I made the following as a comment to a Kos article on methane, but on reflection decided that it was far enough down the comment list to be unlikely to be noticed. I have also added an estimate of how quick and effective cutting CH4 emissions can be.
Unfortunately, given the way most of the world works, methane (CH4) venting may be the solution to our GHG problem, instead of the culprit. Double unfortunately, I do not mean this as snark. There is a large fraction of the population that will not get serious about climate change until we start to have serious repercussions: flooding, drought, heat deaths, crop failures and so on. If there were no methane releases we would have to wait until CO2 (and a little bit of N2O) caused these events. These two gases, and especially CO2, appear to have very long atmospheric half-lives (100s to thousands of years) so we would be stuck with trying to remove these gases from the atmosphere while at the same time battling the ill effects they cause. Conversely, CH4 has a half-life of about 8 years, so there is chance that we could get serious about climate change before it effectively gets locked in by the rising CO2 concentrations.
It is common to talk about CH4 as having about 80 times the global warming potential as CO2 over 20 years, but it is not clear that this is meaningful because the earth maintains a quasi-equilibrium of heat flow in versus heat flow out. As the earth warms because of excess heat in, the average temperature rises, which increases the heat flow out. Methane is about 160 times as effective as CO2 in blocking this heat flow. The value of 80 is total relative amount of total heat flow blocked after accounting for the reduction in the CH4 atmospheric concentration over a 20 year period. However, if methane emissions are actually reduced or eliminated, then heat flow in is fairly rapidly reduced, and the temperature rise of the earth will first be reduced, and then the temperature will actually begin to drop. By contrast, if net CO2 emissions are reduced or eliminated, and its half-life is truly as long as it is thought to be, then the temperature will rise to a new quasi-equilibrium point and then will stabilize.
Instead of using 80 as the relative global warming potential of CH4 over 20 years, it make more sense to note that if anthropogenic emissions are stopped, then the portion of the atmospheric concentration due to anthropogenic emissions will drop in 20 years to only 20% of its current value. This is the entire excess anthropogenic concentration, and not just the last years emissions. Since anthropogenic CH4 is currently a major fraction of the CH4 in the atmosphere the drop in total concentration is would be almost 50% (C(t) = k1/a -k2(exp(-a*t), where C is the concentration at time t, k1 is the relative emission rate, a is the 1/decay time ≈ 1/8 years, and k2 ≈ 0.4 is the natural CH4 emission fraction). This is a big deal, as CH4 is thought to account for approximately 30% current warming. By somewhere near 50 years the anthropogenic increase in the atmospheric concentration would be only about 1%. I don’t expect to last another 20 years, but I am frankly rooting for more natural and even anthropogenic CH4 emissions, with the hope that the repercussions, bad as they may be, will wake people up in time to prevent more serious ecosystem collapse.
