Sunday, October 25, 2009

Cows & CO2

How much do methane emission from livestock (predominantly cows!) contribute to global warming. These emissions are politely called ruminants. Stephen Levitt's new book "Superfreakanomics" (which is getting alot of coverage currently) states:

"The world's ruminants are responsible for about 50 percent more greenhouse gases than the entire transportation sector"

.... really ?

Methane accounts for about 16% of global GHG emissions. How much of this is from ruminants ? I found it difficult to get an exact figure. This source implies 40% is from natural sources. US EPA data says that about 24% of the US's methane are from ruminants. So, going with the higher figure, ruminants account for about 4%.

Transport emissions are about 13.5% of total looking at this graph. The graph also confirms my calculation is roughly right... by stating that about 5% of GHG emissons are attributable to livestock. So, much as I like Stephen Levitt's work .... in this case I think he is way out !

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