Will a hotter climate mean more immigration? In some places, yes, that's quite possible. Earlier this week, a team of researchers led by Princeton's Michael Oppenheimer published a study suggesting that as global warming causes agricultural yields in Mexico to decline, an additional 1.4 million to 6.7 million Mexicans could migrate to the United States by 2080. (The team analyzed data on emigration, crop yields, and climate from 1995 to 2005 in order to make their forecasts.) As always, caveats abound. The social consequences of global warming are always the hardest things to predict.