Eating less meat or none at all has the potential to significantly shrink an individual's diet-related carbon footprint and "can make a valuable contribution to climate change mitigation,"according to a recent study published in the journal Climatic Change.
The study examined the diets of 29,589 meat eaters, 15,751 vegetarians, 8,123 pescatarians (vegetarians who eat fish) and 2,041 vegans between the ages of 20 to 79 in the United Kingdom. Participants took a "food-frequency questionnaire" asking how often in the last year they consumed 130 different food items. Researchers were able to estimate the greenhouse gas emissions, which trap heat and warm up the planet, associated with the various foods.
A heavy meat diet, according to the study's findings, produced nearly double the amount of dietary greenhouse gas emissions per day as a vegetarian diet and about two-and-a-half times more than a vegan diet, which consists of no meat or other animal products.
The United Kingdom-based study found that the typical heavy meat diet — consisting of more than 3.5 ounces of meat per day — generated 15.8 pounds of carbon dioxide equivalent (CO2e) each day. By comparison, an average pescatarian diet contributed 8.6 pounds of CO2e per day. For vegetarians and vegans, their diets produced 8.4 pounds and 6.4 pounds of CO2e, respectively.
All told, the study found that dietary greenhouse gas emissions among meat eaters were between 46 percent and 51 percent higher than fish eaters, 50 percent and 54 percent higher than vegetarians and 99 percent and 102 percent higher than vegans.
"This work demonstrates that reducing the intake of meat and other animal based products can make a valuable contribution to climate change mitigation," the study reads. "Other work has demonstrated other environmental and health benefits of a reduced meat diet. National governments that are considering an update of dietary recommendations in order to define that a ‘healthy, sustainable diet’ must incorporate the recommendation to lower the consumption of animal-based products."
Overall, the production of animal-based foods tends to contribute greater greenhouse gas emissions than plant-based foods, the study reads.
"Production, transport, storage, cooking and wastage of food are substantial contributors to greenhouse gas (GHG) emissions," the researchers added. "These GHG emissions include carbon dioxide (from fossil fuels used to power farm machinery and to transport, store and cook foods), methane (from enteric fermentation in ruminant livestock) and nitrous oxide (released from tilled and fertilized soils)."
Globally, food production contributes up to 29 percent of man-made greenhouse gas emissions, according to a 2012 “Climate Change and Food Systems” report by the agriculture research organization CGIAR. In the United States, 10 percent of the country's total greenhouse gas emissions in 2012 came from "livestock such as cows, agricultural soils, and rice production," according to the U.S. Environmental Protection Agency.
Sasha Lyutse, a policy advocate with the Natural Resources Defense Council, said the findings published in the Climatic Change journal were notable but not surprising, explaining that there have been various studies in the United States and elsewhere highlighting the relatively larger impact meat production has on the environment than plant-based food production.
"From a climate perspective, there have been multiple studies that have shown the relatively heavier impact of meat products and also the relatively heavier impact of some meat products versus others," she said. "Typically, you see that the resources needed to produce beef far exceed the resources needed to produce other animal proteins most of the time."
If all Americans adopted a vegetarian diet, it would be the equivalent of removing 46 million cars from the road, according to estimates from the Environmental Working Group. The organization also found that if an individual eats one less burger a week for one year, it is the same as not driving a car for 320 miles.
Becoming a vegetarian or vegan might not be possible for everyone, but such a lifestyle switch is one of many ways people can take action on climate change at the individual level, said Julian Boggs, federal global warming program director at Environment America.
"We live in a world where we can't just ask everyone to personally [and] dramatically change their lifestyle in order to meet a policy objective just on a one-by-one individual basis," he said. "For folks concerned about global warming, who are actively looking at ways to reduce their carbon emissions, I think that vegetarianism is one way to do it. Biking to work is one way to do it, going solar, reducing the amount of energy used in your home are … all great options. (This) study provides a lot of backing that becoming a vegetarian, or at least reducing your meat intake, is a powerful option."
Lyutse added that food-related carbon footprint studies serve as a good "alerting tool."
"It's an opportunity to get people thinking about the resources that go into growing their food and getting to their plates," she said. "I think once you have people thinking that way, that's a really good place to be. That's what is going to lead to more understanding of the kind of food system that we might want to be moving towards."
Wesley Jarrell, professor emeritus of sustainable agriculture and natural resources at the University of Illinois at Urbana-Champaign, said the study does not appear to factor in the different greenhouse gas emissions associated with meat produced using a grass-fed system and a grain-fed system," the latter of which "inherently is going to probably take quite a bit more energy."
"My feeling would be that there's a lot of hidden assumptions behind all of these numbers," he said.
But the overall trend is pretty clear, Jarrell added.
"Especially if you're vegan, you're going to be releasing a lot less (carbon dioxide) with your diet," he explained. "If you eat a lot of cheese and eggs as a vegetarian, you might be using more carbon, as they indicate in the study. Certainly as a high-meat consumer, you're going to be releasing a lot" of emissions, but it could vary depending on a number of factors, including whether the meat is local, fairly fresh and from a grass-fed system.
Howard Peter Steeves, a philosophy professor at DePaul University whose area of expertise includes vegetarianism, said the study appears to have been "organized and conducted in a sound way."
"Although the numbers for estimates for different greenhouse gas emissions based on different diets are necessarily estimates and guesses, they are conservative estimates and educated guesses," he explained.
Steeves, who has been a vegetarian for nearly 30 years, said the study highlights important issues in the food chain.
"It is, I think, uncontroversial and irrefutably the case that the less we consume animal products, the less we ruin the planet," he continued. "As the authors of the study point out, the main problem is that for those who eat meat, first we as a civilization have to grow crops to feed the animals, and then we have to care for those animals before slaughtering them and feeding them to the meat eaters. That's essentially an extra step in the food chain — not to mention an increase in methane from the animals themselves as they digest the crops. Industrial meat eating is necessarily inefficient in every way."
As Steeves pointed out, flatulent cows, particularly in concentrated animal feeding operations (CAFOs), release a lot of methane, a potent greenhouse gas.
"It's certainly made worse by the fact that we're not feeding (the cows) what they're supposed to eat, which is grass," Boggs added.
"If we can do more to ... encourage more sustainably grown, grass-fed beef, and not put them in concentrated animal feeding operations where they eat corn, [it] can do a lot to reduce that piece of emissions," he explained.
There are a number of other broader policy solutions, both nationally and globally, that could curb carbon emissions from the agricultural industry.
Experts said one area to focus on is no-till agriculture, which can reduce carbon loss from the soil.
"Heavily used and conventionally tilled soil actually emits a lot more carbon than it absorbs," Boggs said. "Different conservation programs to ensure that significant chunks of our land are absorbing — not emitting carbon — is [a] powerful" policy approach.
Encouraging more sustainable farming and food systems through funding and regulatory policy is another key way to cut emissions, experts said.
"The idea of a hamburger that's maybe grown in Brazil by McDonald's and transported up here frozen and knocked out a bunch of rainforest to raise it is probably a bad climate idea," Jarrell said. "(It is) wrong for so many reasons, because you displace the natural vegetation that was very efficient at storing carbon and latching on to it. And you've created a really cheap product that people can buy a lot of to eat and get fat on.
"We need policies that encourage high-quality, local production of food where you don't ship it so far, and so you don't store it so long, and that enhance the natural ecosystem's ability to save carbon or even capture carbon," he added. "Those are the things we should be talking about instead of how to produce as much cheap food as we can."
At the individual level, people concerned about the climate impacts of their diet should consider an "eat less and eat better" approach, Lyutse said. Switching out red meat for poultry a few times per week, for example, is one way to reduce an individual's food-related carbon footprint, she said.
Cutting food waste is also important.
"We waste a tremendous amount of food in this country," Lyutse said. "Upwards of 40 percent of the food we produce never gets eaten."
When a hamburger gets tossed in the trash, that is the equivalent of throwing away the water in a 90-minute shower, Lyutse explained.
"All the water that went into producing that [burger] gets thrown away when you throw away that food," she said. "If you throw away an apple, that's a seven-minute shower. Meat is very resource-intensive to produce. It's almost too precious to waste in that sense. No matter how sustainably we produce any food, if it doesn't ultimately get eaten, that's not a good use of those resources."