As a result, although animals now make up some 49% of agricultural emissions in the United States, a vegan nation would eliminate far less than that. Annual emissions would drop from 623 million tons to 446 million tons a year, the team reports today in the Proceedings of the National Academy of Sciences.

Looking at the nutritional content of crops now produced, the team also found that a plant-only system wouldn’t be able to meet the U.S. population’s requirements for calcium, vitamins A and B12, and a few key fatty acids. “With carefully balanced rations, you can meet all of your nutrient requirements with a vegetarian diet,” White says. “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.”