"Notwithstanding these disabilities, the plaintiffs propose that individual federal judges determine, in the first instance, what amount of carbon-dioxide emissions is 'unreasonable,' App. 103, 145, and then decide what level of reduction is 'practical, feasible and economically viable,' App. 58, 119. These determinations would be made for the defendants named in the two lawsuits launched by the plaintiffs. Similar suits could be mounted, counsel for the States and New York City estimated, against 'thousands or hundreds or tens' of other defendants fitting the description 'large contributors' to carbon-dioxide emissions. Tr. of Oral Arg. 57.
"The judgments the plaintiffs would commit to federal judges, in suits that could be filed in any federal district, cannot be reconciled with the decisionmaking scheme Congress enacted. The Second Circuit erred, we hold, in ruling that federal judges may set limits on greenhouse gas emissions in face of a law empowering EPA to set the same limits, subject to judicial review only to ensure against action 'arbitrary, capricious, . . . or otherwise not in accordance with law.' §7607(d)(9)."