Food and Climate Change
On average about one quarter of rich-world climate emissions come from our food. However, the foods you choose and how they are produced, transported, stored and prepared make a huge difference. The best and worst diets differ in their climate impact by a factor of ten or more!
This page is an homage to Sarah Bridle's fabulous book "Food and Climate Change without the Hot Air", which reviews the scientific literature and serves it up in easy-to-digest portions. The book explains the climate impacts of the main foods in the Western diet, measured in gCO2e/g food. That's the amount of CO2 (or its equivalent) released into the atmosphere per amount of food prepared. I've tried to summarise the most interesting findings.
Food Climate League Table
The tables below present the climate impact of various foods and transportation and preparation methods.
- These figures are typical or average numbers; the real numbers vary depending on the methods of production and storage.
- These figures are for current methods of production and storage - please see Low-Carbon Food Future (below) for what can be improved in future and what probably can't.
- You guessed it! most fruit and vegetables are at the "good" end of this spectrum.
- Because cows' milk is mostly water, it comes out low per gram; but it's often consumed in large quantities.
- Dairy beef is sourced from the male calves of the dairy cows and from retired dairy cows.
The climate impact of the method used for cooking needs to be added to the impact of the food itself and can make a big difference:
- "1 (oven-)baked potato", "4 (oven-)baked potatoes" (in one batch) and "Microwaved potato" compare different ways to cook baked potato: baking a one-person meal in the oven is bad! - see How Many Baked Potatoes Make a Microwave?
- "Boil for 1 40min" shows the climate impact of boiling 125g (final weight) of beans from dry in an open pan for 40 minutes.
- "Pressure-cooker bulk" shows the impact of cooking four 125g portions of beans for 20 minutes in a pressure-cooker.
Vegetarianism vs Veganism
A vegan diet is likely to be most climate-friendly but care is required. A diet including small portions of pork, chicken and eggs is less damaging than a plant-based diet high in either air-freighted fruit and veg or out-of-season salad, which needs to be grown in a heated greenhouse.
A vegetarian diet is likely to cause a lower climate impact than an omnivorous diet. However, a vegetarian diet high in cheese is worse than a non-vegetarian diet avoiding red meat and dairy.
Globally, about one third of food is wasted. In western cultures more than half of that food waste is caused by individuals at home.
- My friend Neil Wilson from Camfridge told me that if fridge shelves were labelled to instruct us which items should be stored where, it would, by reducing wastage, lead to a greater reduction in carbon emissions than his low-energy fridge system.
- Food waste and scraps that go to landfill decompose into methane, with an impact of 3gCO2e/g food. It's better to compost them; even better: use for animal food; absolute best, if safe: feed to hungry humans! eg Oddbox.
I've always been suspicious that food miles take no account of the means of transport. This chart makes this clear:
- The climate impact of shipping an apple 20,000km from NZ or a banana 7,000km across the Atlantic is small compared to the carbon cost of growing, storing and retailing; and small compared to most other foodstuffs.
- A local in-season tomato is best but a tomato trucked from a sun-warmed polytunnel in southern Spain has a minuscule carbon footprint compared to one grown out of season in a heated greenhouse in the UK.
Food Square Miles
Some of the climate impacts calculated for animal agriculture come from the emissions caused where the Amazon and other rainforest is cleared to grow animal feed eg soya.
The converse is also true. 75% of the world's agricultural land is used directly for animal agriculture or indirectly for growing animal feed. This provides 25% of calories consumed by the world population. The other 25% of the world's agricultural land supplies 75% of the world's calories from plant-based food.
If all humans switched to a vegan diet, only 40% of current agricultural land would be required to grow our food. The redundant 60% could be used for renewable energy generation, to grow biofuels and to capture carbon by growing trees - see Geo-engineering By Reforesting.
- Climate science warns that rising temperatures lead to droughts, crop failure and mass starvation of millions of humans. If the humans in the rich world switch towards a more plant-based diet, the planet should be able to supply food for everyone even if half our crops failed.
- If you've ever donated money for famine relief, you might achieve similar by reducing the amount of animal-based food you consume: reducing competition for limited food and leaving more to go round.
Low-Carbon Food Future
We will be able to reduce the climate impact of our diets. For example:
- One basic step that governments and food retailers should take is standardised emissions-labelling.
- Lab-grown meat and dairy might sound weird, but they will radically alter the carbon maths for these foods. This could be particularly useful for cheese-loving vegetarians.
- Salad can be grown out-of-season in Northern Europe without breaking our carbon budget. Vertical farming allows the cultivation of salad (and other seasonal crops) in well-insulated buildings under artificial light, with consequently far lower carbon emissions.
- As we electrify agricultural machinery, food-processing plants and surface transport, and generate more of that electricity from renewable sources, the climate impact of many foods will reduce.
On the other hand, I can't see any way to reduce the large climate impact of the following:
- Traditional beef, lamb and dairy: we can tweak the animal feed to get a small improvement but these animals inevitably produce a massive amount of methane through their lifetime.
- Ammonium nitrate: about 1% of the fertiliser applied to fields ends up as nitrous oxide (a potent greenhouse gas) in the atmosphere; typically for plant-based foods, about one third of the climate impact comes from the fertiliser.
- Air freight: when we switch planes to run on biofuels, air-freighted food will likely become prohibitively expensive - see Carbon-Neutral Flying.
The book is packed with practical climate data on many more foods and food processes eg rice, tea, alcohol, fish, freezing, canning, organic, packaging. So please buy a copy: "Food and Climate Change without the Hot Air".
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