leather (Poore and Nemecek, 2018).

Globally, over 4 in every 5 farmed fields are used to grow food for animals. Producing food for animals including fish and grazing uses 83% of global farmland (Poore and Nemecek, 2018). See also Ruiter et al. (2017).

less than one in every five calories we eat comes from animal products. Poore and Nemecek (2018) find that 18% of global calories (and 37% of protein) come from animal products. Therefore, 83% of farmland produces 18% of calories (and 37% of protein) from animal products. Reversing the numbers (and assuming farmland is used only for growing food) means that 17% of the land produces 82% of calories (and 63% of protein). We round these numbers to 80 and 20% for simplicity but note that the statements would be even more striking by using the exact numbers.) If instead, we were to use the animal-products land to grow plant products, it could produce much more than 20% of the calories (because just 20% of land is currently used to produce 80% of plant-based calories). Specifically, it could provide 80% of calories × 80% of land / 20% of land = 320% of calories i.e. plants can provide 320% / 20% = 16 times as many calories from the same quantity (80%) of land.

If we were to stop eating animal products entirely then we would reduce the amount of land needed for food production by 75%, thus freeing up three quarters of the agricultural land on the planet. We would continue to need 20% of the land to produce 80% of calories from plant foods. We would need to make up the calorie shortfall from stopping eating animal products by increasing the amount of plant products grown by 25% i.e. to 25% of the land. This would therefore free up 75% of the land. (Redoing the calculation using calories and exact numbers gives 17 + 17 * 18 / 82 = 21% of land required to grow all required calories from plants i.e. 79% of farmland is freed up; redoing the calculation using protein and exact numbers instead gives 17 + 17 * 37 / 63 = 27% of land required to grow plant protein i.e. 73% of farmland is freed up.) Note that this is a crude calculation because it does not consider other nutrients. A more detailed protein-based calculation in Poore and Nemecek (2018) gives a reduction of 76% in land use for food, corresponding to 3.1 billion hectares, or about 4,000 square metres per person (2019 population), or about half a football pitch. A UK study (Harwatt and Hayek, 2019) that found that if the UK stops farming animals, it can feed the entire population from the current cropland (including the land currently used to produce animal feed), i.e. freeing up all the existing pasture land (their scenario 2). This pasture freed up for other things amounts to about one third of the entire land area of the UK, or the area of one Olympic-sized swimming pool per person (1290 m^2) (calculated by dividing current pastureland area 84,000 km^2 by the total land area of the UK 243,000 km^2, which gives 34% or roughly one third). Note that we do not currently feed the whole UK from UK land, therefore in addition there is land freed up in other countries as well as in the UK.

Forests already remove about a quarter of all the greenhouse-gas emissions produced by humans. Pan et al. (2011) via the excellent and accessible resource (URL 99).

If we stopped eating animal products entirely and let the land change into natural forest, shrub or grassland, this would remove about 3 kilos of emissions per person per day. The IMAGE integrated assessment model (URL 100) has been used to calculate that “the land no longer required for food production under the “no animal products” scenario could remove… 8.1 GtCO_2 on average each year, with continued but lower uptake after 100 years … as it naturally succeeds to forest, shrubland, or grassland” by Poore and Nemecek (2018). Converting this into kgCO_2e per person per day: (8.1 billion tonnes CO_2 / year) / (7.7 billion people) / (365 days / year) * (1000 kg / tonne) = 2.88 kg / person / day. A UK study found that if all the pastureland of the UK were turned into forest, this would pull about 4.5 kg of carbon dioxide out of the atmosphere per day, per person in the UK (Harwatt and Hayek 2019 scenario 2 finds 108 MtCO_2 per year).

This number can then be equal to, or ideally greater than, the total emissions caused by the food production itself. “6.6 Gt / year of avoided agricultural CO_2e emissions… (which is a 49% reduction in the annual emissions of the food sector).” – Poore and Nemecek (2018).

to produce a significant fraction of the world’s power requirements would also need solar farms, in which large areas of land are covered in panels or mirrors to harness the energy from the sun. See MacKay (2009).

Most climate projections which meet the 1.5°C target assume that someone will invent and deploy new ways to suck carbon dioxide out of the atmosphere in the second half of this century. See for example chapter 3 of IPCC (2018).

If we could carry out BECCS on a large area of land, for example the size of Europe, over 50 years, we could reduce global warming by more than 1°C. IPCC (2018) cites Kriegler et al. (2018) who assume 8 GtCO_2 / year from 375 million ha for their “limited CDR scenarios”.

we have never tested the full BECCS process on anything like this scale so whether or not this would really work remains uncertain, and it is very risky to rely on it. Larkin et al. (2018).

Chapter 38 Making the change

Small things

“If everyone does a little, we’ll achieve only a little”

– David JC MacKay

“Let the small bad things happen and make the big good things happen.”

– Tim Ferriss

It can be overwhelming to think about the importance of the climate challenge and the complexity of the issues. This book demystifies the main causes of emissions from food and gives some ideas about how to start reducing them.

Some people (myself included) exhaust themselves by trying to do everything they can think of to reduce their emissions. But doing “everything you can think of” isn’t a sustainable way to live – you’re likely to burn out or give up.

Here are examples of things that that don’t help much but can exhaust you, compared with other activities that do help a lot:

- Switching to plant milk in tea, while continuing to eat an 8 oz steak once a week.

- Switching the kettle off every time just before it boils, to save on electricity, but using a fossil-fuelled oven for an hour a day (box 12.1).

- Reading every last detail of the ingredients of every food packet to avoid small amounts of milk derivatives or eggs, but then only having time to buy food for today, so that you have to go to the shops again tomorrow (driving 15 minutes in a fossil-fuelled car), as I found I was doing (see chapter 1).

This list emphasizes that you need to keep food decisions in context: consider your other activities that may have much greater impact. Check out the emissions from driving, flying and heating buildings (chapter 1). Once you address the big issues, you can be lenient on yourself in small things – especially the small things that bring you pleasure.

Big things

The most important message from this book is that different foods cause very different emissions. This is good news because it means that most of us can make a big difference to our food climate impact by focusing on a relatively small number of things that we do on most days. To recap the highest emissions foods:

- Beef and lamb are the most emissions-intensive of all the common foods (chapter 24).

- Cheese, butter and pork are the runners-up, causing less than half the emissions of beef and lamb (chapters 9, 5 and 10).

- Chicken, eggs and fish are the lowest-emissions animal products, about half the emissions of cheese (e.g. Fig. 34.1). However, they still cause more emissions than most plant products (e.g. chapter 34).

Psychology research suggests that it’s not very helpful to focus on what to avoid; instead it’s better to focus on what to include. So, to help the climate, look for ways to add more of these foods to your diet:

- Pulses like beans, lentils and peas are full of protein and other nutrients.

- Plant-based substitutes for animal products are improving rapidly (but make sure you’re getting the nutrients you need).

- Nuts and seeds are the plant equivalent of eggs, and are similarly nutritious (chapter 19).

- Eating yesterday’s leftovers saves time and wasted emissions, as well as reducing emissions from landfill.

We’re particularly encouraged to eat more fruit and vegetables for their health benefits. How can we do this?

- Transporting food long distances by boat is not particularly bad for climate change, so tuck in to foods that can last for a long time in the hold of a ship, including apples, oranges and pulses (see chapter 17).

- Steel tin cans and other packaging aren’t as bad for the climate as many people think. As well as being convenient, they also reduce the home cooking time needed (see chapter 14).

- Frozen fruit and vegetables cause much lower emissions than their air-freighted counterparts (chapter 28), as well as preserving a lot of the nutrition.

- And continue to enjoy lots of local, seasonal fruit and vegetables.

Influencing others

Governments and food producers need pressure from citizens to be able to change. They need to know if people want more help to switch to electric cars, or international agreements on aviation, or more money to be invested in producing renewable energy.

Do you want governments to subsidize production of animal products, or of fruit and vegetables? And how much incentive should be given to food producers to change to lower-emissions products and practices? Only governments can create laws that require emissions of foods to be measured and tracked through the food chain, enabling the consumer to make truly informed decisions.

Most importantly for food, governments need to know how we feel about the land around us: whether we want take advantage of land freed up from animal production to plant forests (which can double the climate change benefits), or whether we want to keep the landscape as it is and hope we can fix climate change some other way.

People sometimes ask me how they can reduce the emissions from their diets even further. Often the questioner is already doing all the good big things described above, and has already reduced their emissions down to half or even one third of the average. Can they go down even further?

Suppose such a person works hard to reduce their food emissions by one third again. A bit of maths tells us that this has the same impact on the climate as convincing one friend to reduce their emissions by 10%, down to 90% of the average. Which is easier? Which has the more potential to make a difference later on? That friend might then reduce their emissions further, and then influence their friends. I think the best thing we can all do is to spread the word, and work together to find a comfortable and efficient way to live a low-emissions life, that everyone wants to share!

Being a human

“We don’t need a handful of people doing zero waste perfectly. We need millions of people doing it imperfectly”

– Anne-Marie Bonneau

Several times a day we make a choice about what to eat, so there’s lots of scope for making changes. But there are lot of opportunities to be imperfect. I’m pretty sure it’s not possible to always choose the most climate-friendly foods and still stay sane.

I try to focus on the emissions of something I do regularly, and then experiment with a few different options when I have time, rather than trying to get everything “right” all the time. I realize some people prefer to make one big decision, like never eating a particular food again, rather than make a more complicated mixture of changes. But eating the more climate-friendly options most of the time is a huge step forward for the majority of people. Since all food causes emissions, the additional benefit of always choosing the absolutely most climate-friendly option is both exhausting and subject to the law of diminishing returns.

Movements like Veganuary and Meat-free Mondays mark out a time to be focused on trying new foods, while leaving you time to recover your energy for the rest of the year or week. At first glance, changing to a more climate-friendly diet on one day out of seven could sound like an ineffectual “little thing”. Surely the maximum climate impact is one seventh, or 14%? But we humans are creatures of habit, and it takes effort to create a new habit, especially if the change requires creativity when we’re tired and hungry. By carving out dedicated time to try out new climate-friendly ideas, you start to develop a repertoire of new dishes that you might enjoy so much that you start to eat them at other times too.

Sharing food with others is important, socially and culturally. By changing our diets we might affect our relationships with others, perhaps by offending them with our new choices, or by removing a shared meal. Feastarians are vegetarian all year, except for treats or feasts, which allows them to join in the big occasions when others think meat is essential – e.g. turkey at Christmas or Thanksgiving. Emissions are only one aspect of choosing food – we need to enjoy life as well!

Notes

“If everyone does a little, we’ll achieve only a little.” Taken from Sustainable Energy – Without the Hot Air by David JC MacKay (MacKay, 2009).

“Let the small bad things happen and make the big good things happen.” Taken from the Tim Ferriss blog (URL 101) and discussed more in The 4-Hour Work Week: Escape the 9-5, Live Anywhere and Join the New Rich (Ferriss, 2011).

Switching to plant milk in tea, while continuing to eat an 8 oz steak once a week. If you drink 100 grams of cows’ milk a day in tea, it causes about 200 grams of emissions a day (chapter 4). One 8 oz steak causes 9 kilos of emissions. Sharing the 9 kilos out over 7 days is more than 1 kilo a day, so is greater than the 200 grams of emissions a day from the cows’ milk. The contrast is even greater if you allow for the emissions of making the plant milk.

Steel tin cans and other packaging aren’t as bad for the climate as many people think. Some people think of canned food as being expensive or unhealthy but, although some vitamins are reduced, they can be an easy source of extra plants that make a quick addition to a meal. As demonstrated in Jack Monroe’s “Tin can cook” you can even make a surprisingly wide range of delicious and cheap meals from canned food.

Sharing food with others is important, socially and culturally. Thanks to Rosemary Randall for stimulating insights on this topic. See In Time for Tomorrow? the International Carbon Conversations Handbook for more information www.carbonconversations.co.uk/p/materials.html.

Appendixes

A Climate change

B Impacts of climate change on food

C Food in the future

Appendix A Climate change

The effects of climate change are well documented. For example, we’ve already had an increase of nearly 1°C between the late 1850s and the early 2000s (chapter 1), and we have already seen:

- melting of the Greenland ice sheet, the Antarctic ice sheet, and sea-ice in the Arctic

- rising sea levels and coastal erosion

- land changing to a different type of habitat, which reduces the range of species

- changes in migration and reproduction patterns of birds and fish

As well as impacts on food and water availability. We discuss climate change impacts on food in the next chapter.

Looking ahead, these problems are set to worsen as the temperature rises, with increasing numbers of extreme weather events. In addition to impacts on food production (see the next chapter), there will be adverse effects on human health from diseases such as malaria spreading more widely. Furthermore, climate change is expected to impact the rate of climate change itself. For example, warming causes melting of permafrost, which releases methane – a potent greenhouse gas – which causes more warming. While the poorest people will be the most affected, everyone will be affected to some extent.

The above list summarises why it’s important to reduce greenhouse-gas emissions – the topic of this book’s main chapters. In this chapter we discuss some of the basic terminology. The Appendix after this discusses the specific impacts of climate change of most relevance to food production.

The greenhouse effect

Fig. A.1 shows a diagram to illustrate the greenhouse effect.

First, consider an actual greenhouse, or a window in your house. Sunlight comes in through the glass – mostly this is visible light, that your eyes can see. The sunlight warms up the things inside the greenhouse, or inside your house. Warm things make infrared light. Our eyes can’t see this infrared light, but it is extremely important for the greenhouse effect, and so for understanding climate change.

Although the glass is transparent to visible light, it is not transparent to infrared light. If you were wearing infrared goggles, then you wouldn’t be able to see out of the window! Infrared light gets trapped inside the greenhouse, and so the greenhouse warms up as more and more visible light comes in, and the energy is turned into warmer things and infrared light. That’s why gardeners use greenhouses!

Fig. A.1: The greenhouse effect

Upper: in a greenhouse

Lower: at the Earth’s surface.

The Earth’s atmosphere is like a greenhouse

The Earth’s atmosphere acts like a greenhouse. Most of the air we breathe is nitrogen and oxygen, both of which let the sunlight and infrared light pass straight through them. This means that nitrogen and oxygen don’t cause a greenhouse effect.

The next biggest component of Earth’s atmosphere is carbon dioxide. Just like glass, carbon dioxide is transparent to visible light, but isn’t transparent to infrared light. This means that carbon dioxide in our atmosphere warms up the surface of the Earth, just like glass warms up a greenhouse – hence the name “greenhouse gas” (see Fig. A.1), top.

Our atmosphere is changing

You may have learned about carbon dioxide and oxygen at school: animals (including humans) breathe in oxygen, and breathe out carbon dioxide. On the other hand, plants use carbon dioxide and give off oxygen as waste. In essence the plants take the carbon atom out of the carbon dioxide, leaving just the two oxygen atoms behind. They use this carbon to build up their stem, leaves and roots, adding in small amounts of other nutrients usually taken from the soil.

Fig. A.2: About 5% of the air we breathe out is carbon dioxide.

Over a period of about 60 million years, around 300 million years ago, dead plants were compressed into coal, oil and gas. Since the Industrial Revolution we have been digging up and burning more and more of these fossil fuels, turning them back into carbon dioxide. Figure A.3 shows that over the last 800,000 years the concentration of carbon dioxide has gone up and down between 200 and 300 parts per million. However, in just the past 200 years it increased by over 30%, to more than 400 parts per million. The world has changed unimaginably over that time, from the invention of the light bulb to the rollout of gas and electricity to individual homes. Nowadays fossil fuels are routinely burned by many people without thinking, to heat a radiator or to generate the electricity used to power a light.

Fig. A.3: Carbon dioxide variations in our atmosphere over the last 800,000 years. Inspired by (URL 103) and updated thanks to numbers provided via Our World in Data.

Global warming

The world is getting warmer. Fig. A.4 shows a visualisation of the average temperature each year from 1850 to 2018: bluer colours indicate lower temperatures and redder colours show warmer temperatures. The left side of the box is mostly blue, corresponding to the late 1800s and early 1900s, whereas the far right side of the box contains most of the red colours, corresponding to about the year 2000 onwards.

Fig. A.4: The average annual temperature each year from 1850 (left side of the box) until 2018 (right side of the box), displaying blue for low temperatures and red/brown for higher temperatures. Taken from the beautiful Climate Stripes project (URL 104) from which you can also download stripes graphics for other years and parts of the world. Reproduced with permission from Ed Hawkins.

By analyzing these numbers and more, going back thousands of years, the international scientific consensus is that:

- “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.”

- The world has warmed up by 0.97°C between the late 1850s and the early 2000s.

Using the laws of physics it’s possible to predict the warming effect of all the ingredients of Earth’s atmosphere. Using chemistry we can forecast how long each ingredient is likely to remain in the atmosphere unaltered, or when it will react with other ingredients to produce new molecules. We can also calculate the warming and cooling effects of snow, aeroplane condensation trails, volcanoes, and even changes in the amount of radiation from the sun.

Adding up the effects of all these ingredients over time shows that most of the warming comes from greenhouse gases. More than half of the warming is caused by carbon dioxide. The next most significant greenhouse gases are methane, chlorofluorocarbons (CFCs) and nitrous oxide (laughing gas; see chapter 1).

Sunspots and other changes in solar radiation average out and are unimportant on timescales of more than a decade, over the past two centuries at least. Volcanoes can have a big effect in the year of the eruption but, when added up over time, they have a very small impact. Taking into account all the effects, almost all of the warming over the last two hundred years can be explained by human activities.

Scientists have compiled a wide range of possible scenarios for future human activity. These have been combined with the available science to forecast the amount of global warming expected. The details are complicated; for example they depend on how much the greenhouse gases mix with other gases in the atmosphere. However, one conclusion is clear: if we increase the total of all human greenhouse-gas emissions, then we increase the global temperature at the end of this century. More precisely, if we double the amount of greenhouse gases released, we double the amount of global warming.

In the best-case scenarios we will turn things around and produce less and less greenhouse gases every year until, by 2050, we reach zero emissions, and then start removing greenhouse gases from the atmosphere, using new technologies that are still being investigated. In most of these optimistic scenarios the total human-induced global warming peaks at around 1.5 degrees Celsius. Alternative scenarios that simply extend the emissions of the 2010s take us above 5 degrees Celsius of warming, which could trigger irreversible changes that increase the temperature yet further.

Regional warming

The word “global” in “global warming” hides a complexity that can have serious impacts on humans. When we look in more detail at the temperature of the Earth it turns out that the global average temperature rise of 0.97°C since 1850 is very unevenly distributed across the Earth’s surface.

Have you ever gone to the seaside to cool down on a hot day, or marvelled at the exotic plants that can survive winter near the coast, away from the coldest weather? In both cases, the reason is because water warms up much more slowly than the land. The vast oceans are slow to cool down in winter, and barely heat up in summer.

Some patches of ocean have hardly warmed at all in the past century. On the other hand, some land on most continents has already warmed by more than 1.5°C. The greatest warming is happening at the Arctic, which has now warmed by nearly 3°C.

Looking ahead, the same basic patterns are expected to continue. If greenhouse-gas emissions continue rising at their current rate, warming is expected to increase by more than 10 additional degrees in the Arctic.

Fig. A.5: Average September area of Arctic sea ice, showing how it has nearly halved in the last decades. (URL 105)

Nearly half of all the Arctic sea ice has melted since the 1980s (Fig. A.5). Looking ahead, scientists expect the whole Arctic ice sheet to completely melt in some years. This would seriously threaten the survival of wildlife including the polar bear. If global average warming is limited to 2°C, then we expect the Arctic will be ice-free one summer in every decade. If the warming can be curbed to 1.5°C then this is only expected to happen once a century.

Global average annual rainfall is also expected to change as global warming increases. However, just like the temperature, the local change in rainfall depends on where you are in the world, and on the season.

Over the course of this century, some places like Scandinavia and parts of China are expected to have over 20% more rain each year – other areas like Spain and South Africa are expected to have over 20% less. The timing of rainfall during the year will also be affected. For example the UK will probably have more rain in the winter, and less rain in the summer. Science can’t say whether a particular storm or drought was due to climate change. However, science can say that storms or droughts of a particular severity are 5 times (or 10, or 100 times) more likely. So if we get far more storms than we did before, we can say that most of them are because of climate change – because only a few would have been expected otherwise.

The fact that the temperature changes are different in different places also affects weather patterns, causing much more complicated effects. For example, the relatively fast warming of the North Pole is speculated to cause changes in air currents, which in turn cause longer periods of extreme weather (e.g. heatwaves), which spread across large areas of the Northern hemisphere including the United States and western Europe.

Notes

a diagram to illustrate the greenhouse effect. NASA give a really clear description of this process at the following link: URL 102.

This means that nitrogen and oxygen don’t cause a greenhouse effect. An oxygen molecule is made up of two oxygen atoms, which can jiggle around, moving closer together and further apart from each other. Because the two atoms are exactly the same, it turns out that there is no change in the electric or magnetic field when they move around, which means that oxygen molecules do not emit or absorb visible or infrared light. The same is true for nitrogen molecules, and also for the single-atom noble gases that make up the next most common components of the air.

However, a carbon dioxide molecule is made up of one carbon atom and two oxygen atoms. Imagine your body is a carbon atom and your hands are oxygen atoms. If you stand with your arms outstretched, one on each side, then the three atoms are in a straight line. These atoms can move around if they gain energy from absorbing infrared light. For example you can flap your arms up and down or move your body from side to side.

Unlike in the oxygen molecule, the atoms in a carbon dioxide molecule are of different types. When the atoms in the carbon dioxide molecule jiggle around they cause a changing electric and magnetic field. Just as a ball bobbing on a pond produces ripples on the pond surface, so a changing electric and magnetic fields causes electromagnetic waves, commonly known as radiation or light. Conversely, light can be absorbed by the molecule and make it jiggle. The amount of energy required to make the molecule jiggle corresponds to the light in the infrared part of the electromagnetic spectrum.

Infrared radiation gets absorbed by carbon dioxide and makes it jiggle around. And from time to time the carbon dioxide will emit infrared light and take a break from jiggling for a while. Most of the time this heat travels back down to Earth. These dancing carbon dioxide molecules act like a blanket and keep us from freezing.

“Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.” Taken from the Intergovernmental Panel on Climate Change (IPCC) 2014 Synthesis Report (IPCC, 2014).

The world has warmed up by 0.97°C between the late 1850s and the early 2000s. Specifically, the average near-surface air temperature increase between pre-industrial times (1850-1900) and the recent decade (2006-2015) is 0.97°C (IPCC, 2018). The surface temperature increase is 0.87°C over the same period, however we state the near-surface air temperature in the main text since this is the value used in IPCC (2018) chapter 2 for the carbon budget calculations.

We can also calculate the warming and cooling effects of snow, aeroplane condensation trails, volcanoes, and even changes in the amount of radiation from the sun. You can read a detailed account of all these effects in Myhre et al. (2013).

almost all of the warming over the last two hundred years can be explained by human activities. In 2014 the IPCC wrote “Anthropogenic greenhouse-gas emissions… together with… other anthropogenic drivers… are extremely likely to have been the dominant cause of the observed warming since the mid-20th century” – from Pachauri and Meyer (2014).

if we double the amount of greenhouse gases released, we double the amount of global warming. For example, see figure SPM.10b and figure 2.3 of chapter 2 of IPCC, 2018, which shows a roughly linear relationship between the amount of greenhouse-gas emissions and the predicted warming. See also the earlier more detailed analysis in Myhre et al. (2013).

which could trigger irreversible changes that increase the temperature yet further. This is referenced throughout Pachauri and Meyer (2014) for example: “Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts globally (high confidence).”

the global average temperature rise of 0.97°C since 1850 is very unevenly distributed across the Earth’s surface. For example, see figure 1.3 of M. R. Allen et al. (2018), which shows the temperature change across a map of the world.

water warms up much more slowly than the land. This property is described in physics by the “specific heat capacity”, which is the energy required to raise the temperature of one gram by one °C. By definition of the calorie, it takes one calorie of energy to raise the temperature of one gram of water by one °C. The specific heat capacity of soil depends on the moisture level, and for dry soil is only one fifth that of water, depending on soil type (Bowers and Hanks, 1962). Additionally, water evaporates more as it warms up, which stabilises the warming. When continental soil is dry then evaporation can’t help to keep the soil cool.

Some patches of ocean have hardly warmed at all in the past century. On the other hand, some land on most continents has already warmed by more than 1.5°C. The greatest warming is happening at the Arctic, which has now warmed by nearly 3°C. This is apparent in the top panel of figure 1.3 of M. R. Allen et al. (2018), in which some patches of sea have not increased in temperature (blue colour) and yet central Africa, Canada and Russia have warmed by over 1.5°C (darker red colour). Arctic warming is accelerating because of the melting ice. When sunlight is reflected straight back into the sky from the white ice, it can’t cause warming. However, when the ice melts into water then some of the sunlight warms the water, which then leads to more melted ice…

If greenhouse-gas emissions continue rising at their current rate, warming is expected to increase by more than 10 additional degrees in the Arctic. See the right panel of figure 2.2a from Pachauri and Meyer (2014).

If global average warming is limited to 2°C, then we expect the Arctic will be ice-free one summer in every decade. If the warming can be curbed to 1.5°C then this is only expected to happen once a century. See Meredith and Sommerkorn (2019).

Over the course of this century, some places like Scandinavia and parts of China are expected to have over 20% more rain each year – other areas like Spain and South Africa are expected to have over 20% less. This is shown in figure 2.2b in Pachauri and Meyer (2014).

For example the UK will probably have more rain in the winter, and less rain in the summer. See chapter 11 of Solomon et al. (2007) e.g. their box 11-1 figure 2.

the relatively fast warming of the North Pole is speculated to cause changes in air currents, which in turn cause longer periods of extreme weather (e.g. heatwaves), which spread across large areas of the Northern hemisphere including the United States and western Europe. See Kornhuber et al. (2017) and Mann et al. (2018) and Petoukhov et al. (2013).

Appendix B Impacts of climate change on food

Most of this book looks at how changing our food consumption affects the climate. Here we look at things the other way round – how will climate change affect the future availability of food?

Given the vast array of food choices in the supermarket, it’s hard to predict what might be on the shelves in one year’s time, let alone in 2050. However, the range of ingredients used to make most of our calories is in fact surprisingly limited, and nearly half the world’s calories come from just three crops: rice, wheat and maize. This makes the task of forecasting food supply slightly easier.

Every farmer and gardener knows that the quality and quantity of a crop depend on the temperature and rainfall. By looking back at historical harvests and comparing them with the weather in the respective year, we can estimate how crop yields vary with temperatures and rainfall levels.

It turns out that as a result of climate change some parts of the world will be able to produce more food – for example in a region that was previously slightly too cold for a particular type of plant. Parts of Canada, Scandinavia and Russia are predicted to produce more food in a warmer world. However, most continental and equatorial regions are expected to produce much less food under the projected climate change, particularly South America, Africa, India, southern China, the Philippines and Australia.

We need pollinators, such as bees, to be able to produce edible grains and fruits. Climate change affects the number and spread of these pollinators, which can reduce crop yield. In addition, the spread of crop pests and diseases are affected, which can reduce crop yield further. Increased levels of carbon dioxide can increase yields of some crops, but this is predicted to come at the cost of lower nutrition, particularly in key minerals iron and zinc.

Some parts of the sea are now producing more fish than before, as fish adapt to changing sea temperatures and currents. Overall though, the total supply of fish is expected to decrease, and the communities that have been dependent on fishing for centuries will be hardest hit. One way to counterbalance the declining fish stocks is to grow fish in farms, either in tanks or in cordoned-off parts of the sea (chapter 27). However, sea farms are particularly vulnerable to storms. Furthermore, both fish and land-animal farming depend on availability of feed, which is affected by the same falling yield issues that affect human food. The amount of food we can produce from farmed fish and land animals is also affected by the spread of pests and diseases, which is likely to be worsened by climate change.

Finally, toxins in food tend to build up faster at higher temperatures. For example, aflatoxins (produced by mould) are encouraged by drought during the growing season followed by rainfall during harvest and high temperatures during storage. Aflatoxins cause liver cancer and are associated with stunted growth in children, and in severe outbreaks can cause death.

The impact of food shortages

As chronicled in the Bible, in past millennia the harvested grain was stored for years in case of a drought, or series of droughts. Today, droughts are still a major problem for food production: over 80% of the cost of crop losses from extreme weather events is currently attributed to droughts.

However, thanks to widespread international trade in food we don’t currently need to store grain for years. When a harvest fails in one region, we can just import food from somewhere else where the weather was more favourable. Much of the internationally traded food is produced in highly productive regions, often called “breadbaskets”. It is therefore crucially important to understand how changes in air currents can affect multiple continents at once. (e.g. the Northern hemisphere, see appendix “Climate change”). If a weather system knocks out several of these breadbaskets in the same year, then global food availability is reduced.

Furthermore, access to food currently depends critically on an impressively interconnected web of trade, delivering ingredients just in time to supply factories and consumers. In the same way that a run on banks can cause a financial crisis even if there was no good reason for the initial run, so even an imagined lack of food could cause changes in international trade that can increase food prices. Increased food prices have been found to match up with outbreaks of civil unrest, for example they are thought to have contributed to the French Revolution and more recently there was an increase in food prices of 50% during a period of just over 1 year leading up to early 2008, which was associated with riots in 30 countries.

Notes

Page

nearly half the world’s calories come from just three crops: rice, wheat and maize. See P. K. Thornton and Cramer (2012).

However, most continental and equatorial regions are expected to produce much less food under the projected climate change, particularly South America, Africa, India, southern China, the Philippines and Australia. For more details see Schleussner et al. (2016) and Searchinger et al. (2013).

Increased levels of carbon dioxide can increase yields of some crops, but this is predicted to come at the cost of lower nutrition, particularly in key minerals iron and zinc. See S. Myers et al. (2014), S. S. Myers et al. (2017), Zhu et al. (2018) and the discussion in box 6 of IPCC (2018).

Aflatoxins cause liver cancer and are associated with stunted growth in children, and in severe outbreaks can cause death. For more information see Kepple and Holleman (2018).

over 80% of the cost of crop losses from extreme weather events is currently attributed to droughts. From Kepple and Holleman (2018).

Increased food prices have been found to match up with outbreaks of civil unrest, See Lagi et al. (2011); Bellemare (2014) and C. S. Hendrix and Haggard (2015).

for example they are thought to have contributed to the French Revolution Tilly (1968).

there was an increase in food prices of 50% during a period of just over 1 year leading up to early 2008, which was associated with riots in 30 countries. Brinkman and C. Hendrix (2010).

Appendix C Food in the future

How much might food change in the future? We start by looking back at changes that happened already during the 20th century. Then we look ahead at the projected increase in population and wealth and consider how this affects greenhouse-gas emissions. Finally we speculate on improvements that could help reduce the impact of climate change on food.

Fig. C.1: Fridges through the ages.

Top: “Refrigerator”, 400BC. (URL 106)

Bottom left: 1920s refrigerator. (URL 107)

Bottom right: Modern fridge interior. (URL 108)

The pace of innovation in food

Close your eyes and imagine it’s the year 2040. What did you have for your last meal? What are you looking forward to tucking into later? What will people be eating in 2050?

In some ways it’s hard to imagine things being any different. But look backwards instead of forwards and you see some big changes. Only 100 years ago the home refrigerator was a new invention, but these days the developed-world’s lifestyle would be impossible without it. (Fig. C.1). And in the last 100 years the home freezer and refrigerated transportation has allowed the routine purchase and consumption of pre-prepared meals on a scale unimaginable by our grandparents.

Soft drinks (chapter 21) and packets of potato crisps (chapter 20) are available in most food outlets, yet both came to prominence only in the second half of the 20th century. Massive supermarkets and online shopping allow us to get our food in record time. Many of the changes have been enabled by new technology, which allows companies to better cater to our preferences.

Could the food retailers of the future do an even better job of delivering tasty satiety and convenience? At the moment it looks like other factors will become more important than personal preferences in determining what you’re digesting in twenty years’ time. Poor food choices will cause more health problems (chapter 34), and as a result countries may impose taxes on unhealthy food options – for example sugar taxes to tackle the obesity crisis (chapter 36). In addition, we will be dealing with the impacts of climate change on food production (appendix “Impacts of climate change on food”), at the same time as trying to reduce greenhouse-gas emissions from food.

A growing demand for food

The human population rose from about 2.5 billion people in 1950 up to over 6 billion in 2000, and continues to rise (Fig. C.2). However, this growth rate is slowing down, partly because people are choosing to have fewer children. Opinion is divided over whether the population will continue to rise until the end of the century, or whether it will peak before 2050 and then start to fall. The United Nations 2017 forecast predicts that the number of people is likely to grow to nearly 10 billion in 2050. These extra people will have to be fed.

Fig. C.2: Population forecast showing the past rise in population (blue larger dots) and the United Nations forecast (red small dashes). Data from the UN via URL 109.

The recommended daily allowance of calories depends on age and physical activity levels but (as dieters will know) it is around 2000 kCal for women and 2500 kCal for men. Do you notice people around you (or yourself) putting on a bit of extra weight as they get older? It turns out that as people earn more money, they also tend to eat more!

Economic forecasts predict rising incomes, which is good news as it takes many people out of poverty, but is not such good news for the majority of people’s waistlines. Putting this together with the population forecasts predicts a more than 50% increase in demand for food between 2005 and 2050.

More meat, and more emissions

What sort of food will our future selves want to buy? As people get more money, they tend to eat more meat, as well as eating more food generally. A surprisingly tight correspondence has been found between the amount of meat people eat and their income:

- On an annual salary of around $10,000, people eat about 40 grams of meat a day, which corresponds to about 2 chicken breasts a week.

- This reaches 100 grams of meat a day as salaries approach $30,000.

- Worldwide, the amount of animal-based protein eaten per person has risen by over 50% since the 1970s.

The global trend for more meat is important for climate change because animal products contribute more to global warming than other types of food. Combined with the rising population, the rising demand for meat could almost double greenhouse-gas emissions from food.

Even ignoring other considerations of land and water availability, because of greenhouse-gas emissions alone we simply cannot scale up agriculture to satisfy consumer demand.

Mitigating the impacts of climate change on food

On top of all this, we will have to deal with the impacts of climate change on food (appendix “Impacts of climate change on food”). Research is ongoing into agriculture that is more resilient to the effects of climate change. Genetic engineering and accelerated traditional plant breeding can lead to varieties that cope better with higher temperatures, or are more resilient to extreme weather. Better crop protection and storage can also reduce food wasted along the supply chain, particularly in countries not already using the latest technology.

Fig. C.3: The black eyed bean (cow pea) might become more widely grown due to its weather resilience. (URL 110) (URL 111) (URL 112)

In addition, some currently less popular crops may become grown more widely. For example the black-eyed bean (often called the cow pea; see Fig. C.3) is particularly drought-tolerant and has been studied by NASA on space stations.

The effects of climate change are already being seen around the world, including an increased number of extreme weather events. Although sometimes tragic for the people involved, devastation gives us a chance to do better in future. We need to be ready to build back up the towns and food production systems in ways that are more resilient to climate change, and that actually help to reverse climate change (see chapter 37).

Notes

“Refrigerator”, 400BC. (URL 106) This ancient “Yakhchal” evaporation cooler was built in Iran in about 400BC. There is a large underground storage area, and ice that was brought from the local mountains in winter would have lasted all summer.

The United Nations 2017 forecast predicts that the number of people is likely to grow to nearly 10 billion in 2050. See United Nations (2019).

It turns out that as people earn more money, they also tend to eat more! Research shows that as the Gross Domestic Product (GDP) of a country increases so too does the daily number of calories consumed by each person (see the right panel of figure 2 in Tilman and Clark 2014).

Economic forecasts predict rising incomes, which is good news as it takes many people out of poverty, but is not such good news for the majority of people’s waistlines. See economic forecasts by the Food and Agriculture Organisation (Alexandratos and Bruinsma, 2012).

more than 50% increase in demand for food between 2005 and 2050. See Alexandratos and Bruinsma (2012).

A surprisingly tight correspondence has been found between the amount of meat people eat and their income: Shown in the left panel of figure 2 of Tilman and Clark (2014).

Worldwide, the amount of animal-based protein eaten per person has risen by over 50% since the 1970s. See Alexandratos and Bruinsma (2012) and figure 9 in Ranganathan et al. (2016).

animal products contribute more to global warming than other types of food. See figure 1 of Springmann et al., 2018.

the rising demand for meat could almost double greenhouse-gas emissions from food. Springmann et al. (2018) forecast a rise of about 87%.

the black-eyed bean (often called the cow pea; see Fig. C.3) is particularly drought-tolerant See P. Thornton, 2012.

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Index

The index does not include entries for the endnotes of each chapter. If you need to search the endnotes, we recommend using the ebook edition, which is available at no cost from all the usual suppliers.

IPCC Special Report: Global Warming of 1.5°C, 1

1.5°C emissions budget, 1, 2, 3

2030 emissions budget, 1

2050 emissions budget, 1

3 kgCO_2e yardstick, 1

aflatoxins, 1,

see also toxins

Africa emissions/p/d, 1, 2

age, food waste, by, 1

air transport, see transport, air allergies

insect, 1

nut, 1

seafood, 1

almond butter, 1

almond milk, 1, 2,

see also plant milk

home-made, 1

reducing emissions, 1

almonds, 1

bitter, 1

fertilizer, 1

gCO_2e per gram, 1

water, 1

alternatives

beef, 1

eggs, 1

increased emissions, 1

meal, shakes, 1

plant-based, 1

rice, 1

aluminium, gCO_2e per gram, 1

ammonium nitrate, fertilizer, 1

animal efficiency, 1

deforestation, 1

inefficiency, 1

nutrition, 1

v. plant, 1, 2

animal feed, 1

animal inefficiency, see animal efficiency

animal manure, see manure

apple pie, 1

reducing emissions, 1

apples, 1

fertilizer, 1

gCO_2e per gram, 1

transport, 1

apricots, cyanide in, 1

aquafaba, 1

cake, in, 1

chocolate mousse, 1

eggs replacement, 1

Arctic, 1,

see also ocean

atmosphere

changing, 1

chemistry, 1

Australia, 1

average emissions, 1

bacon, see ham

baked beans, see beans

baked potatoes, 1, 2

baking, eggs in, 1

bananas, 1

gCO_2e per gram, 1

transport, 1

bar charts, see stacks

bath emissions, 1

beans, 1

cocoa, 1

cooking, 1

dried, 1

fertilizer, reduced, 1

flatulence, 1

french, gCO_2e per gram, 1, 2

gCO_2e per gram, 1

green, see french beans

haricot, 1

navy, 1

nitrogen fixed by, 1

pressure cooking, 1

solutions, major, 1

soya, 1

steak, compared, 1

tinned, 1

BECCS, 1,

see also CCS

untested, 1

beef, 1

alternatives, 1

chicken, compared, 1

cow life, 1

dairy, 1

dairy v. prime, 1

deforestation, 1

efficiency, 1

gCO_2e per gram, 1

ham, compared, 1

lamb, compared, 1

manure emissions, 1

manure from, 1, 2

methane, 1, 2

nitrous oxide, 1, 2

prime, 1

prime v. dairy, 1

reducing emissions, 1

solutions, major, 1

soya for, 1

beer, 1

bread, waste, from, 1

draught, 1

fertilizer, 1

gCO_2e per gram, 1

insects as ingredient, 1

transport, 1

bees, see pollinators

beet sugar, 1

beetroot greens, 1

Berry, Mary, 1

big things, 1

bioenergy, 1

CO_2, 1

Bioenergy with Carbon Capture and Storage, see BECCS

biofuels, see bioenergy

bitter almonds, 1

black pudding, 1, 2

black tea, 1

black-eyed bean, drought tolerance, 1

body-building drinks, see whey

bottled water, 1, 2

bottles, 1,

see also cartons

plastic, 1

plastic, glass, compared, 1

plastic, tins, compared, 1

recycling, 1

bottling, see preserving

bowel cancer, 1

boxes

fruit, 1

vegetables, 1

bread, 1

baking efficiency, 1

beer, waste, in, 1

breakfast, 1

driving, compared, 1

factory, 1

fertilizer for, 1

fibre, 1

food waste, reducing, 1

gCO_2e per gram, 1

leftovers, 1

milk, compared, 1

sandwich, in, 1

wheat plants, 1

wholemeal fibre, 1

breadbaskets, 1

breakfast, 1

bread, 1

cereal, 1

coffee, 1

dairy, 1

eggs, 1

higher-emissions, 1

low-emissions, 1

milk, 1

nutrition, 1

reducing emissions, 1

summary, 1

typical-emissions, 1

broiler chicken, 1

buffalo

cheese, 1

ruminants, 1

burps, methane in chicken, 1

cow, see cow, burps

butter

almond, 1

apple pie, in, 1

cake, in, 1

nut, 1

peanut, 1, 2

seed, 1

solutions, major, 1

tikka masala, 1

toast, on, 1

vegetable oil replacing, 1

vegetable spread, compared, 1

cabbage, 1

gCO_2e per gram, 1

cake, 1

reducing emissions, 1

vegan, 1

cancer

bowel, 1

fibre, 1

liver, 1

candy, see sweets

cane sugar, 1

canned, see tinned

canning, see preserving

canteen, see catering

v. home-cooking, 1

cappuccino, 1,

see also latte

car, see driving

carbon

soil, in, 1

trees, in, 1

carbon capture and storage, see CCS

carbon dioxide, see CO_2

cardboard

cups, 1

gCO_2e per gram, 1

carrot, 1, 2

gCO_2e per gram, 1

leaves, 1

cartons,

see also bottles

milk, 1

plastic in, 1

cashew milk, 1

catering food waste, 1, 2

cauliflower, rice, 1

CCS, 1, 2

incentives, 1

cereal, 1,

see also breakfast cereal

breakfast, 1, 2

corn, 1

gCO_2e per gram, 1

milk with, 1

plant milk, with, 1

rice, 1

wheat, 1

CFCs, global warming, 1

changing atmosphere, 1

changing your diet, see diet change

chart, emissions, 1

cheese, 1

alternatives, 1

buffalo, 1

curds in, 1

emissions, 1

gCO_2e per gram, 1

goat, 1

ham, emissions compared, 1

manufacture, 1

nuts, 1

pizza, 1

plant, 1

potato crisps, 1

reducing emissions, 1

rennet, 1

sheep, 1

solutions, major, 1

vegan, 1, 2

gCO_2e per gram, 1

chemistry, atmosphere, 1

cherry tomatoes, 1, 2

cherry, coffee, 1

chicken, 1

beef, compared, 1

broiler, 1

curry, 1

efficiency, 1, 2, 3

farming, 1

feed, 1, 2

emissions, 1

insects, 1

gCO_2e per gram, 1

growth, 1

ham, emissions compared, 1

manure, 1

methane, burps, 1

organic, 1

packaging, 1

per capita, 1

refrigeration, 1

sandwich, 1

solutions, major, 1

tikka masala, 1

transport, 1

chicken-less tikka masala, 1

chickpeas, 1,

see also aquafaba

tikka masala, 1

chips, see fries

chips, potato, see potato crisps

chlorofluorocarbons, see CFCs

chocolate, 1,

see also cocoa

cocoa trees, from, 1

chocolate mousse, 1

aquafaba, 1

citizens influencing government, 1, 2

civil unrest in food shortages, 1

Claire Perry, see Perry, Claire

clean energy

defined, 1

electricity, proportion of, 1

Cleopatra, 1

climate change, 1

animal migration, 1

animal reproduction, 1

Appendix, 1

coastal erosion, 1

food availability, 1

food impacts, 1

global warming, 1

greenhouse gases, 1

ice sheet, melting, 1

income and, 1

malaria, 1

mitigating (food), 1

pollinators and, 1

sea levels, rising, 1

solutions, 1

forests, 1

solar power, 1

CO_2

atmosphere, in, 1

bioenergy, 1

concentration, historical, 1

concentration, rising, 1

food yield, and, 1

forests, removed by, 1

global warming, 1

greenhouse gases, 1

CO_2 equivalent

grams, see gCO_2e

methane, 1, 2

nitrous oxide, 1, 2

co-products

defined, 1

emissions, 1

coastal erosion, 1

cobbler, see apple pie

cochineal from insects, 1

cocoa

beans, 1

deforestation for, 1

fertilizer, 1

gCO_2e per gram, 1

pods, 1

trees, chocolate from, 1

coconut milk, see plant milk

coffee, 1,

see also latte

breakfast, 1

cherry, 1

milk in, 1

seeds, see beans

composting v. landfill, 1

condensation trails, 1

consumers

incentives, 1

subsidies, 1

continental warming v. ocean, 1, 2

cooking

beans, 1

cake, 1

eggs, energy required, 1

emissions, 1

potato crisps, 1

corn, breakfast cereal, 1

country-sized statistics, 1

cow

burps, methane, 1, 2, 3, 4

daily growth, 1

daily intake, 1

diet, methane, effect on, 1

efficiency, 1

farts, methane, 1

grass feed, 1

life, beef, 1

life, effect on emissions, 1, 2

methane, 1

methane per day, 1

pasture-fed, 1

pat, see manure

poo, see manure

cow pea, see black-eyed bean

cows’ milk,

see also milk

almond milk, compared, 1

cream, 1,

see also butter,

see also milk

apple pie, in, 1

cake, in, 1

gCO_2e per gram, 1

nuts replacing, 1

scrambled eggs, with, 1

tikka masala, 1

yogurt replacing, 1

crickets, 1

crisps, see potato crisps

crumble, see apple pie

cups, 1

curds, 1

cheese, in, 1

curry, 1

chicken, 1

cyanide in fruit, 1

dairy

breakfast, 1

vegetable oil replacement, 1

dairy beef, 1

prime, v., 1

David MacKay, see MacKay, David

deforestation

animal efficiency, 1

beef, 1

cocoa, for, 1

cups, disposable, 1

international agreements, 1

organic, reduced from, 1

problems caused, 1

soya, 1, 2, 3, 4

sweets, for, 1

Delia Smith, see Smith, Delia

demand, food, increasing, 1

Denmark fat tax, 1

dessert, 1

detailed figures v. gut feeling, 1

diabetes, type II, 1

diet

Mediterranean, 1

specialist, 1

ultra-low-emissions, 1

vegan, 1

vegetarian, 1

diet change, 1

10+% effect, 1

100% or not, 1

difficulties, 1

incentives, 1

medical advice for, 1

minerals, 1

protein, 1

vitamin B12, 1

vitamins, 1

dietary guidelines, 1

broader scope, 1

fruit, 1

health, 1

meat, 1

sugar, 1

vegetables, 1

vitamin D, 1

dinner, see evening meal

disposable cups, 1

donkey cheese, 1

double counting, see co-products

draught beer, 1

dried beans, 1

drinks, 1

leftovers, 1

packaging, 50%, 1

take-out, 1

driving

bread, compared, 1

emissions, 1

gCO_2e per gram, 1

rice, compared, 1

steak, compared, 1

droughts, 1, 2

tolerant plants, 1

drying, see preserving

duckweed, chicken feed, 1

Earth system feedback, 1

ebook version, 1

edible food waste, 1

edible v. inedible food waste, 1

efficiency

animal, 1

animal v. plant, 1

beef, 1

chicken, 1, 2, 3

cows, 1

ham, 1

plant v. animal, 1

vertical farms, 1

eggs, 1

aquafaba replacement, 1

baking, 1

breakfast, 1

cake, in, 1

chicken feed, 1

chocolate mousse, 1

cooking, 1

energy in cooking, 1

gCO_2e per gram, 1

mayonnaise, 1

omelette, 1

pancake, 1

reducing emissions, 1

scrambled, 1, 2

solutions, major, 1

substitutes, 1

elections, impact of, 1

electricity

clean energy, proportion, 1

fossil fuels, proportion from, 1

gCO_2e per gram, 1

toast, for, 1

elephant, hindgut fermenter, 1

emissions

by country, 1, 2, 3

chart, 1

cheese, 1

chicken feed, 1

co-products, 1

fertilizer, 1

fish, 1

fish farming, 1

fish size, by, 1

fishing, fuel, 1

food, whole day, 1

frozen food, 1

green vegetables, 1

labelling, see food labelling

non-CO_2, 1

per person per day, 1, 2

3 kgCO_2e, 1

6 kgCO_2e, 1

protein, chart, 1

pub, 1

reducing, see reducing emissions

taxes, 1

tins, 1

vegan, 1

vegetarian, 1

whole day food, 1

yardstick, 1

emissions budget

1.5°C, 1, 2

2030, 1

2050, 1

CO_2 component, 1

defined, 1

non-CO_2 component, 1

emissions, food

25% of total, 1

components of, 1

map, 1

non-food, compared, 1

production method effect, 1

emissions, personal, see flatulence

endnotes, 1

enteric fermentation, 1

errata, 1

espresso, 1,

see also latte

evening meal, 1

air transport, 1

higher-emissions, 1

low-emissions, 1

reducing emissions, 1

steak, 1

summary, 1

typical-emissions, 1

extreme weather, 1

factory bread, 1

fairness, food, 1

farmers, see producers

farming

area used, 1

chicken, 1

fish, 1

organic v. conventional, 1

subsidies, 1

vertical, 1

farmland, repurposing, 1, 2

farts, see flatulence

feastarians, 1

feedback, Earth system, 1

fermentation, enteric, 1

Ferriss, Tim, 1

fertilizer

almonds, 1

ammonium nitrate, 1

apples, 1

beans, 1

beer, 1

bread, 1

cocoa, 1

emissions, 1

manure, 1

nitrous oxide, 1

peanuts, 1

plant milk, 1

rice, 1

tomatoes, 1

vegetables, 1

vertical farms, 1

wine, 1

fibre

bread, in, 1

cancer, 1

flatulence and, 1

whole day, 1, 2

fish, 1

chips, and, 1

decreasing numbers, 1

emissions, 1

emissions by size, 1

farming, 1, 2

emissions, 1

soya, 1

wheat, 1

feed, 1

insects, 1

fuel emissions, 1

gCO_2e per gram, 1, 2

increasing numbers, 1

pie, 1

reducing emissions, 1

reducing emissions, 1

solutions, major, 1

fizzy drinks

everywhere, 1

gCO_2e per gram, 1

plastic bottles, 1

flatulence

fibre and, 1

methane, 1

floods, 1

flour

cake, in, 1

gCO_2e per gram, 1

insects, 1

flying

emissions, 1

steak, compared, 1

food

climate change impacts, 1

climate change, mitigating, 1

demand increasing, 1

fresh, frozen compared, 1

future trends, 1

income and consumption, 1

innovation in, 1

international trade, 1

non-perishable, 1

perishable, 1

prices, civil unrest, 1

rainfall and yield, 1

shortages, 1

temperature and yield, 1

transport, air, 1

unhealthy, taxes, 1

wild v. cultivated, 1

yield decreases, 1

yield increases, 1

yield, CO_2 and, 1

food fairness, 1

food labelling, 1

influencing behaviour, 1

mandatory, 1, 2

need for, 1

traffic light, 1

trial (2008), 1

food packaging, see packaging

food production v. solar power, 1

food shortages, French Revolution, 1

food waste, 1,

see also leftovers

30% of total, 1

bread, saving, 1

by age, 1

catering, 1, 2

catering, 10%, 1

constituents, 1

home, 70%, 1

landfill, 1

reducing emissions, 1

top tips, 1

vegetable box and, 1

forests, CO_2 removed by, 1

fossil fuels

clean energy proportions, 1

electricity, proportion of, 1

greenhouse gases, 1

freeze-dried insects, 1

freezer as innovation, 1

freezing, see preserving

freight, sea, see transport, sea

french beans

gCO_2e per gram, 1, 2

nitrogen, fix, 1

fresh v. frozen food, 1

fries, 1, 2

gCO_2e per gram, 1

oven emissions, 1

processing, 1

frozen food

emissions, 1

refrigeration, 1

v. fresh, 1

fruit, 1

boxes, 1

dietary guidelines, 1

soft, 1

storing, long-term, 1

transport, 1

winter, 1

fuel, fishing, emissions, 1

gCO_2e defined, 1

gCO_2e per gram

almonds, 1

aluminium can, 1

apples, 1

bananas, 1

beans, 1

baked, 1

french, 1, 2

tinned, 1

beef, 1

beer, 1

bread, 1

cabbage, 1

cardboard, composted, 1

cardboard, landfill, 1

carrots, 1

cereal, 1

cheese, 1

vegan, 1

chicken, 1

cocoa, 1

cod, 1

cream, 1

driving, 1

eggs, 1

electricity, 1

fish, 1, 2

fizzy drinks, 1

flour, 1

french beans, 1, 2

fries, 1

glass, 1

ham, 1

lamb, 1

landfill, cardboard, 1

lettuce, 1

lighting, 1

milk, 1, 2

milk powder, 1

orange juice, 1

oranges, 1

peanut butter, 1

peanuts, 1

plant milk, 1

plastic, 1

potato crisps, 1

potatoes, 1

Quorn, 1

raspberries, 1

recycled plastic, 1

relish, 1

rice, 1

salmon, 1

sea transport, 1

spaghetti bolognese, 1

spices, 1

steak, 1

steel, 1

strawberries, 1

sugar, 1

sweetcorn, 1

tap water, 1

tea, 1

tin can, 1

aluminium, 1

tomatoes, 1

tomatoes, greenhouse, 1

train, 1

transport

air, 1

sea, 1

truck, 1

vegan cheese, 1

vitamin tablets, 1

water heating, 1

water, tap, 1

wine, 1

yogurt, 1

genetic engineering, 1

genetically modified yeast, 1

giga defined, 1

glass, gCO_2e per gram, 1

global warming, 1

“global” defined, 1

climate change, 1

goat

cheese, 1

ruminants, 1

goop, grey, 1

Gore, Tim, 1

government

citizens influencing, 1, 2

international action, 1

role of, 1

grass, cow feed, 1

green beans, see french beans

green vegetables, 1

greenhouse effect, 1

greenhouse gases, 1

climate change, 1

CO_2, 1

emissions defined, 1

fossil fuels and, 1

methane, 1

nitrous oxide, 1

greenhouses v. vertical farms, 1

grey goop, 1

grill, oven, compared, 1

groundnuts, 1,

see also peanuts

GROW Campaign, Oxfam, 1

growth, chicken, 1

Gt defined, 1

gut feeling v. detailed figures, 1

gut health, 1

ham, 1,

see also pigs

beef, compared, 1

cheese, compared, 1

chicken, compared, 1

dry-cured, 1

efficiency, 1

gCO_2e per gram, 1

pizza, 1, 2

reducing emissions, 1

solutions, major, 1

haricot beans, 1

health, 1

dietary guidelines, 1

heating emissions, 1

heatwaves, 1

hemp milk, see plant milk

herbs, 1

higher-emissions

breakfast, 1

evening meal, 1

lunch, 1

snacks, 1

whole day, 1

hindgut fermenters

elephants, 1

horses, 1

rabbits, 1

v. ruminants, 1

home, food waste, 70%, 1

home-cooking

canteen, v., 1

tinned, v., 1

horse

cheese, 1

hindgut fermenter, 1

hot chocolate, 1

house, selling your, 1

ice sheet, melting, 1

imperial ton, see tonne

incentives,

see also taxes

CCS, 1

consumers, 1

diet change, 1

producers, 1

income

food consumption and, 1

rising, and climate change, 1

inedible food waste, 1

inedible v. edible food waste, 1

inefficiency

animal, see animal efficiency

influencing others, 1

innovation in food, 1

insectivore, 1

defined, 1

insects

as food, 1

beer, ingredient, 1

chicken feed, 1

cochineal, 1

fish feed, 1

flour, 1

freeze-dried, 1

international trade, food, 1

jam, toast and, 1

Jamie Oliver, see Oliver, Jamie

Jean-Baptiste Moreau, see Moreau, Jean-Baptiste

jelly, see jam

juice, orange, see orange juice

juices, 1

kangaroo, 1

lab protein, 1

labelling, see food labelling

lactic acid, 1

lactose, 1

lamb

beef, compared, 1

gCO_2e per gram, 1

solutions, major, 1

tikka masala, 1

landfill

cardboard

gCO_2e per gram, 1

composting, v., 1

cups, 1

food waste, 1

methane, 1, 2

plastic bottles, 1

latte, 1, 2

laughing gas, see nitrous oxide

laws

seat belt, 1

smoking, 1

leftovers, 1, 2

bread, 1

drinks, 1

pig food, 1, 2

salad, 1

vegetables, 1

legumes, see beans

lentils, solutions, major, 1

lettuce, 1

gCO_2e per gram, 1

lifetime, methane, 1, 2

lighting

emissions, 1

gCO_2e per gram, 1

little things, 1

liver cancer, 1

locusts, 1

low-emissions

breakfast, 1

evening meal, 1

lunch, 1

snacks, 1

whole day, 1

lunch, 1

higher-emissions, 1

low-emissions, 1

reducing emissions, 1

summary, 1

typical-emissions, 1

luxuries, 1

macadamia milk, see plant milk

MacKay, David, 1, 2

stacks (bar charts), 1

making a difference, 1

malaria, climate change and, 1

manure, 1

beef, from, 1, 2

chicken, 1

effect on beef emissions, 1

effect on milk emissions, 1

fertilizer, 1

handling, 1

methane from, 1, 2

nitrogen in, 1

nitrous oxide from, 1, 2, 3

oxygen, effect of, 1

pigs, quantity, 1

slurry pit, 1

marmalade, orange, 1

Marmite, see vegetable spread

Mary Berry, see Berry, Mary

mayonnaise, eggs in, 1

meal alternatives, 1

meal worms, 1

meat

dietary guidelines, 1

increasing consumption, 1

low-emissions, taxes?, 1

nutrition, 1

pizza, 1, 2

taxes, 1

Meat-free Mondays, 1

medical advice, diet change, 1

Mediterranean diet, 1

methane

almond milk, from, 1

beef, 1, 2

chicken burps, 1

CO_2 equivalent, 1, 2

cow, 1

cow burps, 1, 2, 3, 4

cow diet, affected by, 1

cow farts, 1

cow, per day, 1

global warming, 1

greenhouse gases, 1

landfill, 1, 2

lifetime, 1, 2

manure, 1, 2

paddy fields, 1

permafrost, 1, 2

ruminants, 1

wetlands, 1

metric tonne, see tonne

microbes, nitrous oxide from, 1

microplastics, 1

microwave

conventional oven, v., 1

potatoes, 1

migration, animal, 1

milk, 1,

see also butter,

see also cream,

see also milk powder

almond, see almond milk

alternatives, see plant milk

annual cycle, 1

bread, compared, 1

breakfast, 1

breakfast cereal, 1

cartons, 1

cereal, with, 1

coffee, in, 1

cow life, effect of, 1

gCO_2e per gram, 1, 2

manure emissions, 1

plant, 1

powder, gCO_2e per gram, 1

reducing emissions, 1

semi-skimmed, 1

skimmed, 1

tea, in, 1

minerals, diet change, 1

mixed nuts, 1

Moreau, Jean-Baptiste, 1

mould, toxins, 1

mycoprotein, 1,

see also Quorn

navy beans, 1

nitrogen

beans, fixed by, 1

french beans fix, 1

manure, in, 1

nitrogen fertilizers, see fertilizers

nitrous oxide

beef, from, 1, 2

CO_2 equivalent, 1, 2

fertilizers, 1

global warming, 1

greenhouse gases, 1

laughing gas, 1

manure, from, 1, 2

microbes, from, 1

non-CO_2 emissions, 1

non-food emissions

bath, 1

cooking, 1

driving, 1

flights, 1

food, compared, 1

heating, 1

lighting, 1

oven, 1

shower, 1

train, 1

non-perishable food, 1

air transport, 1

non-ruminants

donkey, 1

horse, 1

North Pole, 1

nut butter, 1

nut cheese, 1

nutrition,

see also fibre,

see also protein,

see also vitamins

animal efficiency, 1

breakfast, 1

meat, 1

whole day, 1, 2

nuts, 1, 2,

see also almonds,

see also peanuts

allergies, 1

cream, replacing, 1

defined, 1

mixed, 1

oat milk, see plant milk

obesity

cost, 1

incidence, 1

sugar tax and, 1

ocean warming, 1

continental, v., 1, 2

Oliver, Jamie, 1

omelette, eggs in, 1

on tap beer, see draught beer

orange juice, 1,

see also juices

gCO_2e per gram, 1

plastic bottles, 1

orange marmalade, 1

oranges, 1

gCO_2e per gram, 1

transport, 1

organic

chicken emissions, 1

deforestation reduced, 1

farming, v. conventional, 1

out-of-season v. seasonal, 1

oven

apple pie, 1

cake, 1

conventional v. microwave, 1

emissions, 1, 2

fries, 1

pizza, 1

potatoes, 1

grill, compared, 1

Oxfam’s GROW Campaign, 1

oxygen, effect on manure, 1

packaging

almond milk, 1

chicken, 1

drinks, 1

plant milk, 1

potato crisps, 1

Paddington Bear, 1

paddy fields

methane, 1

rice, 1, 2

pancake, eggs in, 1

parsnip, 1

passata, 1

pastry, apple pie, 1

pasture-fed cows, 1

peaches, cyanide in, 1

peanut butter, 1, 2

gCO_2e per gram, 1

peanuts, 1

fertilizer, 1

gCO_2e per gram, 1

peas, solutions, major, 1

pepperoni pizza, 1

peppers, 1

perishable food, 1

permafrost, methane, 1, 2

Perry, Claire, 1

personal emissions, see flatulence

pickling, see preserving

pie, fish, 1

reducing emissions, 1

pig food

leftovers, 1, 2

seed cake, 1

soya, 1

wheat, 1

pig out, 1

pigs,

see also ham

food consumption, 1

lifecycle, 1

manure, quantity, 1

weight gain, 1

pigs’ blood, 1

pizza, 1

cheese, 1

ham, 1, 2

meat feast, 1, 2

oven emissions, 1

pepperoni, 1

reducing emissions, 1

plant

accelerated breeding, 1

cheese, 1

efficiency, v. animal, 1, 2

plant milk, 1,

see also almond milk

cereal, with, 1

gCO_2e per gram, 1

plant-based alternatives, 1

plastic

bags, taxes, 1

bottles, 1

fizzy drinks, 1

landfill, 1

orange juice, 1

water, 1

cartons, in, 1

cups, disposable, 1

gCO_2e per gram, 1

recycled, 1

yogurt pot, 1

pods, cocoa, 1

polar bear, 1

pollinators, climate change, 1

polytunnels, 1

vertical farms, compared, 1

poo, see manure

population

by year, chart, 1

rising, 1

pork, see ham

potato chips, see potato crisps

potato crisps, 1

cheese, 1

cooking, 1

everywhere, 1

gCO_2e per gram, 1

packaging, 1

processing, 1

potato wedges, 1

potatoes, 1,

see also fries baked, 1, 2

cooking, 1

gCO_2e per gram, 1

growing, 1

microwave, 1

oven emissions, 1

reducing emissions, 1

pre-prepared meals, 1

preserving vegetables, 1

pressure cooking beans, 1

prime beef, 1

dairy, v., 1

processing

almond milk, 1

fries, 1

plant milk, 1

potato crisps, 1

producers, incentives, 1

production method, effect, 1

protein

cheese, vegan, 1

diet change, 1

emissions, chart, 1

lab, 1

mycoprotein, 1

Quorn, 1

vegan cheese, 1

whey, 1

whole day, 1

pub emissions, 1

pulses, solutions, major, 1

Quorn, 1,

see also mycoprotein

gCO_2e per gram, 1

tikka masala, 1

rabbits, hindgut fermenters, 1

rainfall, 1

food yield and, 1

range v. single-no. estimate, 1

raspberries

air transport, 1

gCO_2e per gram, 1

recycled plastic, 1

gCO_2e per gram, 1

recycling

bottles, 1

tins, 1

reducing emissions

almond milk, 1

apple pie, 1

beef, 1

breakfast, 1

cake, 1

cheese, 1

eggs, 1

evening meal, 1

fish, 1

pie, 1

food waste, 1

ham, 1

lunch, 1

milk, 1

pie, fish, 1

pizza, 1

potatoes, 1

rice, 1

sandwich, 1

snacks, 1

tikka masala, 1, 2

tomatoes, 1

refrigerated transport, 1

refrigeration, 1

chicken, 1

emissions cost, 1

frozen food, 1

plant milk, 1

salad, 1

vegetables, 1

regional warming, 1

relish, gCO_2e per gram, 1

rennet, in cheese, 1

reproduction, animal, 1

repurposing farmland, 1, 2

restaurant, see catering

rice, 1

alternatives, 1

breakfast cereal, 1

cauliflower, 1

gCO_2e per gram, 1

reducing emissions, 1

rice milk, see plant milk

riots, see civil unrest

rumen, 1

defined, 1

ruminants

buffalo, 1

defined, 1

goat, 1

hindgut fermenters, v., 1

methane, 1

sheep, 1

salad, 1

leftovers, 1

refrigeration, 1

winter, 1

salmon, 1

gCO_2e per gram, 1

sandwich, 1

bread emissions, 1

chicken, 1

reducing emissions, 1

steak, 1

toasted, 1

vegetable spread in, 1

sausage, 1

scrambled eggs, 1, 2

scurvy, 1

sea freight, see transport, sea

sea ice, 1

sea levels, rising, 1

sea transport, see transport, sea

seasonal v. out-of-season, 1

seat-belt laws, 1

seed butter, 1

seed cake, pig food, 1

seeds, 1,

see also nuts

semi-skimmed milk, 1

shakes, meal alternatives, 1

sheep

cheese, 1

ruminants, 1

shower emissions, 1

single-no. estimate v. range, 1

skimmed milk, 1

slugs, 1

slurry pit, manure, 1

Smith, Delia, 1

smoking

laws, 1

taxes, 1

smoothies, 1

snacks, 1

higher-emissions, 1

low-emissions, 1

reducing emissions, 1

summary, 1

typical-emissions, 1

snow, global warming, 1

soda, see fizzy drinks

soft drinks, 1

soft fruits, 1

soil, carbon in, 1

solar farms, 1

solar power, 1

food production, v., 1

solar radiation, global warming, 1

solutions

climate change, 1

major, 1

unimportant, 1

soya

Argentina, big producer, 1

beans, 1

beef, for, 1

Brazil, big producer, 1

chicken feed, 1

deforestation, 1, 2, 3, 4

fish farming, 1

pig food, 1

producers, main, 1

soya milk, see plant milk

spaghetti bolognese, 1

gCO_2e per gram, 1

specialist diet, 1

spices

gCO_2e per gram, 1

tikka masala, 1

spinach, 1

stacks

explained, 1

MacKay, 1

statistics, country-sized, 1

steak, 1

beans, compared, 1

cow life, effect of, 1

driving, compared, 1

evening meal, 1

flying, compared, 1

gCO_2e per gram, 1

non-food comparisons, 1

sandwich, 1

steel, gCO_2e per gram, 1

storage

almond milk, 1

storms, 1, 2

strawberries, 1

gCO_2e per gram, 1

transport, 1

subsidies, 1

consumers, 1

farming, 1

reducing high-emission, 1

substitutes, see alternatives

sugar, 1

beet, 1

cake, in, 1

cane, 1

chocolate mousse, 1

dietary guidelines, 1

gCO_2e per gram, 1

tax, 1, 2, 3

obesity and, 1

transport, 1

summary

breakfast, 1

evening meal, 1

lunch, 1

snacks, 1

supper, see evening meal

Sustainable Energy – Without the hot air, 1

sweetcorn, gCO_2e per gram, 1

sweets, 1

deforestation for, 1

take-out drinks, 1

tap water, 1

gCO_2e per gram, 1

taxes, 1

emissions, 1

fat, Denmark, 1

meat, 1

plastic bags, 1

smoking, 1

sugar, 1, 2, 3

unhealthy food, 1

tea, 1

black, 1

gCO_2e per gram, 1

milk in, 1

transport, 1

water heating, 1

temperature

food yield and, 1

toxins and, 1

tikka masala, 1

chicken, 1

chicken-less, 1

Quorn, 1

reducing emissions, 1, 2

Tim Ferriss, see Ferriss, Tim

Tim Gore, see Gore, Tim

tinned

beans, 1

home-cooking, compared, 1

vegetables, 1

tins, 1

emissions, 1

gCO_2e per gram, 1, 2

glass bottle, compared, 1

minor contribution, 1

plastic bottle, compared, 1

recycling, 1

toast, 1, 2

butter on, 1

electricity for, 1

jam and, 1

toastie, see sandwich, toasted

tofu, 1

tomato puree, 1

tomato sauce, 1

tomatoes, 1

cherry, 1, 2

fertilizer for, 1

gCO_2e per gram, 1

greenhouse

gCO_2e per gram, 1

reducing emissions, 1

tikka masala, 1

ton, see tonne

tonne defined, 1

top tips, food waste, 1

toxins

mould, 1

temperature and, 1

train

emissions, 1

gCO_2e per gram, 1

transport

air

evening meal, 1

food, 1

gCO_2e per gram, 1

raspberries, 1

sea, compared, 1

solutions, major, 1

vegetables, 1

almond milk, 1

apples, 1

bananas, 1

beer, 1

chicken, 1

fruit, 1

non-perishable food, 1

oranges, 1

plant milk, 1

refrigerated as innovation, 1

sea, air, compared, 1

sea, gCO_2e per gram, 1

strawberries, 1

sugar, 1

tea, 1

truck, 1

gCO_2e per gram, 1

vegetables, 1

wine, 1

trees, carbon in, 1

truck transport, 1

gCO_2e per gram, 1

turnip, 1

leaves, 1

type II diabetes, 1

typical-emissions

breakfast, 1

evening meal, 1

lunch, 1

snacks, 1

whole day, 1

ultra-low-emissions diet, 1

US emissions/p/d, 1, 2

vegan, 1

cake, 1

cheese, 1, 2

gCO_2e per gram, 1

protein, 1

vitamins, 1

cheese, ingredients, 1

cheese, nutrition, 1

defined, 1

emissions, 1

Veganuary, 1

Vegemite, see vegetable spread

vegetable box, food waste, 1

vegetable oil

butter, replacing, 1

dairy replacement, 1

vegetable spread

butter, compared, 1

sandwich, in, 1

vegetables, 1,

see also salad

air transport, 1

boxes, 1

dietary guidelines, 1

fertilizer for, 1

leftovers, 1

preserving, 1

refrigeration, 1

tinned, 1

transport, 1

winter, 1

wonky, 1

vegetarian, 1

defined, 1

emissions, 1

vertical bars, see stacks

vertical farms, 1

vitamin B 1

diet change, 1

whole day, 1

vitamin D

dietary guidelines, 1

whole day, 1, 2

vitamins

cheese, vegan, 1

diet change, 1

gCO_2e per gram, tablets, 1

vegan cheese, 1

volcanoes, global warming, 1

warming, regional, 1

water

almonds, 1

bottled, 1, 2

plastic bottles, 1

rice, 1

tap, 1

gCO_2e per gram, 1

water heating

gCO_2e per gram, 1

tea, 1

wee, animal, see manure

wetlands and methane, 1

wheat

bread, for, 1

breakfast cereal, 1

chicken feed, 1

fish farming, 1

pig food, 1

whey, 1

whey protein, 1

whole day

fibre, 1, 2

food emissions, 1

nutrition, 1, 2

protein, 1

vitamin B 1, 2

vitamin D, 1, 2

wholemeal bread, 1

wild food, 1

wine, 1

fertilizer, 1

gCO_2e per gram, 1

transport, 1

winter

fruit, 1

salad, 1

vegetables, 1

wonky vegetables, 1

world book, 1

yardstick

3 kgCO_2e, 1

emissions budget, 1

yeast extract, see vegetable spread

yeast, genetically modified, 1

yogurt, 1

cream, replacing, 1

gCO_2e per gram, 1

plastic pot, 1

Acknowledgements

I am very grateful to the team at UIT Cambridge / Green Books and especially my editor, Niall Mansfield, for lots of patience, excellent suggestions and for deeply understanding the subject and style of what I was trying to write. I am indebted to Althea Wilkinson for tireless work and encouragement, particularly on the endnotes and references – this book would have had many fewer references without you. I am extremely grateful to Angelina Frankowska for many hours of invaluable discussions about the emissions numbers and references, and to Christian Reynolds and Ximena Schmidt, for loads of fun and thought-provoking conversations and ideas that influenced this book.

I am very grateful to Joseph Poore for answering numerous questions about his dataset. Huge thanks to Hannah Ritchie for making Fig. 1.1 and providing the data to make Fig. 3 of appendix “Climate change”. Thank you to Christian Holler for writing and helping me get set up using the latex files on which this book is based. Thanks to Ben Dare for fixing many LaTeX issues and references. Thanks to Ant Holloway for the sleeve photo of the author.

I am especially grateful for detailed comments from Jeff Forshaw, Bojana Bajzelj, James Hand, Aled Jones, Ed Pope, Rick Bruintjes, Adam Amara, Pete Smith, John Bridle, Nicola Terry, Ro Randall, Tom Heap, Tim Williams, Alison Fletcher, Andrew Markwick, Eileen Jensen, Oliver Jensen, Katherine Denby, Isobel Atkin, and Tom Quested.

I am also grateful for helpful discussions with Claire Abbott, Jade Ajagun-Brauns, Ursula Arens, Ali Birkett, Myles Allen, Tim Benton, Renata Bertazzi Levy, David Bodanis, Benjamin Bodirsky, Ian Boyd, David Brightman, John Crawford, Neil Chalmers, Joanne Cook, Sue Davies, Jane Dennet-Thorpe, Bob Doherty, Helen Downie, David Drewry, Maia Elliott, Jack Elvin-Poole, Lisa Emberson, Joe Fennell, Helen Ferrier, Les Firbank, Jeff Fordham, Emma Foster, Lucy Foster, Emma Garnett, Tara Garnett, Rosie Green, Bruce Grieve, Howard Griffiths, Joanna Groves, Jason Halford, Rachael Hand, Duncan Harding, Jennie Hargreaves, Francesca Harris, Flora Hetherington, Leah Holmes, Hugh Hunt, Matt Holl, Claire Hoolohan, Julian Huppert, John Ingram, Tim Jervis, Lisa Johnson, Tilly Johnson, Anthony Jones, Alana Kluczkovski, Laura Knowlson, Elmar Kriegler, Ilias Kyriazakis, Tim Lang, India Langley, Carys Lavin, Alice Larkin, Henry Leveson-Gower, Melissa Lord, Mark Lynas, Jennie Macdiarmid, Andrew Markwick, Rachel Marshall, Wayne Martindale, Niall MacCrann, Carly McLachlan, John Mclaughlin, Geoff McBride, Lauryn McLaughlin, Dale Mellor, Mark Miodownik, Hugh Mortimer, Jo Mylan, Emma Nichols, Ian Noble, Victor Okafor, Katie Percival, Martyn Poliakoff, Caroline Pung, Mark Reed, Martin Rees, Maria Sanchez Poncela, Andrea Scalco, Ruth Slater, Elta Smith, Bjoern Soergel, Luke Spadavecchia, Laurence Stamford, James Stockdale, Sara Summerton, Savvas Tassou, Jacqueline Tereza da Silva, Sara Turnbull, Pippa Tyrell, Peter Wooton-Beard, Lucy Yates and Joe Zuntz.

Thanks to the University of Manchester for supporting me while writing this book, and for paying to enable the book to be available for free online. I have also been supported in this work by funding from N8 Agrifood, STFC, the University of Manchester and a University of Manchester Wellcome Trust Manchester Institutional Strategic Support Fund award [204796/Z/16/Z].

I am also grateful to the Greenhouse Gas and Dietary choices Open-source Toolkit (GGDOT) team and the Take a Bite out of Climate Change (takeabitecc) team, and all the anonymous people who asked pertinent questions in my talks and at GGDOT and takeabitecc events. Thanks also to all my colleagues for their patience when I kept disappearing to work on this book.

Most of all, huge thanks to my family Keith, Scott, Jasmine, Mum and Dad for all your encouragement, support and interest, and for many excellent ideas and questions which changed how I wrote the book.

Copyright

First published in 2020, in England, by

UIT Cambridge Ltd.

PO Box 145

Cambridge

CB4 1GQ

England

Tel: +44 1223 302 041

Web: www.uit.co.uk

Copyright © 2020 UIT Cambridge Ltd.

All rights reserved.

Without the hot air® is a registered trademark of UIT Cambridge Ltd.

Sarah Bridle has asserted her right to be identified as the author of this work in accordance with the Copyright, Designs and Patents Act 1988.

The information and instructions in this book have been included for their instructional value. Neither the publisher nor the author offers any warranties or representations in respect of their fitness for a particular purpose, nor do they accept any liability for any loss or damage arising from their use. Neither the publisher nor the author makes any representation, express or implied, with regard to the accuracy of information contained in this book, nor do they accept any legal responsibility or liability for any errors or omissions that may be made. This work is supplied with the understanding that UIT Cambridge Ltd and its authors are supplying information, but are not attempting to render professional or other services.

The publishers have endeavoured to contact all copyright holders, but will be glad to correct in future editions any inadvertent omissions brought to their notice.

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. UIT Cambridge Ltd acknowledges trademarks as the property of their respective owners.

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