The Boulder Climate Case Explained: Can Local Governments Make Fossil Fuel Companies Pay For Climate Harm?

The U.S. Supreme Court opens its new judicial term, known as the October Term, on October 5, 2026. Kicking things off is the major Boulder climate case, scheduled for argument on that opening day, placing a consequential dispute over climate liability before the justices at the start of their new term.

In Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County, Boulder wants fossil fuel companies ExxonMobil and Suncor to help pay for local climate costs. The companies argue that state law cannot impose responsibility on them for harm caused by worldwide emissions. The immediate question is whether federal law prevents these claims from proceeding. The Court must also consider whether it has authority to decide that question at this stage. (Supreme Court docket, No. 25-170, order of February 23, 2026.)

What Is Boulder Asking The Companies To Pay For in Its Climate Case?

The City of Boulder and Boulder County seek compensation for past and future local climate impacts, including wildfire protection, flood damage, water supplies and public infrastructure.

Their argument is that taxpayers should not bear all these costs when the companies allegedly contributed to the harm while profiting from fossil fuels. Boulder expressly disclaims asking the court to stop fossil fuel production or impose emissions limits. It wants the companies to pay their share of the resulting local costs.

This makes the lawsuit a dispute over the allocation of climate costs, although the companies argue that imposing those costs would itself regulate emissions.

Is This Simply A Lawsuit About Misleading Advertising?

The allegations are broader. Boulder advances two main theories: the companies misled the public about climate risks, and they knowingly produced and sold fossil fuels at levels that contributed to harmful climate change.

Its claims include public and private nuisance, trespass, unjust enrichment and civil conspiracy. These concern interference with public rights or property, harmful invasions of property, unfairly retained benefits and coordinated wrongful conduct. Each has its own legal requirements. (Respondents’ Brief, p. 4.)

A separate claim under Colorado’s consumer protection statute was dismissed without prejudice, with permission to amend. It is not part of the Supreme Court’s current review. Alleged deception nevertheless remains relevant to the other claims. (District Court Order, June 21, 2024, pp. 79, 81.)

How Could Producers Be Responsible When Other People Burned The Fuels?

Boulder’s theory connects the companies’ conduct to the products’ intended use. It alleges that the companies supplied and promoted fossil fuels while knowing that burning them would contribute to dangerous climate change. It also alleges that concealing those risks encouraged continued consumption.

Under that theory, responsibility would not necessarily rest only with the person or business releasing the emissions. A producer’s contribution to the chain of events could also matter. These remain allegations requiring proof, rather than an established basis for liability. (Amended Complaint, paragraphs 13–18.)

The companies object that moving the claim further up the supply chain changes neither the source of the alleged injury nor its global nature. That disagreement affects both the federal law challenge and the later question of causation. (Petitioners’ Brief, pp. 37–39.)

Have The U.S. Courts Already Found The Companies Responsible?

No. In May 2025, the Colorado Supreme Court ruled, by five votes to two, that federal law did not require dismissal of Boulder’s claims. It expressly left their ultimate merits undecided. (2025 CO 21, paragraph 2 and voting statement.)

At the dismissal stage, courts generally accept properly pleaded factual allegations as true to assess whether a claim can proceed. This gives plaintiffs an opportunity to prove their case; it does not establish that their allegations are correct.

Boulder has therefore overcome a legal barrier, but it has not obtained a finding of liability or a damages award. (District Court Order, June 21, 2024, pp. 67–69.)

Why Is The Case Back Before The Supreme Court?

The earlier dispute concerned which court should hear the lawsuit. Boulder filed in state court, but the companies sought to move the case to federal court, a process called removal. In 2022, the Tenth Circuit rejected the asserted grounds for removal.

That ruling did not prevent the companies from raising federal law as a defense in state court. A federal defense can defeat a state claim even when it does not provide grounds to move the lawsuit into federal court. (Tenth Circuit Opinion, February 8, 2022, pp. 3, 21–24.)

The present dispute concerns whether the claims are legally barred. After the Colorado Supreme Court rejected the companies’ federal law defenses, they asked the U.S. Supreme Court to overturn that ruling. The Court’s current review therefore addresses a different question from the earlier fight over the forum. (Supreme Court docket, No. 25-170.)

Why Do ExxonMobil And Suncor Say Federal Law Blocks The Case?

Their argument starts with the geography of climate change. Emissions cross state and national borders, and the companies contend that Colorado cannot use its own law to impose responsibility for that global process.

They rely on the Constitution’s allocation of power, limits on state authority beyond state borders, federal control of foreign affairs and the Clean Air Act. Preemption describes federal law overriding an otherwise applicable state law.

The distinction between their arguments matters. A statutory ruling would interpret the Clean Air Act. A broad constitutional ruling could restrict state authority independently of that legislation.

Preemption scholars supporting Boulder warn that declaring cross-border harm inherently federal could undermine state remedies in other fields too. Their position is that the Court must identify a legal basis for overriding state law, rather than infer one simply from the problem’s scale. (Preemption Scholars’ Amicus Brief, pp. 2–6.)

Can A Damages Award Really Amount To Emissions Regulation?

Damages can influence behaviour. A company facing substantial liability may change its operations to avoid further claims. The contested question is whether that influence makes this lawsuit an impermissible form of emissions regulation.

The companies say a Colorado jury would effectively set standards for worldwide fossil fuel activity by deciding what conduct was wrongful and attaching financial consequences to it. (Petitioners’ Brief, pp. 37–39.)

Boulder answers that its claims address production, sales and deceptive marketing, while the Clean Air Act regulates emissions sources. It argues that an indirect effect on fossil fuel demand does not establish a conflict with federal law. (Respondents’ Brief, pp. 10–11, 43.)

The Colorado Supreme Court majority rejected the idea that a large damages award automatically amounts to prohibited regulation. It distinguished Kurns, where federal legislation occupied the entire relevant regulatory field. The dissent considered the distinction unconvincing because Boulder’s alleged injuries depend on global emissions. (2025 CO 21, paragraphs 58–59; Samour dissent, paragraphs 90–95.)

Didn’t The Supreme Court Already Reject Climate Nuisance Claims?

In American Electric Power Co. v. Connecticut in 2011, the Supreme Court rejected federal common law nuisance claims seeking court-ordered limits on power plants’ carbon dioxide emissions. Federal common law means rules developed by federal judges rather than enacted by Congress. The Court held that the Clean Air Act displaced that judicial route because Congress had assigned the relevant regulatory task to the Environmental Protection Agency.

Crucially, the Court left the availability of state law claims open, explaining that it depended on the federal statute’s preemptive effect. Displacement of federal common law and preemption of state law are distinct inquiries. The 2011 judgment therefore did not decide that every state climate damages claim was barred.

Boulder’s case puts that unresolved boundary before the Court. The absence of a federal common law remedy does not, by itself, answer whether a state remedy survives.

What Does The Clean Air Act Leave States Free To Do?

The Clean Air Act combines federal oversight with substantial state responsibilities. It also contains provisions preserving certain state powers and remedies.

Jonathan Adler’s amicus brief supporting Boulder emphasises this shared structure. An amicus brief is a submission from someone who is not a party, offering arguments to assist the Court. Adler argues that federal environmental legislation generally supplements state authority rather than replacing it altogether. (Adler Amicus Brief, pp. 9–17.)

That does not mean every state claim survives. In International Paper Co. v. Ouellette, the Supreme Court allowed water pollution claims under the law of the state where the pollution originated, while barring the affected state’s law from governing the out-of-state source.

The lesson is that two questions may arise: whether state law can apply at all, and which state’s law can apply. Preserving a state remedy does not necessarily give Colorado unrestricted authority over conduct elsewhere. (International Paper Co. v. Ouellette, 479 U.S. 481, 494–500 (1987).)

Could The Supreme Court Decide It Cannot Hear The Case Yet?

Yes. When granting review, the Court expressly added a question about its statutory and constitutional jurisdiction, meaning its authority to decide the dispute. (Order of February 23, 2026, No. 25-170.)

One issue is finality. Supreme Court review of state court decisions generally requires a final judgment, but Boulder’s damages lawsuit is still pending. The companies argue that the Colorado Supreme Court completed a separate proceeding that qualifies for immediate review. Professor Derek Muller supports that interpretation in an amicus brief taking no position on the climate claims. (Muller Amicus Brief, pp. 2–4.)

Boulder argues that the state court merely reviewed an interim ruling. It also disputes whether losing a defense before any liability judgment gives the companies the concrete injury necessary for constitutional standing. The companies point to the rejection of their defense, increased exposure to liability and continuing litigation costs. (Respondents’ Brief, pp. 11–22; Petitioners’ Reply Brief, pp. 3–6.)

A jurisdictional dismissal would leave the Colorado ruling in place at this stage without resolving the underlying federal law dispute nationwide.

Why Are Foreign Affairs Relevant To A Local Compensation Claim?

The alleged harm in Boulder is local, but the activities and emissions connected to it extend worldwide.

The United States supports the companies. Its brief argues that state damages claims targeting overseas fossil fuel activity could disrupt diplomacy, conflict with other countries’ laws and interfere with national decisions about international climate liability. (United States Amicus Brief, pp. 26–28.)

Boulder answers that incidental international effects do not displace traditional state authority to remedy domestic injuries. It argues that the companies have not identified a conflict with an express federal policy carrying the necessary legal force. (Respondents’ Brief, pp. 41–42.)

The issue is how far federal control of foreign affairs limits local remedies when the conduct causing the alleged harm crosses national borders.

If Boulder Can Proceed, What Would It Still Have To Prove?

Boulder would still need to establish the requirements of its individual claims and show a legally sufficient connection between the companies’ conduct and its injuries.

This involves both factual causation and legal causation: did the conduct contribute to the harm, and is the connection sufficient for the law to attach responsibility? The district court found those connections plausibly alleged, including allegations about foreseeable climate consequences.

The court also rejected the idea that contributions from multiple actors necessarily eliminate responsibility. That does not settle how responsibility would ultimately be proved or allocated. (District Court Order, June 21, 2024, pp. 65–69.)

Boulder would also need to substantiate the costs for which it seeks recovery. Its complaint identifies categories of expenditure; a successful compensation claim would require evidence connecting recoverable losses to the alleged wrongdoing. (Amended Complaint excerpts, Joint Appendix, pp. 42–84.)

What Are The Possible Outcomes Of The Supreme Court Case?

The main possibilities are:

• The Court decides it lacks jurisdiction. The Colorado ruling remains in place at this stage, and the Court gives no substantive answer to the federal law challenge.

  
  

• The Court rejects the asserted federal barriers. Boulder can continue pursuing its claims, with proof and other defenses still to be addressed.

  
  

• The Court finds that federal law bars the claims. Its ruling could require dismissal or further proceedings applying the legal rule it adopts.

These possibilities arise from the questions the Court accepted for review. None involves the Supreme Court itself awarding Boulder compensation. (Questions Presented, No. 25-170.)

What Does Justice Alito’s Withdrawal Mean For The Case?

On September 28, 2026, the Supreme Court’s clerk informed the parties that Justice Alito would no longer participate in the case. The letter gives no reason for his withdrawal, so the court record does not establish why he stepped aside. His absence leaves eight justices to decide the case, assuming no further withdrawals. (Clerk’s letter to counsel, No. 25-170, 28 September 2026.)

The main consequence is the possibility of a 4–4 split. If the Court divides equally on whether to uphold or reverse the Colorado Supreme Court’s judgment, that judgment would stand. The companies would need five of the eight participating justices to overturn it. However, an equally divided affirmance would create no binding Supreme Court precedent for other climate cases. The Court has expressly distinguished leaving a lower court’s judgment in place from establishing a legal rule. (Neil v. Biggers, 409 U.S. 188, 192 (1972).)

For Boulder, that outcome would preserve its ability to pursue the claims under the Colorado ruling. It would not establish that the companies are liable or that Boulder is entitled to compensation. The Colorado Supreme Court expressly left the ultimate merits unresolved.

The withdrawal therefore introduces an important possibility: Boulder could preserve its position while the wider legal uncertainty remains. That is a procedural implication, not a prediction of the votes. Eight justices can still produce a majority decision with national consequences.