As the world heats up, it moves. This is true on the molecular level as well as on the species level. All creatures, from the ancient cedars of Lebanon to the microbes in the deep thermal vents at the bottom of the Pacific Ocean, have evolved within a basic temperature range, and if that range changes too much, they have to find a more habitable climate niche. For humans, the decision to stay or go from extremely hot places is often dependent on money, which buys access to cooling systems, clean water, and food.
