In recent years, plaintiffs’ attorneys and public-interest groups have brought common law actions seeking injunctive relief or damages for air emissions they claim cause climate change. Because climate change is a global phenomenon, these actions have targeted both in-state and out-of-state sources. Does state common law reach this far?

A state’s common law is founded in its police powers, which are among the powers that the Constitution generally reserved to the states. By contrast, the Constitution specifically delegates to Congress the power to regulate interstate commerce. A state’s police powers therefore do not extend beyond its borders. For this reason, the Supreme Court in the last century discovered a limited “federal” common law to address interstate pollution at a time when there were no federal laws regulating such interstate concerns. Missouri v. Illinois, 180 U.S. 208, 241 (1901). As the Court observed, “[i]f state law can be applied, there is no need for federal common law; if federal common law exists, it is because state law cannot be used.” City of Milwaukee v. Illinois, 451 U.S. 304, 314 n.7 (1981) (Milwaukee II).

Given that federal common law was a gap-filling exercise, the federal common law cause of action was always narrow. Once Congress has spoken to a matter, no gap in the regulatory compact exists, and there is no room for federal common law. In this circumstance, any federal common law that might otherwise exist is “displaced.” Given the separation of powers concerns implicated by this regime, there is a presumption in favor of displacement. Matter of Oswego Barge Corp., 664 F.2d 327, 335 (2d Cir. 1981). As the Supreme Court has observed, “[t]he question is whether the field has been occupied, not whether it has been occupied in a particular manner.” Milwaukee II, 451 U.S. at 325-27.

By contrast, because the Constitution reserves to the states preexisting police powers, “preemption” of state common law is subject to a different analysis. Whereas federal common law is readily displaced by congressional action, state common law is preempted if federal law occupies the field, or state law stands as an obstacle to full implementation of federal law. Int’l Paper Co. v. Ouellette, 479 U.S. 481, 491-94 (1987).

Against this background, the Supreme Court has observed that “the fact that control of interstate pollution is primarily a matter of federal law…[makes it] clear that the only state suits that remain are those specifically preserved by [federal legislation].” 479 U.S. at 492. And to the extent “savings clauses” found in federal environmental legislation preserve state law, they do so only to the extent they do not “interfere with the achievement of the ‘full purposes and objectives of Congress’” in enacting that legislation. Id. at 493. For example, the Court has held that the Clean Water Act “precludes a court from applying the law of an affected state against an out-of-state source.” Id. at 494.

If federal common law is displaced by environmental legislation and state common law is preempted as to out-of-state sources, what then of efforts to use state common law to address global issues like climate change? See, e.g., County of Marin v. Chevron Corp. et al., Case No. 1702586 (Superior Court of Cal., filed July 17, 2017); County of San Mateo v. Chevron Corp., et al., Case No. 17CIV03222 (Superior Court of Cal., filed July 17, 2017). Can a court in one state apply the common law of 49 “source” states and of potentially numerous other foreign jurisdictions to resolve interstate and global issues, or are there structural limits arising from the Constitution that preclude a state common law cause of action for global climate change?

In AEP v. Connecticut, 131 S.Ct. 2527 (2011)—a case rejecting the existence of federal common law for global climate change—the Court observed that it “remains mindful that it does not have the creative power akin to that vested in Congress.” As to state common law, the Court continued: “Nor have we ever held that a State may sue to abate any and all manner of pollution originating outside its borders.” Id. at 2536.

Federal common law for interstate pollution arose in the early 1900s because state common law did not reach interstate pollution and there was no federal environmental regulation to fill the gap. There is now federal legislation. Under our constitutional system, state common law is not a roving mandate for one sovereign to advance its policies nationally or globally by enforcing the police powers of another sovereign or by exercising its police powers as to another sovereign or its citizens. For these reasons, state police powers do not give rise to a cause of action to regulate or to remedy global climate change. State courts should be mindful of the constitutional limits of their authority and dismiss these types of cases.