The emergence of the pronuclear Greens represents an important schism in modern environmentalism. For decades, groups like the Sierra Club and Greenpeace have pushed an antinuclear agenda and contended that the only energy path for the future is the widespread deployment of wind turbines and solar panels. But fear of carbon emissions and climate change has catalyzed a major rethinking. As Brand puts it in a new documentary, Pandora’s Promise, which explores the conversion of antinuclear activists to the pronuclear side: “The question is often asked, ‘Can you be an environmentalist and be pronuclear?’ I would turn that around and say, ‘In light of climate change, can you be an environmentalist and not be pronuclear?’ ”

Newfound support can only help the nuclear-energy sector, but it remains to be seen whether nuclear will play a major role in the burgeoning global electricity market, which has grown by about 3 percent per year since 1985. It’s already clear that the Greens’ pronuclear stance won’t have a significant impact on the American electricity market over the next decade or so, for a simple reason: the shale-gas revolution here has produced abundant supplies of low-cost natural gas. In 2010, one of the largest electric utilities in the country, Exelon, said that for new nuclear projects to be economically viable, natural gas would have to cost at least $8 per million Btu. Today, the price is about $3.50, and the shale-gas boom means that a price anywhere near $8 is exceedingly unlikely for years to come. Four nuclear reactors are now being built in the United States—the Vogtle 3 and 4 reactors in Georgia and the Summer 2 and 3 reactors in South Carolina—but the projects are going forward only because regulators in those states have allowed the utilities that own them to recover costs from ratepayers before the projects are finished.