Climate Law Heats Up

By John R. Puri

Thursday, September 17, 2026

 

When Americans are expected to conform to the law, it’s essential for them to know where different kinds of law reside. Laws governing murder and burglary are left to the states; authority over immigration law rests with the federal government. But where exactly lies climate law, if such a thing even exists?

 

That is the question before the Supreme Court this term in Suncor Energy v. Boulder County. The case began when the Colorado county filed suit in state court against two oil and gas companies, Suncor and ExxonMobil, for financial damages. It alleges that these multinational corporations, by selling and promoting fossil fuels across the country and beyond, knowingly contributed to global climate change. As a result of these actions, Boulder contends, the county faces higher costs from extreme weather.

 

Before a Colorado court considered the suit on its merits, Suncor and Exxon argued that it lacked the authority to do so. Colorado’s highest court disagreed, so the defendants appealed to the U.S. Supreme Court. The justices will hear the case in October and decide on it next year. At stake is nothing less than the nature of federalism.

 

To the energy companies and their allies, Boulder’s lawsuit is an attempted end run around the legislative process. After failing to enact climate legislation in Congress, activists are trying to force their desired policies on the country through the courts. This is not the first time a subnational government has sued over greenhouse gases. In 2011, after several states sued electric utilities in federal court to limit their emissions, the Supreme Court ruled in American Electric Power Co. v. Connecticut that the Clean Air Act displaced any federal common-law claims. Now, the defendants argue, climate activists are evading American Electric Power (AEP) by shifting to state courts. They fear that a win for Boulder would devastate energy production by opening the door to lawsuits in 50 different jurisdictions.

 

Boulder County maintains that it is simply seeking compensation for local damages, not a nationwide injunction on emissions. While most originalists engaged on the issue are with Suncor, conservative law professor Jonathan Adler has taken the other side. He believes the companies are the ones trying to evade the law by asking the Supreme Court to terminate all state litigation before it can be heard. Though he doesn’t endorse Boulder’s injury claims, Adler told me that he thinks the energy sector has resorted to inventing a constitutional principle to stop the suits from going forward.

 

Both parties assert that victory for the other side would imperil self-government. The energy companies’ supporters argue that allowing Boulder’s suit to proceed would allow plaintiffs in one state to regulate conduct in other states. A municipality in Colorado could effectively tax an oil company in Texas without the people of the latter state having any say. Under the Constitution, such interstate regulation is delegated exclusively to the federal government. State governments — including their judiciaries — may govern activity only within their own borders.

 

In an amicus brief for the case, Adler responds that a radical federal preemption of local torts is what would truly erode federalism, and he argues that environmental protection was historically the domain of the states. It remains so today, as nothing in the Constitution or federal law purports to remove this power, even when environmental injuries cross a border. Relief for Suncor would leave battered municipalities “without recourse under any State’s law, while leaving source States free to authorize the conduct that generates the harm — converting a principle of equal sovereignty into a one-way immunity for source States.”

 

Boulder’s argument has a favorable precedent in the 2023 case National Pork Producers Council v. Ross. There, the Supreme Court ruled that the interstate commerce clause did not prohibit California from banning pork imports from suppliers that did not match the state’s strict animal-cruelty standards. Pig farmers in other states predicated their challenge on the dormant commerce clause — an implied prohibition on state laws that excessively burden interstate commerce — of which many originalists are skeptical. They failed to persuade a majority.

 

From that defeat, however, some conservatives see opportunity in Suncor. In their eyes, the Court in Pork Producers invited petitioners to present deeper arguments against extraterritorial regulation, rooted in the Constitution’s very structure of state sovereignty. The justices may finally endorse jurist Michael McConnell’s old amicus brief against California’s law, breaking ground on a new legal arena: “States generally may not punish people for deeds done in other states,” and no state can “block interstate commerce for the purpose of coercing or influencing the way people behave in other states.”

 

That is the decision the energy companies hope for. Carbon emissions, they attest, are inherently a national issue — international, actually — subject solely to federal law. Colorado can no more govern emissions from another state than it can regulate those from another country.

 

On Suncor’s side is a pair of rulings that share a name, Milwaukee v. Illinois. If carbon emissions are comparable to pollution in their harms, as Boulder County claims, these precedents should apply. In 1972, the Supreme Court ruled that interstate water pollution fell under federal common law and that relevant suits should therefore be filed in federal court. Nine years later, adjudicating the same controversy, the justices found that the Clean Water Act’s regulatory scheme had since displaced common-law nuisance claims.

 

Likewise, the energy companies argue that the Clean Air Act further preempts any climate torts, mirroring what the Court found in AEP. But therein lies an unsettling wrinkle: What if federal law does not regulate carbon emissions after all?

 

AEP turned on a 2007 precedent infamous among conservatives: Massachusetts v. EPA. There, in a 5–4 decision, the Court ruled that the Clean Air Act authorized the Environmental Protection Agency to regulate carbon emissions only because they qualified as “air pollutants” under the statute. Therefore, states could sue the EPA if it failed to properly regulate carbon emissions. Echoing their previous dissent, Justices Samuel Alito and Clarence Thomas concurred pointedly in AEP, “for the sake of argument because no party contends otherwise,” that Massachusetts was decided correctly.

 

Legal analyst Steve Milloy has noticed that, while the Trump administration claims in an amicus brief that the Clean Air Act grants the EPA exclusive authority to regulate carbon emissions, the administration explicitly rejects that position by rescinding the agency’s so-called endangerment finding. This 2009 determination provided the legal basis for the EPA to regulate emissions as a harmful pollutant. In rescinding it, Trump’s EPA concluded that the Clean Air Act “does not authorize the Agency to prescribe emission standards in response to global climate change concerns.”

 

Democratic states have already sued to reinstitute the endangerment finding under the Massachusetts precedent, and their case will probably reach the Supreme Court. Many conservatives are excited at this prospect, believing that the current Court would overturn Massachusetts if given the chance. None of the Court’s majority from 2007 remains, whereas three of the four dissenters are still on the bench.

 

But consider what happens if this foundational precedent falls away. If the EPA may not regulate carbon emissions, then federal statute does not preempt state-level climate suits, as the energy companies in Suncor argue. And if the Clean Air Act does not displace federal common law over carbon emissions, as AEP held, then federal nuisance torts are presumably reopened for business. Boulder County could refile its claim in federal court and even seek an injunction against energy producers rather than mere damages. Technically, conservatives would have gotten what they had wished for.

 

Even the best scientific models can’t perfectly predict the weather, but we can forecast with certainty that there are more storms ahead for climate law.