Even as California professes optimism in its legal fight against President Donald Trump’s rollback of tailpipe emissions limits, the state is eyeing a fallback plan that could test how much its residents are willing to sacrifice to fight climate change.

Trump has proposed gutting the state’s ability to regulate greenhouse gas discharges from cars and trucks. If he succeeds, Sacramento officials say they could take other steps to make gasoline-powered cars costlier to operate, and restrict their access to California highways, while at the same time offering even bigger subsidies and other perks for battery-powered vehicles.

“We’re looking at other ways to reduce pollution by regulating either the purchase or use of cars and light trucks that don’t involve setting standards on the vehicles themselves,” Mary Nichols, the head of the California Air Resources Board, said in an interview. “That could be a whole bunch of things. Limits on registrations. Fees and taxes.”

The only impediment would be convincing residents to foot the bill. So far, 60 percent of the state’s likely voters think emissions standards should go higher, even though most expect that fighting climate change will boost gasoline prices, according to a Public Policy Institute of California poll released last month. Just over half say they’d pay more for electricity from renewable sources.

“We’ve been tracking how people feel about reducing greenhouse gases during very good economic times and very bad times,” Mark Baldassare, the institute’s director, said in an interview. “We’ve seen consistent results, so this is one area where public opinions in California are settled.”

But Sacramento never gets a blank check, Baldassare said. A case in point is a Republican-backed initiative on the November ballot to revoke a recent 12-cent-per-gallon increase in gasoline taxes, plus higher fees on diesel engines and vehicle registrations. The proceeds would be earmarked for road building, but so far the vote is too close to call, Baldassare said.

“People are conflicted,” he said. “The desire to cut taxes is pretty much an instinct lots of voters have. But traffic is also bad, and they want something done about the roads.”

On August 2, the National Highway Traffic Safety Administration and Environmental Protection Agency proposed capping federal fuel economy requirements at a fleet average of 37 miles per gallon starting in 2020. Under Obama-era mandates, the average would have risen to roughly 47 mpg by 2025. This fuel economy freeze would cap emissions standards, too. The agencies also proposed revoking California’s authority to set greenhouse gas limits more stringent than the federal government’s, and to require the sale of electric cars.

California, 16 other states and the District of Columbia have already filed a lawsuit challenging the rollback’s scientific underpinnings. Sacramento officials promised another lawsuit if Trump finalizes his plan to eliminate the state’s ability to set tougher greenhouse gas regulations than federal standards.

Nichols said she’s optimistic about the state’s legal position. But she also described her fallback plan of limiting registrations or adjusting fees.

“These are all tools governments can use. They’re less effective and politically acceptable, but they do exist,” Nichols said.

Voter Polls

Nichols is banking on a deep reservoir of support for Sacramento’s clean air policies. Two out of three California adults — including all income and education groups — say climate change is extremely or very important to them personally, Baldassare said. This compares to one out of two in a nationwide ABC News poll in June, and it’s a difference that reflects the routine exposure of Californians to droughts, wildfires and triple-digit temperatures, he said.

In other poll responses, 62 percent of likely California voters say they want the state to set its own climate change policies, not the federal government, and half say these will result in more jobs for the state. Fifty-three percent say they approve of California Governor Jerry Brown’s handling of environmental issues, or double the rating for Trump.

But it’s only been 15 years since Californians chased Democratic Governor Gray Davis from office in a recall. He didn’t help himself by tripling car registration fees less than 10 days before the vote.

Practical Challenges

The practical challenges of enacting such policies will be magnified, at least initially, when Brown, 80, leaves office in January after serving as California’s governor longer than anyone else. Nichols, 73, recently had her term as head of ARB extended until 2020, but she has said publicly she’ll stay only if the next governor wants her.

“Whoever wins, we’ll be going from a governor who’s had four terms to one who hasn’t even been in office one day,” Baldassare said. “There will be a steep learning curve in terms of working with the legislature.”

Republican candidate John Cox has made the gas tax repeal the centerpiece of his attack on rising living costs during Brown’s eight-year tenure. While the vote on the repeal itself is too close to call, Cox trailed Gavin Newsom, the Democratic candidate, by a 55-31 margin last month, Baldassare said.

Candidate Comments

Matt Shupe, a Cox spokesman, declined to comment on whether he would support Nichol’s fallback plan. A spokesman for Newsom had no immediate comment but pointed to an Aug. 2 tweet from the candidate.

“Once again, we see an administration willing to ignore the facts and endanger the health of Californians and people across our country,” Newsom wrote. “Climate change is real. Rolling back these standards is feckless and irresponsible — California will not stand for it.”

Dan Sperling, a member of the state’s Air Resources Board, acknowledges the anti-tax fervor that runs through the state’s politics. But he said Sacramento will still have plenty of options if Trump constricts its ability to limit greenhouse gas emissions from tailpipes.

“States have lots of authority to manage their transportation systems, so we could adopt a whole range of fiscal and regulatory tools to reduce pollution and congestion,” Sperling said.

One example, he said, might be a revenue-neutral plan that levies fees on vehicles that discharge greenhouse gases, and provides subsidies for vehicles that don’t.