SAN DIEGO — The United States is on the verge of losing more than half of its low-carbon energy as the fight against climate change reaches a critical point – a reality the country hasn’t fully grappled with.

That’s according to findings recently published by researchers at UC San Diego, Harvard University and Carnegie Mellon University in the journal Proceedings of the National Academy of Sciences.

The paper – “U.S. nuclear power: The vanishing low-carbon wedge” – paints a picture of an industry on the verge of collapse. Facing economic competition from cheap natural gas, a significant number of U.S. nuclear power plants could be retired in the coming years, the authors wrote.

“We’re asleep at the wheel on a very dangerous highway,” said Ahmed Abdulla, co-author and fellow at the School of Global Policy and Strategy at the University of California, San Diego. “We really need to open our eyes and study the situation.”

The country now has a choice of abandoning nuclear power altogether or embracing the next generation of smaller, more cost-effective reactors, the report says.

However, the researchers argue, the second option is unlikely as it would require accelerating the regulatory review process and a sizable infusion of public money.

“It’s really surprising that one of our best weapons in our fight against climate change is at risk of utter collapse because of the economic and political challenges and not the technical ones,” Abdulla said.

While it might be a longshot, the promise of nuclear power has captured the imagination of many younger academics in recent years.

More students are pursuing nuclear engineering degrees than at any time since the early 1980s, with graduation rates in the field tripling between 2001 and 2015, according to survey data from the Oak Ridge Institute for Science and Education.

“Where else are you going to get a job where you can tell your grandkids that you saved the world?” said Per Peterson, a professor in the University of California, Berkeley’s department of nuclear engineering. “They don’t think they’re going to get rich.”

Still, environmental organizations have remained largely skeptical about the value of nuclear energy, given anxiety about safety and its cost. While advocacy groups have expressed concerns about replacing phased-out nuclear plants with fossil-fuel-powered plants, many would rather focus on supporting renewable sources.

“The danger is that the amount of subsidy that nuclear would require would suck all the energy out of supporting the other renewables,” said Edwin Lyman, a physicist at the Union of Concerned Scientists.

“There’s almost nothing that can be done to make nuclear a significant contributor in the next few decades, even if you throw billions of dollars at it,” he said. “The people who promote nuclear power have tunnel vision.”

Dan Jacobson, state director of Environment California, echoed those general concerns.

“Nuclear power in its current form has been an incredibility expensive way to boil water,” he said. “If you’re really trying to decarbonize our grid, we would rather spend those billions on efficiency, conservation and renewables.”

Nuclear energy produces roughly 20 percent of nation’s power supply, compared with about 17 percent for all renewables combined, according to the U.S. Energy Information Administration. Wind and solar, for example, produce about 7.6 percent of the country’s power.

While aggressive efforts continue to develop batteries for storing intermittent sources of electricity from solar and wind, utilities in recent years have embraced natural gas. The fossil fuel now produces nearly 32 percent of U.S. power.

Given recent trends, nuclear industry scientists question whether renewables would be able to offset the losses from retiring nuclear plants in time to stave off the worst consequences of climate change.

“The reality is you cannot actually replace 20 percent of the need with wind and solar, unless you want to wallpaper every square inch of many states,” said Christian Back, vice president of nuclear technologies and materials at General Atomics. “It’s not efficient enough.”

Back said that given the right support from the federal government, nuclear reactors now operating can, in many cases, be retrofitted to improve safety and lifespan, while smaller, more cost-effective plants can be introduced within the next decade.

“This is a situation like NASA when you’re putting someone on the moon where the government needs to recognize the long-term benefit and investment that’s required and help support that,” she said. “This is where political will matters.”

The paper also suggested that many in the public don’t take nuclear energy seriously because they don’t realize the urgency of the situation. Specifically, the research points to the need to aggressively decarbonize the energy sector by midcentury because carbon dioxide emitted today will remain in the atmosphere for hundreds of years, baking in the effects of global warming for generations to come.

If the country is going to embrace nuclear energy, it should do so as quickly as possible to help stave off the impacts of climate change, said George Tynan, associate dean of the Jacobs School of Engineering at UC San Diego.

“You realize that we’re almost out of time because of the development timescales,” he said. “If new nuclear technologies are going to have a material impact on carbon emission in the midcentury, then they have to be demonstrated in the marketplace in the next decade or so.”

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