ExxonMobil and Suncor Energy are asking the Supreme Court to do something the tobacco industry tried and failed to accomplish for decades: make it impossible for state and local governments to sue them in state court. If the court sides with the oil companies, the ruling would not just end one lawsuit in Boulder, Colorado. It would effectively close the courthouse door on every similar climate case in the country.

The case is called Suncor Energy versus the County Commissioners of Boulder County. Boulder officials filed their lawsuit in Colorado state court back in 2018, arguing that Exxon and Suncor knew burning fossil fuels would cause serious climate damage, hid that knowledge from the public, and should now help pay for the consequences that local taxpayers are absorbing: flood defenses, wildfire recovery, infrastructure built for a climate that no longer exists. The Colorado Supreme Court cleared the case to move toward trial. So Exxon and Suncor appealed directly to the US Supreme Court, asking the justices to throw it out entirely.

What the companies are arguing

Their legal theory goes like this: federal law should govern climate cases that cross state lines, and that federal law "preempts," meaning overrides, any state court from hearing Boulder's claims. Preemption is a real and well-established legal principle. Congress can pass federal laws that wipe out state laws. The question here is whether it actually did that.

The companies point partly to the federal Clean Air Act. The problem is that the Clean Air Act says explicitly that controlling air pollution "at its source is the primary responsibility of states and local governments." Using that law to argue states have no authority here is a stretch that legal observers have noticed.

When the Clean Air Act argument runs thin, the companies fall back on a more exotic claim: that Supreme Court decisions from roughly a century ago created an unwritten "federal common law" governing environmental disputes, and that this unwritten law still exists somewhere in the structure of the Constitution, even though Congress later declared states have primary jurisdiction.

Dennis Fan, the founder and director of the Appellate Litigation Clinic at Columbia Law School, who wrote a brief in the case, put it bluntly: "The hope of the industry side is that this is going to be the death blow. The industry is going for the home run, they're going for the grand slam. They're thinking, 'if we win this argument, there will never, ever be climate change litigation again.'"

Why the tobacco comparison matters

Fan also noted that the court's own recent history cuts against the oil companies. "For decades, the tobacco industry tried to get the Supreme Court and other courts to stop state court litigation from happening against the tobacco industry, and they failed every single time." As recently as April, the Supreme Court ruled in a separate case that federal preemption requires an actual constitutional text or a federal statute, not just an implied structural argument.

That history is why the court's decision to take this case is itself notable. Normally, a case works its way through lower courts before the Supreme Court touches it. Boulder's case hasn't finished in state court yet. Fan called the court's choice to intervene now "an incredibly weird thing to have happen."

What's at stake beyond Boulder

If the justices rule for Exxon and Suncor, the decision would likely apply to dozens of similar lawsuits filed by cities and states across the country. Those cases represent one of the few remaining legal mechanisms by which local governments can attempt to recover costs they're already paying because of climate change. Lose that mechanism, and those costs stay entirely on taxpayers.

If the court sides with Boulder, or decides the case isn't properly before it yet, the lawsuit continues in Colorado state court and the broader wave of climate litigation stays alive. The court's ruling is likely months away. The costs Boulder is paying are not.