> 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!