State of Connecticut et al. v. American Electric Power Company, Inc. et al., 564 U.S. 410 (2011).

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Eight states, New York City and three land conservation groups sued AEP, three additional electric power companies and the Tennessee Valley Authority arguing that the power company’s greenhouse gas emissions levels constituted a public nuisance because they contributed to climate change. Before the Supreme Court, AEP argued that the Clean Air Act displaced state common law causes of action. The Supreme Court held that pursuant to the Clean Air Act, the EPA was the dominant regulator of emissions, and the Act displaced the common law of nuisance.  After Massachusetts, the EPA took steps to regulate emissions from light-duty trucks, other vehicles, and power plants.  Based on these actions as well as the statutory provisions, the Court concluded that the Act evinced an intent to preempt common law claims.