Amicus Brief: Boulder, Colorado’s Effort to Set National Climate Policy Violates the Constitution’s Federal Structure

Suncor Energy (U.S.A.), et al. v. County Commissioners of Boulder County, et al. 

Boulder, Colorado wants to set national climate policy—and it is trying to use state courts to do the work. Boulder filed state law claims against two international oil companies—Suncor Energy and BP— in Colorado state court, seeking damages for financial  harms it blames on global climate change, including wildfires, extreme heat, droughts, and flooding. The Colorado Supreme Court allowed the case to proceed. The Supreme Court of the United States will now decide whether federal law bars the claims.

Boulder is not alone. Approximately 40 similar suits are pending in state courts around the country. States and localities are using state tort claims to hold fossil fuel companies liable for global greenhouse gas emissions—emissions that occur across the country and around the world, including by the suing localities, like Boulder, themselves. If these cases proceed, any state or locality could project its preferred climate and energy policy nationwide through state tort law, subjecting energy companies to a patchwork of overlapping and potentially conflicting legal obligations.

CIR’s amicus brief in this case argues that the Constitution’s horizontal federalist structure forecloses Boulder’s approach. Each state is the sovereign equal of every other. No state may govern citizens and businesses in other states. But that is exactly what Boulder is trying to do. The only way the oil companies could avoid the global emissions Boulder complains of would be to cease lawful operations across the country and around the world. Boulder’s lawsuit is not a local tort claim. It is an attempt by one city to impose energy and climate policy on the entire nation.

Why This Case Matters

The stakes of this case extend far beyond Boulder and the named defendants. At its core, this is about whether one state—or one city—can dictate rules for citizens and businesses everywhere else.

The Constitution’s federal structure protects individual liberty in part by letting Americans “vote with their feet.” When a state’s policies become too burdensome, people and businesses can relocate to a state that better reflects their preferences. That option disappears when one state can impose obligations on people across the country who had no ability to influence that policy at their own state’s ballot box.

If Colorado can effectively regulate national greenhouse gas emissions through state tort litigation, so could every other state. Courts across the country would apply their own standards to the same national conduct, creating a complex web of conflicting obligations that would chill or shut down lawful industries. Energy producing states that affirmatively encourage energy production—and the citizens who have chosen to live under those policies—would have their choices overridden by a single city’s lawsuit.

CIR filed this brief as part of its Project to Restore Competitive Federalism. Protecting the federal structure sometimes means pushing back against federal overreach. But it also means ensuring that states do not overstep their own constitutional limits. This case and the approximately 40 similar cases pending in courts around the country, present precisely that threat.

This case also parallels CIR’s ongoing challenge to New York’s greenhouse gas reporting rule, where New York similarly seeks to project its regulatory authority beyond its borders. Neither Boulder nor Albany can govern the citizens and businesses of other states.

Background

The U.S. Constitution creates a federal system with both vertical and horizontal dimensions. Vertical federalism is about how power is allocated between the national government and the states—the dimension most familiar from debates about Congress’s enumerated powers.

Horizontal federalism governs the relationships among the states themselves. Three principles anchor horizontal federalism. First, each state is the sovereign equal of every other; no state has special status in the national government or special privileges over its neighbors. Second, each state’s sovereignty is coextensive with its territory—a state’s law presumptively ends at its border. Third, no state may interfere with the sovereign prerogatives of other states.

Together, these principles mean that a state may not impose its law on citizens and businesses in other states. The Supreme Court has enforced these principles across many doctrinal areas—personal jurisdiction, the dormant Commerce Clause, punitive damages for out-of-state conduct, and interstate sovereign immunity—without always identifying the common constitutional thread running through them.

In National Pork Producers Council v. Ross (2023), the Court suggested that a structural extraterritoriality principle is embedded in the Constitution as a whole, not merely in specific clauses. This case gives the Court the opportunity to apply that principle to an increasingly common pattern: state-court litigation designed to impose one state’s preferred national policy on the rest of the country.

Americans’ individual liberty depends in part on having genuinely different state policy choices available. When states can project their authority across borders through tort litigation, that competitive federalism breaks down—and with it, one of the Constitution’s most important safeguards for freedom.