Just as a thought experiment, suppose this is true. Then what should humanity do? What is moral? What is politically possible?
If you can't grant this assumption then please do not reply. If you must reply, please just politely say that you can't assume that, and please don't get mean.
Some would say we should do one or more of these things. You can add others.
1] Still go down fighting, even if it means reducing the standard of living of the mass of people in advanced nations, but not effecting the rich there or the poor nations much at all. I include the rich because late says we can't fight them so we must surrender to their power.
2] Carry on as we are now, doing nothing more or less. [This what we have been doing for the last 30 - 50 years.]
3] Change what we are doing in the advanced nations by giving a large UBI to everyone so they can live a happier life, for the several to many years we have left. Don't worry about inflation and the long term because there will be no long term. Don't worry, either, about the extra damage to the bio-sphere this will do because, who cares, we are *all* going to die an early death in any and all cases.
4] Be nicer to the other people around you, because we are *all* going to die an early death in any and all cases.
5] Be nicer to the 3rd world, because we don't need to take wealth from them anymore because the end is very near.
Remember, here I'm assuming that there is a 99% chance that civilization is doomed. That if any humans survive into 2200 they will be hunter-gathers, or herders, or maybe slash and burn gardeners. And the world will not cool off for at least 100K years.
6] What should we do about climate refugees? IMHO, if we let them into our advanced nations, they will be more likely to react to the climate disasters with violence, than the native born citizens.
OTOH, it is the Christian thing to do and is required by treaties and UN rules.