> Methane emissions decay gradually, with an average lifetime of about 12 years (“perturbation lifetime”, which is what matters for climate purposes).
> This will increase by roughly 35% if methane concentrations double, or decrease roughly 25% if concentrations return to pre-industrial levels.
Methane is actually 150x-ish worse than CO2, but it breaks down over time. Ameliorated over a long time it's 25-30x worse.
Rough part is that breaking down methane depends on OH radicals in the air, of which there are a fixed amount. The more methane there is, the slower methane is broken down. If there were a sudden massive release of methane, it would stay at that 150x potency for a very long time. Fun!
To make the complexity really mind-blowing, no, the amount is not fixed. It varies, and temperature is one of the largest factors. But it's not a simple relation, because air currents are also very important, and temperature also changes those.
This statement caused me to do some light research. I discovered that methane is 25 times as potent as carbon dioxide at trapping heat in the atmosphere.