Environmental advocates are cautiously optimistic after the Supreme Court left California’s nation-leading auto emissions standards in place — at least for the moment.

The Supreme Court declined to hear a challenge from Ohio and 16 other conservative states that aimed to strip California of its authority to adopt vehicle emissions standards stricter than federal benchmarks. However, days earlier, justices announced they will decide whether red-state fuel producers have legal standing to sue the U.S. Environmental Protection Agency for alleged financial losses caused by California’s stringent fuel economy standards and electric vehicle mandate.

State policymakers and environmental advocates view the Supreme Court’s decision to leave California’s regulatory powers intact as a triumph. But, as an adversarial presidential administration is poised to take office, experts say they anticipate a flurry of legal objections over nearly all forthcoming California clean air policies.

“The Supreme Court was right to turn away this radical request by Republican-led states to upend decades of law letting California cut pollution and clean our air,” said Daniel Villaseñor, a spokesperson for Gov. Gavin Newsom. “California’s authority was codified in the Clean Air Act by none other than Republican Richard Nixon, who recognized that California should continue serving as a lab for innovation to show the nation what’s possible with smart policy.”

The battle to alleviate air pollution and reduce planet-warming gases will be waged largely in the courts over the next four years, according to experts. And the legal strategy, they say, will need to focus on defending California’s aggressive clean air rules as much as it will be about ushering in new regulation.

“It’s good news, at least in the short term,” said Joe Lyou, president of California-based nonprofit the Coalition for Clean Air. “Everyone’s concerned about what’s going to happen in the long term. But this is a good start to what will undoubtedly be a long, long battle over clean air over the next four years. A lot of it is going to be up to the lawyers.”

Several industry groups have already filed litigation to contest California’s rules, including a ban on new sales of gasoline vehicles in 2035.

Last week, when the Supreme Court announced it would review a legal challenge over how California regulations affected fuel producers, it signaled its willingness to consider objections to California’s vehicle emission rules. However, the justices won’t be weighing the merits of the case, only whether the fuel companies have the right to sue.

The District of Columbia Court of Appeals had previously ruled the lawsuit invalid, in part, because fuel producers are challenging California emission standards adopted in 2012. Because car manufacturers already comply with the standard, there is no feasible remedy for their claims, experts say.

Another part of the fuel producers’ argument is that the Clean Air Act only grants California the ability to regulate conventional vehicle pollution for clean air — such as smog-forming nitrogen oxides — not planet-warming gases such as CO2 to address global warming.

“Their argument is this authority was given to California because they have really bad smog problems, not because of climate change,” said Ann Carlson, the founding director of the Emmett Institute on Climate Change & the Environment at UCLA. “And therefore, they shouldn’t be able to regulate greenhouse gases under this special power they have.”

But many environmental advocates say that argument may be moot. California air regulators have long maintained that air quality issues in major California cities — including smoggy Los Angeles — are so severe that electric vehicles are necessary to meet pollution standards. Air pollution and greenhouse gas emissions go hand in hand, they say.

“You have a technology, in these zero emission vehicles, that can reduce the full spectrum of pollution,” said Alice Henderson, lead counsel for transportation and clean air policy at the Environmental Defense Fund, an organization that has helped defend California rules. “And it is sort of laughable to think that these air agencies should be forced to ignore that technology.”

But the fight to enshrine clean air rules is not just legal sparring. For Lyou, it’s about the health consequences of inhaling air pollution. According to the California Air Resources Board, air pollution contributes to roughly 5,000 premature deaths each year in Southern California.

“It really comes down to whether people are going to have asthma attacks, whether people die prematurely or whether people have heart attacks,” Lyou said. “These are lives at stake.”