Climate change is not an existential threat, although it is a serious problem. I suspect that while millions or even hundreds of millions may be impacted, the majority of humans will survive and adapt to it. A reduction in the population, even if forced upon us without choice, would help correct the problem. There is much debate about which humans exactly are impacted (the poor in third-world low-lying countries?) or if the ones causing the most impact will be the ones killed (from rich Western countries?), but there is some population threshold beyond which our per capita consumption levels and high standard lifestyles will come into balance with the realities of climate and the environments around us. This is different from facing a large asteroid, where one such impact can literally end all terrestrial animal life on the planet on a much shorter time scale.

More on the notion that climate change is not an existential threat here, from a Professor of Atmospheric Science at the University of Washington: https://cliffmass.blogspot.com/2019/08/is-global-warming-exi...