The Supreme Court term began Monday with oral arguments in Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County, the most important climate liability case to reach the Court in more than a decade. The Court will consider whether federal law—either through the Constitution or the Clean Air Act—preempts climate change tort suits filed under state law against energy producers.
The case originates from a 2018 suit filed by Boulder County, a county in Colorado devastated in recent years by both wildfires and floods. Boulder seeks to impose state tort liability on two large energy producers, Suncor and Exxon, for damages resulting from climate change. Boulder alleges that these companies promoted and sold fossil fuels while misrepresenting their dangers, thereby exacerbating global climate change and ultimately inflicting harm on Boulder’s residents and property. Boulder brings state-law tort claims against Suncor and Exxon, including nuisance, trespass, unjust enrichment, and deceptive trade practices, and seeks compensation and adaptation costs for the local harms caused by climate change.
Earlier efforts to hold fossil fuel companies liable under federal law have failed. A ruling in Boulder’s favor would allow state judges and juries to decide whether counties and states may impose tort liability on greenhouse gas producers for local injuries. In other words, such a ruling would keep state tort suits open as an avenue for climate litigation. Conversely, a ruling in favor of Suncor and Exxon would close or narrow that avenue, potentially shutting down dozens of similar, ongoing suits.
The questions before the Court in Suncor are about jurisdiction and federal preemption: first, whether the Supreme Court has statutory and Article III jurisdiction to hear the case; and second, whether federal law should preempt state-law claims seeking relief for local injury allegedly caused by the damaging effects of greenhouse gas emissions.
Monday’s argument offered few clear signals about how the Court will rule, but it revealed where the fault lines lie. The Court’s three liberal judges appeared more supportive of Boulder, while the questions from Chief Justice John Roberts and Justice Brett Kavanaugh seemed to favor the energy companies. Justice Samuel Alito’s notable recusal from the case opens the door to a possible 4-4 split, which would leave the Colorado Supreme Court’s ruling for Boulder in place, without setting binding precedent. Another possible outcome is dismissal of certiorari as improvidently granted, meaning the Court decides it should not have taken the case in the first place.
Below, we break down the top takeaways from the oral argument, including: the Justices’ attention to the jurisdictional question; the headwinds facing Suncor’s extraterritoriality and structural constitutional theories; the Justices’ divided views on what room the Clean Air Act leaves for state tort claims; and some Justices’ concerns about the flood of copycat suits.
Jurisdiction Attracted Attention from Four Justices
At oral argument, jurisdiction occupied a relatively small share of the argument, but Justice Clarence Thomas raised the issue at the outset in his questioning of both Suncor’s and the government’s counsel. Justices Elena Kagan, Sonia Sotomayor and Ketanji Brown Jackson returned to jurisdiction repeatedly, particularly in questioning Suncor’s counsel. With Justice Alito recused, dismissal based on jurisdiction would require two conservative Justices (either Roberts, Thomas, Neil Gorsuch, Kavanaugh, or Amy Coney Barrett) to join Justices Kagan, Sotomayor and Jackson for a majority dismissing for lack of jurisdiction.
Before reaching the merits, the Court must decide whether it has the power to hear the case at all, given that Boulder’s case is still pending in Colorado trial court. The Supreme Court may review state-court cases only after final judgement by the state’s highest court. Here, the trial court denied Suncor’s motion to dismiss, and the Colorado Supreme Court agreed that Boulder’s claims could go forward. Suncor is therefore asking the U.S. Supreme Court to step in to what Boulder argues is only an interlocutory appeal, not a final judgment—raising the threshold question of whether the Supreme Court has jurisdiction to do so.
Suncor argued that the Colorado Supreme Court’s ruling nonetheless counts as a final judgement because it ended a separate, “self-contained” proceeding in that court. Boulder responded that the ruling was an ordinary interlocutory appeal that the Court lacks jurisdiction to review, and that Suncor has not suffered the kind of concrete injury required for the Court to hear the case.
Justice Sotomayor was the most skeptical of the Court’s jurisdiction to hear the case. She noted that Colorado’s Supreme Court heard the appeal under Colorado Appellate Rule 21, which authorizes both writ-type and appellate review, but never articulated which appellate jurisdiction it was exercising. If the Supreme Court was unsure, she asked, “shouldn’t we be certifying this question to the Colorado court instead of us deciding it?”
Several Justices also questioned whether Suncor had suffered an immediate judicially cognizable injury as a result of the Colorado Supreme Court’s ruling, which Suncor’s counsel described as eliminating its central federal defense in the state case, costing Suncor what the counsel called, citing Murphy v. NCAA, “the right to be free from state regulation.” Justice Sotomayor commented, “I don’t know that we’ve ever talked of spending money on litigation as a constitutional injury,” while Justice Jackson suggested that it was “premature” to review Suncor’s defenses “piecemeal,” given that Suncor’s other federal defenses, including personal jurisdiction, remain pending in state court.
The Merits in a Nutshell
On the merits, Suncor and Exxon, supported by the federal government, offer three theories why federal law preempts Boulder’s claims: (1) the Constitution’s structure, through the principles of equal state sovereignty and a bar on state regulation of conduct beyond their borders, preempts state claims based on interstate emissions; (2) the federal Clean Air Act, alongside the Supreme Court’s interstate pollution precedents, preempts state claims; and (3) the doctrine of foreign affairs preemption bars the claims because they interfere with the nation’s conduct of foreign policy. Boulder dismisses each of these preemption doctrines, instead arguing that its claims seeking compensation under state tort law for local injuries do not regulate interstate emissions, conflict with the Clean Air Act, or intrude on federal foreign policy. Of these three theories, the first two dominated the argument.
Suncor’s Extraterritoriality Theory Faced Headwinds
Suncor’s constitutional argument rested on two “closely related” “principles”: “equal sovereignty” and “extraterritoriality.” Extraterritoriality was especially salient throughout the argument. Suncor’s counsel, Kannon Shanmugam, argued in his opening statement that “the Constitution’s prohibition on extraterritorial regulation precludes a state from extending its law beyond its borders to regulate global conduct with global effects” based only on “attenuated effects” within the state.
Several Justices were skeptical of this assertion. Chief Justice Roberts pressed Shanmugam to concede that an actor in one state can sometimes be held liable for harms that it causes in another. The Chief later pointed the government’s lawyer, Principal Deputy Solicitor General Sarah Harris, to “familiar situations,” such as internet and mass-tort cases, where one state’s courts adjudicate conduct affecting many other states. Justice Kagan asked Shanmugam to explain why ordinary choice-of-law principles would not resolve the dispute. Justice Jackson went further, observing that Suncor’s proposed test for extraterritoriality—which asks whether there are “direct, traceable, and particularized effects” in the state—sounded “very close to a causation standard or test” and asking why the Court should constitutionalize that question.
Justice Barrett, however, pushed in the opposite direction. She asked Boulder’s counsel to imagine that Colorado’s legislature enacted a law expressly regulating emissions in the other 49 states and then asked whether Colorado could accomplish essentially the same thing through tort law. Her question implied that this, in her view, is what Boulder is attempting here.
Justices Sotomayor, Kagan, and Jackson also suggested the Court may not need to reach extraterritoriality at all. Justices Sotomayor and Kagan noted that the parties had not argued, and the lower court had not addressed, the extraterritoriality issue before it reached the Supreme Court. Justice Sotomayor observed that Suncor had raised extraterritoriality only in its reply brief and asked whether it had therefore forfeited the defense. Justice Jackson came at the issue from a different angle, noting that the trial court had already found that Boulder had plausibly alleged causation, that Suncor had not appealed that ruling, and that the litigation had not yet developed enough factual detail to identify the relevant sources of pollution. “Maybe they lose because they can’t actually trace this to any particular source,” she said, suggesting that the Court should wait for the state courts to develop these facts before taking up Suncor’s constitutional theories. Together, these questions suggest that the Court’s liberal Justices may be looking for a procedural off-ramp, resting on what Suncor failed to raise below rather than on the merits of its theories.
Several Justices Were Skeptical of Suncor’s Structural-Constitutional Arguments
Several Justices appeared similarly dubious about Suncor’s structural-constitutional argument, particularly the claim that the principle of equal sovereignty makes climate regulation an area of “uniquely federal interests that dictate the application of federal [as opposed to state] law.”
Justice Kagan questioned the basis for Suncor’s claim that this default rule of federal law was a part of the plan of the 1787 Constitutional Convention, asking: “[W]here is the text for that? Where’s the support for that? Where’s the precedent for that? Where’s the anything for that?” Justice Gorsuch also seemed skeptical, asking: “Is there something in the Constitution that prohibits the application of Texas law to a Texas defendant?” Both Justices also seemed frustrated that Suncor’s structural-constitutional and extraterritoriality theories blurred together and were entangled, with Justice Kagan chiding Suncor’s counsel for constantly “switching back and forth between your two theories.”
Justice Kavanaugh, by contrast, appeared broadly supportive of Suncor but reluctant to invent new constitutional doctrine. He suggested that “we don’t have to reinvent the wheel” because notable statutory interpretation energy precedents—including Milwaukee I, Milwaukee II, Ouellette, and AEP—already established that “this kind of pollution is a federal law matter unless Congress speaks otherwise.”
The Justices Wrestled With States’ Role in Environmental Regulation
The Justices were divided over what room the Clean Air Act leaves for state tort law. If, as Suncor and the government argued, the Act preserves only suits under the law of the source state, there is no space for Boulder’s claims under Colorado law. Justices Kavanaugh and Barrett seemed receptive to Suncor’s argument, but Justices Barrett and Gorsuch also questioned whether that theory would leave some harms with no remedy at all.
State courts normally have broader lawmaking powers than federal courts—but a narrow body of judge-made “federal common law” has developed in areas involving strong national interests. The Court once used federal common law to resolve disputes between states over cross-border pollution. But after Congress enacted the Clean Air and Clean Water Acts, the Court held that those statutes had displaced that federal common law. A central question in Suncor is whether those federal statutes also displaced state law.
Suncor argues that interstate pollution is an “inherently federal” area that states have no power to regulate. Boulder responds that states can apply their own law to injuries caused by out-of-state emissions because the federal statutes, while displacing the federal common law, did not similarly preempt state common-law actions for environmental harms.
Justice Kavanaugh was highly critical of Boulder’s position that the Clean Air Act “resurrected” state tort law after displacing federal common law. He called it an “all-time elephant in mousehole in terms of what Congress would have done there,” invoking the legal presumption that Congress does not make major policy changes without clear language. Justice Barrett agreed with Suncor that it “can’t possibly be correct” that when Congress enacted the Clean Water and Air Acts, “state law somehow sprung into effect” in an area long held to be exclusively federal.
Even so, Justices Barrett and Gorsuch appeared open to at least some residual state authority over environmental regulation. Justice Barrett suggested that state authority may have existed all along, in which case the Clean Air Act would not have needed to affirmatively “authorize” state tort suits for states to retain such authority. Both Justices also pressed the government on whether its theory would leave a regulatory gap whenever the Clean Air Act does not give Environmental Protection Agency (EPA) authority over a particular environmental harm, such as greenhouse-gas emissions. When Harris, the government’s counsel, replied that no federal common-law causes of action would exist in such situations, Justice Gorsuch noted the anomaly that position would produce: federal common law provided a cause of action before Congress passed the Clean Air Act, but afterward “nobody can sue at all,” even where the Act gave EPA no authority to address the harm.
The Justices were clearly grappling with the scope of federal and state common law in the environmental context and the extent to which each has been displaced by the Clean Air Act. Neither Justice Gorsuch nor Justice Barrett seemed fully persuaded by either side’s broad theories, and their votes may prove pivotal to the outcome of the case.
Chief Justice Roberts and Justice Kavanaugh Appeared Receptive to Suncor’s Consequentialist Arguments
Chief Justice Roberts and Justice Kavanaugh—who have both sought to reorient the Court’s jurisprudence toward the nation’s history and tradition—seemed more concerned about the potential consequences of ruling against Suncor than with Boulder’s historical claim that tort claims of this kind have traditionally been a matter of state law.
Chief Justice Roberts raised concerns about the volume of litigation that may follow a favorable ruling for Boulder: “if you prevail,” the Chief Justice observed, “the next day, a municipality in every single state will file a lawsuit, they’ll probably copy your pleadings, and then there will be at least 50 . . . different cities” bringing similar suits. Boulder’s counsel responded that there are many examples where “a course of conduct causes mass liability across the nation,” and that courts have “deal[t] with them . . . through litigation,” citing litigation over asbestos and opioids.
The Chief Justice pushed back on the asbestos analogy, noting that “there’s always going to be greenhouse-gas emissions affecting every state . . . [s]o it’s not as if anything other than your litigation is going to address it.” Justice Kavanaugh worried that this class of litigation “is going to bankrupt …these various defendants and certainly other defendants out there.” Boulder’s counsel responded that States have traditionally had authority to apply their own tort law against actors who cause harm within their borders. Justice Kavanaugh replied that, in such circumstances, state law would not apply unless “specifically preserved” by the Clean Air Act.
Looking Ahead
The argument left several paths open. With Justice Alito recused, the Court could split 4-4, leaving the Colorado Supreme Court’s ruling for Boulder in place; it could dismiss for lack of jurisdiction; or it could reach the merits and decide whether federal law forecloses state-law climate suits like Boulder’s. Justices Gorsuch and Barrett will be the key votes to watch, and even if a majority of the Justices agree on the outcome, they may reach it through different routes, leaving a fractured set of opinions. The Court’s ultimate decision will shape the fate of Boulder’s suit and dozens of similar suits nationwide.
