Washington — When the Supreme Court returns to the bench Monday for the first time since late June, it will kick off its new term with a major case involving an effort by the city and county of Boulder, Colorado, to hold fossil-fuel producers accountable for the impacts of global climate change.
The lawsuit from Boulder is one of dozens filed by states and local governments against energy companies in state courts that seek money damages for past and future harms that they allege are caused by the buildup of greenhouse gases in the atmosphere, which has led to global warming.
The long-running dispute brought by Boulder targets Exxon Mobil, the nation’s largest energy company, and Suncor Energy, which operates two oil refineries in Colorado. The suit remains in its early stages, and the issue before the Supreme Court is whether the suit can proceed or is barred by federal law. A win for Boulder from the Supreme Court wouldn’t mean it will ultimately prevail against the fossil-fuel producers in state court.
“This is not a judgment about whether these cases will succeed. It’s a judgment about whether folks get to make their case,” said Jonathan Adler, a law professor at William & Mary who has written about federalism and environmental law and filed a friend-of-the-court brief in support of Boulder. “And even if they get to make their case, the scope of what they can pursue could well be narrowed and might well be narrowed significantly.”
Boulder’s lawsuit dates back to 2018. Filed in state court, the city and county allege that Exxon and Suncor’s conduct has caused or contributed to climate change, which has in turn forced Boulder to confront extreme heat, larger and more frequent wildfires and damage to the ecosystem, among other issues.
Boulder officials raised five claims under state law. They argue that the energy companies’ production and allegedly deceptive marketing of fossil fuels has led to “unchecked” use of their products that has caused a rapid rise in the concentration of greenhouse gases in the atmosphere.
Exxon and Suncor attempted to move the case to federal court, but that effort was unsuccessful. The companies also asked the Boulder County District Court to dismiss the case on the grounds that federal law foreclosed the claims against them. When the state court denied that request, the companies asked the Colorado Supreme Court to step in.
The state high court sided with the city and county of Boulder, and Suncor and Exxon appealed to the U.S. Supreme Court.
In addition to considering whether federal law precludes Boulder’s state-law claims, the Supreme Court asked lawyers for both sides to address whether it has jurisdiction to review the Colorado Supreme Court decision.
Only eight of the nine justices will participate in the arguments Monday, as the Supreme Court said last week that Justice Samuel Alito had chosen to recuse himself from the case. No reason was given for Alito’s decision. His financial disclosure for 2025 shows that he had individual holdings in two energy companies, ConocoPhillips and Phillips 66. He did not report individual stocks in either Exxon or Suncor.
Alito’s absence leaves open the possibility that the Supreme Court divides 4-4 in the case. If that happens, the decision of the lower court — the Colorado Supreme Court, in this case — would stand.
A “national problem”
Lawyers for Exxon and Suncor argued in Supreme Court filings that the Constitution and the Clean Air Act preclude claims that seek to address harms caused by interstate greenhouse-gas emissions. The Clean Air Act, they said, did not invite state law to apply to disputes involving interstate pollution.
If the Colorado Supreme Court’s decision is upheld, “it would authorize all fifty States, the tens of thousands of municipalities, and even the hundreds of millions of individuals in our country to ask local courts to establish countless, conflicting climate policies for the Nation,” Exxon and Suncor lawyers argued.
Additionally, the energy companies and the Trump administration, which supports Exxon and Suncor in the case, warned that efforts like Boulder’s to secure relief for the effects of greenhouse-gas emissions — including those released abroad — undermine the government’s control over foreign affairs.
“Such lawsuits would create an end-run around the United States’ existing diplomatic channels for addressing climate change in favor of innumerable state judicial ones,” lawyers for Exxon and Suncor said. “And the imposition of potentially devastating liability on fossil-fuel producers will undercut the government’s pursuit of primacy in global energy production.”
Because greenhouse gases emitted from sources in every state and around the world cannot be unmixed and traced, the companies warned that allowing all 50 states to apply their own laws would result in confusion. Only a “neutral, uniform federal law” can resolve disputes over the regulation of air and water, they said.
“It’s a national problem, so it requires a national solution,” Michael Williams, solicitor general of West Virginia, told reporters during a briefing Wednesday.
West Virginia and 25 other states are backing Suncor and Exxon Mobil and argue that Boulder’s lawsuit jeopardizes their ability to achieve their own policy goals on energy production and environmental protection.
“We don’t take issue with the idea that a state can actually regulate sources within its own borders. So if West Virginia wants to regulate a coal plant in West Virginia, we claim the right to do that,” Williams said. “In the same way, if Colorado wants to regulate emissions coming from Colorado in Colorado, they’re free to do that as well. What they’re not free to do is say, hey you emitters, anywhere in the world … we’re going to make you pay money for any of those emissions anywhere in the world.”
But lawyers for Boulder urged the Supreme Court to dismiss the appeal on the grounds that it does not have jurisdiction. If the justices opt not to, they said the Colorado Supreme Court decision should be upheld.
“Does anything implicit in the Constitution bar this suit?” they wrote in a filing. “Nothing does.”
Boulder noted there is often litigation to address the local impacts of problems that could benefit from international solutions, like food contamination, human trafficking and the fentanyl crisis. The city and county’s effort to hold energy companies liable is just another example, they said.
“That climate change is a global problem does not disempower states from redressing its local harms either,” they wrote in a filing. “This litigation is not an attempt to solve climate change; it merely asks that petitioners bear their fair share of local costs incurred in part because of their tortious conduct.”
Boulder also pushed back on the energy companies’ argument that the Clean Air Act preempts its claims, and said that law governs emissions, not the conduct of the upstream fossil-fuel producers. Plus, lawyers for the city and county said they did not sue for emissions, but over allegedly deceptive marketing and production, which the Clean Air Act does not regulate.
“Indeed, avoiding liability would not require reducing emissions at all — only telling the truth, so the public can make informed consumption decisions free of the distorting effect of petitioners’ misrepresentations,” they said.
The Trump administration argues that Boulder’s suit invites “needless diplomatic friction” with the foreign countries where Exxon and Suncor produce and sell their fossil fuels. But Adler, the William & Mary professor, noted that the Trump administration has withdrawn from international agreements that seek to address global warming and greenhouse-gas emissions.
The foreign-affairs argument “seems to suggest that any time the executive branch claims that it would like to negotiate in a space that could be implicated by companies being held liable for damages that they may have contributed to, that would really give the executive branch the ability to preempt any sort of litigation that it wanted. That can’t be the law,” he said. “If there was an actual conflict between an actual treaty, of course that could preempt state law. But we don’t even have that.”
Adler also said that Congress could weigh in and restrict suits against fossil-fuel companies for the harms tied to their products. In fact, it took similar action in 2005 when lawmakers passed a federal law that shields gun manufacturers from civil lawsuits that seek to hold them accountable for harms stemming from the criminal misuse of their firearms.
“If Congress believes that what’s going on here is a combination of plaintiffs’ lawyers and activists trying to make energy less available or less affordable, or to otherwise create pressure on fossil-fuel companies, Congress has the tools to address that,” he said. “That’s a job for the legislature, not a job for the courts.”
A decision from the Supreme Court is expected by summer of 2027.
