The U.S. Supreme Court heard oral argument on Oct. 5 in Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County, a dispute testing whether one state's tort law can assign liability for worldwide greenhouse-gas emissions. Roughly 60 states and localities have filed similar climate-damages suits, and the justices' decision will shape the entire docket.

The argument proceeded without Justice Samuel Alito, who recused himself only a week before the hearing — a sudden, last-minute step in an already controversial case.

What is the case about?

Boulder County and the City of Boulder sued Suncor and Exxon Mobil in Colorado state court, seeking billions of dollars for climate harms — wildfires, drought, and flooding — allegedly caused by the companies' production, refining, promotion, marketing, and sale of fossil fuels worldwide. Plaintiffs pleaded state-law theories including public nuisance and public deception.

The Colorado Supreme Court rejected the companies' preemption arguments. It reasoned that Boulder sought only damages, not an order abating pollution, and that regulating fuel production and sales falls within traditional state responsibility rather than emissions control.

The U.S. Court of Appeals for the 2nd Circuit reached the opposite conclusion in 2021's City of New York v. Chevron Corp., holding that "artful pleading cannot transform the City's complaint into anything other than a suit over global greenhouse gas emissions" — a case "simply beyond the limits of state law."

What did the justices signal at argument?

Chief Justice John Roberts described Boulder's suit as "an effort to reduce emissions" and warned that if Boulder prevails, "the next day, a municipality in every single state will file a lawsuit." Justice Elena Kagan said the lawsuit "depends on . . . this idea that the defendants are responsible for excessive emissions."

Justice Amy Coney Barrett pressed on why a tort suit should stand when Colorado could not constitutionally enact a law capping emissions in other states.

Why does the Constitution's structure matter?

The energy companies argue that structural preemption bars Boulder's claims on two grounds:

• One state may not impose its policies on sister states; state sovereignty carries inherent territorial limits.
• Allocating responsibility for international emissions intrudes on the federal government's exclusive foreign-affairs power.

The companies rely on a line of precedent that does not turn on any conflicting federal statute. In 1968's Zschernig v. Miller, the Court struck down an Oregon inheritance law for intruding on foreign affairs. In 2003's American Ins. Ass'n v. Garamendi, the Court held a California disclosure law must yield to presidential foreign policy expressed in executive agreements containing no preemption clauses.

On interstate emissions, Justice Oliver Wendell Holmes, Jr. wrote in 1907's Georgia v. Tennessee Copper Co. that "the states by their union made the forcible abatement of outside nuisances impossible to each" — the remedy lies in original-jurisdiction suits in the Supreme Court. The Court reaffirmed in 2011's American Electric Power Co. v. Connecticut that for interstate disputes, "borrowing the law of a particular State would be inappropriate."

How does Boulder answer?

Boulder invokes the 10th Amendment, arguing the Constitution "bestows only limited powers on the federal government" and reserves "all other legislative power" to the states — so preemption requires a textual hook in the Constitution or a federal statute.

The companies counter that states never possessed power over sister states or foreign affairs in the first place. The Court wrote in 1995's U.S. Term Limits v. Thornton that "no state can say, that it has reserved, what it never possessed," and in 2007's Massachusetts v. EPA observed that a state "cannot negotiate an emissions treaty with China or India."

On the damages-versus-regulation question, the companies cite 2012's Kurns v. Railroad Friction Products Corp., where the Court held "regulation can be . . . effectively exerted through an award of damages," and 1987's International Paper Co. v. Ouellette, barring affected states from doing "indirectly what they could not do directly."

What is at stake for practitioners?

The state bench is split: 26 states filed an amicus brief supporting the energy companies, while Colorado and 18 other states backed Boulder. Several states — Iowa, Oklahoma, Tennessee, Utah, and Texas — have enacted laws limiting climate-change liability, and West Virginia has declared an official policy promoting oil and gas development.

A ruling for Boulder would open the courthouse doors to dozens of copycat suits applying varying state tort standards to global emissions. A ruling for Suncor on structural or foreign-affairs preemption grounds would end most state-law climate-damages litigation and guide lower courts on contested interstate phenomena beyond emissions. Decision is expected by term's end.