How will global warming change the world’s systems of power? Alfred McCoy argues that American global hegemony will end around 2030, replaced by China as world leader, but Chinese hegemony will last only for about 20 years—and that by 2050, climate change will have brought environmental catastrophe to both countries, and the rest of the world, with consequences that are almost unimaginable. His new book is To Govern the Globe: World Orders and Catastrophic Change.