What would happen if all Americans went vegan?

Katie Langin in Science:

Consider the hamburger. Producing this staple of the U.S. diet takes 25 kilograms of animal feed, 25 square meters of land, and about 220 liters of water—all for four patties. Statistics like those have persuaded some scientists and environmental activists that eating less meat could have a big impact on carbon and other greenhouse gas emissions. But what would happen if every American made the switch to a plant-only diet? According to a new study, a nation of 320 million vegans would reduce greenhouse gas emissions from agriculture by some 28%, far less than the amount now produced by the livestock industry. The authors claim the switch could also lead to deficiencies in key nutrients—including calcium and several vitamins.

“Our logic was to start at the extreme scenario [and work backward from that],” says Robin White, the study’s lead author and an animal sciences researcher at Virginia Polytechnic Institute and State University in Blacksburg. She and fellow animal sciences researcher Mary Beth Hall, of the U.S. Department of Agriculture’s Dairy Forage Research Center in Madison, began by estimating the impact of converting all land now used by the livestock industry to cropland for human food. That would increase the amount of agricultural waste—corn stalks, potato waste, and other inedibles now fed to livestock—and eliminate the animals that now eat much of it. Burning the excess waste would add some 2 million tons of carbon to the atmosphere, they estimate. Fertilizer demands would also go up while the supply of animal manure dwindled. That would mean making more artificial fertilizer, adding another 23 million tons of carbon emissions per year. 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.

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