Does any faithful reader of Offsetting Behvaiour know enough physics to answer a question for me? I don't understand why NZ should be trying to reduce its methane emissions from cows as part of an anti-global-warming strategy.
This post is not about whether global warming is real and man-made, whether the benefits of reduced carbon emissions outweigh the benefits, or what role a small country like New Zealand should take as part of a global strategy. It is simply about the science of methane.
I am puzzled about why we should worry about methane emissions, given that they result from a circular process whereby carbon in grass is converted into methane by cows, but then carbon is reabsorbed from the atmosphere to re-grow the grass.
I understand that methane is considered to be twenty-times more potent than carbon dioxide as a greenhouse gas. (A nice primer on the science of this is here: HT Marginal Revolution.)
But I also have read that methane quickly oxides into carbon dioxide, with a half-life of only seven years. Yes, increasing our number of cows would increase the steady-state levels of methane in the atmosphere, but once our cow numbers are in steady state, won't the on-going net flow of greenhouse gas emission from that stock of cows be zero?