In January, 2000, during the run-up to the New Hampshire primaries, Presidential candidates in the Granite State were confronted by a young man—a recent Dartmouth graduate—wearing a red cape, orange long johns, and yellow-painted galoshes. He called himself Captain Climate, and asked any candidate within shouting distance, “What’s your plan?” All the candidates ignored him, except one.

That candidate was John McCain, then the senior United States senator from Arizona. McCain went on to win New Hampshire’s Republican primary and then to lose the nomination to George W. Bush. He had been troubled enough by the shouted question that he returned to Washington that spring and held a series of hearings on climate change. At the first hearing, he apologized for not having a plan to deal with the problem, but said that everyone—especially policymakers—should be “concerned about mounting evidence.” “I had a genuine sense that he wanted to know the best information,” Kevin Trenberth, a scientist from the National Center for Atmospheric Research who testified at one of the hearings, later recalled.

McCain then did come up […]