[fencepost]

Methane does break down much faster than CO2, but over the time scales being discussed here it's MUCH more powerful. From memory so probably somewhat off it's >80x more potent a greenhouse gas over a decade, dropping to only 20x more potent when measured over a century.

The big problem is tipping points. There are a lot of things where an initial big hit can be something you don't recover from, no matter how light the impact might seem when measured over years.