For decades, a host of environmental groups has labored to close the Diablo Canyon nuclear plant.

Now, one wants to keep it open.

The new Save Diablo Canyon coalition aims to persuade Californians that the state’s last nuclear plant is an indispensable asset, not a danger.

California can’t possibly achieve its global warming goals without Diablo, coalition members argue. The seaside plant, near San Luis Obispo, produces 8 percent of all electricity generated within the state, and pumps no greenhouse gases into the sky.

“It felt wrong to me that we would close down a plant like that for reasons that are clearly irrational,” said the coalition’s organizer, Michael Shellenberger, who has long advocated for nuclear power as an answer to climate change. “Once they consider the brute numbers here, people will be won over.”

The group has recruited some major names, including James Hansen, arguably the nation’s most prominent climate scientist. On Friday, the group sent Gov. Jerry Brown and five other top state officials a letter urging them to help keep the plant running for decades to come. Diablo’s original operating licenses expire in 2024 and 2025.

And, in an odd twist, the group also sent the letter to the chief executive of Pacific Gas and Electric Co., which owns Diablo but has not yet committed to renewing the plant’s licenses. Save Diablo Canyon hopes to tip PG&E off the fence.

“We urge you not to allow unrelated conflicts, politics, ideology or irrational fears to get in the way,” the letter reads.

The group has not and will not accept money from PG&E, or any other energy company, Shellenberger said. So far, funding has come from philanthropists Rachel and Roland Pritzker.

The federal Nuclear Regulatory Commission decides whether to extend a plant’s license. But for reasons specific to Diablo, several California agencies could play a big part in deciding the plant’s fate.

New lease in question

The State Water Resources Control Board, for example, is weighing whether to force Diablo to replace its current cooling system with potentially costly towers. And the State Lands Commission, chaired by Lt. Gov. Gavin Newsom, is considering whether to give PG&E a new lease for state-owned tidelands at the plant. The water intake and outflow chutes for the plant’s existing cooling system lie on those tidelands, and the current leases expire in 2018 and 2019.

Newsom, not coincidentally, was among the officials addressed in the coalition’s letter. At a Lands Commission meeting in December, he expressed doubt that Diablo would still be open in 10 years.

Diablo has long been the subject of fierce debate, starting before it opened in 1985.

Earthquake faults, discovered only after construction began, nearly surround the plant. PG&E was forced to install major retrofits, including support beams and concrete buttresses, before the Nuclear Regulatory Commission granted the plant its operating licenses. Massive protests tried, and failed, to block its opening.

PG&E in 2009 announced that it would ask the commission to renew the plant’s licenses and keep it open for another 20 years. But the utility put that effort on hold after Japan’s Fukushima Daiichi accident in 2011. CEO Tony Earley told The Chronicle last year that the utility had not ruled out extending Diablo’s life span but had other, more pressing issues to deal with first.

Enter Shellenberger and his coalition.

Cofounded think tank

The Berkeley resident has a long history of rankling traditional environmentalists. In 2004, he wrote with Ted Nordhaus an essay called “The Death of Environmentalism” that argued the movement had grown too calcified to deal with a major crisis like global warming, and too fixated on narrow policy solutions like raising fuel standards on cars.

He cofounded the Breakthrough Institute think tank in Oakland, and last year co-authored “An Ecomodernist Manifesto.” Both the institute and the manifesto call for fighting climate change through technological innovation, rather than restricting energy production. Both are staunchly pro-nuclear. He is also developing a new organization, Environmental Progress, to advocate for cheap energy and nuclear power in the developing world.

Other eco-minded thinkers have reached the same conclusions as Shellenberger. They have so far failed to persuade most environmentalists, who believe the risk of a meltdown and the difficulties of dealing with radioactive waste outweigh any benefits.

“We went off on a romantic version of environmentalism instead of a pragmatic version,” said Stewart Brand, former publisher of the Whole Earth Catalog and a member of Save Diablo Canyon. “You can’t solve climate change without this. You do the math ... and you just can’t get there without something like nuclear.”

Both Brand and Shellenberger consider the dangers of nuclear power vastly overblown and note that it requires far less land than large-scale solar or wind facilities. As for the fault lines near Diablo, Shellenberger says the Nuclear Regulatory Commission has the technical expertise to judge whether the plant is seismically safe.

“If I didn’t think the NRC was an independent and competent agency, I would not support nuclear power at all in the United States,” he said.

Diablo’s critics aren’t likely to be swayed. Many are already familiar with Shellenberger and his arguments, and say he underestimates both nuclear power’s dangers and expense.

Eventually will close

“Diablo Canyon is going to close — you can’t run these plants forever,” said Damon Moglen with Friends of the Earth, an environment group born out of the fight to block Diablo Canyon’s opening. “So the real question is, what does the future of California’s energy look like? We are going to have an energy system that is clean, efficient and greenhouse gas-free, and it will be based on renewable energy and storage.”

And PG&E? The utility remains on the fence about relicensing Diablo, said spokesman Blair Jones.

“While we believe the carbon-free energy provided by Diablo Canyon is consistent with the governor’s vision to reduce (greenhouse gas) emissions, we have not made a decision to move forward with license renewal as we await additional feedback on seismic research and are evaluating the steps needed to obtain state approvals,” he said.

David R. Baker is a San Francisco Chronicle staff writer. E-mail: dbaker@sfchronicle.com Twitter: @DavidBakerSF