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Food and Agriculture Organisations of United Nations

   Methane (CH4) emissions from enteric fermentation. Ruminant animals (cattle, buffalo, sheep and goat) produce methane as part of their digestive process. In their rumen (stomach), microbial fermentation breaks down carbohydrates into simple molecules that can be digested by the animals. Methane is a by-product of this process. Highly fibrous feed rations cause higher CH4 emissions per unit of energy ingested. Non-ruminant species, such as pigs, do also produce methane but amounts are much lower by comparison (enteric fermentation from cattle, buffalo, small ruminants and pig, but not from poultry, is included in this assessment).

Carbon dioxide (CO2) emissions from energy consumption. Energy consumption occurs along the entire livestock supply chains producing CO2 emissions. At feed production level, it mostly relates to the production of fertilizers and to the use of machinery for crop management, harvesting, processing and transportation. 

Livestock and Climate Change

A widely cited 2006 report by the United Nations Food and Agriculture Organization, Livestock's Long Shadow, estimates that 18 percent of annual worldwide GHG emissions are attributable to cattle, buffalo, sheep, goats, camels, pigs, and poultry. But recent analysis by Goodland and Anhang finds that livestock and their byproducts actually account for at least 32.6 billion tons of carbon dioxide per year, or 51 percent of annual worldwide GHG emissions.

Climate change and population growth are major stressors on livestock production.

Animal agriculture is responsible for 18 percent of greenhouse gas emissions, more than the combined exhaust from all transportation.