Governors' Biofuels Coalition

By just about any measure, the movement to battle climate change has grown so large that the truths of Al Gore’s decade-old movie now seem more mainstream than inconvenient.

In Paris in December, 195 nations agreed to reduce greenhouse gases. In the United States, 70 percent of Americans say that climate change is real. Pope Francis has joined the call for action. Hundreds of thousands of people have come together for climate marches in Paris and New York, and demonstrators recently held fossil-fuel protests on six continents.

“That’s what I call momentum,” Daniel R. Tishman, the chairman of the board of the Natural Resources Defense Council, said in its recent annual report. “This isn’t just the wind at our backs; these are the winds of change.”

But the movement that started with a straightforward mission — to get more people to appreciate the dangers of climate change as a precursor to action — is feeling growing pains. What may seem like a unified front has pronounced schisms, with conflicting opinions on many issues, including nuclear power and natural gas, that are complicating what it means to be an environmentalist in this day and age.

Consider some of the biggest points of contention:

Nuclear

The factional boundaries are not hard and fast, with groups shifting their positions as the science and waves of activism evolve. The environmental movement has always been a congregation of many voices, and some disagreement should be expected on such complex and intractable problems as saving the planet. Still, the tensions remain strong.

There are sharp disagreements over whether nuclear plants should be part of the energy mix to reduce greenhouse gas emissions. Disasters like that at the Fukushima plant in Japan have undercut confidence in the technology, but it remains attractive to the Obama administration and many in the environmental movement, including James E. Hansen, a retired NASA climate scientist.

Supporters argue that nuclear plants can produce enormous amounts of power without the carbon dioxide that burning coal and natural gas produce. They also point out that the energy sources replacing existing plants tend to come from natural gas, causing greenhouse emissions. That was the case in New England when the Vermont Yankee plant was shut down, and in California after the closing of the plant at San Onofre.

California has decided to wind down the Diablo Canyon reactors by 2025, a lengthy transition that could allow a buildup of renewable energy sources to replace the lost power. The nuclear power debate extends to questions of whether to develop a new generation of plants that supporters say would be less expensive and safer, or whether to extend the lives of existing plants.

Opponents of nuclear energy argue that the move to renewable energy sources would not require a new generation of nuclear plants. Naomi Oreskes, a Harvard historian who has written about the tactics of those who spread doubt about climate change, said proponents of nuclear power had not proved that the risks of operating the plants, and the waste they produce, could be managed.

“We all agree that there is urgency to this matter,” she said in an email interview. “So do we really want to bet the planet (literally) on a technology with such a bad track record? And that even when it works takes decades to build?”

She has called the pronuclear arguments from environmentalists “a new, strange form of denial,” pointedly using a word associated with those who have disputed the validity of climate science itself.

Natural gas

Burning natural gas produces less carbon dioxide and smog-producing pollutants than burning coal, so environmental groups such as the Sierra Club and even President Obama once praised it as a “bridge” to renewable fuels: that natural gas plants could replace coal plants until alternate sources like solar and wind power could take over.

More recently, however, the environmental effects of hydraulic fracturing, or fracking, which is used to extract fossil fuels, and growing worries about the greenhouse gas methane, which often leaks when natural gas is produced and transported, have led many scientists and activists to call natural gas a “bridge to nowhere.” (The Sierra Club now has a “Beyond Natural Gas” campaign.)

Climate campaigners like Bill McKibben have argued that the potency of methane as a greenhouse gas, especially in the short term, might make it worse than coal. He calls this “the terrifying chemistry” of warming, though others have disputed his interpretation of the science.

Mr. McKibben has described those who favor natural gas as a way to reduce greenhouse emissions as believers in “painless environmentalism, the equivalent of losing weight by cutting your hair.”

The fight has made its way into the Democratic campaign for the presidency: Senator Bernie Sanders of Vermont called for a national ban on fracking, while Hillary Clinton has suggested that the technology should be carefully regulated and that, if natural gas is a bridge to alternate energy sources, “we want to cross that bridge as quickly as possible.” Those putting together the Democratic Party platform narrowly rejected the call for a ban.

Fossil-fuel companies

Two distinct camps have emerged on the best strategy for dealing with companies like Exxon Mobil. One camp wants to attack their very existence, and to hurt their businesses and reputations as a way of accelerating the transition to renewable technologies like wind and solar.

Universities and institutional shareholders like pensions and church endowments are being pressed to sell their stock in fossil-fuel companies, to fight projects like the Keystone XL pipeline and to disrupt construction of fossil-fuel facilities.

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