Comment by m0zg

I've run the numbers and it looks like all cattle on earth emit something like 150MT of methane per year. Multiplied by 20 (to get CO2 equivalent), that's 3GT. That's about 8% of the yearly total CO2 emissions (37GT). Certainly not negligible, but not earth shattering either. For comparison, per-capita CO2 emissions in the US are 16.5 metric tons. Per cow methane emissions are about 100kg per year or 2-3 tons in CO2 equivalent.