The food we eat is responsible for an astounding one-third of global greenhouse gas emissions caused by human activities, according to two comprehensive studies published in 2021.
“When people talk about food systems, they always think about the cow in the field,” says statistician Francesco Tubiello, lead author of one of the reports, appearing in last June’s Environmental Research Letters. True, cows are a major source of methane, which, like other greenhouse gases, traps heat in the atmosphere. But methane, carbon dioxide and other planet-warming gases are released from several other sources along the food production chain.
Before 2021, scientists like Tubiello, of the Food and Agriculture Organization of the United Nations, were well aware that agriculture and related land use changes made up roughly 20 percent of the planet’s greenhouse gas emissions. Such land use changes include cutting down forests to make way for cattle grazing and pumping groundwater to flood fields for the sake of agriculture.
But new modeling techniques used by Tubiello and colleagues, plus a study from a group at the European Commission Tubiello worked with, brought to light another big driver of emissions: the food supply chain. All the steps that take food from the farm to our plates to the landfill — transportation, processing, cooking and food waste — bring food-related emissions up from 20 percent to 33 percent.
To slow climate change, the foods we eat deserve major attention, just like fossil fuel burning, says Amos Tai, an environmental scientist at the Chinese University of Hong Kong. The fuller picture of food-related emissions demonstrates that the world needs to make drastic changes to the food system if we are to reach international goals for reducing global warming.
Change from developing countries
Scientists have gained a clearer understanding of global human-related emissions in recent years through databases like EDGAR, or Emissions Database for Global Atmospheric Research, developed by the European Union. The database covers every country’s human-emitting activities, from energy production to landfill waste, from 1970 to the present. EDGAR uses a unified methodology to calculate emissions for all economic sectors, says Monica Crippa, a scientific officer at the European Commission’s Joint Research Centre.
Crippa and colleagues, with help from Tubiello, built a companion database of food system–related emissions called EDGAR-FOOD. Using that database, the researchers arrived at the same one-third estimate as Tubiello’s group.
Crippa’s team’s calculations, reported in Nature Food in March 2021, split food system emissions into four broad categories: land (including both agriculture and related land use changes), energy (used for producing, processing, packaging and transporting goods), industry (including the production of chemicals used in farming and materials used to package food) and waste (from unused food).
The land sector is the biggest culprit in food system emissions, Crippa says, accounting for about 70 percent of the global total. But the picture looks different across different nations. The United States and other developed countries rely on highly centralized megafarms for much of their food production; so the energy, industry and waste categories make up more than half of these countries’ food system emissions.
In developing countries, agriculture and changing land use are far greater contributors. Emissions in historically less developed countries have also been rising in the last 30 years, as these countries have cut down wild areas to make way for industrial farming and started eating more meat, another major contributor to emissions with impacts across all four categories.
As a result, agriculture and related landscape shifts have driven major increases in food system emissions among developing countries in recent decades, while emissions in developed countries have not grown.
For instance, China’s food emissions shot up by almost 50 percent from 1990 to 2018, largely due to a rise in meat-eating, according to the EDGAR-FOOD database. In 1980, the average Chinese person ate about 30 grams of meat a day, Tai says. In 2010, the average person in China ate almost five times as much, or just under 150 grams of meat a day.
In recent years, Crippa says, six economies, the top emitters, have been responsible for more than half of total global food emissions. These economies, in order, are China, Brazil, the United States, India, Indonesia and the European Union. The immense populations of China and India help drive their high numbers. Brazil and Indonesia make the list because large swaths of their rainforests have been cut down to make room for farming. When those trees come down, vast amounts of carbon flow into the atmosphere (SN: 7/3/21 & 7/17/21, p. 24).
The United States and the European Union are on the list because of heavy meat consumption. In the United States, meat and other animal products contribute the vast majority of food-related emissions, says Richard Waite, a researcher at the World Resources Institute’s food program in Washington, D.C.
Waste is also a huge issue in the United States: More than one-third of food produced never actually gets eaten, according to a 2021 report from the U.S. Environmental Protection Agency. When food goes uneaten, the resources used to produce, transport and package it are wasted. Plus, the uneaten food goes into landfills, which produce methane, carbon dioxide and other gases as the food decomposes.
Meat consumption drives emissions
Climate advocates who want to reduce food emissions often focus on meat consumption, as animal products lead to far greater emissions than plants. Animal production uses more land than plant production, and “meat production is heavily inefficient,” Tai says.
“If we eat 100 calories of grain, like maize or soybeans, we get that 100 calories,” he explains. All the energy from the food is delivered directly to the person who eats it. But if the 100 calories’ worth of grain is instead fed to a cow or a pig, when the animal is killed and processed for food, just one-tenth of the energy from that 100 calories of grain goes to the person eating the animal.
Methane production from “the cow in the field” is another factor in meat consumption: Cows release this gas via their manure, burps and flatulence. Methane traps more heat per ton emitted than carbon dioxide, Tubiello says. So emissions from cattle farms can have an outsize impact (SN: 11/28/15, p. 22). These livestock emissions account for about one-third of global methane emissions, according to a 2021 U.N. report.
Shifting from meats to plants
U.S. residents should consider how they can shift to what Brent Kim calls “plant-forward” diets. “Plant-forward doesn’t mean vegan. It means reducing animal product intake, and increasing the share of plant foods that are on the plate,” says Kim, program officer at the Johns Hopkins Center for a Livable Future.
Kim and colleagues estimated food emissions by diet and food group for 140 countries and territories, using a similar modeling framework to EDGAR-FOOD. However, the framework includes only the food production emissions (i.e. agriculture and land use), not processing, transportation and other pieces of the food system incorporated in EDGAR-FOOD.
Producing the average U.S. resident’s diet generates more than 2,000 kilograms of greenhouse gas emissions per year, the researchers reported in 2020 in Global Environmental Change. The group measured emissions in terms of “CO2 equivalents,” a standardized unit allowing for direct comparisons between CO2 and other greenhouse gases like methane.
Going meatless one day a week brings down that figure to about 1,600 kilograms of CO2 equivalents per year, per person. Going vegan — a diet without any meat, dairy or other animal products — cuts it by 87 percent to under 300. Going even two-thirds vegan offers a sizable drop to 740 kilograms of CO2 equivalents.
Kim’s modeling also offers a “low food chain” option, which brings emissions down to about 300 kilograms of CO2 equivalents per year, per person. Eating low on the food chain combines a mostly plant-based diet with animal products that come from more climate-friendly sources that do not disturb ecological systems. Examples include insects, smaller fish like sardines, and oysters and other mollusks.
Tai agrees that not everybody needs to become a vegetarian or vegan to save the planet, as meat can have important cultural and nutritional value. If you want to “start from the biggest polluter,” he says, focus on cutting beef consumption.
But enough people need to make these changes to “send a signal back to the market” that consumers want more plant-based options, Tubiello says. Policy makers at the federal, state and local levels can also encourage climate-friendly farming practices, reduce food waste in government operations and take other actions to cut down the resources used in food production, Waite says.
For example, the World Resources Institute, where Waite works, is part of an initiative called the Cool Food Pledge, in which companies, universities and city governments have signed on to reduce the climate impacts of the food they serve. The institutions agree to track the food they purchase every year to ensure they are progressing toward their goals, Waite says.
Developed countries like the United States — which have been heavy meat consumers for decades — can have a big impact by changing food choices. Indeed, a paper published in Nature Food in January shows that if the populations of 54 high-income nations switched to a plant-focused diet, annual emissions from these countries’ agricultural production could drop by more than 60 percent.