In two major decisions today that will interest the readers of this site, the Supreme Court held that the class alleging gender discrimination against Wal-Mart was improperly certified in Wal-Mart v. Dukes and that the EPA's governance of carbon-dioxide regulation under the Clean Air Act displaced the federal common law public nuisance suit brought by various states and municipalities in AEP v. Connecticut. The holding in both cases was unanimous, though not without underlying disagreement. In Dukes, the justices split 5-4 over whether to dismiss the suit outright (the majority decision) or whether to remand for further consideration as a 23(b)(3) class action (Justice Ginsburg's position, joined by Justices Breyer, Kagan, and Sotomayor). In AEP, the justices split 4-4 on whether the plaintiffs had standing to sue (presumably the same split as in Massachusetts v. EPA), and Justice Alito wrote separately, joined by Justice Thomas, to emphasize that his decision rested on the assumption that the Clean Air Act applied to carbon dioxide emissions (the position he rejected in Massachusetts v. EPA) (Justice Sotomayor, who was involved in the suit below, recused).
Those who didn't see our earlier discussion on Dukes, which pulled in various thinkers and practitioners, should check it out now and compare with the actual decision. The Manhattan Institute also wrote a fair amount on the AEP global-warming-as-public-nuisance case in last fall's Trial Lawyers, Inc.: Environment.
Josh Blackman summarizes Dukes here and AEP here. Walter Olson assesses Dukes here. And as Blackman notes, the Dukes decisions, both majority and dissent, are replete with citations to our dear departed friend Richard Nagareda's published writings, both The Preexistence Principle and the Structure of the Class Action, 103 Colum. L. Rev. 149, 176, n. 110 (2003) and Class Certification in the Age of Aggregate Proof, 84 N. Y. U. L. Rev. 97, 131-132 (2009).