Another question I had: what does methane become once it breaks down? It becomes CO2 (a relatively minor greenhouse gas per unit weight, but long-lived) and H2O, right? H2O is no big problem in the lower troposphere. It just rains out. But in the stratosphere… it can stick around for much longer and impact the climate.

How much does this matter for methane? I would imagine methane floats up pretty high into the upper reaches of the atmosphere. Does it keep going? What stops it from getting to the thermosphere and (ultimately) exosphere?