Over the many months EPA administrator Scott Pruitt signaled his intention to revisit the Obama administration's emission limits for 2022 through 2025 vehicles, California warned that it would not go along with any reductions.

The state has been allowed to set its own emission standards for decades, it noted, and it has every intention of sticking with the reductions in greenhouse gases it pioneered.

Now that Pruitt has officially issued a determination to engage in new rulemaking that will allow vehicles to emit more carbon dioxide, automakers are deeply fearful they will have to comply with two separate sets of CO2 standards.

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But the powerful head of the California Air Resources Board, Mary Nichols, is holding out hope that a deal between the state and national regulators remains possible—as long as the EPA doesn't try to "steamroll" California.

The news comes in a story by Bloomberg first published late Tuesday, and updated Wednesday morning, that quotes Nichols as saying there's still a chance to reach a joint decision on revising the standards.

She notes that Pruitt's decision last week simply kicks off a lengthy processing of rulemaking, including discussions with affected bodies like CARB, and public comment on any proposals for revised regulations.

Mary Nichols, chief, California Air Resources Board

Mary Nichols, chief, California Air Resources Board

"Reason could prevail," Nichols told attendees on Tuesday at the Future of Energy Summit in New York City, organized by Bloomberg New Energy Finance.

"There's a way to get to success, unless your goal is to roll over California and not allow us to have any standards."

In this case, rolling over the state would mean the EPA would attack or revoke the waiver signed in 2010—the latest of many over decades—that allows the state to set its own emission rules, recognizing the historical precedent that it had done so well before the EPA existed.

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EPA administrator Pruitt told Congress last July he didn't feel such action was warranted "at this time," but the embattled Cabinet member has also said repeatedly a single set of national standards is necessary.

That's what automakers want too, to prevent them having to track total CO2 emissions in the group of more than a dozen states that have adopted California's standards, which encompass more than a third of the nation's car buyers.

Nichols said she's amenable to tweaking the rules to make it easier for automakers to meet the overall emission-reduction goals, as long as such tweaks don't affect the continuing reductions in emissions of carbon dioxide from light vehicles going forward.

Golden Gate Bridge, connecting San Francisco and Marin County, California

Golden Gate Bridge, connecting San Francisco and Marin County, California

California is hardly letting up on its fight against any and every regulatory rollback on emissions, however.

“Scott Pruitt wants to let major polluters off the hook," California's attorney general Xavier Becerra said in a statement released Tuesday condemning what he called the "illegal repeal" of a regulation in effect since 1995.

"That is unconscionable, and it is illegal.”

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Known as the "Once In, Always In" policy, it "requires major sources of hazardous air pollutants—such as petroleum refineries and chemical plants—to permanently take action to reduce their emissions."

Accordingly, Becerra and the California Air Resources Board have sued the EPA in the DC Circuit Court of Appeals.

The California plaintiffs claim the repeal "contravenes the intent of Congress expressed in the Clean Air Act" and the reversal of the longstanding provision is both arbitrary and capricious.