Supreme Court Opens Term With Boulder Climate Suit Against Exxon, Suncor

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Key Points

  • The Supreme Court opened its October Term 2026 on Monday, Oct. 5, by hearing Suncor Energy v. Boulder County (No. 25-170), the first argument of the term.
  • Justice Samuel Alito is not participating, so eight justices heard it; a 4-4 tie would leave in place the Colorado ruling that lets Boulder’s lawsuit proceed.
  • The court is weighing whether federal law bars state-law climate damage claims, plus a question it added: whether it has jurisdiction at this early stage.
  • The Trump administration backs Suncor and ExxonMobil, and the outcome could shape dozens of similar state and local climate suits.

The Supreme Court opened its new term on Monday with the Boulder climate case, a dispute SCOTUSblog calls one of the most significant business cases of the 2026-27 term. On Monday, the justices weighed whether two Colorado local governments can use state law to make oil companies help pay for damage they blame on climate change.

What happened

Boulder County and the City of Boulder sued Suncor Energy and ExxonMobil in Colorado state court in April 2018. They allege the companies knew for decades that fossil fuels would harm the climate, misled the public, and contributed to climate change by producing, refining and marketing fuel. They seek money for repairs, emergency services and property damage they link to floods, extreme heat and wildfires, and say the suit is not about regulating emissions.

The companies tried and failed to move the case to federal court and to have it dismissed. In May 2025, the Colorado Supreme Court concluded that “federal law did not preempt Boulder’s claims and that those claims could therefore proceed under state law,” Boulder County said in a statement. Suncor and ExxonMobil petitioned the U.S. Supreme Court in August 2025, and the justices agreed to hear the case on Feb. 23, 2026, according to the Supreme Court docket for No. 25-170.

The question the companies asked 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.” When it granted review, the court added a second question of its own: whether it has “statutory and Article III jurisdiction to hear this case.”

Latest development

Update (Mon 5 Oct, 1:50 p.m. ET): The justices heard the case Monday as the first argument of the new term, with eight justices taking part. Kannon Shanmugam argued for Suncor and ExxonMobil, Principal Deputy Solicitor General Sarah Harris for the United States, and Kevin Russell for Boulder. Chief Justice John Roberts pressed the companies and the government on why state suits should be barred here when such litigation has been allowed in similar contexts. “I guess I’m not quite sure what makes this situation different from all those other ones where we’ve allowed (it),” Roberts told Harris, Reuters reported. Justice Brett Kavanaugh said multiple federal court decisions “make crystal clear that interstate air and water pollution are matters for federal law unless Congress specifically preserves state law,” while Justice Elena Kagan said, “I don’t see why we wouldn’t permit it under the Clean Air Act either,” referring to state-law nuisance suits, according to The Colorado Sun. Justice Ketanji Brown Jackson suggested the court may be stepping in too soon, saying the discussion made her think “we’re really early in this case.” Shanmugam answered that with billions of dollars sought in these suits, “we need an answer to this question sooner rather than later.” A decision is expected by the end of June, Reuters reported.

The biggest late change came one week before argument. On Sept. 28, the clerk of the court told counsel by letter that Justice Alito will not continue to participate. The letter gave no reason. NPR reported that environmental organizations and watchdog groups had called for his recusal because of his investments in Phillips 66 and ConocoPhillips.

That leaves eight justices. A 4-4 split would let the Colorado decision stand, as NPR and SCOTUSblog have noted. The added jurisdiction question gives the court another possible exit. The court normally reviews only final state court decisions. Boulder says the Colorado ruling was not final because the case went back to the trial court and has not been tried; the companies say it settled the federal question and fits an exception.

The court’s day call set one hour: 20 minutes for the companies’ lawyer, Kannon Shanmugam; 10 minutes for Principal Deputy Solicitor General Sarah M. Harris, for the United States in support of the companies; and 30 minutes for Kevin Russell, for Boulder. A second case, Johnson v. United States Congress (No. 25-735), on veterans’ benefits challenges, was also scheduled for Monday.

Why it matters

Boulder is not alone. Dozens of similar suits by states and local governments against energy companies are moving through the courts, and Colorado Newsline counts more than 30 filed to date. A ruling here could decide whether claims like these can proceed under state law at all, a core question about how federal and state law fit together.

Suncor and ExxonMobil argue that climate change is an interstate and international problem only federal law can govern, citing the Constitution’s structure, the Clean Air Act and federal control of foreign affairs. In their petition, they warned of “potentially crushing monetary liability.” The Trump administration’s brief told the justices that “the Constitution rejects that butterfly-effect theory of state authority,” SCOTUSblog reported.

Boulder responds that nothing in the Constitution’s text or the Clean Air Act blocks its claims, and that Congress could act if it wanted to shield the industry. Twenty-six states led by Alabama back the companies, while Colorado, California and 17 other states back Boulder, according to a case preview by Cornell Law School’s Legal Information Institute.

Consumers have a stake too. Briefs backing the companies argue such liability would push up energy prices, with one calling the suit a “de facto carbon tax.” Climate economists backing Boulder counter that “the economic evidence does not support the claim” that making producers pay would destabilize the American economy.

What happens next

The court posts argument transcripts and audio recordings on its argument transcripts page; the transcript of this argument had not been posted as of early Monday afternoon ET.

The justices will discuss the case in private conference, a step explained in our guide to how the Supreme Court reaches its rulings. A decision is expected later in the term; the court does not announce opinion dates in advance. Arguments continue on Tuesday with Anderson v. Intel Corp. Investment Policy Committee.

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