A climate lawsuit filed eight years ago by the City of Boulder and Boulder County went before the U.S. Supreme Court for oral arguments on Monday, bringing a long-running local case before the nation’s highest court with implications for similar climate lawsuits around the country.
As the justices heard arguments in Washington, dozens of Boulder residents and climate advocates gathered outside the Boulder County Historic Courthouse, where speakers said residents should not have to bear the growing costs of wildfires, extreme heat, drought and other effects of climate change on their own.
“Boulder deserves to have our day in court to hold these corporations accountable for the costs our community is having to bear,” said Micah Parkin, co-founder and executive director of 350 Colorado.
The Supreme Court is not deciding whether the oil companies are responsible for Boulder’s climate costs. The question is whether the city and county can pursue their claims under Colorado law in state court, where they filed the case and have fought for years to keep it, or whether federal law blocks those claims. The ruling could determine whether other state and local governments can pursue similar claims under state law.
Boulder County and the City of Boulder sued ExxonMobil and two Suncor entities in 2018, alleging the companies contributed to climate change through the production and sale of fossil fuels while misleading the public about the risks. The local governments are seeking money to help cover climate-related costs that they say would otherwise fall largely on taxpayers.
Boulder argues that it is seeking compensation under state law for harms suffered in Colorado, not trying to regulate greenhouse gas emissions nationally. Exxon and Suncor counter that the alleged damages stem from global emissions and therefore cannot be addressed through the laws of a single state.
The Colorado Supreme Court rejected the companies’ argument in 2025 and allowed Boulder’s lawsuit to proceed. Exxon and Suncor asked the U.S. Supreme Court to review that decision, and the justices agreed to take the case earlier this year. Monday’s arguments marked the latest, and potentially most consequential, stage of an eight-year legal fight in which the courts have not yet addressed the substance of Boulder’s allegations.
The Supreme Court has several options. It could decide not to resolve the dispute at this stage, leaving the Colorado Supreme Court’s ruling in place and allowing Boulder’s case to proceed. It could side with Boulder on the broader legal question, also allowing the lawsuit to move forward. Or it could side with Exxon and Suncor and rule that federal law blocks Boulder’s claims under Colorado law, potentially ending the local case and jeopardizing similar lawsuits elsewhere.
Because Justice Samuel Alito has recused himself, an evenly divided 4-4 court is also possible. In that event, the Colorado Supreme Court’s ruling would stand and Boulder’s case could proceed, but the U.S. Supreme Court would set no nationwide precedent.
Justices press both sides on how far their arguments reach
Kannon Shanmugam, representing Exxon and Suncor, opened Monday’s arguments by calling Boulder’s lawsuit “an unprecedented effort to use state law to regulate global conduct.”
The companies made a similar argument when they asked the Supreme Court to take the case. “Boulder, Colorado, cannot make energy policy for the entire country,” they wrote in their petition. They argued that state law cannot be used to impose the costs of global climate change on a group of energy producers selected by a single municipality.
Kevin Russell, representing Boulder, pushed back on the companies’ argument that allowing the lawsuit to proceed would let Colorado impose its laws beyond the state’s borders.
“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 said.
“Applying state law to such cases has never been viewed as one state impermissibly projecting its law nationwide,” he added.
During oral arguments, the justices questioned both sides on the divide between state and federal authority.
Justice Elena Kagan compared aspects of Boulder’s case to lawsuits against tobacco and opioid companies, where governments also argued that companies misled the public about the harms caused by products they sold.
When the companies’ attorney argued that Boulder’s case was different, Kagan pushed back.
“I’m waiting to see the distinction, because this complaint talks a lot about misrepresentations that are made by the defendants,” she said.
Exxon and Suncor argue that the Clean Air Act, the federal law governing air pollution, blocks Boulder’s claims under Colorado law. Justice Sonia Sotomayor questioned why that law would also prevent claims involving alleged misleading marketing of fossil fuels.
Justice Brett Kavanaugh appeared sympathetic to the oil companies’ arguments, citing what he described as Supreme Court precedent establishing interstate pollution as a federal matter.
“This kind of pollution is a federal law matter, unless Congress speaks otherwise,” Kavanaugh said.
He also said that a wave of similar lawsuits could bankrupt the companies and expose other businesses to liability.
“Anyone is a potential defendant for a suit like this. Any manufacturer, any business,” he said.
Chief Justice John Roberts also questioned what would happen if local governments around the country pursued their own cases.
The justices also questioned whether the case has reached the Supreme Court too soon, with some suggesting the dispute may not yet be ready for the justices to resolve.
Boulder officials take the fight to Washington
Boulder County Commissioners Claire Levy, Marta Loachamin and Ashley Stolzmann and Boulder City Manager Nuria Rivera-Vandermyde were in Washington for Monday’s arguments.
“This case is not about asking the courts to solve or even mitigate the effects of climate change. It is, simply, about fairness and trying to survive,” Loachamin said.
Rivera-Vandermyde said local governments should not have to bear all of the costs they attribute to climate change.
“We believe communities should be able to seek a fair share of the costs associated with the impacts they are experiencing,” she said.
In Boulder, residents rally outside the courthouse
Back in Boulder, residents and climate advocates outside the Boulder County Historic Courthouse carried signs that read “Boulder vs. Big Oil,” “Greed fuels the fire” and “Make Big Oil pay.”
Speakers included Boulder Mayor Aaron Brockett, Marshall Fire survivor Kelly Watts, local young people who signed amicus briefs in the case, and Parkin of 350 Colorado.
Brockett pointed to money Boulder is already spending on wildfire resilience, home hardening and infrastructure.
“But the costs are growing and they cannot all simply be passed onto our residents and taxpayers,” Brockett said.
Other speakers described the power shutoffs Boulder has had to endure due to wildfire risk, worsening air quality and the emotional toll of living with increasing climate and wildfire threats.
A decision from the Supreme Court is expected by the end of its term next summer.
