The US Supreme Court has begun hearing a major climate case that could shape dozens of lawsuits against oil companies.

The case, Suncor Energy v. County Commissioners of Boulder County, was argued on October 5, the first day of the court’s new term. Boulder city and county sued ExxonMobil and Suncor in 2018, saying the companies knew about climate risks for decades and hid them.

The companies argue the case should be decided under federal law, not state law, and that the Clean Air Act overrides the claims. Boulder points to a 2021 wildfire that destroyed more than 500 homes as evidence of damages.

Justices sounded cautious. Amy Coney Barrett called the companies’ argument “a little slippery,” while Brett Kavanaugh warned a ruling could bankrupt energy firms. Justice Samuel Alito is recused. About 60 similar suits are pending nationwide.

The case could decide whether dozens of similar lawsuits stay in state courts or move to federal court. Oil companies prefer federal court, where they argue federal law blocks the claims. A ruling is expected by next summer. Whatever the court decides, it will shape climate litigation for years.