Double Canyon è l'ultimo impianto nucleare ancora in funzione in California. La sua costruzione fu fortemente contestata, 1900 attivisti vennero arrestati nel 1981 durante una manifestazione di protesta, ma solo dopo Fukushima il fronte dei contrari si è allargato. Ora la Pacific Gas & Electric ha comunicato che allo scadere delle licenze, nel 2024, chiuderà la centrale essendo in grado di offrire "la stessa quantità di energia, a prezzi inferiori agli attuali, utilizzando esclusivamente fonti rinnovabili, eolico e solare". Da un lato la conferma che si possono fare profitti anche senza distruggere il pianeta, dall'altro un precedente per altri stati che stanno valutando l'abbandono del nucleare.

Few nuclear power plants have been as contentious as Diablo Canyon. The plant, which went online in 1985 after years of ferocious opposition, sits on a gorgeous stretch of California coastline, surrounded by several earthquake faults and reliably producing enormous quantities of power - almost a tenth of California’s in-state generation. It also reliably kills enormous quantities of marine life with a cooling system that depends on huge intakes and discharges of seawater. David Brower, the executive director of the Sierra Club, got so angry with the organization when it refused to oppose the plant that he left to establish Friends of the Earth.

Mr. Brower, who died in 2000, would have been pleased with last week’s news. After long negotiations that involved, among others, Friends of the Earth and the Natural Resources Defense Council, the plant’s owner, Pacific Gas and Electric, announced that it would shut down Diablo Canyon when licenses for its two reactors expire in 2024 and 2025 and that it would replace the power with lower-cost, zero-carbon energy sources.

Approvals will be needed from two state agencies, the California State Lands Commission and the state’s Public Utilities Commission. Both should say yes; this is an event of potentially great significance for the future of energy generation in this country and for the health of the earth itself- and not just because a bunch of sometimes quarrelsome forces (unions, environmental groups, the power company) came together to make it happen.

First, the agreement is a recognition by PG&E, which generates a big chunk of its electrical output (and revenues) from Diablo Canyon, that it can provide the same amount of energy at lower costs by investing in wind and solar power and in energy efficiency improvements throughout the system, including its customers. As one negotiator put it, the deal is further evidence that “the age of renewables has arrived” - at least in California, which has long led the nation in energy innovation and last year passed a law requiring state-regulated utilities to get half their electricity from renewable sources by 2030.

Equally important, the agreement could serve as a positive example for other states and nations that may in time need to replace aging nuclear plants without increasing carbon emissions. However old and creaky some of them may be, America’s 99 nuclear reactors produce nearly a fifth of the nation’s power and two-thirds of its low-carbon energy; at a time of mounting fears about climate change, the country would be foolish to shut them down prematurely. When the time comes to retire them, it would be no less foolish to replace their power with anything other than zero-carbon sources like wind, or solar or energy efficiency.

One governor who understands this is New York’s Andrew Cuomo. Mr. Cuomo has proposed an ambitious clean-energy agenda that includes not only substantial investments in wind and solar power, but also subsidies to keep open several upstate nuclear plants that are at risk of closing because of low electricity prices driven by cheap natural gas.

Mr. Cuomo would be happy to close down the Indian Point plant, north of New York City. Indian Point has a terrible track record and last week was forced to shut down one reactor. But losing the upstate plants, he argues, would mean increased reliance on fossil fuels and the greenhouse gas emissions they generate until the day when renewables kick in. A similar drama is playing out in Illinois, where Exelon, a big power producer, has threatened to close down two money-losing nuclear plants unless it gets help from the Illinois legislature.

From a climate perspective, the smart strategy in such cases would be to hold on to the nuclear plants until a California-like transition to greenhouse-gas-free electricity is feasible. Not every state has California’s natural blessings, or its aggressive renewable energy mandates. But its commitment and imagination are worth emulating.