Well I initially thought the same thing (as some rando who put negligible thought or research into it). Then it was pointed out by a science youtuber that mass

Well I initially thought the same thing (as some rando who put negligible thought or research into it). Then it was pointed out by a science youtuber that mass migration of people is a problem, which I promptly ignored. However upon reflection, suppose the population of Mexico did try to go north due to drought. Mexico outnumbers the US army by 126:1, so it's definitely not something to dismiss out-of-hand. Also a lot of manufacturing is done there. So it may not be a "die of heat" type existential threat for people in North America, but it seems plausible that a collapse of the system type existential threat is possible.