The U.S. Supreme Court will hear Suncor Energy, Inc. v. County Commissioners of Boulder County on the first day of the October 2026 Term, marking the first climate-change tort suit against major oil companies to reach the justices. The case asks whether state-law claims against energy companies for their role in causing climate change are preempted — or, in the companies' framing, superseded — by federal law.

The backdrop is a preemption docket that defies easy patterning. Last term alone produced two major rulings pointing in different directions.

In Monsanto Co. v. Durnell, the court held 7-2 that the Federal Insecticide, Fungicide, and Rodenticide Act expressly preempts state tort liability based on a failure-to-warn theory. Justice Brett Kavanaugh wrote the majority. Justice Ketanji Brown Jackson dissented, joined by Justice Neil Gorsuch.

Then, in Watson v. Republican National Committee, the court ruled 5-4 that the federal statute fixing the date of federal elections does not preempt states from counting absentee ballots received within five days of the election. Justice Amy Coney Barrett wrote for the court and declared: "In sum, the election-day statutes require the electorate's choice to be made on election day. That occurs so long as election day is the deadline for individuals to vote—as it is in Mississippi. But the election-day statutes do not set a deadline for ballot receipt, so they do not prevent Mississippi from counting ballots postmarked before election day yet received afterward." Justice Samuel Alito dissented, joined by Justices Clarence Thomas, Gorsuch and, in part, Kavanaugh.

The doctrinal framework

Article VI of the Constitution contains the Supremacy Clause, which makes the Constitution and federal laws the supreme law of the land. Where federal and state law conflict, federal law controls and state law yields. As the court has stated, "any state law, however clearly within a State's acknowledged power, which interferes with or is contrary to federal law, must yield."

The court traditionally identifies two preemption pathways. Express preemption arises when a federal statute says so in terms. Implied preemption comes in three forms: conflict preemption, where federal and state law are mutually exclusive; objectives or obstacle preemption, where state law frustrates a federal objective; and field preemption, where Congress clearly intended federal law to occupy an entire area.

The Boulder litigation

The county commissioners of Boulder County and the city of Boulder sued Exxon Mobil Corporation and three Suncor Energy entities in Colorado state court. They seek damages for the role the companies' production, promotion, refining, marketing and sale of fossil fuels allegedly played in exacerbating climate change. Boulder pleaded public nuisance, private nuisance, trespass, unjust enrichment and civil conspiracy, alleging the companies knowingly contributed to climate change while misleading the public about the dangers of their products. Boulder says it has incurred and will incur millions of dollars in costs to protect against wildfires, flooding and drought. It does not seek to enjoin oil and gas operations or enforce emissions controls.

The Colorado Supreme Court ruled that federal law does not preempt Boulder's claims and remanded, expressing no view on the merits. The court found no express preemption provision in the Clean Air Act, no field preemption because the act does not occupy emissions regulation — and in fact contains two savings clauses preserving stricter state standards and common-law rights — and no conflict preemption because compliance with both the act and state tort law is possible, and damages claims that do not regulate emissions pose no obstacle to the act's purposes.

Why Suncor strains the categories

The case fits none of the court's established preemption boxes. Unlike Monsanto, no Clean Air Act provision explicitly preempts state tort liability. There is no conflict: both regimes can be obeyed simultaneously, and the act expressly preserves state authority over air quality. Nor is there a plausible field-preemption argument.

The energy companies press three theories instead.

First, they argue the Constitution itself forecloses state regulation of interstate pollution. "States have no residual or inherent power under our Constitution to regulate in this area, and no federal law authorizes state common-law claims for harms caused by diffuse interstate and international emissions," their brief states. That is a striking claim against the background of the 10th Amendment, which has always been understood to let states act unless the Constitution forbids it. Acceptance of the argument could preempt any state environmental law regulating activity with interstate effects.

Second, the companies argue the Clean Air Act preempts state tort liability unless it affirmatively authorizes it — inverting the usual presumption against preemption. "If state law could not be applied before the enactment of the Clean Air Act, it thus follows that state law remains inapplicable unless the Clean Air Act affirmatively authorizes it," they write.

Third, they invoke implied dormant foreign-affairs preemption: the claims "infringe on the federal government's exclusive authority over foreign affairs" by seeking redress for the effects of international emissions. The court has used this doctrine before, unanimously in Crosby v. National Foreign Trade Council, striking down Massachusetts' Burma sanctions law, and 5-4 in American Insurance Assn. v. Garamendi, preempting California's Holocaust-era insurance disclosure law. But extending it to Suncor would mark a substantial expansion — potentially limiting state tort liability whenever a multinational corporation is involved.

What is at stake for practitioners

The justices will confront a case that sits outside the court's long-articulated preemption categories and turns on novel constitutional and foreign-affairs theories. A ruling for the energy companies could displace the presumption against preemption, cabin state police power over interstate effects, and effectively end the wave of state-court climate litigation. A ruling for Boulder would send the case back to Colorado and preserve the state-law tort route. The Colorado Supreme Court's savings-clause analysis gives respondents a textual anchor, while petitioners ask the court to locate preemption in constitutional structure rather than statute. The stakes are heightened by the political intensity now surrounding climate policy.