Why is that a worry? Half of the land on earth is a desert, and 70% of earth is covered by ocean, most of which is also a desert. If we had enough people in rich countries who would want to spend their money on moving to new places, we would already have floating cities and many more desalination plants, and those places simply by growing food for themselves, changing their local climate to a nicer one, and by contributing to science, would solve the climate problems we are going to face.