By Shaina Cole | Contributing Writer, Rocky Mountain Voice
A lawsuit that started with three Colorado local governments and a stack of state tort claims will open the U.S. Supreme Court’s new term.
On Monday, Oct. 5, the justices hear argument in Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County, the first case of October Term 2026. It is the first time the Court will decide on the merits whether federal law bars state-law climate-damages claims of this kind against fossil-fuel companies.
The city of Boulder, Boulder County and San Miguel County sued Suncor and ExxonMobil in 2018. San Miguel County’s claims were later transferred to a separate case, leaving the city and Boulder County as the plaintiffs before the Supreme Court.
They want the companies to help cover local costs tied to a warming climate, from wildfire damage to public-health bills. The claims are ordinary state-law torts: public and private nuisance, trespass, unjust enrichment, civil conspiracy.
What is not ordinary is the reach.
The companies say Boulder is trying to use one state’s law to govern the production and sale of fossil fuels across the country and around the world, and that the Constitution and the Clean Air Act forbid it.
How it got here
The case has reached the Supreme Court twice before, over the separate question of whether it belonged in federal court. This time the merits are in play.
In May 2025 the Colorado Supreme Court let the suit go forward. The court held that “Boulder’s claims are not preempted by federal law and, therefore, the district court did not err in declining to dismiss those claims.”
The claims “do not seek to regulate GHG emissions,” the majority wrote, but instead focus on the companies’ “upstream production activities” and conduct the Clean Air Act does not address.
The companies asked the U.S. Supreme Court to step in.
On Feb. 23, 2026, the justices agreed, and then added a question of their own. Beyond the preemption fight, the Court told both sides to argue whether it even has the jurisdiction to hear the case at this stage.
That second question is a live off-ramp. The justices could decide the case is premature and send it back without ruling on the climate claims at all.
What the companies argue
The petitioners’ brief, filed by Kannon Shanmugam, says the answer to both questions is yes.
The brief argues there are “certain areas in which state law cannot apply,” and that climate-change claims are one of them. The Clean Air Act, it argues, reinforces a constitutional rule that states cannot regulate emissions beyond their own borders.
The Trump administration’s Justice Department is on the companies’ side.
In its merits brief, signed by Deputy Solicitor General Sarah Harris, the government opens with a question and its own answer. “Can one city wield one State’s law to dictate how the rest of the world must address a global problem with global effects? The Constitution supplies the answer: Absolutely not.”
The brief says 60 states and localities have filed near-identical suits. The Solicitor General’s office filed without being invited by the Court and was granted its own time at the lectern on Oct. 5.
An analysis by Harvard’s Environmental & Energy Law Program called that unsolicited filing part of the administration’s wider effort to shut down climate-liability suits.
That effort is rooted in an April 2025 executive order, “Protecting American Energy From State Overreach,” in which President Trump directed the attorney general to identify and move to stop state laws and lawsuits burdening domestic energy.
The order singled out states that “have also sued energy companies for supposed ‘climate change’ harm under nuisance or other tort regimes.”
What Boulder argues
Boulder’s brief says the companies are the ones overreaching, and that they got to the Supreme Court too early.
“This case should begin and end with jurisdiction,” the brief argues. It says the case is far from a final judgment, and that the Colorado Supreme Court “has not yet even decided whether respondents state a claim under state law.”
On the merits, Boulder says the Clean Air Act does not touch these claims. “The statute regulates point-source emissions, not the upstream production, sale, or marketing of products that later produce them,” the brief says. “It certainly does not charge the EPA with regulating deceptive marketing of fossil fuels.”
Boulder also points to Congress.
Legislation that would give the companies the immunity they are seeking is pending on Capitol Hill, its brief notes, and the courts should not do that work first.
The panel of critics
The case has drawn more than 70 friend-of-the-court briefs.
In September, the Law & Economics Center at George Mason University’s Antonin Scalia Law School gathered four legal figures connected to amicus briefs supporting the companies for a webinar previewing the argument.
University of Virginia law professor Saikrishna Prakash, who filed on his own behalf, walked through where he thinks Boulder’s theory leads.
If Boulder can pin liability on two producers, he argued, it can reach thousands of others, and not just producers. Steel, concrete, cattle — anything that generates greenhouse gases.
And not just in Colorado.
“It implies that New York City, Pensacola, Florida, Anchorage, Alaska, you know Boulder, Idaho, they can regulate the entire United States,” he said, and then the rest of the world. Other countries would return the favor. “Russia could regulate activities in Moscow, Idaho,” he said. “France could regulate activities in Paris, Texas.”
Megan Wold of Cooper & Kirk, whose firm filed for Republican Senators Ted Cruz, Chuck Grassley, Mike Lee and Ted Budd, laid out what she called a fork in the road.
Read one way, Boulder is regulating out-of-state production, which she said the Constitution and the federal foreign-affairs power forbid. Read the other way, it is regulating emissions, which the Clean Air Act preempts.
“Either way that you conceive of what Boulder is doing,” she said, “they are prohibited one way or the other from doing it.” Wold also noted her firm represents clients in the parallel litigation over New York’s and Vermont’s climate laws.
Phil Goldberg, filing for the National Association of Manufacturers, put the case in a longer line of climate suits going back to the Court’s 2011 ruling in American Electric Power Co. v. Connecticut (AEP), which held that the Clean Air Act displaced federal common-law claims seeking to curb power-plant carbon emissions, while leaving open whether it also bars state-law claims.
His brief argues that AEP established federal law as the starting point for climate claims, and that repackaging them under state consumer-protection or tort theories cannot escape that.
Since 2017, he said, three dozen or more suits have followed, “like throwing legal spaghetti on the wall and seeing what sticks.”
He pointed to the money behind the label its own backers use. “They’ve called this an indirect carbon tax,” Goldberg said. “One of the lawyers for Boulder went on local Colorado radio a few years ago and said the idea was raising the price of these fuels so they’ll incorporate their true costs.”
George Mason law professor Todd Zywicki, who filed a brief with the Center for Individual Freedom, was the bluntest of the four.
He called the suits an effort “backed by deep pocketed billionaires” to “force their preferred lifestyle on the whole rest of the world,” and returned to a phrase more than once. “The process is the punishment,” he said, describing each case as bet-the-company litigation the plaintiffs can file endlessly.
His filed brief makes a narrower point: consumer-protection versions of these climate claims, he writes, have been dismissed by what one court called a “growing chorus of state and federal courts,” and if the justices reach such claims they should treat them as precluded for the same reasons as the tort claims.
What Oct. 5 decides, and does not
Asked where the two possible outcomes leave things, the panelists mostly agreed.
A ruling for the companies, Zywicki predicted, would push the plaintiffs toward consumer-protection theories the Court may not resolve, keeping the fight alive. A ruling the other way, he said, would be “a feeding frenzy.”
Wold saw a wider effect on state legislatures weighing climate superfund laws like New York’s and Vermont’s. A strong decision, she said, “might knock the wind out of the sales of lobbyists,” though a narrow one would send drafters “back to the drawing board.”
A ruling for the companies could reach far beyond Colorado.
A ruling for Boulder would send the case back to keep fighting over whether it can prove its claims.
And if the justices decide the jurisdictional question against the companies, they may never reach the climate question this term at all.
The decision is expected by summer 2027.