This is what keeps me up at night. If we don't find an efficient way to extract CO2 and methane from the atmosphere, I fear that mankind might go extinct.
Mankind is absurdly resilient. We are like rats or cockroaches but a hundred times more adaptable. Billions of people could die. We might lose 99% of species. But human extinction is out of the question. We could live in bubbles of air under the ocean huddled around nuclear reactors if we needed to. Roaches couldn't do that (without our help).
I suppose governments probably have that fairly well doomsday planned.