If Trump’s EPA abandons climate policy, could California take over on greenhouse gases?
Legal experts, including a former federal official and UCLA professor, say California could go it alone if the federal government stops regulating greenhouse gases. One reason to try is to protect the state’s clean-car economy.
In summary
Legal experts, including a former federal official and UCLA professor, say California could go it alone if the federal government stops regulating greenhouse gases. One reason to try is to protect the state’s clean-car economy.
California has long cast itself as the nation’s climate conscience — and its policy lab.
Now, as the Environmental Protection Agency moves to revoke the backbone of federal climate rules — the scientific finding that greenhouse gases threaten human health — one of the state’s top climate officials is weighing a provocative idea put forward by environmental law experts: If Washington retreats, California could lead on carbon-controlling regulation.
Absent what’s known as the endangerment finding, the EPA may soon consider abandoning the legal authority under the Clean Air Act to regulate greenhouse gases from vehicles, power plants and other sources, furthering the Trump Administration’s stated aim to dismantle U.S. climate policy.
While decrying the prospect of such a move, climate advocates say a repeal would yield a silver lining: California and other states could in theory set their own greenhouse gas rules for cars and trucks, regulations previously superseded by federal authority.
Cars and trucks represent more than a third of California’s greenhouse gas emissions. A long shot regulatory gambit could clean some of the nation’s dirtiest air – and keep the state’s clean-car transition alive.
“All options are currently on the table,” Lauren Sanchez, chair of the California Air Resources Board, told CalMatters in an interview.
Authority states have never had before
A former federal official and expert on the Clean Air Act – who is also a law professor at UCLA – first floated this idea.
Ann Carlson wrote in the law journal Environmental Forum that an aggressive federal action against climate policy “could, ironically, provide states with authority they’ve never had before.”
The Trump administration now argues that greenhouse gases do not endanger health and that regulation is more harmful — a claim widely rejected by scientists, businesses and environmental groups, as well as states, including California.
The Phillips 66 refinery in Wilmington, on Sept. 30, 2025. Photo by Stella Kalinina for CalMatters
“If greenhouse gases aren’t covered by the Clean Air Act,” Carlson told CalMatters, “then California could presumably regulate them — and so could every other state.”
Carlson, who ran the National Highway Traffic Safety Administration until last year and has written extensively about the landmark law, argues that the act only preempts state rules for pollutants it actually covers. States “have a pretty strong legal argument” to regulate greenhouse gases, she said.
The EPA, for its part, argues that states would still be barred from setting their own standards, arguing that its broad authority over air pollution covers even emissions the agency chooses not to regulate. That’s a view shared by the Alliance for Automotive Innovation, a trade association and lobbying group, which supported overturning California’s phaseout of new, gas-powered cars, as well as the American Trucking Associations, which has opposed some of California’s rules on trucks.
Carlson said that argument doesn’t hold up. In her Environmental Forum article, she wrote: “If Congress didn’t intend the act to cover greenhouse gases, as the administration argues, then it’s hard to believe Congress intended to preempt states and localities from regulating them.”
In other words, she says, preemption has its limits.
Other experts agreed the idea is worth considering.
Ethan Elkind, who directs the climate program at UC Berkeley’s Center for Law, Energy and the Environment, said that states are free to “do whatever they want,” as long as the federal government hasn’t preempted them.
Not a slam dunk for California to step in
For the better part of a century, California has worked to curb air pollution at the state and local level. The state’s vanguard status positions it well to test Trump’s move to curb federal climate regulation, say experts.
“I personally would be advocating that they move ahead,” said Mary Nichols, a former air board chair. “And if I were there, I would be looking to gain support for doing it.”
California holds a unique status under federal law. It can set tougher tailpipe-emission standards than the rest of the country — a recognition of its early leadership in fighting smog. Since 1968, the state has obtained more than 100 federal waivers for its vehicle rules, and other states can adopt California’s standards under certain conditions.
UC Berkeley law professor Daniel Farber said the state could even take a dual-track approach. “We don’t really think we need a waiver,” he would argue after EPA abandons the field, “but just in case we do: yes, give us one.”
California’s latest clash with Washington stems from a decades-long dance over who sets the nation’s toughest clean-car rules.
The state’s strict vehicle rules have helped spur innovations from catalytic converters to cleaner fuel to electric cars. The regulatory push began in Los Angeles after skies grew so smog-choked they stung peoples’ eyes.
In 1966, California adopted the nation’s first tailpipe standards. When Congress passed the 1970 Clean Air Act, it gave the state rare authority to set tougher rules — making California both a laboratory and a trailblazer, so long as it secured a federal waiver.
In 2002, California passed the nation’s first law regulating greenhouse gas emissions from vehicles. The Supreme Court’s 2007 Massachusetts v. EPA ruling confirmed those gases are pollutants under federal law, leading to the Obama administration’s 2009 “endangerment finding” that they harm public health.
Such a move would fit California’s pattern of pushing first and asking permission later. In 2005, the state adopted its greenhouse-gas standards for vehicles and sought a waiver before it was even clear whether carbon qualified as pollution under federal law. The EPA initially denied that request in 2008 but reversed course a year later, granting the waiver in 2009.
“So this wouldn’t necessarily be a slam dunk approach for the state to take, but I think the legal avenue is now there,” said Elkin, of UC Berkeley.
Targeting cars with new regulation
If California tried to regulate greenhouse gases on its own, it would have both experience and infrastructure to rely on. The process would look a lot like how the state has written past clean-car rules — except this time, the target would be carbon itself.
California’s clean-car rules have operated within the permission-seeking framework set up by the Clean Air Act — until this year, when Trump and Congress moved to block the state’s plans to phase out gas cars and tighten diesel-truck standards. Trump’s EPA then went further by proposing to repeal the 2009 endangerment finding, framing it as a win for “consumer choice.”
Most of the state’s climate programs already run under authority of California’s own groundbreaking state laws: clean-energy mandates for utilities, a carbon-trading program for businesses, even standards to cut the carbon in fuels.
Cars are different. They’re sold into a national market, and tailpipe emissions have long been federally preempted — one reason California has needed Washington’s permission to go its own way.
If the state decides to test those limits, regulators would need to draft new rules and open them to public review — a process that could take years.
California has already started down the path of new rules for clean cars and trucks. Last month, the Air Resources Board began the process of crafting clean car rules in response to the Trump administration’s rollback of the state’s new gas-car ban — a revocation the state is also fighting in court. In December, the board plans to begin the process of writing new emissions rules for trucks.
The automobile association declined to comment on the new rulemaking effort. Patrick Kelly, vice president of energy and environmental affairs for American Trucking Associations, said the group would work with its state affiliate to “respond to specific proposals. “
“More broadly, (our group) supports achievable national standards and opposes a patchwork of state and local standards that Congress sought to avoid,” Kelly wrote in an email.
Gov. Gavin Newsom swears in incoming California Air Resources Board Chair Lauren Sanchez on Oct. 1, 2025. Photo courtesy of Office of the Governor
Asked by CalMatters whether the new rulemakings could become the vehicle for California to go its own way under Trump, Sanchez, the air board chair, said it’s an option staff is studying.
“It’s something that staff is looking into, and I look forward to digging into myself,” Sanchez said.
No downside to trying, and some upsides
Even if legal experts like the idea in theory, UC Berkeley’s Dan Farber says California going forward alone is a longshot in practice.
“There’s a chance you would win,” Farber said, of the argument that the state could directly regulate greenhouse gas emissions from cars. “You’re buying a lawsuit, but other than litigation expenses, I don’t think there’s much downside in trying to do it.”
Farber and others point out that the Trump administration and car and truck manufacturers would almost certainly sue to block state-level efforts to regulate greenhouse gases.
The Alliance for Automotive Innovation warned, in comments to the EPA, that if states were not preempted, any unregulated emission “would then become fair game,” creating conflicting standards across the country. Automakers have long argued that letting states write their own climate rules would create a costly patchwork of standards, raising prices for consumers and complicating production for a national market.
California is in somewhat of a legal quandary. The Clean Air Act requires California to meet national pollution standards, and the state still has some of the most air-polluted regions in the country.
The state’s solutions rely heavily on clean-car and truck rules to meet those requirements. If California falls short, it could lose federal highway funding, a situation that Sanchez called a “no-win, Catch 22.”
After decades of regulation and incentives, California has built a reputation as a leader in electric cars, and experts said if the state pushes further on policy, that could help keep California’s clean-car transition alive and its electric-vehicle goals within reach.
Nick Nigro, founder of Atlas Public Policy, said California could also risk getting ahead of consumers if it goes it alone. Electric cars proved less popular than policymakers expected when it originally passed its goal to do away with sales of new gas-powered cars.
“What is clear is that the program was not overwhelmingly popular amongst the public, even in California, right?” Nigro said. “That’s usually a flag for policymakers.”
Craig Segall, an independent consultant and former state air board deputy, said there’s another factor to consider: by preserving demand and infrastructure for EVs, the state could maintain a beachhead for innovation that a future president might build on.
With no coherent federal policy to compete in the global EV market, California could again use its regulatory and investment muscle — just as it once did in helping spawn electric car maker Tesla — to push the market forward.
“What the feds are basically signaling here is that the field is open for anyone who’s serious about being a competitive car or truck company in five years,” Segall said. “One of those paths is: the world’s fourth largest economy figures out ways to take its manufacturing economic capacity and just plow ahead.”
