>I've only ever heard the claim that climate change is civilization ending as a strawman from so-called climate skeptics

Did you see what happened in Europe with a rather small mass migration 10/15 years ago due to Arab Spring ? People have short memories.

Can you imagine what will happen when 100 of thousands start migrating north when they can no longer feed themselves and maybe even work outside ? Italy was close to sinking boats coming across the the sea. Other countries in the EU started building walls. And even Germany took a slight right turn. Once these large migrations start, I expect bombs will be dropped. Same applies to North America.