In the long term, people will just migrate away from the badly-affected areas, towards areas that are positively affected by global warming, i.e. more northern

In the long term, people will just migrate away from the badly-affected areas, towards areas that are positively affected by global warming, i.e. more northern parts that are currently too cold to farm/live/... It's not something that will happen overnight, but neither is global warming. At the end of the day (or century rather), it'll just be a couple million people migrating, same as what happened in the last ice ages, just on a massively larger scale.