[JURIST] The US Supreme Court [official website] ruled [opinion, PDF] 6-2 Tuesday in Environmental Protection Agency v. EME Homer City Generation [SCOTUSblog backgrounder] that the Environmental Protection Agency (EPA) [official website] did not overstep its authority when it issued a regulation limiting power plants’ emissions that cross state lines. The US Court of Appeals for the District of Columbia Circuit ruled [JURIST report] in 2012 that the EPA overstepped its authority because its regulation, known as the Transport Rule, did not square with Congress’ intention to have individual states, rather than the EPA, set emissions policies to meet federal standards. In an opinion by Justice Ruth Bader Ginsburg, the court reversed the DC Circuit’s ruling:

In sum, we hold that the Clean Air Act (CAA) [text, PDF] does not command that states be given a second opportunity to file a [state implementation plan] after EPA has quantified the State’s interstate pollution obligations. We further conclude that the Good Neighbor Provision does not require EPA to disregard costs and consider exclusively each upwind State’s physically proportionate responsibility for each downwind air quality problem. EPA’s cost-effective allocation of emission reductions among upwind States, we hold, is a permissible, work-able, and equitable interpretation of the Good Neighbor Provision.

Justice Antonin Scalia filed a dissenting opinion, joined by Justice Clarence Thomas. Justice Samuel Alito took no part in the consideration or decision of the case.

The court heard arguments in the case in December after granting certiorari [JURIST reports] last June. The questions before the court were (1) whether the court of appeals lacked jurisdiction to consider the challenges on which it granted relief; (2) whether states are excused from adopting state implementation plan (SIPs) prohibiting emissions that “contribute significantly” to air pollution problems in other states until after the EPA has adopted a rule quantifying each state’s interstate pollution obligations; and (3) whether the EPA permissibly interpreted the statutory term “contribute significantly” so as to define each upwind state’s “significant” interstate air pollution contributions in light of the cost-effective emission reductions it can make to improve air quality in polluted downwind areas, or whether the act instead unambiguously requires the EPA to consider only each upwind State’s physically proportionate responsibility for each downwind air quality problem.