If the U.S. went vegan, emissions would drop. But there’s a catch, a new study says

Black Angus cows stand together in their paddock. Cows produce methane, a potent greenhouse gas.
Black Angus cows stand together in their paddock. Cows produce methane, a potent greenhouse gas. AP

If the entire United States went vegan, it could be great for the environment. But it’s a lot more complicated than advocates for an all-vegan country might hope, a new study found.

Agriculture and forestry alone make up a quarter of the United States’ total greenhouse emissions, according to the U.S. Environmental Protection Agency — and animals produce roughly half of those agricultural emissions, Science Magazine reported.

That means animal agriculture is a perennial target for those hoping to cut emissions and tackle global warming. So what would happen if all 320 million Americans went vegan, entirely eliminating animals from our diets — and from our farming and ranching practices?

A new study published in the Proceedings of the National Academy of Sciences found that such a radical diet change would slash U.S. greenhouse gas emissions from agriculture by 28 percent. But the study — authored by Robin White, of the Virginia Tech department of animal and poultry science, and Mary Beth Hall, a U.S. Department of Agriculture researcher in Madison, Wisc. — also found that an animal-free diet would harm Americans’ nutrition.

And you might be wondering about the math, too: If animals produce 49 percent of U.S. agriculture’s greenhouse emissions, shouldn’t eliminating animals cut emissions by the same amount — that is, 49 percent?

For better or worse, it’s not that simple, scientists told Science Magazine. Eliminating animals altogether would leave behind tons of corn stalks, potato waste and other plant byproducts that right now end up in livestocks’ stomachs. And if that uneaten waste got burned to eliminate it, the waste would churn out 2 million tons of carbon dioxide a year, the researchers told Science Magazine.

With no more livestock-produced manure, demand for artificial fertilizer would rise as well, Science Magazine reported, driving an additional 23 million tons in carbon emissions each year.

So even though 65 percent of farm-related emissions come from methane belched by cows and from putting nitrous oxide fertilizer and waste in the ground, according to the World Resources Institute, a Washington-based think tank, taking animals out of agriculture altogether doesn’t solve the problem.

Cutting out animals would hurt Americans’ diets, too.

“Although modeled plants-only agriculture produced 23% more food, it met fewer of the US population’s requirements for essential nutrients,” the study says.

White, one of the study’s authors, told Science Magazine that it’s not surprising an all-vegan diet in the U.S. would lead to deficiencies in calcium, vitamins A and B12, and important fatty acids.

“With carefully balanced rations, you can meet all of your nutrient requirements with a vegetarian diet,” White told the magazine. “But the types of foods that seem to do that, we don’t currently produce in sufficient quantities to make it a sustainable diet for the entire population.”

That’s not to say that eating a little (or a lot) less meat on an individual level can’t have an impact on your carbon footprint, though – especially considering how much of our individual greenhouse emissions come from meat consumption.

The meat consumed by the average family of four, for example, puts out more greenhouse emissions than driving two cars would produce, according to the BBC. Yet it’s fuel efficiency – not hamburger and chicken nugget bans – that policymakers hoping to tackle greenhouse emissions focus on.

“Most people don’t think of the consequences of food on climate change,” Tim Benton, a food security expert at the University of Leeds, told the BBC. “But just eating a little less meat right now might make things a whole lot better for our children and grandchildren.”