## Facts

- Eight states and the City of New York, along with three nonprofit land trusts, sued five major electric power producers alleging their CO₂ emissions contributed to global warming and caused or threatened harms to public health, property, and natural resources.
- Plaintiffs sought injunctive relief under federal common-law interstate public nuisance (and alternatively state nuisance law) to cap and progressively reduce defendants’ CO₂ emissions from fossil-fuel-fired power plants.
- The district court dismissed the suits as presenting a nonjusticiable political question.
- The Second Circuit vacated and remanded, holding the claims justiciable, concluding plaintiffs sufficiently alleged standing, and ruling that the Clean Air Act did not displace federal common law because EPA had not yet regulated greenhouse gases from power plants.
- The Supreme Court granted review; Justice Sotomayor did not participate.

## Issues

1. Whether the Clean Air Act and the regulatory authority it confers on EPA displace a federal common-law public nuisance action seeking abatement of CO₂ emissions from power plants.
2. Whether plaintiffs may proceed, if at all, on state-law nuisance theories in light of potential federal statutory preemption.

## Decision

- The Court held (8–0) that the Clean Air Act and the EPA actions it authorizes displace any federal common-law right to seek abatement of CO₂ emissions from fossil-fuel-fired power plants.
- On threshold questions (including standing and jurisdiction), the Court affirmed the Second Circuit by an equally divided Court, leaving that portion of the judgment in place without a majority rationale.
- The Court reversed the Second Circuit’s merits holding recognizing a federal common-law nuisance cause of action and remanded.
- The Court declined to decide whether state-law nuisance claims are available, leaving that question (including any preemptive effect of federal law) for consideration on remand.

## Legal Principles

- Federal common law may exist in limited areas of uniquely federal interest, including certain interstate pollution disputes, but it yields when Congress enacts legislation that speaks directly to the issue.
- Displacement of federal common law turns on whether the statute addresses the relevant question; it does not depend on the extent to which an agency has already exercised its delegated authority.
- The Clean Air Act provides a comprehensive mechanism for regulating emissions from stationary sources, including standards-setting, petitions for rulemaking, and judicial review, making federal common-law injunctive regulation of emissions inappropriate.
- Displacement of federal common law is distinct from preemption of state law; the latter requires separate analysis not resolved by a finding of displacement.

## Conclusion

The Supreme Court ruled that the Clean Air Act assigns regulation of greenhouse gas emissions from power plants to EPA and thereby displaces federal common-law public nuisance suits seeking emissions caps and reductions, while leaving any state-law nuisance claims to be addressed on remand under preemption principles.


Am. Elec. Power Co. v. Connecticut, 564 U.S. 410 (2011)