Environmental impact of meat production
Greenhouse gas emissions
In the US, methane emissions associated with ruminant livestock (6.6 Tg CH 4, or 164.5 Tg CO 2e in 2013) are estimated to have declined by about 17 percent from 1980 through 2012. Globally, enteric fermentation (mostly in ruminant livestock) accounts for about 27 percent of anthropogenic methane emissions, and methane accounts for about 32 to 40 percent of agriculture's greenhouse gas emissions (estimated as 100-year carbon dioxide equivalents) as tabulated by the IPCC. Methane has a global warming potential recently estimated as 35 times that of an equivalent mass of carbon dioxide. The magnitude of methane emissions were recently about 330 to 350 Tg per year from all anthropogenic sources, and methane's current effect on global warming is quite small. This is because degradation of methane nearly keeps pace with emissions, resulting in a relatively little increase in atmospheric methane content (average of 6 Tg per year from 2000 through 2009), whereas atmospheric carbon dioxide content has been increasing greatly (average of nearly 15,000 Tg per year from 2000 through 2009).
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