The Climate Impact of Eating Animal Products
Food and Its Link to Climate Change
The climate impact of eating animal products is tremendous due to its contribution to greenhouse gas (GHG) emissions. Food production accounts for one–quarter of the world’s total greenhouse gas emissions and takes up half of the planet’s habitable surface. Meat has had a particular impact on land. The mass of animals raised for slaughter on Earth now outweighs wildlife by a factor of 15–to–1. This is equivalent to for every person on the planet, there are approximately three chickens.
Meat and dairy specifically account for around 14.5% of global greenhouse gas emissions, according to the UN’s Food and Agricultural Organization (FAO). Based on the most recent report from the Intergovernmental Panel on Climate Change (IPCC), if the world is to meet its target of limiting global warming to well below 2°C, some degree of diet shift will be necessary.
If it is to strive for the most optimistic target of keeping warming to 1.5°C, changes to diet may be even more crucial. Comparing the impact of greenhouse gas emissions from meat, dairy and other diets, as well as whether changes to the production and transportation of meat could help stem their climate impact.
How Emissions from Meat, Dairy and Other Foods Compare
There are several ways to assess the climate impact of different food groups. The chart below compares the average greenhouse gas emissions produced per kilogram of different food products. The analysis, which is based on a study published in Science magazine in 2018, considers all the factors that go into producing food, including the land required for production, the farming process and the transportation and selling stages.
The chart illustrates how the climate impact of beef and lamb dwarfs that of other foods. This is partly due to the biology of how these animals digest food, according to the head of the Oxford Martin School at the University of Oxford, the products from ruminant animals—sheep, cows and their relatives, animals with four stomachs—tend to have greater greenhouse gas effects.
Cows and sheep are “ruminants”—meaning that their stomachs contain specialized bacteria capable of digesting tough and fibrous material, such as grass. The digestive process causes the animals to belch out methane, a greenhouse gas that is around 28–34 times (pdf) more powerful than CO2 over a 100–year period.
However, the chart illustrates that producing beef is more than twice as carbon–intensive as producing lamb. One reason for this is that cows take longer to grow and reproduce, which means the production of beef requires much more feed and land than other types of meat.
The conversion of land for beef production and animal feed is a leading cause of deforestation in many tropical regions, including in the Amazon, where a recent spike in forest fires and clearing has been linked to cattle ranching. A nutritionist at the Public Health School of Harvard University compares eating beef raised on grain produced in the Amazon to coal–fueled power plants—the worst thing you could possibly do.
Based on a 2020 study on all of Earth’s biomes from 1992 to 2015 (Tagesson et al.), the cutting down of tropical forest causes the release of long–held stores of carbon (tropical deforestation as a whole accounts for around 8% of global greenhouse gas emissions).
Grazing cattle need plentiful supplies of grass—so farmers often use nitrogen fertilizer on their fields to stimulate plant growth. The production of nitrogen fertilizer causes the release of CO2 and the potent greenhouse gas nitrous oxide (N2O). It is worth noting that emissions from beef can vary greatly depending on the region.
The resource–intensive nature of cattle rearing also explains why, on average, cheese and other dairy products have a higher climate cost than pork and poultry. Also, chickens and pigs are not ruminants and so do not produce as much methane (pdf).
The chart also shows that, on average, farmed prawns have a larger climate impact than other types of seafood. This is partly due to the fact that some parts of Southeast Asia have seen a boom in industrial–scale aquaculture.
In these systems, prawns are fed with high amounts of fish feed, much of which is wasted and taken up by other marine microorganisms which then release methane into the atmosphere. According to a 2001 Nature Geoscience paper, aquaculture also often requires carbon–rich mangroves to be cut down, which causes large amounts of CO2 to be released.
In comparison to meat and dairy, plant–based foods have much smaller carbon footprints. On average, emissions from plant–based foods are 10 to 50 times smaller than those from animal products, according to the 2018 Science magazine study.
Notable exceptions on the chart above include coffee and chocolate. Coffee is mostly grown in tropical regions and its production often involves using high amounts of nitrogen fertilizers, which mostly explains why it has a larger climate impact by kilogram than other plant–based foods. Chocolate’s climate impact is mostly caused by the land–use change required to produce cocoa.
However, it is worth noting that both coffee and chocolate do not contribute much to nutrition, according to a senior researcher at the Oxford Martin School and head of research at Our World in Data, who conducted the above chart analysis.
One thing to be conscious of when comparing these products is serving size. Many are shocked by coffee’s footprint—and that’s not to say that coffee doesn’t have a reasonably high environmental footprint—but that the serving size is typically smaller. The chart below shows the average greenhouse gas emissions for different food products per 100g of protein, rather than for weight alone.
This chart shows that, when protein is considered rather than mass, dark chocolate has the highest footprint. However, it is worth noting that chocolate typically contains a very small amount of protein in comparison to animal products such as beef and lamb—and therefore a consumer would need to eat much more of it to obtain the same amount of protein.
Switching To Vegetarian, Vegan or Other Diets Can Help Reduce Emissions
Given that the climate impact of plant–based foods is typically 10 to 50 times smaller than that of animal products, it follows that switching from a largely meat–based diet to a vegetarian or vegan diet could help reduce emissions. The chart below shows how much greenhouse gases could be stemmed if the world were to adopt various different diets.
The error bars in the above chart show the spread of results from different studies. Data without error bars are from one 2018 IPCC study only. The analysis comes from a report by the IPCC, an independent research group made up of the world’s leading climate scientists. The report defines the different diets referenced in the chart above as follows:
- Vegan: a completely plant–based diet.
- Vegetarian: a diet of grains, vegetables, fruits, naturally–occurring sugars, oils, eggs and dairy and around one serving of meat or seafood per month.
- Flexitarian: a diet in which 75% of meat and dairy is replaced by cereals and pulses (this includes at least 500g of fruit and vegetables and at least 100g of plant–based protein per day—and no more than one portion of red meat a week).
- Healthy Diet: a diet based on global dietary guidelines, which involves eating less meat and more fruit and vegetables.
- Fair and Frugal: a diet assuming food is shared equally across the world with each person consuming 2,800 calories a day (involves a relatively low level of animal product consumption).
- Pescetarian: a vegetarian diet that includes seafood.
- Climate Carnivore: a diet where 75% of red meat is replaced with other meats.
- Mediterranean: a diet of vegetables, fruits, grains, naturally–occurring sugars, oils, eggs, dairy, seafood and moderate amounts of poultry, pork, lamb and beef.
In the IPCC’s special report on climate change and land, the team of scientists analyzed recently published scientific papers that look into how these different diets could help stem greenhouse gas emissions.
The chart above displays the total amount of greenhouse gases that could be saved each year by 2050 if the world were to adopt each of these diets, when compared to a status quo scenario for 2050. This scenario is based on projections of continued population growth and rising meat intake from the United Nations (UN) Food and Agricultural Organization (FAO) 2012 Report Revision (pdf). The chart shows the savings in terms of millions of tonnes of CO2 equivalent [CO2e]—a measure used to compare the emissions from various greenhouse gases.
These savings come from both, ridding the world of the greenhouse emissions associated with livestock production, and also from sparing land that would otherwise be needed for livestock rearing. The analysis shows that a global switch to veganism would deliver the largest emissions savings out of any other dietary shift.
According to the analysis, a switch to veganism could save almost 8bn tonnes of CO2e a year by 2050, when compared to the status quo scenario. By comparison, all food production currently causes around 13.7bn tonnes of CO2e a year.
Data taken from the most recent Global Forests Assessment undertaken by the UN FAO shows that the steep reduction in emissions would partially stem from the freeing up of large amounts of land, which could be used to plant forests capable of removing CO2 from the atmosphere.
The IPCC report states that under the most extreme scenario where no animal products are consumed at all, adequate food production in 2050 could be achieved on less land than is currently used, allowing considerable forest regeneration, and reducing land–based greenhouse gas emissions to one third of the status quo scenario case for 2050.
Separate independent research finds that the emissions savings from a global switch to veganism could actually be as high as 14.7bn tonnes of CO2e a year. The second highest emissions savings would be delivered by a global shift to vegetarianism which, in the analysis, still includes around one serving of meat or fish a month. An adoption of this diet could save 6bn tonnes of CO2e a year by 2050.
Following a shift to “flexitarianism”—a diet where three–quarters of meat and dairy is replaced by plant–based alternatives. A global shift to this diet could save just over 5bn tonnes of CO2e a year by 2050.
It is worth noting that, while veganism offers large emissions savings when compared to a status quo scenario, the additional benefits become smaller when compared to vegetarianism and flexitarianism. The analysis also shows that a global shift to “healthy” eating could offset around 4.5bn tonnes of CO2e a year by 2050.
In addition, new research published in the Proceedings of the National Academy of Sciences (PNAS), of national healthy eating guidelines recommend that citizens eat less meat, and more fruits and vegetables. The Public Health England’s Eatwell Guide suggests the average citizen should eat less red and processed meat and consider choosing low–fat alternatives to dairy.
A study published in 2016 found a global shift towards more plant–based diets that are in line with standard dietary guidelines could reduce global mortality rates by 6–10% by 2050 in addition to reducing emissions by 29–70%, when compared to the status quo scenario.
Sources:
Interactive: What is the climate impact of eating meat and dairy?
https://interactive.carbonbrief.org/what-is-the-climate-impact-of-eating-meat-and-dairy/
by Daisy Dunne, Published: 14/09/2020
Design credit: Tom Prater and Joe Goodman.
Video credit: Martin Harvey
Data Sources:
Poore & Nemecek (2018)
https://science.sciencemag.org/content/360/6392/987
Heller & Keoleian (2018)
http://css.umich.edu/sites/default/files/publication/CSS18-10.pdf
Khan et al. (2019)
https://impossiblefoods.com/mission/lca-update-2019/