California is at risk of a 15.5-million-tonne increase in cumulative global warming emissions between now and 2030 if the state’s regulator, the Public Utilities Commission (PUC), does not aggressively plan to replace Diablo Canyon’s nuclear generation with clean energy resources, according to a Union of Concerned Scientists (UCS) study.

UCS said that with about four years left before the shutdown of the two nuclear reactors – the only ones in the state – the PUC has not prepared sufficiently for what happens next.

The study predicts existing natural gas power plants will fill the supply gap when Diablo Canyon closes, resulting in global warming emissions roughly equivalent to what 306,000 passenger vehicles would emit over the same time period. Additionally, UCS estimated 1,890 tonnes of nitrogen oxide pollution would result from the spike in natural gas power.