No need, we'll do it ourselves

https://theintercept.com/2023/10/29/william-nordhaus-climate-economics/

Terrible numbers get thrown around. But scientists mean what they say. Kevin Anderson, professor of energy and climate change at the University of Manchester in the U.K. and Uppsala University in Sweden, asserts that “something like 10 percent of the planet’s population — around half a billion people — will survive if global temperatures rise by 4 C.” He notes, with a modicum of hopefulness, that we “will not make all human beings extinct as a few people with the right sort of resources may put themselves in the right parts of the world and survive. But I think it’s extremely unlikely that we wouldn’t have mass death at 4 C.”

Johan Rockström, director of the Potsdam Institute for Climate Impact Research in Germany and a leading researcher on climate tipping points and “safe boundaries” for humanity, projects that in a 4 C warmer world, “it’s difficult to see how we could accommodate a billion people or even half of that.”

Hans Shellenhuber suggests that if we get to around 2c or thereabouts, 4c is inevitable becase of cascading tipping points we won't be able to stop.

plagues fit the role better