The use of animals to convert plant proteins and nutrients into meat, milk, eggs and other animal products is hugely inefficient (see (1) Metabolism). High inputs are required (land, water, chemical fertilizers, pesticides) and high outputs are generated (greenhouse gases, acidifying gases, eutrophying substances) (see (1.1), (1.2)). On the one hand, animal agriculture contributes significantly to climate change through its direct greenhouse gas emissions and land lost to carbon sequestration. On the other hand, habitats are minimized, animals and plants are displaced and killed, complete ecosystems are destroyed, and species are extirpated through the clearing of forests, through high water consumption, through acidifying gases, and through eutrophying and toxic substances. This ultimately leads to a loss of biodiversity.

Climate change and biodiversity loss are closely related and mutually reinforcing (positive feedback loop).