A 500 g packet of butter has a footprint of 4.7 kg of CO2 equivalent. If a car does 200 grams of CO2e / km, distance by car on the store trip would have to be over 23 km to match the butter.
Most atmospheric methane produced photo oxidizes to CO2 after about 20 years though.
CH4 + 2O2 -photons---> C02 + 2H20
I'm not sure what time scale of heat per mass equivalencies are based on in your example; there is approximately 28 : 1 heat/mass eq. ratio at the 100 year scale, during which time the heating effect decreases exponentially with the decrease in methane concentration[0]. After 100 years the ratio is approximately 1:1 since almost all methane has decomposed.
20 years is a very relevant timescale since we need to prevent the tipping point of melting artcitc methane deposits and loss of reflection from permafrost areas.
Yea, I agree. Cows also live about 20 years, so even not breeding cows wouldn't solve this problem. The morality of eating butter is kind of a moot point when all the production mechanisms are already in place and they aren't flexible.
A possible solution would be methane fixing bacteria (methanotrophs) in the guts of cows or in the ocean where
> 75% of the current concentration atmospheric methane originates. The ocean also contains a significant amount in solid form that gets released as temps rise. [0]
