By Sharon Kimathi, Energy and ESG Editor, Reuters Digital

Climate activists protest amid a hearing by oil firms against officials in Boulder, Colorado, at the US Supreme Court building in Washington, D.C., US. REUTERS/Jonathan Ernst

Boulder's city and county governments have accused the two companies of helping drive climate change and misleading the public about the risks of fossil fuels. 

The burning of fossil fuels releases greenhouse gases including carbon dioxide into the atmosphere, trapping heat and raising average global temperatures over time.

Boulder aims to hold the companies liable for past and future costs associated with climate change such as infrastructure repairs, environmental damage, emergency management and harms to public health.

The court has a 6-3 conservative majority. But conservative Justice Samuel Alito has recused himself from participating in this case, as he owns stocks in oil majors including Exxon and Suncor, meaning the ruling will be made by eight justices and not nine.

The claimants argue that the Justices siding with the oil companies could mean unduly limiting the authority of states to pursue climate-related litigation, while the defendants say that Boulder's claims intrude on an area governed by the Clean Air Act.

Liberal Justice Sonia Sotomayor questioned the oil companies' claim that the Clean Air Act prevents states from suing them. She said the court has allowed similar cases under the Clean Water Act and suggested the same reasoning could apply here.

"I don't see why we wouldn't permit it under the Clean Air Act either," Sotomayor ⁠said.

Liberal Ketanji Brown Jackson said some of the questions asked by her colleagues during the arguments "make me think that we're really early in this case" and "that this is sort of premature from the standpoint of this court exercising ⁠its jurisdiction."

Nearly 60 state and local governments ‌have brought ⁠similar suits seeking billions of dollars from fossil fuel companies, with more continuing to be filed, Exxon and Suncor told the justices.

The defendants argue that the case has the potential to unleash chaos if local governments across the country were permitted to sue these companies.

Conservative Chief Justice John Roberts pressed Kevin Russell, a lawyer for the Boulder officials, on the practical implications of siding with his position.

"Presumably, if you prevail, the next day a municipality in every single state will file a lawsuit, they'll probably copy your pleadings, and then there will be at least 50 ... causes of action filed," Roberts said. "How do you think that would work out on the ground?"

Conservative Justice Brett Kavanaugh, who seemed to favor the arguments of the oil companies, said the court's prior rulings make "crystal clear that interstate air and water pollution are matters for federal law unless Congress specifically preserves state law." Kavanaugh pressed Russell to address "a wall of precedent" that could undermine Boulder's stance.

A ruling by the Supreme Court in favor of the companies could lead to many similar climate cases being dismissed.

Energy companies and trade groups, along with states allied with them, have built a largely winning record before the justices over the past two decades ⁠in cases involving climate liability and the reach of federal environmental regulation.

The Supreme Court's decision is expected by the end of June.

Workers paint images for Martyrs' Day, which marks the Eritrean War of Independence at Bar Vittoria, a historic cafe in central Asmara, Eritrea. REUTERS/Giulia Paravicini

Markus Covert, professor of bioengineering at Stanford University, celebrates with Karl Deisseroth, a co-winner of the 2026 Nobel Prize in Physiology or Medicine, at Stanford University's James H. Clark Center in Stanford, California, U.S. REUTERS/Manuel Orbegozo 

Today’s spotlight shines a light on the winners of this year’s Nobel Prize in Physiology or Medicine, American Karl Deisseroth and Germans Peter Hegemann and Georg Nagel for