In response to an EPA proposal to freeze emissions and fuel economy standards, California said it will not honor federal vehicle certifications if the proposal goes through.

"The California Air Resources Board (CARB) has proposed amending the California Low-Emission Vehicle III Greenhouse Gas Emission Regulation to ensure that cars and light-duty trucks for model years 2022-2025 continue to meet California standards even if Federal standards are frozen," reads a statement from CARB reprinted in Green Car Congress.

Under a 2012 agreement with the EPA (which regulates emissions standards, including those of carbon dioxide) and NHTSA (which has statutory authority over fuel economy), California agreed that cars would be "deemed to comply" with California standards if they were approved by the federal agencies under standards as strict as the state's. Now the state says it will repeal that provision of its regulations if NHTSA and the EPA roll back increases that all three agencies and the automakers agreed to at that time.

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"To ensure that the effects of any federal weakening for model years 2021 through 2025 are not felt in California, CARB is proposing amendments to its LEV III greenhouse gas emission regulations to clarify that the “deemed to comply” option is available only for the currently adopted federal greenhouse gas regulations,"  the statement reads.

This is the first step toward the divergence of federal and state standards that have been harmonized since 2012.

Automakers, which lobbied the Trump Administration to loosen the standards, insisted at the same time that their top priorities were to have a single national standard and to have regulatory certainty about what standards would be in force going forward.

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Based on California's statement, it now looks like automakers may get neither.

Under California's new statement, If the EPA, and NHTSA succeed in freezing fuel economy standards, automakers may have to have to recertify cars in California that are already certified nationally. That's exactly the situation the automakers have said they want to avoid.

To address this problem, the Trump Administration proposal lays out a plan to rescind California's legal waiver to set its own fuel economy standard, which would render the California statement moot. California was granted that right in 1970 under the Clean Air Act, both because it has unique climate problems that trap smog in the air over California cities and because the state started regulating air quality and vehicle emissions before the federal government did.

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The joint EPA/NHTSA proposal, dubbed the Safer and Affordable Fuel Efficient Vehicles Proposed Rule (SAFER), suggests that the 1975 Energy Policy and Conservation Act never granted California the right to set its own standards. The EPA and the NHTSA noted that the 1970 Clean Air Act gives the EPA the right to refuse to grant the state an emissions waiver.

Revoking an existing waiver, however, would be unprecedented, says Simon Mui, senior scientist for California vehicles and fuels at the Natural Resources Defense Council. When it granted the state's current waiver, the EPA approved of California's current plans in perpetuity (if not necessarily the idea of allowing the state to raise standards further.) "It would be a really high legal bar for the EPA to revoke the waiver," he said in an interview with Green Car Reports.

"To revoke the waiver, the EPA would have to show that California no longer has unique problems with air quality or climate change or that California was arbitrary and capricious in setting its standards," Mui said. "In short, they would have to construct a world where California doesn't have wildfires, sends all its water to the ocean, and where California's emissions standards aren't helping."

In conjunction with 16 other states, California has already launched a lawsuit against the EPA over the proposal to freeze the standards, virtually guaranteeing that the proposal will be tied up in court for years with an uncertain result—the other outcome the automakers lobbied against.