Even the most pessimistic models do not predict human extinction. Life existed on earth before the carboniferous period, and will exist even if atmospheric carbon goes back to pre-carboniferous levels. There will certainly be drastic changes in the environment that reduce arable land, cause water shortages, and other negative effects if this happens and thus it's a good idea to decarbonize energy production. But this hyperbolic narrative of extinction is counterproductive, and makes people question whether proponents of decarbonization are really making an effective judgement around the tradeoff of energy cost and carbon emissions.

I do not believe that all nuclear stockpiles will remain untouched during this not-extinction-but-close-enough. And after the first nukes fly, who knows how many more will follow.

I believe it was about 4 degrees C warmer than now two interglacial periods ago

Most critters got through it, even hominids.

The opportunity is slowing global warming down enough to match the upcoming ice age, not too soon, not too late.