Humanity’s greatest land empire was made possible by non-human climate change. Many phenomena, real and imagined, have been attributed to global warming. From rising ocean levels to increased agricultural yields to tornadoes to polar vortices to droughts to rapes to car thefts, global warming now stands as the cause of just about anything. And because of current political dogma, man is ultimately blamed for all these evils (and occasional goods). Now a recent study in Proceedings of the National Academy of Sciences argues that there is a correlation between increasing global temperatures and the rise of the Mongolian empire. According...