Your review of Ian Goldin, Geoffrey Cameron, and Meera Balarjan’s Exceptional People: How Migration Shaped Our World and Will Define Our Future (Princeton, Connecticut: Princeton University Press, 2011) points out that migration is the most effective tool for reducing global poverty (“The Future of Mobility,” May 28, 2011). Indeed, this has always been the case. As Europe and America age, they will need young workers from poor countries, thus helping both worlds. But it is surprizing to read about one of the book’s “insights” concerning global warming. In particular, the authors knock down “wild predictions” that climate change will create vast numbers of refugees by the mid-century. They foresee only floods as the problem, and they argue that most flood victims go home when the floods recede. What about droughts, though? And what about rising sea levels? Although it is difficult to pin down the exact number of refugees from such natural disasters, climate change is not likely to be weathered by minor dislocations. Which is why it is prudent to agree with the book’s conclusion that migration will “define our future.” It surely will. Perhaps even more than the authors envisage.