The U.S. Supreme Court agreed in February 2026 to hear the Boulder climate change lawsuit against ExxonMobil and Suncor Energy, a case that will decide whether cities, counties, states, and tribes can use state tort law to make fossil fuel companies pay for climate damages. The ruling will not decide whether the companies are actually liable. It will decide whether cases like Boulder’s are allowed to exist.
What Boulder Is Suing Over
Boulder County, the City of Boulder, and San Miguel County filed suit in Colorado state court in 2018. They allege ExxonMobil and Suncor knew for decades that burning fossil fuels drives climate change, and that instead of disclosing the risks the companies funded campaigns to obscure the science and misrepresent the danger of their products.
The lawsuit does not ask a court to shut down oil and gas operations or impose emissions limits. It asks the companies to pay their “fair share” of the local costs of climate-related harm: wildfire response, flood control repairs, drought management, and infrastructure fixes. The plaintiffs estimate those costs will exceed $100 million through 2050.1Boulder County Government. Climate Lawsuit The legal theories are public and private nuisance, trespass, unjust enrichment, and civil conspiracy. A separate claim under the Colorado Consumer Protection Act was dismissed as time-barred in June 2024, with leave to amend.2Sabin Center for Climate Change Law. Board of County Commissioners of Boulder County v. Suncor Energy The complaint expressly disclaims any request to enjoin oil and gas operations, enforce emissions controls, or seek relief tied to activities on federal lands.3Sabin Center for Climate Change Law. Board of County Commissioners of Boulder County v. Suncor Energy – Complaint
The Question the Supreme Court Agreed to Decide
On February 23, 2026, the Court granted certiorari on a single central question: whether federal law precludes state-law claims seeking relief for injuries caused by the effects of interstate and international greenhouse gas emissions on the global climate. The Court also directed the parties to brief a threshold jurisdictional question it raised itself: whether the Court can even hear the case, given that the Colorado Supreme Court’s ruling was interlocutory rather than a final judgment.4Supreme Court of the United States. Suncor Energy v. County Commissioners of Boulder County, No. 25-170
Suncor and Exxon filed their merits brief on May 14, 2026. The plaintiffs’ response is due July 27, 2026. Oral arguments are expected in the fall of 2026, and a decision is anticipated by mid-2027.5SCOTUSblog. Supreme Court Agrees to Hear Case on Colorado Dispute Over Climate Change
The Preemption Fight
The core dispute is whether the Clean Air Act, or federal common law, blocks a state from applying its own tort law to companies whose products cause emissions that cross state and national borders. The energy companies say yes. Boulder says no.
The closest existing precedent is American Electric Power Co. v. Connecticut, decided 8–0 by the Supreme Court in 2011. Justice Ruth Bader Ginsburg’s opinion held that the Clean Air Act displaced any federal common-law right to seek abatement of greenhouse gas emissions, because Congress had assigned that balancing task to the EPA and left “no room for a parallel track” through federal common-law litigation.6Justia. American Electric Power Co. v. Connecticut, 564 U.S. 410 But AEP did not decide whether the Act also preempts state-law nuisance claims. The plaintiffs there had raised state-law theories but abandoned them on appeal, and the Court explicitly left open the “availability vel non of a state lawsuit.”7Columbia Law School. American Electric Power v. Connecticut
The Colorado Supreme Court answered that open question on May 12, 2025, ruling 5–2 that Boulder’s claims can proceed. Justice Richard Gabriel’s majority opinion worked through each preemption theory and rejected them all. On federal common law, the majority reasoned that once the Clean Air Act displaced it under AEP, federal common law no longer exists as a vehicle to preempt state law. On the Clean Air Act itself, the court found no express preemption of state common-law torts, no field preemption (pointing to savings clauses preserving state remedies), and no conflict preemption, because Boulder seeks money damages rather than an injunction that would interfere with federal regulatory goals.8Justia. County Commissioners of Boulder County v. Suncor Energy, 2025 CO 21
Justice Carlos Samour Jr., joined by Justice Boatright, dissented. Samour warned the ruling gave local municipalities a “green light to act as its own republic” on interstate and international air pollution and predicted a “patchwork of inconsistent local standards that will beget regulatory chaos.” He urged the U.S. Supreme Court to step in.9Spencer Fane. Colorado Supreme Court Rules That Boulder’s Tort-Based Climate Change Damages Lawsuit Will Proceed in State Court The Court did.
The Trump administration is arguing the industry’s side. In September 2025, the Solicitor General filed an amicus brief contending that state tort law cannot reach greenhouse gas emissions occurring outside a state’s borders, that the Clean Air Act preempts such claims, and that plaintiffs cannot dodge preemption by framing their cases around fossil fuel marketing rather than emissions.10Harvard Environmental and Energy Law Program. Boulder and Endangerment Finding
The EPA Endangerment Rescission Wild Card
In February 2026, the EPA rescinded the 2009 endangerment finding that had served as the scientific and legal basis for regulating greenhouse gases from motor vehicles under the Clean Air Act. The final rule concluded the agency never had statutory authority to regulate greenhouse gas emissions under Section 202(a)(1), calling such regulation “costly and futile.”11Beveridge & Diamond. EPA Strikes at the Roots of Federal GHG Regulations: Rescinds Endangerment Finding for Motor Vehicles
That creates a tension for the industry’s Supreme Court argument. The companies say the Clean Air Act preempts state climate suits because Congress delegated greenhouse gas regulation to the EPA. But if the EPA itself now says it lacks authority to regulate greenhouse gases, the delegation argument loses its foundation. The EPA anticipated the problem, asserting in the rule’s preamble that the Act “continues to preempt state common-law claims” regardless of the rescission.12Salata Institute, Harvard. The Legal Reasoning Behind the Endangerment Rescission Boulder’s lawyers are expected to argue the opposite: if the federal government is walking away from greenhouse gas regulation, there is less reason to block states from pursuing their own remedies.13Stateline. Supreme Court Takes Up Climate Case Testing Local Lawsuits Against Oil Companies
What Happens to Other Climate Cases in the Meantime
Roughly three dozen similar lawsuits are pending across the country, and the Court’s decision to take Boulder froze many of them. Defendants in State of Hawaii v. BP asked the trial court to continue a stay, citing the need for “potentially dispositive guidance.” A New Jersey appellate court placed Platkin v. Exxon Mobil in abeyance pending the Boulder ruling. Defendants in Shoalwater Bay Indian Tribe v. Exxon Mobil in Washington requested a stay of all proceedings.14Columbia Law School. Climate Litigation Updates
Not every court has waited. On March 24, 2026, the Maryland Supreme Court affirmed the dismissal of climate lawsuits brought by Baltimore, Annapolis, and Anne Arundel County against 26 oil and gas companies. Justice Brynja Booth wrote for the majority that the localities’ claims were a “backhanded attempt to regulate carbon emissions” preempted by the Clean Air Act, and that the plaintiffs also failed to state valid claims under Maryland law. A dissent argued the majority had constructed a “classic strawman” by treating the cases as emissions-regulation suits rather than fraud and deceptive-marketing claims.15Maryland Matters. Maryland Supreme Court Climate Cases Dismissed
In North Carolina, the Business Court dismissed Town of Carrboro v. Duke Energy in February 2026, ruling the claims raised nonjusticiable political questions and that tracing local infrastructure damage to a company’s alleged disinformation campaign would require “rank speculation.”16WUNC. Judge Dismisses Carrboro Lawsuit Against Duke Energy Over Climate Change A New Jersey trial court dismissed Platkin v. Exxon Mobil in February 2025, finding the state’s consumer-protection-framed claims were “entirely about addressing the injuries of global climate change” and therefore preempted; that court explicitly rejected the reasoning of the Hawaii Supreme Court, which had allowed Honolulu’s similar claims to proceed.17Sabin Center for Climate Change Law. Platkin v. Exxon Mobil Corp. – Dismissal The Honolulu case reached the Supreme Court as Sunoco LP v. City and County of Honolulu, and in January 2025 the Court denied review, leaving Honolulu’s claims intact. It was the fourth time since 2023 the Court had declined to hear an oil-company appeal in a climate deception lawsuit before taking Boulder.18Center for Climate Integrity. Supreme Court Denies Big Oil Request to Review Climate Lawsuit
The Federal Government’s Parallel Offensive
The Boulder amicus brief is part of a wider federal campaign against state climate accountability. On April 30, 2025, the Department of Justice sued Hawaii and Michigan to preemptively block those states from pursuing climate liability litigation against fossil fuel companies. The next day, the DOJ sued New York and Vermont over newly enacted “climate Superfund” statutes that impose liability on fossil fuel companies for historical emissions.19U.S. Department of Justice. Justice Department Files Complaints Against Hawaii, Michigan, New York, and Vermont
The Hawaii suit was dismissed with prejudice in April 2026 after the court found the federal government lacked standing, ruling the alleged injuries were speculative.20Sabin Center for Climate Change Law. United States v. Hawaii21U.S. Department of Justice. Justice Department Files Motion for Summary Judgment to Challenge New York’s Climate Change Superfund Act22U.S. Department of Justice. Justice Department Files Motion for Summary Judgment to Challenge Vermont’s Climate Superfund Law
What a Ruling Would Mean
Boulder is the first time the Supreme Court will squarely address whether federal law bars state-law tort claims over climate change damages. A ruling that federal law preempts these claims would effectively end the current wave of municipal and state climate litigation. A ruling the other way, or a finding that the Court lacks jurisdiction to decide now, would let scores of cases advance toward discovery and trial for the first time.
Boulder County Commissioner Ashley Stolzmann said when the Court took the case: “We must hold oil companies accountable for the significant harm they’ve caused our communities.” The companies and their allies describe the litigation as an attempt to impose a “chaotic patchwork” of local regulations on a global industry.23Boulder County Government. U.S. Supreme Court Decides to Hear Climate Case Against ExxonMobil and Suncor Entities With arguments expected in the fall of 2026, the answer is more than a year away.