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Isn't methane much more of an offender than CO2?

No, co2 is bigger by quite a bit. Methane is increasing rapidly which is a big concern because of potential feedback effects.

https://en.m.wikipedia.org/wiki/Greenhouse_gas

One molecule of methane is worse than one molecule of CO2. But there is more CO2 than there is methane, so the total 'warming' by CO2 is worse.

Except we've already reached higher saturation (for black body radiation absorption) with CO2 than with methane. So, there is certainly a strong case to be made that methane is more impactful in the short-term than CO2 in terms of climate warming.

I haven't heard that before and it sounds conceptually incompatible with generally accepted concepts like the globally remaining CO2 budget (how could we have a budget, if we've already reached the CO2 saturation point and adding more doesn't worsen the problem?). Do you have a source for this?

Well the climate never becomes completely insensitive to further increases in CO2 concetration - lookup the band saturation effect. I wasn't citing a specific source, only pointing out that different gases absorb at different wavelengths, some of which (like methane) have potential to absorb much more with increasing concentration. IIRCC there are other factors, like the persistence time in the atmosphere, that make CO2 more worrysome.

I took this edx course on climate modeling a few years ago that was fantastic if you want to dig deeper and the professor does cover these topics (which I'm likely butchering) - https://courses.edx.org/courses/UChicagoX/PS280x/2015_T1/cou...

Methane decays relatively rapidly.

Relatively quickly, but it’s also really potent. 25-36 times worse over the first century, despite the decay period of 12 years: https://www.epa.gov/ghgemissions/understanding-global-warmin...

(Note that while linked page says 28-36, another page on the same site says 25).

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