The threat of climate change is leading some Democratic presidential candidates to favor nuclear energy.

While Democrats and some Left environmental groups have traditionally been skeptical of nuclear energy on safety and cost grounds, a faction of candidates for president is embracing nuclear energy — which provides most of America’s zero-carbon power.

“I don't think nuclear is tricky anymore with Democrats,” said Josh Freed, who runs the clean energy program at the center-left think tank Third Way. “What we have seen over last the several years is nuclear has emerged as an area where there’s growing acknowledgment across the climate debate that it needs to be an option."

Candidates advocating for nuclear power span the ideological spectrum, including liberal Sen. Cory Booker of New York, Washington Gov. Jay Inslee — who is running a climate-centric campaign — and former Rep. John Delaney of Maryland, a centrist.

“We have to be open to all low carbon and zero-carbon potential sources of energy given the urgency of this effort,” Inslee told reporters at a March renewable energy industry conference in Washington, D.C.

Booker told the Washington Examiner at a recent campaign stop in Columbia, S.C., that nuclear energy “has to be part of the equation if we want to move quickly toward a carbon-free future.”

Delaney also embraces the all-of-the-above zero-carbon approach, noting that renewables aren’t ready to provide all of the nation’s carbon-free power because solar and wind are limited by weather conditions from providing electricity on a 24-hour basis without the help of batteries.

“I am supportive of nuclear energy as a transition fuel off fossil fuels,” Delaney told the Washington Examiner. “I am hesitant to eliminate any energy sources before we have the proper technology in place.”

Sen. Amy Klobuchar, D-Minn., meanwhile, supports "safe nuclear power" to help the U.S. achieve "energy independence," according to her Senate website.

But nuclear’s future is clouded by a dire financial picture.

Utilities are faced with the premature closure of several nuclear plants due to increased competition from low-cost natural gas power plants, wind, and solar.

Only one new reactor has been completed in the last three decades in the U.S., with recent projects canceled or delayed because of mounting expenses.

Energy Secretary Rick Perry last week issued a $3.7 billion federally-backed loan guarantee to keep the Vogtle nuclear power plant in Georgia afloat after years of cost overruns and project delays. It is the only reactor under construction in the U.S.

All of this is bad news for climate change.

Nuclear energy provides almost 60 percent of the country's carbon-free electricity, more than all other zero-carbon sources combined.

A November 2018 report by the Union of Concerned Scientists found that more than one-third of America’s nuclear plants will or could be closed within the next decade and that they would be replaced by carbon-emitting natural gas or coal. The report said closing the at-risk plants early could result in a cumulative 4 to 6 percent increase in U.S. power sector carbon emissions by 2035 from burning more natural gas and coal.

Jason Bordoff, a former energy adviser to President Barack Obama and the director of Columbia University's Center on Global Energy Policy, said that Democrats running for president in 2020 should support policies to sustain and advance nuclear power.

“The Paris climate goal of limiting temperature rise to well below 2 degrees Celsius is barely within reach at this point, and if we are to have any chance of making it we need to embrace all zero-emission technologies, including advanced nuclear power, through policies that create incentives to continue operating existing plants and invest in new technology,” Bordoff said.

Booker has led the Senate Democratic push for small advanced nuclear reactors, which are unproven but are supposed to be cheaper and safer because they produce less waste.

Booker helped pass a bipartisan bill that became law in December that speeds the federal licensing process for advanced nuclear reactors and caps cost for companies

Fellow presidential candidates Sens. Kamala Harris of California, Bernie Sanders of Vermont, and Kirsten Gillibrand of New York all voted against the bill. None of them returned requests for comment about their current position on nuclear.

To be sure, the most liberal 2020 Democrats are more hostile to nuclear energy. Sanders has previously called for phasing out nuclear energy, praising California in 2016 for closing its last nuclear plant. Rep. Tulsi Gabbard, D-Hawaii, wrote on her campaign website that she opposes "continued reliance on nuclear energy in the U.S."

Booker, however, has continued to push for advanced nuclear energy during the presidential campaign, introducing a bill last week with Energy and Natural Resources Committee Chairwoman Lisa Murkowski, R-Alaska, that would require the Energy Department to create a 10-year strategy to support advanced nuclear technology and extend the length of federal power purchase agreements from 10 to 40 years. This would encourage the federal government to buy power from nuclear projects, which have a longer lifespan than other energy sources.

“A lot of people are, I think, against nuclear energy because their mind and imaginations [are] on the nuclear power plants of the 1950s and 1960s,” Booker told the Washington Examiner, explaining his support for advanced reactors. “The next generation of nuclear power plants that should be built in this country are profoundly more safe.

Inslee also said he supports investment into advanced nuclear reactors but cautioned there have to be “significant improvements in nuclear to allow it to continue to flourish.”

“The cost has to come down to make it competitive with other sources,” he said.

Inslee and other candidates are less committal about whether they endorse actions by states such as Illinois, New York, and New Jersey that have moved to compensate nuclear plants to keep them operating for their zero-carbon value. Inslee said subsidies should be considered on a “plant-by-plant basis.”

Other climate hawks argue that wind and solar, which have provided most of the new power-generating capacity in the past two years, are ready to replace nuclear power.

“Nuclear power is a high-cost, high-risk energy source,” said Matthew McKinzie, senior adviser of the National Resources Defense Council Action Fund. “It’s not clean energy. We need to address the very real safety and proliferation risks before contemplating it as a climate solution.”