▶ Watch Video: U.S. Supreme Court wrestles with bid by energy companies to block major climate suit
Washington — The Supreme Court on Monday grappled with a complex dispute involving an effort by the city and county of Boulder, Colorado, to hold energy companies accountable for the effects of global climate change.
Eight of the court’s nine justices heard nearly two hours of oral arguments in the case Suncor Energy v. Commissioners of Boulder County. Justice Samuel Alito recused himself from the case, the Supreme Court said last week.
No reason was given for Alito’s decision to sit out the case. His financial disclosure for 2025 shows that he had individual holdings in two energy companies, ConocoPhillips and Phillips 66. Alito did not report holding individual stocks in either Exxon Mobil or Suncor Energy, the two companies that Boulder filed its lawsuit against in 2018.
Alito’s recusal leaves open the possibility that the Supreme Court deadlocks 4-4 in the case. That outcome would mean the decision of the Colorado Supreme Court would stand, allowing Boulder’s case to proceed.
Boulder’s dispute against Exxon and Suncor remains in its early stages. At issue before the Supreme Court is whether the lawsuit can proceed or is barred by federal law. The high court also asked lawyers for both sides to address whether it has jurisdiction to review the Colorado Supreme Court’s decision.
In questions to both Kannon Shanmugam, who argued on behalf of Exxon and Suncor, and Sarah Harris, the principal deputy solicitor general, Justice Brett Kavanaugh repeatedly said that four of the Supreme Court’s decisions dating back to 1972 make clear that interstate air and water pollution are matters of federal law.
“We don’t have to reinvent the wheel, because we’ve said this multiple times and Congress, presumably when doing the Clean Air Act and doing the Clean Air Act amendments, has relied on this court’s precedents establishing that this kind of pollution is a federal-law matter, unless Congress speaks otherwise,” he said.
The Trump administration is backing Exxon, the nation’s largest oil company, and Suncor, which operates two oil refineries in Colorado, in the case. Boulder’s lawsuit, Harris said, “egregiously exceeds” constitutional limits of state authority.
“Interstate air pollution is an inherently federal area, and Congress hasn’t authorized this suit in the Clean Air Act,” she said.
But Justice Ketanji Brown Jackson stressed that the Supreme Court’s review is “premature.”
“It feels like we don’t really know enough to be confident that the theories that you are proposing are actually applicable here,” she told Harris.
Boulder’s lawsuit against Suncor and Exxon
The lawsuit from the city and county of 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.
Boulder alleges in its suit that Exxon and Suncor’s conduct has caused or contributed to climate change, which has in turn forced the city and county to confront extreme heat, larger and more frequent wildfires and damage to the ecosystem, among other issues.
The city and county raised several claims under state law and argued 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’s high court sided with the city and county of Boulder, and Suncor and Exxon appealed to the U.S. Supreme Court.
“It’s taken a long time to get to this point, but it feels very positive that that effort that we started in this exact location eight years ago has gotten to the stage of going to the Supreme Court, and then hopefully the next step of having a full hearing in court,” Boulder Mayor Aaron Brockett said after a rally in downtown Boulder on Monday.
“People care very much about climate change in Boulder. They recognize the existential threat that it provides to our society, and so people are very supportive of this lawsuit,” Brockett added.
The Supreme Court’s arguments
Shanmugam, who argued on behalf of Exxon and Suncor, told the justices during arguments that the Constitution and the Clean Air Act preclude claims that seek to address the harms caused by interstate greenhouse-gas emissions. He also warned that efforts like Boulder’s to secure relief from the effects of air pollution undermine the government’s control over foreign affairs.
Shanmugam called Boulder’s lawsuit an “unprecedented effort” to use state law to regulate global conduct, which is not allowed under the nation’s constitutional system.
“A state does not have the power to regulate out-of-state conduct based solely on attenuated effects on the state,” he said.
Shanmugam warned that if Boulder’s lawsuit is allowed to go forward, 90,000 municipalities could file similar challenges and “have the ability to make national and international energy policy by asking juries to impose catastrophic damages on selected fossil-fuel producers.”
Chief Justice John Roberts, too, noted that if Boulder prevails before the Supreme Court, local governments in every state will file their own lawsuits similar to Boulder’s.
“How would you think that will work out on the ground?” he asked Kevin Russell, who argued on behalf of Boulder.
Russell stressed that even if Boulder’s case can move forward, more litigation over the specifics of the suit will follow.
But Roberts also said there are other instances where the Supreme Court has allowed state-court lawsuits involving issues with wide impacts to go ahead.
“There are a lot of familiar situations where conduct outside of a state has broad effects from other states and all that, and yet we allow state courts in a particular state to bring litigation that affects that, whether it’s a mass tort sort of thing or maybe complaints about operations of the internet,” the chief justice said. “I guess I’m not quite sure what makes this situation different from all those other ones where we’ve allowed them to proceed in state court.”
Justice Elena Kagan, meanwhile, said the case against the energy companies appears similar to lawsuits brought against tobacco companies in the 1990s and pharmaceutical companies in response to the opioid epidemic.
“This is chapter three,” she said, noting that state claims against those companies could proceed.
But Kavanaugh said later that “this court has consistently said that air and water pollution are different in our federal enclaves.”
Lawyers for Boulder city and county are urging the Supreme Court to dismiss the appeal on the grounds that it does not have jurisdiction. If the justices opt not to, they say the Colorado Supreme Court decision should be upheld.
“Since the founding, states have had the power to provide tort remedies for injuries occurring within their borders, even when the conduct causing those injuries occurred elsewhere,” Russell told the justices.
He also argued that Congress “stands at the ready” to intervene and enact federal law that preempts “unreasonable state laws.”
“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,” Russell wrote in a filing.
He also told the justices that Boulder did not sue for emissions, which are regulated by the Clean Air Act, but over allegedly deceptive marketing and production, which that law does not regulate.
“It is not an effort to reduce emissions,” Russell said. “Under our deception theory, they can continue to produce as much fossil fuels as they like and contribute to as much air pollution and greenhouse gas emissions, as the market will bear when consumers are properly informed about the consequences of that decision.”
A decision from the Supreme Court is expected by summer of 2027.
