The Clean Air Act (CAA) gives the EPA the power to regulate pollution-generating emissions from both stationary sources, such as factories and power plants, and moving sources, such as cars, trucks, and aircraft. After the Supreme Court’s decision in Massachusetts v. EPA, which held that under the CAA the EPA must regulate greenhouse-gas emissions from cars and trucks, the EPA began regulating greenhouse-gas emissions from stationary sources as well. The CAA prescribes a complex permitting scheme for major stationary sources that emit 250 tons per year of “any air pollutant” (or 100 tons per year for certain types of sources). But for the sake of administrability the EPA did not want to extend that scheme to those stationary sources that only emitted greenhouse gases, so the EPA modified the scheme to provide that sources would not become newly subject permitting on the basis of greenhouse-gas emissions in amounts less than 100,000 tons per year.
In Utility Air Regulatory Group v. EPA, several states and agency challenged the EPA’s rule, arguing that the agency lacks statutory authority to regulate greenhouse-gas emissions for statutory sources in this way. The decision was a compromise that split the Court: the conservative bloc plus Justice Kennedy rejected the EPA’s broadest view of its power over greenhouse gas emissions under the CAA, but the Justices voted 7–2 to allow the EPA to impose air-pollution control strategy on many of the power plants and other fixed sources of greenhouse gases. Justice Scalia delivered the opinion of the Court, joined in full by only Chief Justice Roberts and Justice Kennedy. Justices Thomas and Alito joined that opinion to conclude that EPA may not regulate all forms of greenhouse-gas emissions just because it has authority to do that in some contexts, such as emissions from the tailpipes of automobiles and trucks (as required by Massachusetts v. EPA). Those Justices ruled that the CAA’s permitting provisions are not ambiguous and that the EPA’s “tailoring” of those requirements (by raising the triggering threshold from 250 tons to 100,000 tons for greenhouse gases) was “patently unreasonable.”
Despite these minor defeats for the EPA, the agency walked away from this battle the victor: Justices Ginsburg, Breyer, Sotomayor, and Kagan joined the Court’s opinion to rule that the EPA does have the power—if it is already regulating a specific source because it emits other kinds of air pollution—to also require that source to use the best available technology to control greenhouse gases. The result of this case is that the EPA is left in a similar position to how it was before the litigation: it is able to regulate greenhouse-gas emissions from some stationary sources without having to regulate all such sources.