Washington — The Supreme Court returns Monday for its first session since late June, opening the new term with a major case over whether the city and county of Boulder, Colorado, can hold fossil-fuel companies financially responsible for the effects of climate change.
Boulder’s lawsuit is among dozens brought by states and local governments in state courts against energy companies. The cases seek damages for past and future injuries allegedly linked to the accumulation of greenhouse gases in the atmosphere and the resulting global warming.
The long-running case names Exxon Mobil, the nation’s largest energy company, and Suncor Energy, which operates two oil refineries in Colorado. The litigation is still in its early stages, and the Supreme Court must decide whether it can move forward or whether federal law blocks it. Even a ruling for Boulder would not determine whether the city and county ultimately win their claims 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 studies 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 case was filed in state court in 2018. The city and county contend that Exxon and Suncor’s conduct caused or contributed to climate change, forcing them to address extreme heat, larger and more frequent wildfires, ecosystem damage and other consequences.
The local governments brought five claims under Colorado law. They allege that the companies’ production and deceptive marketing of fossil fuels encouraged their “unchecked” use, contributing to a rapid increase in atmospheric greenhouse-gas concentrations.
Exxon and Suncor sought to transfer the case to federal court, but that effort failed. The companies then asked Boulder County District Court to dismiss the lawsuit, arguing that federal law barred the claims. After the state court rejected that request, they turned to the Colorado Supreme Court.
Colorado’s highest court ruled for Boulder, prompting Suncor and Exxon to appeal to the U.S. Supreme Court.
The justices will consider not only whether federal law prevents Boulder’s state-law claims, but also whether the Supreme Court has jurisdiction to review the Colorado Supreme Court’s ruling.
Only eight justices will hear Monday’s arguments. The Supreme Court announced last week that Justice Samuel Alito had recused himself from the case, without providing a reason. His 2025 financial disclosure lists individual holdings in ConocoPhillips and Phillips 66, though it does not show individual stock holdings in Exxon or Suncor.
Alito’s absence raises the possibility of a 4-4 split. In that event, the Colorado Supreme Court’s decision would remain in effect.
A “national problem”
In Supreme Court filings, attorneys for Exxon and Suncor argued that the Constitution and the Clean Air Act block claims involving damage from interstate greenhouse-gas emissions. They said the Clean Air Act does not permit state law to govern disputes involving pollution that crosses state lines.
Upholding the Colorado Supreme Court, the companies argued, “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.”
The energy companies and the Trump administration, which supports them, also warned that lawsuits like Boulder’s could interfere with the federal government’s authority over foreign affairs. That concern applies to claims involving greenhouse gases emitted outside the United States, they said.
“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,” Exxon and Suncor’s lawyers wrote. They added that potentially devastating liability for fossil-fuel producers could weaken the government’s effort to maintain primacy in global energy production.
The companies also argued that greenhouse gases released by sources across the United States and around the world cannot be separated and traced to individual locations. Allowing all 50 states to impose their own rules, they warned, would create uncertainty and conflicting obligations. Disputes over air and water regulation, they said, require a “neutral, uniform federal law.”
“It’s a national problem, so it requires a national solution,” Michael Williams, West Virginia’s solicitor general, told reporters at a Wednesday briefing.
West Virginia and 25 other states are supporting Suncor and Exxon Mobil. They contend that Boulder’s lawsuit threatens their ability to pursue their own goals for 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 emitters, anywhere in the world … we’re going to make you pay money for any of those emissions anywhere in the world.”
Boulder’s attorneys, however, asked the Supreme Court to reject the appeal, arguing that the justices lack jurisdiction to hear it. If the court declines to dismiss the case on that basis, they urged the justices to uphold the Colorado Supreme Court’s decision.
“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.
