I think the idea is even in those 12 years, it's way more damaging than CO2 will be. Over 100 years, it is 28 times more damaging than C02, despite not being in the atmosphere for most of that time.
Plus doesn't it just break down into CO2 anyway, meaning that methane does its direct damage, plus creates more CO2.
It only creates "more CO2" if the carbon atom wasn't part of the carbon cycle to begin with. That's the case for natural gas, but not for biological sources.
Plus doesn't it just break down into CO2 anyway, meaning that methane does its direct damage, plus creates more CO2.