Avoiding the worst consequences of climate change—the raison d’être of modern environmentalism—requires a rapid worldwide reduction in carbon dioxide and other greenhouse gas emissions. Achieving that reduction demands that we clean up the energy sector, the world’s largest single source of emissions. And cleaning up electricity means transitioning away from coal—which is particularly dirty and ubiquitous—toward less emissions-intensive sources like natural gas, wind, solar, hydro, and—perhaps—nuclear power.

It isn’t an easy transition to make. Coal has the luxury of being abundant, reliable, and if you don’t factor in health and climate-related costs (which you should), extremely cheap. Potential alternatives like wind and solar are unproven at large scales and offer unique technical challenges . And while natural gas is in some ways a like-for-like replacement that’s cleaner than coal, it’s still a fossil fuel, and it still produces significant greenhouse gas emissions (it also has profound over-reliance issues).

Enter nuclear power. In terms of carbon-free energy output, there’s no comparison: nuclear fuel contains an order of magnitude more energy than other sources. In the United States, about 20 percent of all electricity is generated by only 62 plants, which operate day and night, rain or shine. Aside from the relatively few emissions associated with plant construction, operation, and uranium mining, nuclear power produces no greenhouse gases.

Critics cite the accidents at Fukushima, Chernobyl, and Three-Mile Island as proof that nuclear energy isn’t safe. Yet various back-of-the-envelope estimates suggest that, on a kilowatt hours basis, nuclear power has caused fewer deaths globally than any other established energy source, including wind and solar (this is due to a number of factors, including nuclear power’s gargantuan energy output, the relative infrequency of nuclear accidents, and the difficult task of attributing deaths to radiation exposure). And while nuclear reactors do generate waste, some of which may have proliferation risks, safe and secure long-term storage is more a question of political will than technical limitations.

So why don’t more environmentalists support nuclear power? One reason is historical (and tautological)—environmentalists have never supported nuclear energy. A better reason involves risk assessment: why support nuclear power when other carbon-free energy sources carry less risk? This is justified: renewable sources like wind and solar are safe, emission-free, and increasingly cost-competitive. A turbine and sun-powered future offends very few.

But renewables may not be enough. Avoiding the worst consequences of global warming will require limiting further carbon emissions to between 370-540 gigatons worldwide. Globally, we produce around 9.5 gigatons of carbon every year, increasing about 3 percent annually. If nothing changes, we’ll pass the critical threshold within 50 years.

We’ve never faced something this large or this important before. Climate change irreversibly affects every square inch of the planet, threatens one in six species with extinction, and carries profound human impacts that we’re only beginning to understand.

We all agree that we need more renewables. But if climate change is our first and overarching priority, then we may need nuclear. It’s not a silver bullet solution—not by any stretch—but it’s a proven method of generating massive amounts of power emissions-free. It enjoys political support from the right—an untraditional but all-important climate ally—and it may help solve some of the technical limitations of a renewables-dominated grid. Actively promoting its safe and secure expansion—or at the very least, not taking it off the table—should be a policy that more environmentalists seriously consider.

Next in this series: An Argument For “No”