Republican attorneys general left Supreme Court climate arguments more confident than they arrived, casting Boulder’s lawsuit against oil companies as an energy tax other states never voted on.
Alabama Attorney General Steve Marshall and Utah Attorney General Derek Brown told reporters Monday afternoon they liked what they heard after the U.S. Supreme Court opened its 2026-27 term with oral arguments in Suncor v. Boulder.
The case asks whether Boulder County and the city of Boulder can force Exxon Mobil Corp. and Suncor Energy into Colorado state court over alleged climate harms tied to global greenhouse gas emissions. Oil companies say federal law preempts those claims. A ruling could decide whether dozens of similar climate lawsuits across the country move forward under state law.
The Center Square reported that Marshall, who led a 26-state amicus brief urging the Court to take the case, said his confidence rose after the full argument.
"We were confident coming in. I feel even better having heard the whole argument, particularly if you listen to Justice [Brett] Kavanaugh’s line of questioning,"
Marshall added that Kavanaugh “feels like this is a fairly straightforward case.” Brown also signed the brief, attended the arguments, and said he was optimistic about how the Court would rule.
Boulder County and the city of Boulder sued Exxon Mobil and Suncor in 2018 under Colorado law. They alleged the companies knowingly contributed to climate change through the production, promotion, and sale of fossil fuels while concealing or misrepresenting alleged dangers to the public.
Boulder sought damages for harms it attributed to climate change, including wildfires, flooding, and extreme weather affecting local residents and property. The companies answered that because Boulder ties its alleged injuries to global emissions, federal law preempts the claims and blocks them from proceeding under Colorado law.
The Colorado Supreme Court rejected that preemption argument without ruling on the merits of Boulder’s underlying claims. The U.S. Supreme Court then agreed to review that decision and chose the dispute to open oral arguments for the new term, a docket that also features high-stakes fights tracked closely by conservatives, including climate suits, AR-15 bans and Trump policy cases.
Marshall’s 26-state coalition pressed the Court to take the case. Brown signed on. Their shared concern was simple: one state’s courts should not set energy costs and legal exposure for the rest of the country.
During argument, Justice Elena Kagan compared Boulder’s theory to earlier waves of public litigation.
"In multiple respects, this suit appears to be based on the old 1990s tobacco suits that were brought by states and local governments basically saying that big tobacco had made representations, misrepresentations, which had caused people to... overuse the product, causing harm to those governments,"
S1’s account notes she framed opioids as a second chapter and climate suits as a potential third. Justice Brett Kavanaugh pushed back on that comparison and pointed to long-standing Court treatment of interstate pollution.
"I thought the answer was that this Court has consistently said that air and water pollution are different in our federal enclaves,"
That exchange mattered to Marshall. He told reporters Kavanaugh’s questioning was a reason he felt better leaving the building than entering it. The companies’ core pitch remained federal preemption: global emissions are not a local nuisance Colorado courts can police against out-of-state energy producers.
Brown cast the stakes in constitutional terms rather than climate science terms. He said the real issue is whether one state can impose its will on another.
"Ultimately it comes down to the real issue of, they call it the sovereignty concept, of whether one state can impose their will on another state,"
He went further on costs. “They’re imposing what’s in effect an energy tax on other states,” Brown said. “My state is right next to Colorado, and it would have an impact on my state, even though we didn’t get a vote.”
Brown also warned of a cascade. If Boulder’s model stands, he asked, do states suddenly face a slew of lawsuits in which all 50 try to load burdens onto the other 50? He tied that risk to the original bargain of the Union: states gave up the power to punish one another’s commerce in exchange for a uniform national system.
That red-state posture fits a broader pattern of Republican attorneys general taking interstate policy fights to the justices, including when red-state AGs sued blue states at the Supreme Court over abortion-pill shield laws.
Optimism from the AGs did not mean a one-sided bench. Chief Justice John Roberts, Justice Amy Coney Barrett, and Justice Neil Gorsuch also posed challenging questions to the oil companies about the scope and consequences of their preemption argument.
Roberts noted familiar situations in which conduct outside a state still has broad effects inside it, and state courts are still allowed to hear the case.
"There are a lot of familiar situations where conduct outside of a state has broad effects from other states... and yet we allow state courts in a particular state to bring litigation that affects that,"
He added he was not quite sure what makes this dispute different from those other ones the Court has allowed to proceed in state court. Roberts also raised practical implications if municipalities nationwide filed similar suits, the same sprawling-liability problem Brown amplified after the session.
For companies, the fear is open-ended exposure: local governments nationwide converting contested climate policy into damages actions against a shifting list of energy defendants. For Boulder, the pitch is local injury and state tort law. The justices have to decide which frame controls before any jury ever hears a climate model.
Steve Milloy, a senior fellow at the Energy and Environment Legal Institute and a former Trump EPA transition team member, provided a statement after the hearing. He described nearly two hours of almost exclusively procedural argument and said industry counsel closed on the structural problem.
"After almost two hours of almost exclusively procedural argument, the case was best summed up by the oil industry layers at the very end: Allowing the Boulder lawsuit to proceed in state court would allow an unlimited number of plaintiffs to sue and unlimited number of defendants, a situation that both parties had objected to on an international level. Moreover, because of its global aspect, climate is inherently a political question that would require resolution by Congress."
That last point is the policy core conservatives keep returning to. If the injury is planetary and the remedy is national energy policy, the venue is Congress, not a Colorado trial court applying state law to global emissions.
The same Court has been a decisive forum on separation-of-powers and executive authority questions important to the right, including when the Supreme Court let Trump keep deporting illegal immigrants to third countries.
No decision came down Monday. No timeline was announced in the account of the arguments. What is clear is the downstream map.
If the Court sides with the companies on preemption, Boulder’s case and a field of similar state-law climate suits could be stopped at the threshold. If the Court sides with Boulder on the gateway question, those suits proceed under state law even though the alleged causal chain runs through worldwide emissions.
Marshall’s coalition did not show up to argue weather patterns. It showed up to argue constitutional structure: one state’s preferred climate theory should not become a national energy levy enforced by local courts. Brown’s “energy tax” line was the plain-English version of that claim.
Conservatives watching the term already treat the Court as the last backstop when lower courts or blue-state policy shops try to nationalize disputed rules, a dynamic also visible when the Trump administration asked the Supreme Court to restore its third-country deportation policy after an appeals court setback.
Monday’s argument mixed tobacco analogies, pollution precedent, sovereignty warnings, and pointed questions for both sides. Marshall left more confident. Brown left focused on whether Colorado can export costs to Utah without a vote. Kavanaugh’s pollution distinction gave the AGs their clearest public hook. Roberts’ skepticism kept the companies from claiming a free ride.
State attorneys general came to stop a model of litigation that turns contested national energy policy into local damages claims. Taxpayers in states that never sued should not pen the check for Boulder’s theory of the atmosphere.