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For Immediate Release


Abby Figueroa, 510-809-1564,

Press Release

Nuclear Power’s Planned Exit from California May Trigger Rise in Emissions and Pollution if Regulators Fail to Act Aggressively, Scientists Say

Carbon emission surge as high as 15.5 million metric tons over next decade could be avoided.

With less than four years left before Diablo Canyon Power Plant near San Luis Obispo starts shutting down the state’s last two nuclear reactors, experts at the Union of Concerned Scientists (UCS) say energy regulators have not prepared sufficiently for what happens next.  

California is at risk of a 15.5 million metric ton increase in cumulative global warming emissions between now and 2030 if the state’s Public Utilities Commission (PUC) does not aggressively plan to replace Diablo Canyon’s nuclear generation with clean energy resources, according to a UCS analysis released today. The study predicts existing natural gas power plants will fill the supply gap, resulting in global warming emissions roughly equivalent to what 306,000 passenger vehicles would emit over the same period. Additionally, UCS estimated 1,890 metric tons of nitrogen oxide pollution would result from the spike in natural gas power. 

“What’s most troubling is how avoidable this potential surge in carbon emissions and pollution is and how little has been done at the PUC to prepare for what happens after the reactors shut down,” said Mark Specht, the study’s author and an energy analyst at UCS. 

When PG&E announced it planned to close the facility in favor of investing in energy efficiency, renewable energy and other zero carbon sources, UCS supported the decision. Nuclear power produces very low carbon emissions, but in order to operate safely and securely, it requires stringent regulatory oversight. The Diablo Canyon Nuclear Plant is one of the nuclear plants in the United States at the highest risk of an earthquake-induced meltdown and would require costly seismic upgrades to reduce this risk.

Replacing the Diablo Canyon plant with natural gas-fueled power plants is problematic because burning natural gas contributes to global warming pollution and produces nitrogen oxides that create smog and aggravate respiratory health. Natural gas already supplies a substantial portion of California’s current electricity needs. It is heavily used during evening hours when demand spikes and renewable power is no longer generated.  

“If the PUC does not act fast, they will create a situation where the natural gas generation we’re trying to get off the grid will be the only obvious short-term solution to fill the gap left by Diablo Canyon’s shutdown,” said Adenike Adeyeye, Western States Energy Manager at UCS. “Firing up the state’s natural gas plants is a quick fix, but it has immediate and disproportionate health impacts on the people and communities living closest to those plants and the long-term impact of adding millions more tons of carbon pollution to the atmosphere.”

Diablo Canyon produces about 16,000 gigawatt-hours of power each year, or 8 percent of California’s in-state generation. In 2018, California passed Senate Bill 1090 that requires the PUC to avoid any increase in emissions of greenhouse gases because of Diablo Canyon’s retirement.  

“The PUC is waiting until the seventh inning to come up with its game plan,” said Specht. “With so much at stake right now as California faces the twin challenges of safety shutoffs during wildfire season and rotating outages during heat waves, not planning for what happens after the reactor retirements is reckless. Furthermore, allowing a surge in natural gas power will be a huge step backward for a state striving towards 100 percent clean energy in 25 years.”

The UCS study calls for the PUC to move swiftly and order large procurements of wind, solar and energy storage over the next decade, gigawatts more than has already been planned for. The analysis found that it is even possible for the state to experience a decline in global warming emissions after Diablo Canyon’s closure if the PUC targets are aggressive enough. 

“By 2025, nuclear power will only be found in California’s history books, but climate change will be here and worsening if regulators don’t act fast,” said Adeyeye. “The PUC can avoid an increase in cumulative emissions and pollution after Diablo Canyon’s retirement, but time is running out.”



The Union of Concerned Scientists is the leading science-based nonprofit working for a healthy environment and a safer world. UCS combines independent scientific research and citizen action to develop innovative, practical solutions and to secure responsible changes in government policy, corporate practices, and consumer choices.

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