Earlier quoted context omitted.
Decades – we don't have decades to fix this. Also, it decays into CO2, so to claim that its effects are temporary is misleading. On top of that, as long as the carbon is in a CH4 bond, it traps at least 20× as much radiation. Please don't dismiss the significance of methane emissions.
How many years do we have to fix this then? Alternatively, at what point will activists start saying we passed the point of no fix and give up their activism?
Honestly dude, rise above the cynicism (if that's how you meant to come across). You're a goddamn adult, and a well-educated engineer at that. Your current standard of living is at risk because of climate change (also millions of lives in poorer countries, but whatever). Spend 10 seconds on a Google search. "Activists" don't owe you any answers.
Never forget, despite what the sensationalists will tell you, climate change is very much fixable. Clean energy and better land management can and will get us there – and eventually, maybe in 200 years, we'll sequester enough carbon to get back to 350ppm. The question is about what happens in the meantime: if we act fast, we'll only get decades of food insecurity, war, and displacement, mostly in poorer countries [2]. If we delay further, we'll simply see much worse, and at home as well. But the "point of no return" rhetoric is nonsense and does nothing but paralyze people.
By the way, one of the easiest and fastest ways to catalyze at-scale solutions would be a revenue-neutral carbon tax at the source, effectively internalizing the social costs of climate change and letting the free market do its thing. (Look up "fee and dividend"; lots of folks are working on this already.)
[1] unless we hit some really unlucky runaway feedback loop, which is possible. [2] plus the disease epidemics and terrorism that come along with it – we don't live on an island.