Collapse

And there should be capacity to do multiple things at once - e.g. lessen dependence upon Chinese computer chip manufacturing and curb Russian aggression for a fraction of the cost that it would have been later after it succeeded in conquering Ukraine and set some kind of limit on giving billions of aid to eliminate people living in Gaza and do some kind of absolute bare minimum effort to save the planet from our abuses of it.

100b will buy you nothing. That's like a tenth of Us military budget.

The heating alone would do that, yes. It's the knock-on effects. As CO~2~ rises, the ocean slowly acidifies. As the ocean increasingly acidifies, oxygen producing lifeforms (approximately 70% of the oxygen we consume is produced in the ocean) increasingly die out. The Amazon Rainforest (a large producer of oxygen on land) is on fire. What will we breathe? It's an ecological apocolypse, not merely from getting hot (which your comment seriously underestimates the direct effects of) but from the previously mentioned oxygen crash, and hundreds of other effects that we know about and can reliably predict.

edit: some light reading: https://en.wikipedia.org/wiki/Ocean_acidification

DarkNightoftheSoul already helpfully answered that (with link attribution!:-) but I did want to add that I never said that it would - I said that it may, as in in the absolute worst case scenario. By comparison, the ending of a nation, like Ukraine, Russia, the USA, or China, pales by comparison, given how on the other side we are talking something affecting all human habitation on the planet, with the worst case scenario possible being to bring it to an end, though even if that doesn't happen there will be other effects. Like for one, perhaps no more coffee or chocolate, which historically were grown closer rather than farther from those equatorial zones that you mentioned. Even if the thought of billions of deaths doesn't motivate us, at the very least the thought of losing our cafe mocha lattes should!