Boulder Climate Lawsuit Heads to Supreme Court Monday

On Monday, Oct. 5, the U.S. Supreme Court will open its fall 2026 term with a case that could decide who pays for the damage climate change is already doing to American towns and cities. At issue is the Boulder climate lawsuit, in which the City of Boulder and Boulder County, Colorado, are suing ExxonMobil and Suncor Energy for what they allege are the costs of dealing with wildfires, floods, extreme heat, and drought.

According to Boulder County, the companies knowingly contributed to the harmful alteration of the climate while concealing the dangers of their products and misleading the public about it. The county says the question at the heart of the case is simple: should fossil fuel companies pay their fair share of the rising costs of climate impacts in Colorado, or should Boulder taxpayers bear those costs alone?

What happened

Boulder first sued the oil companies back in April 2018, alleging public nuisance, private nuisance, trespass, unjust enrichment, violations of the Colorado Consumer Protection Act, and civil conspiracy. In a 5-2 ruling in May 2025, the Colorado Supreme Court sided with the city and county, concluding that federal law did not preempt Boulder's claims and that they could proceed under state law. The companies then asked the U.S. Supreme Court to step in, and the justices agreed to hear the case.

Arguments are scheduled to begin at 10 a.m. Eastern (8 a.m. Mountain Time), with a livestream available through the Supreme Court. Boulder will be represented by attorney Kevin Russell, who will argue and take questions from the justices. The central legal question the companies are asking the Court to decide is whether federal law precludes state-law claims seeking relief for injuries allegedly caused by the effects of interstate and international greenhouse-gas emissions on the global climate.

In the days before argument, the case took an unexpected turn. According to press reports, Justice Samuel Alito informed the parties on Sept. 28 that he will not participate in the case. In a letter from the Court's clerk, no rationale was given, but the recusal matters enormously: with a conservative-dominated Court and one justice sidelined, a 4-4 tie would simply affirm the Colorado Supreme Court's ruling without setting a national precedent, leaving Boulder's case alive.

Why it matters

This isn't just about one Colorado city. More than 30 similar climate accountability lawsuits are pending across the country, brought by states, counties, and cities trying to recover the costs of sea-level rise, wildfires, storms, and extreme heat. None has yet reached trial, and how the Supreme Court rules here could lift or crush all of them at once.

A broad ruling for ExxonMobil and Suncor would end not only Boulder's suit but potentially dozens of others, and could create a template for arguing that other diffuse, transboundary harms are beyond state tort law too, reported by legal analysts at UCLA Law's Legal Planet. A narrow win for the companies could kill some claims while leaving the deception allegations — which center on marketing and concealment inside Colorado — intact.

On the other hand, a ruling for Boulder would send the case back to Colorado for discovery, opening the door for plaintiffs to demand internal documents about what the companies knew about climate risks and when they knew it. An unlikely alliance has formed in support of Boulder: in a statement reported by the coalition behind the case, seven Colorado cattle ranchers filed a brief saying they are living through the climate impacts scientists warned about for years, and that rising temperatures threaten the economic viability of their way of life. More than a dozen former EPA administrators from both parties also backed Boulder, arguing that nothing in the Clean Air Act preempts Colorado's state-law claims.

What to watch next

First, watch the argument itself. The justices surprised both sides by adding a question no party asked them to decide: whether the Court even has the authority to hear the case at this stage, since the Colorado ruling being reviewed is an interim one, not a final judgment. If the Court concludes it lacks jurisdiction, the case would simply proceed in Colorado state court — effectively a win for Boulder.

Second, watch for signs of a middle path. Legal experts say the narrowest outcome — and the one observers are paying least attention to — is a split decision that resolves only part of the companies' argument. The fossil fuel companies have briefed their foreign-affairs preemption theory sparsely, which could leave room for the Court to rule narrowly on the Clean Air Act question alone.

Finally, watch the timeline. A decision is expected before next summer, and whatever the Court decides will ripple through every pending climate liability case in America. For a generation that will live with the costs of climate damage longer than anyone else, the question of who pays — taxpayers or the companies that profited — is about as personal as law gets. You can follow the argument live on Monday through the Boulder County release, which links to the Court's livestream.