US Supreme Court Appears Split on Boulder Climate Lawsuit Against Exxon and Suncor

The US Supreme Court began its 2026-27 term on Monday by taking up one of the most consequential climate cases it has ever heard, and the justices did not appear close to agreement. At issue is whether Boulder County and the city of Boulder in Colorado can pursue a state-court lawsuit seeking damages from ExxonMobil and Canada's Suncor Energy for climate-related harm, or whether federal law shuts such claims down.

Only eight justices took part. Justice Samuel Alito recused himself on September 28 without giving a reason, after environmental groups pointed to his holdings in oil company shares. That leaves open the possibility of a 4-4 tie, which would leave the Colorado Supreme Court's decision allowing the case to proceed in place.

What Boulder is claiming

The two local governments sued in 2018 under Colorado tort law. They argue the companies misled the public about how their products contribute to climate change, and that local taxpayers are now paying for the consequences through heat, drought and wildfire damage. After years of procedural fights, Colorado's top court let the case go forward in a 5-2 ruling in May 2025. The case has still not reached trial.

The companies say that if Boulder succeeds, nearly 60 similar suits already filed by states and cities would gain momentum. Their lawyer, Kannon Shanmugam, told the court that tens of thousands of municipalities could effectively set national and international energy policy by asking local juries to award huge damages. He also noted that around 90% of greenhouse gas emissions occur outside the United States. The Trump administration joined the argument on the companies' side, with Principal Deputy Solicitor General Sarah Harris saying the suit goes well beyond the limits of state authority.

Where the justices landed

Justice Brett Kavanaugh was the companies' strongest ally on the bench. He pointed to a line of earlier rulings, including two Milwaukee pollution cases, International Paper v. Ouellette and American Electric Power v. Connecticut, which he said establish that interstate air and water pollution is a federal matter unless Congress says otherwise. He also questioned whether a small state jury is equipped to make decisions that the court once said even federal judges were poorly placed to make.

Others were less convinced. Justice Elena Kagan likened the case to the tobacco and opioid lawsuits that state and local governments brought over alleged corporate deception, and asked where the companies found support for their claim that states surrendered this power. Chief Justice John Roberts offered his own analogy: someone who throws a rock across a state line can still be sued where it lands.

Justice Amy Coney Barrett, widely seen as a possible swing vote, challenged the companies' reading of the Clean Air Act's saving clause, noting that it speaks of preserving state remedies rather than authorising them. She also pressed Boulder's lawyer on whether Colorado could, in theory, try to cap emissions in the other 49 states.

Justices Sonia Sotomayor and Ketanji Brown Jackson raised a different concern: whether the court should be stepping in at all at such an early stage, before Colorado courts have worked through the facts.

Boulder's defence

Kevin Russell, representing Boulder, argued that states have always been able to offer tort remedies for injuries inside their borders even when the conduct happened elsewhere. He framed the case as one about deception rather than emissions, saying the companies could keep producing as much fuel as they wish as long as consumers are properly informed.

What comes next

Alabama and 25 other states filed a brief backing the oil companies, while 19 attorneys general sided with Boulder. A decision is expected before the term ends in mid-2027. For global energy companies, including those with large investor bases outside the US, the ruling will determine whether climate liability is fought in dozens of local courtrooms or settled at the federal level.

This is an original summary based on public reporting. See our editorial policy for how we source, write, and correct our stories.