Like millions of other Americans, I first learned about climate change in the summer of 1988. For its day, it was a scorcher: Yellowstone National Park burst into flames; the Mississippi River ran so low that almost four thousand barges got backed up at Memphis; and, for the first time in its history, Harvard University shut down owing to heat. It was on an afternoon when the mercury in Washington, D.C., hit ninety-eight degrees that James Hansen, then the head of nasa’s Goddard Institute for Space Studies, told a Senate committee that “the greenhouse effect has been detected and is changing our climate now.” Speaking to reporters after the hearing, Hansen went a step further: “It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here.”

Hansen’s warning was certainly not the first. A report to President Lyndon Johnson […]