Deniers of climate change sometimes quip that claims about global warming are more about political science than climate science. They are wrong on the science, but may be right with respect to its political implications. A hotter world, writes Andrew Guzman, will bring unprecedented migrations, famine, war, and disease. It will be a social and political disaster of the first order.

In Overheated, Guzman takes climate change out of the realm of scientific abstraction to explore its real-world consequences. He writes not as a scientist, but as an authority on international law and...