What Suncor v. Boulder County Means for Local, State Lawsuits

Suncor v. Boulder County, a case currently before the Supreme Court, is about climate change, but could also have implications for federalism and the future of many kinds of state and local lawsuits.

In 2018, the city and county of Boulder, Colo., and San Miguel County sued two international oil companies that are active in the state, seeking damages. The suit says the companies knowingly contributed to climate change and deceived customers about the harms of their fossil fuel products. The governments want the companies to shoulder some of the costs of climate change mitigations.

The state Supreme Court ruled in 2025 that the case could proceed to trial.

Suncor and Exxon, the oil companies named in the suit, meanwhile, asked the Supreme Court to overturn that ruling and stop the case. They say that, despite Boulder’s claims to the contrary, the suit is, essentially, an effort to regulate them and is pre-empted by federal law and/or the Constitution. The Trump administration supports the companies.

The Supreme Court’s ruling could impact dozens of other local government climate lawsuits and, potentially, state and local governments’ abilities to sue over other harms, legal experts say. State courts themselves have been split over whether federal law pre-empts states and governments from bringing similar deception cases against fossil fuel companies, with Minnesota and Maryland landing on opposite sides this year.

The Supreme Court heard arguments on the case in early October but is not expected to have a final decision until June or July. Several state and local climate lawsuits, including in California and New Jersey, are on pause pending a ruling, as the Supreme Court decision in Suncor v. Boulder could affect them.

The Stakes

The case’s outcome could impact issues ranging from how much of the costs of climate change will be borne by taxpayers to what legal avenues state and local governments have.

“The stakes is whether state courts can be a player in the fight against climate change,” says Harold Koh, Sterling Professor of International Law at Yale.

Some believe the implications extend beyond climate change. Anti-gun violence groups say cities have used similar legal theories to Boulder’s to fight ghost gun dealers. And local governments have sued in state court over harms they suffered from nationally distributed products or conduct that affects multiple states, including in response to PFAS contamination and opioids, say the National Association of Counties, National League of Cities and others.

Preventing municipalities from making these kinds of suits “really upends our entire understanding of the judicial system and federalism,” argues Corey Riday-White, legal director at the Center for Climate Integrity, a nonprofit that supports climate lawsuits against oil companies.

But the White House says Boulder’s suit opens the door to one state meddling in the affairs of another and in national and global matters. Under similar logic, the White House argues, “Oklahoma could seek to regulate Maine’s schools on the theory that social and economic effects of a poor education are felt nationwide (including in Oklahoma).”

If the Supreme Court sides with oil companies, many state and local lawsuits could be halted. Meanwhile, Chief Justice John G. Roberts Jr. suggested that a victory for Boulder would lead to a flood of similar suits from “a municipality in every single state.”

The Center for Climate Integrity

Ripple Effects

There are many possible outcomes, with varying implications for other cases.

On the one hand, justices might decide the case is outside their purview or that it’s too soon for them to weigh in. In that event, the suit would continue in state courts for now. Or justices might write a ruling so narrowly that it only really applies to Boulder and doesn’t much impact other cases. Or they might agree to stop Boulder’s case but disagree over the reason why, which then would not set a legal precedent.

On the other hand, they might take stronger action. Justices could decide federal law bars Boulder from suing over climate change damages, while allowing its deceptive marketing claims to stand. Most climate lawsuits (including from Massachusetts and Honolulu) fully or partially rest on deception claims and therefore could continue, says Michael Gerrard, founder of the Sabin Center for Climate Change Law. However, if justices instead rule that both kinds of charges are barred, many climate cases would be wiped out.

The legal reasoning matters: If justices decide Boulder's suit is pre-empted by the Clean Air Act, non-climate change related cases wouldn’t be affected; but if they say it's pre-empted on constitutional grounds, the implications might be further reaching, Gerrard says.

And if justices decide in favor of the oil companies, it is likely they’ll focus their decision tightly on specific attributes of climate change rather than issuing a wide-ranging ruling, says William Buzbee, Georgetown law professor and faculty director of the Georgetown Climate Center.

Still, Koh says there could be broad implications if justices agree with a particular line of oil companies and the White House’s argument: that Boulder’s case should be stopped from going to trial because it would be too difficult for the local governments to prove the damages they experienced are from emissions from in-state oil company activities, versus from similar activities occurring elsewhere in the world. That might affect other cases in which causation is complicated.

“Their claim is that you can never measure causation, and therefore you have to dismiss everything at the outset,” Kohl says. “It could have impacts on similar cases like opioids or other nationwide suits about the harmful effects of various products.”

Much remains to be seen. But a ruling against Boulder wouldn’t be the end of local and state governments’ climate efforts.

“If this case is dismissed, there’s still many other things that states can do to fight climate change,” Gerrard says. “It's just that they would no longer have the option of suing the oil companies.”