In Massachusetts v. EPA, 549 U. S. 497, this Court held that the Clean Air Act authorizes federal regulation of emissions of carbon dioxide and other greenhouse gases, and that the Environmental Protection Agency (EPA) had misread that Act when it denied a rulemaking petition seeking controls on greenhouse gas emissions from new motor vehicles. In response, EPA commenced a rulemaking under §111 of the Act, 42 U. S. C. §7411, to set limits on greenhouse gas emissions from new, modified, and existing fossil-fuel fired power plants. Pursuant to a settlement finalized in March 2011, EPA has committed to issuing a final rule by May 2012.
The lawsuits considered here began well before EPA initiated efforts to regulate greenhouse gases. Two groups of plaintiffs, respondents here, filed separate complaints in a Federal District Court against the same five major electric power companies, petitioners here. One group of plaintiffs included eight States and New York City; the second joined three nonprofit land trusts. According to the complaint, the defendants are the largest emitters of carbon dioxide in the Nation. By contributing to global warming, the plaintiffs asserted, the defendants’ emissions substantially and unreasonably interfered with public rights, in violation of the federal common law of interstate nuisance, or, in the alternative, of state tort law. All plaintiffs ask for a decree setting carbon-dioxide emissions for each defendant at an initial cap, to be further reduced annually.
