The havoc caused to the world environment by the billions of animals we breed, raise and kill for food each year is staggering. The United Nations has identified animal agriculture as ‘one of the most significant contributors to today’s most serious environmental problems’, including climate change, widespread land clearing, species extinction, high use of freshwater, rainforest destruction, spreading deserts, air and water pollution, acid rain, soil erosion and loss of habitat. Vast areas of forest are cleared to grow crops to feed farmed animals. The methane produced by these animals is the largest single cause of greenhouse gas emissions. Large quantities of excrement produced by animal industries leak into rivers and oceans as pollution.