(This article was reprinted with permission from the edition of that finest of fine publications, n+1) Over the course of the past century, mean global temperatures increased by .6 degrees C. This change seems slight but isn’t: in the winter of 1905 my great-grandfather, a coppersmith, installed the roof on a new reef-point lighthouse two miles from Lake Michigan’s shore. Each morning he drove out across the open ice in a horse and buggy laden with his copperworking tools; today the water that far from shore never freezes, much less to a depth that could support a horse’s weight. Well…