The U.S. Supreme Court begins its new term by reviewing a closely watched climate litigation case. On October 5, the Court will hear arguments in Suncor Energy Inc. v. County Commissioners of Boulder County on whether communities or states may use state tort law to hold energy companies liable for alleged harms associated with global climate change.

Boulder is one of roughly two dozen municipalities, along with nine states, that are seeking billions of dollars from oil companies for alleged climate-related harms. In Boulder’s case, the county filed a lawsuit in 2018 using public nuisance laws to redress in-state harms from deceptive marketing practices and upstream production activities. Boulder contends that Suncor and ExxonMobil deceived the public about the role of fossil fuels in climate change and are responsible for damages incurred by local authorities to mitigate harm to the community.

Suncor and the other defendants failed to have the case removed to federal court, arguing that interstate and international greenhouse gas emissions fall under federal authority. They filed a motion to dismiss with the state district court, which was also denied. The Colorado Supreme Court reviewed the question of whether federal law preempts Boulder’s state-law claims and ruled in May 2025 that the case should proceed under Colorado law.

In August 2025, Suncor and Exxon asked the Supreme Court to consider the case; their petition was granted in February 2026.

 The U.S. Supreme Court has outlined two questions for the litigants to address on October 8. In addition to the merits question concerning preemption, the Court has raised a threshold question of timing: whether it has statutory and Article III jurisdiction to hear the case.

Boulder argues that the Supreme Court lacks jurisdiction to review the case at this stage. They contend that the companies “merely asked the state court to review the district court’s ruling and, ultimately, reverse it.” In the Brief for Respondents, Boulder states that no final judgment was entered and that the petitioners were impatient, running “to this Court at the case’s outset” rather than letting “the state judicial process play out.”

Suncor and Exxon insist that the state court process has in fact played out, that the Colorado Supreme Court acted “as a court of first resort, rather than an appeals court” when it ruled the state-law tort claims were not federally preempted.

If the Court accepts jurisdiction and moves to the merits of the case, the Court’s decision could have significant implications for the federal preemption question in similar climate-change lawsuits. Board of County Commissioners of Boulder County v. Suncor Energy (U.S.A.), Inc. was just the second state climate lawsuit to survive an appeal to a state’s highest court.

Boulder argues its claims do not infringe on federal authority because it seeks damages for deceptive marketing practices that allegedly harmed the community, rather than the abatement or regulation of emissions. It therefore contends that the claims should proceed under state tort law rather than federal common law.

In City of New York v. Chevron Corp., the Second Circuit dismissed a similar argument about the absence of a demand for regulatory relief, remarking that these climate-change lawsuits are beyond the limits of state law. The real goal of New York City’s lawsuit, according to the court, was “to effectively impose strict liability for the damages caused by fossil fuel emissions no matter where in the world those emissions were released (or who released them).”

Earlier this year, the Maryland Supreme Court offered a similar warning as it dismissed three climate-change lawsuits. Justice Brynja Booth wrote: “No amount of creative pleading can masquerade the fact that the local governments are attempting to utilize state law to regulate global conduct that is purportedly causing global harm.”

Lawsuits from Boulder and Honolulu have been cleared by each state’s high court to proceed to trial. Cases from New York City and three Maryland communities have been dismissed by those states’ high courts. Many expect that the Supreme Court’s decision will clarify the federal preemption question in relation to climate change litigation. The fact that almost 70 merits-stage amicus briefs were accepted by the Court illustrates the high stakes of next week’s hearing.

Members of Congress take opposing positions on whether Boulder is impermissibly applying Colorado law extraterritorially. A group of 90 Democrats and Independents argue that Boulder seeks to apply Colorado tort law to obtain restitution for damages allegedly caused by the defendants’ deceptive marketing practices. They contend that the lawsuit does not seek to regulate emissions outside of the state and therefore does not intrude on federal authority.

An amicus brief of 74 Republican Members of Congress states that the Colorado decision “would allow a patchwork of conflicting state laws around the country to govern matters of uniquely federal concern.” The Constitution grants Congress and the President the power to set energy policy, enact environmental standards, and direct foreign policy.

Former Attorney General William Barr claims that a fundamental defect in Boulder’s case is that it intrudes on foreign policy. He warns that a “state liability regime that imposes its own costs on American companies for global emissions would necessarily alter that national balance.” Suncor claims that Boulder’s lawsuit is an attempt to set not only foreign policy but economic policy as well.

Suncor and several supporting amici argue that allowing state courts to assign liability and damages for global emissions would effectively permit states to set national energy and climate policy.

Boulder maintains that state courts may impose liability for local harms allegedly caused by the defendants’ conduct, even though the alleged climate-related effects involve global fossil-fuel production and emissions. A brief from the Natural Resources Defense Council supports Boulder’s position, arguing that climate attribution science has advanced to the point that scientists can quantify fossil fuel producers’ “contributions to specific extreme weather events.” A brief from climate economists disputes concerns that making energy producers pay damages would destabilize the American economy. They assert that insulating these companies from bearing the social cost of carbon is a market inefficiency that needs correction.

Last year, David Bookbinder, who previously represented Boulder in the case, described the lawsuit as “a somewhat convoluted way to achieve the goals of a carbon tax,” explaining that “the people who use the products pay for the damage that they cause.” He also said that if state courts imposed liability for the costs of global climate change, the immediate result would be every fossil-fuel producer declaring bankruptcy.

Courts in California, New Jersey, and Delaware have halted state climate litigation pending the Supreme Court’s decision. At present, Honolulu v. Sunoco is proceeding with discovery in Hawaii state court.

Justice Samuel Alito has recused himself from the case without explanation. A 4-4 split would leave the Colorado Supreme Court’s decision in place without establishing a controlling Supreme Court precedent on the preemption question. The Wall Street Journal warns that “absent a definitive ruling from the Justices, climate lawfare will proliferate.”