According to reports by the Food and Agriculture Organization of the UN, factory farming has made animal agriculture the No. 1 contributor to global warming (it is significantly more destructive than transportation alone), and one of the Top 2 or 3 causes of all of the most serious environmental problems: air and water pollution, deforestation, loss of biodiversity,... Eating factory-farmed animals* which is to say virtually every piece of meat sold in supermarkets and prepared in restaurants* is almost certainly the single worst thing that human do to the environment.