Environmental vegetarianism is the belief that the production of meat and animal products at current and likely future levels, especially through factory farming is environmentally unsustainable. Industrialization has led to intensive farming practices and diets high in animal protein, primarily in developed nations and mainly the United States. According to the National Academy of Sciences (NAS) "Most of the world's population today subsists on vegetarian or near-vegetarian diets for reasons that are economic, philosophical, religious, cultural, or ecological."[50] Thus, the main protest of environmental vegetarians is primarily of intensive farming in developed nations.
According to the United Nations Population Fund "Each U.S. citizen consumes an average of 260 lb. of meat per year, the world's highest rate. That is about 1.5 times the industrial world average, three times the East Asian average, and 40 times the average in Bangladesh."[51]
All modern, intensive farming practices consume large amounts of fossil fuel and water resources and lead to emissions of harmful gases and chemicals. Animal agriculture is one of the largest sources of greenhouse gases — responsible for 18% of the world’s greenhouse gas emissions as measured in CO2 equivalents. By comparison, all transportation emits 13.5% of the CO2. It produces 65% of human-related nitrous oxide (which has 296 times the global warming potential of CO2) and 37% of all human-induced methane (which is 23 times as warming as CO2). It also generates 64% of the ammonia, which contributes to acid rain and acidification of ecosystems [7]. The habitat for wildlife provided by large industrial monoculture farms is very poor, and modern industrial agriculture is a threat to biodiversity compared with farming practices such as organic farming, permaculture, arable, pastoral, and rainfed agriculture.
Animals fed on grain, and those that rely on grazing need far more water than grain crops.[52] According to the USDA, growing the crops necessary to feed farmed animals requires nearly half of the United States' water supply and 80% of its agricultural land. Additionally, animals raised for food in the U.S. consume 90% of the soy crop, 80% of the corn crop, and a total of 70% of its grain.[53] In tracking food animal production from the feed trough to the dinner table, the inefficiencies of meat, milk and egg production range from 4:1 energy input to protein output ratio up to 54:1.[54] The result is that producing animal based food is typically much less efficient than the harvesting of grains, vegetables, legumes, seeds and fruits. This criticism could not be applied to animals that are grazed rather than fed, especially those grazed on land that could not be used for other purposes.
The UN Food and Agriculture Organization has concluded that the livestock industry, accounting for 30% of the Earth's surface, contributes more to global warming (18%) than does all vehicles combined (13.5%).