American Electric Power Company v. Connecticut, 564 U.S. 410 (2011), was a United States Supreme Court case in which the Court, in an 8–0 decision, held that corporations cannot be sued for greenhouse gas emissions (GHGs) under federal common law, primarily because the Clean Air Act (CAA) delegates the management of carbon dioxide and other GHG emissions to the Environmental Protection Agency (EPA).

The plaintiffs sought to cap-and-abate the defendants' GHG emissions under public nuisance law due to ongoing contributions to global warming.

[1] They alleged that the defendants are the five largest emitters of GHGs in the United States, collectively emitting 650 million tons of carbon dioxide annually.

The six factors are: This ruling is significant in American Electric Power v. Connecticut because using the six-factor test that was established in Baker v. Carr, the district court dismissed the plaintiffs' suit as presenting a non-justiciable political question because of the "impossibility of deciding the issue without an initial policy determination of a kind clearly for nonjudicial discretion.

In Massachusetts v. Environmental Protection Agency, the court held that the CAA gives the EPA the task of regulating carbon dioxide and other GHG emissions.

This is significant in the American Electrical Power v. Connecticut case because it establishes that carbon dioxide and GHG emissions regulations set by the EPA supersede federal common law.

[8] The Supreme Court rejected the plaintiffs' claim and the Second Circuit's holding that federal common law is not displaced since the EPA had not exercised its authority by setting emissions standards for the defendants' plants.

However, after the Second Circuit delivered its opinion and prior to the Supreme Court's judgment, the EPA had taken several relevant actions following Massachusetts v. Environmental Protection Agency, which included issuing the Endangerment Finding and establishing the Tailoring Rule, affecting the nation's largest greenhouse gas emitters.

With the ruling in Massachusetts v. Environmental Protection Agency setting precedent, the court held that the authority of the EPA to regulate GHGs delegated by the CAA displaces any federal common law right of state, city, and private parties to seek abatement of carbon-dioxide emissions from fossil-fuel fired power plants.

[2] The decision in this case confirms the EPA's primacy as the regulator of GHGs initially established in Massachusetts v. Environmental Protection Agency and limits the possibility of claiming federal common law public nuisance for climate change litigation.

Kivalina v. ExxonMobil Corporation followed the Supreme Court's decision in denying federal public nuisance claims of damages allegedly caused by GHGs as decided in American Electric Power Company v. Connecticut.

In Comer II, the court held that the CAA displaced the plaintiffs' public nuisance claim as in American Electric Power Company v. Connecticut and also preempted state law.