(Bloomberg) -- With his proposal to roll back fuel economy and emissions standards for cars and trucks Thursday, President Donald Trump drew a line in the California sand.

The nation’s most populous state wasted no time crossing it.

“California will fight this stupidity in every conceivable way,” California Governor Jerry Brown said in a tweet.

The dispute -- which rattled automakers, among others -- centers on an element of the Trump proposal that would revoke California’s authority under the Clean Air Act to set rules more stringent than the federal ones limiting tailpipe greenhouse gas emissions as well as an electric-vehicle sales mandate.

The state has since 1970, when smog in Los Angeles became a rallying cry for the nascent environmental movement, employed tailpipe emissions rules that have been tougher than the federal government’s.

“For 48 years -- since one of my heroes, then-Governor Ronald Reagan, requested it -- California has had a waiver from the federal government to clean our own air,” action-movie star and former California governor Arnold Schwarzenegger tweeted. “If the president thinks he can win this fight, he’s out of his mind.”

In a desert state long at war with the whims of Mother Nature, emissions regulations are not just legal or regulatory issues.

“There’s a great irony in Trump releasing this plan just as California is burning,” said Ann Carlson, a University of California at Los Angles law professor. “We’re already seeing catastrophic forest fires as a result of climate change, and the administration’s answer is that everyone should drive a Hummer.”

The rollback is “especially hard to take,” Carlson said, because Trump officials invoked concern for human life lost in traffic accidents to justify it, while conspicuously failing to show the same concern for fire victims.

According to Trump officials, freezing the requirements will slow the pace at which new cars are getting more expensive, and so, allow people to replace older and less-safe vehicles more rapidly.

If he can undermine the waiver, Trump would destroy the state’s ability to require manufacturers to sell zero emission cars. ZEV’s are the state’s best available tool, Carlson said, to limit not just greenhouse gases that fuel climate change, but also pollutants like ground-level ozone which contribute to smog. Some of the nation’s worst smog, she said, continue to plague both Los Angeles and the state’s San Joaquin valley.

ZEVs need to make up as many as 40 percent of sales by 2030 if California is to meet its CO2 reduction targets, according to estimates by the state’s Air Resources Board staff.

But on a call with reporters Thursday, Bill Wehrum, the assistant administrator for the Environmental Protection Agency’s Office of Air and Radiation, said the agency only wants to limit California’s right to regulate greenhouses gases, and not pollutants like ozone.

“There’s pretty strong evidence that Congress intended the federal government to be the primary regulator” for both fuel economy and emissions, he said, adding that the Trump team hopes Washington and Sacramento can still negotiate a unified set of emissions regulations. “It makes no sense in the world to have a two-car world.”

Deaf Ears

So far, the Trump arguments are falling on deaf ears west of the Sierra Madre mountains that separate California from the rest of the U.S. Dan Sperling, a member of the state’s Air Resources Board, “the waiver issue is non-negotiable.”

California “will examine all 978 pages of fine print to figure out how the Administration can possibly justify its absurd conclusion that weakening standards to allow dirtier, less efficient vehicles will actually save lives and money,” Air Resources Board Chair Mary Nichols said in a statement. “Meantime, California remains fully committed to a rigorous 50-state program with a full range of vehicle choices. That program is in effect right now and will remain so for the foreseeable future.”

Traditionally, a dozen states have followed California’s lead on air pollution, and Colorado recently signed on, too. Combined, these states account for more than a third of all U.S. auto sales. And officials from some of those states joined California in its protests Thursday.

States React

“The Administration’s proposal to weaken these rules will cause the American people to breathe dirtier air and pay higher prices at the pump,” said Xavier Becerra of California, Maura Healey of Massachusetts and attorneys general from 18 other states in a statement Thursday. “We are prepared to go to court to put the brakes on this.”

California and its allies will argue the Trump Administration has violated the Administrative Procedures Act’s protocols for resetting tailpipe emission standards, and the EPA’s statutory obligation to reduce harmful pollution from vehicles.

“California certainly does have a chance to win a fight in court," said Michael Gerrard, an environmental law professor at Columbia Law School. “There has never been a decision on whether an administration can withdraw a waiver, since no previous administration has ever tried.”

Willing to Negotiate

So far, Becerra said in a conference call, California hasn’t seen any concrete evidence that Trump officials are willing to negotiate. “We don’t think they’ve been serious,” he said.

Automakers say they hope to avoid a situation in which they have to build one set of car’s for California’s standards and another for the rest of the nation. Or, worse, to be on the sidelines as a drawn-out fight moves through the courts.

“We look forward to finding common ground with federal and state regulators that allow us to operate under a single national program for fuel economy and greenhouse gases in the future,” Toyota Motor Corp. said in a statement.

In a statement from a pair of trade associations, carmakers urged negotiations between Sacramento and Washington.

“With today’s release of the administration’s proposals, it’s time for substantive negotiations to begin,” the Alliance of Automobile Manufacturers and the Association of Global Automakers said in a statement.

Andrew Wheeler, the EPA’s acting administrator, told a Senate panel on Wednesday that he would “certainly welcome” a compromise deal with California and would be willing to forgo challenging that state’s authority to set its own automobile efficiency requirements as part of such a pact.

But Carlson, the UCLA law professor, said compromise may be difficult to reach.

“I don’t see any room for negotiations when you’re starting point is to eviscerate California’s ability to regulate,” she said.

--With assistance from Kartikay Mehrotra.

To contact the reporter on this story: John Lippert in Chicago at jlippert@bloomberg.net

To contact the editors responsible for this story: Craig Trudell at ctrudell1@bloomberg.net, ;Jon Morgan at jmorgan97@bloomberg.net, Elizabeth Wasserman

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