Supreme Court to weigh whether states can sue over greenhouse gas emissions in Boulder case
The Supreme has placed a high-profile climate lawsuit brought by the City of Boulder and Boulder County against ExxonMobil and Suncor on its calendar, a move that could decide whether federal law blocks state-law claims tied to interstate greenhouse gas emissions. The case matters now because the question of preemption could determine whether local governments can seek monetary relief for floods, wildfires and other alleged climate harms in state courts.
Supreme Court places City of Boulder and Boulder County case on calendar
On Monday the U. S. Supreme Court officially added the case to its docket after ExxonMobil and Suncor filed a petition asking the justices to decide whether federal law prevents state-law claims that arise from interstate emissions. The energy companies sought review following a May 2025 Colorado Supreme Court decision that affirmed the ability of local jurisdictions to pursue compensatory relief for climate-related damages in state court.
Colorado Supreme Court ruling in May 2025 allowed most claims to proceed
The Colorado Supreme Court’s May 2025 decision allowed a suite of state-law claims to move forward, including public nuisance, trespass and unjust enrichment. The state court did, however, dismiss one consumer protection claim as time-barred. The Colorado court rejected the argument that federal law categorically preempted all the local claims, clearing the path for most of the case to continue in state court.
ExxonMobil and Suncor argue Clean Air Act and federal common law preempt state suits
In their petition the energy companies asked the high court to determine whether the Clean Air Act or federal common law displace state-law causes of action that address interstate greenhouse gas emissions. Below, those defendants argued unsuccessfully that the claims were preempted by the Clean Air Act or should be governed exclusively by federal common law; that setback prompted the companies to seek Supreme review.
City of Boulder and Boulder County seek monetary damages for wildfires and floods
The local governments are pursuing monetary relief for environmental harm they tie to fossil-fuel emissions, alleging the defendants misled the public about the climate risks of their products. The complaint cites concrete harms such as wildfires and floods as the types of climate-related damages for which the City of Boulder and Boulder County seek compensation.
Dismissed consumer protection claim and a dissent warning of regulatory patchwork
While most claims were allowed to proceed, the Colorado Supreme Court concluded one consumer-protection claim was time-barred and therefore could not be litigated. A dissenting justice in the state decision warned that allowing state-law suits could produce a ‘‘chaotic patchwork’’ of local regulations on what the dissent described as an issue inherently international in scope, a concern the energy companies highlighted in pressing for review.
By taking the case, the Supreme Court will consider whether the federal statutory and common-law frameworks should displace state-court remedies—an outcome that would directly affect the City of Boulder and Boulder County and could set a nationwide precedent for similar suits. Oral arguments are scheduled for the Court’s next term, which begins in the fall, when justices will weigh the petition’s central question about the reach of federal law over interstate emissions.
What makes this notable is the potential for a single decision to either preserve state courts as venues for climate-related relief or to channel those disputes exclusively into a federal framework; the choice will shape where and how municipalities can pursue damages tied to greenhouse gas emissions. The timing matters because the Colorado ruling in May 2025 already allowed litigation to proceed at the state level, and the Supreme’s acceptance of review pauses that trajectory pending the justices’ resolution.
For the parties, the immediate effect is procedural: the state-court pathway that survived the Colorado Supreme Court challenge will now be subject to a definitive ruling from the nation’s highest court. The broader implication is a possible nationwide shift in who can sue over interstate emissions and under what body of law such suits may be heard.
