Boulder County and the City of Boulder are suing Suncor Energy and ExxonMobil in Colorado state court for damages tied to climate change impacts, arguing the companies knowingly contributed to greenhouse gas emissions while misleading the public. Suncor and Exxon say the claims are precluded by federal law governing interstate and international emissions. The U.S. Supreme Court will hear the companies’ appeal of a Colorado Supreme Court ruling that let the suit proceed, with argument set for October 5, 2026.
LATEST DEVELOPMENT · FEB 23, 2026
The U.S. Supreme Court granted certiorari on February 23, 2026 and will hear argument on October 5, 2026 on whether federal law precludes state-law claims seeking damages for harms attributed to interstate and international greenhouse-gas emissions, after the Colorado Supreme Court held on May 12, 2025 that the Clean Air Act does not preempt Boulder’s claims. The Solicitor General will argue as amicus. The ruling will govern some two dozen climate-liability suits brought by states, counties and cities against oil majors.
BACKGROUND
Boulder County and the City of Boulder sued Suncor Energy and ExxonMobil in Colorado state court in April 2018, seeking damages under state tort law for the costs of adapting to climate change, including heat waves, wildfires, drought and flooding, that the local governments attribute to the companies’ fossil fuel production and decades of alleged deception about its climate effects. The companies removed the case to federal court, touching off a five-year jurisdictional fight that went to the Tenth Circuit twice and to the U.S. Supreme Court once, ending in April 2023 when the Supreme Court declined to disturb rulings sending the case back to Boulder County District Court.
Once back in state court, Suncor and Exxon argued that the Clean Air Act and related federal law displace or preempt Boulder’s public nuisance, trespass, unjust enrichment and civil conspiracy claims because the alleged harm flows from interstate and international greenhouse gas emissions, a field they say only Congress and federal regulators can govern. The Colorado Supreme Court rejected that argument on May 12, 2025, holding 5-2 that Boulder’s claims may proceed under state law, and the case returned to the district court for further proceedings on the merits.
Suncor and Exxon then petitioned the U.S. Supreme Court, which granted certiorari on February 23, 2026. The Court agreed to decide whether federal law precludes these state-law damages claims and, unusually, added its own second question on whether the Court has statutory and Article III jurisdiction to hear the case at all. The Solicitor General was granted leave to argue as amicus curiae in support of the energy companies, splitting argument time with petitioners’ counsel. Oral argument is set for October 5, 2026, the first argument of the Court’s new term, with a decision expected sometime in the 2026-27 term.
The case has become the lead vehicle for roughly two dozen similar climate damages suits filed by states, counties and cities against oil and gas majors across the country. A ruling for Suncor and Exxon on preemption could effectively end that wave of litigation, while a ruling for Boulder would let those cases proceed toward trial on the merits in state courts.
TIMELINE
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OCT 5, 2026HEARINGOral argument scheduled at the Supreme CourtThe Supreme Court is set to hear oral argument as the first case of its October 2026 term.
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JUL 28, 2026PROCEDURALSolicitor General granted divided argument timeThe Court granted the Solicitor General’s motion to participate in oral argument as amicus curiae in support of petitioners Suncor and Exxon, splitting argument time.
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FEB 27, 2026PROCEDURALSupreme Court adds jurisdictional question for briefingIn addition to the preemption question presented in the cert petition, the Court directed the parties to brief and argue whether the Court has statutory and Article III jurisdiction to hear the case.
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FEB 23, 2026PROCEDURALU.S. Supreme Court grants certiorari
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AUG 8, 2025APPEALSuncor and ExxonMobil petition the U.S. Supreme Court for certiorari
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MAY 12, 2025JUDGMENTColorado Supreme Court holds the Clean Air Act does not preempt Boulder’s state-law claims
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APR 24, 2023PROCEDURALSupreme Court denies certiorari on removal jurisdictionThe U.S. Supreme Court denied Suncor and Exxon’s petition seeking review of the Tenth Circuit’s affirmance of the remand order, allowing the case to proceed in Boulder County District Court.
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FEB 2022APPEALTenth Circuit again holds case belongs in state courtOn remand, the Tenth Circuit again ruled that the case should proceed in Colorado state court rather than federal court.
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MAY 24, 2021PROCEDURALSupreme Court vacates and remands in light of BP v. BaltimoreThe U.S. Supreme Court granted certiorari, vacated the Tenth Circuit’s judgment, and remanded for reconsideration of additional removal grounds in light of its decision in BP p.l.c. v. Mayor of Baltimore.
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JUL 7, 2020APPEALTenth Circuit affirms remand to state courtThe Tenth Circuit Court of Appeals affirmed the district court’s remand order, holding it lacked jurisdiction to review most of the asserted grounds for removal.
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SEP 5, 2019PROCEDURALFederal district court remands case to Colorado state courtJudge William J. Martinez of the U.S. District Court for the District of Colorado rejected all grounds for removal asserted by Suncor and Exxon and sent the case back to Boulder County District Court.
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APR 17, 2018FILINGBoulder County, the City of Boulder and San Miguel County sue Suncor and ExxonMobil in Colorado state court