I n 2007, the Supreme Court issued its decision in Massachusetts v. EPA , its first pronouncement on climate change and still one of the most important environmental law decisions in the past decade. By a vote of 5-4, the Court held that the Environmental Protection Agency (EPA) in 2003 had improperly denied a petition asking the agency to regulate greenhouse gas (GHG) emissions from new motor vehicles under the Clean Air Act (CAA). Contrary to EPA's position, the Court said that the CAA definition of "air pollutant" was unambiguously broad enough to include GHGs. Accordingly, the Court reversed the lower court decision upholding the petition denial. This report confines itself to the Massachusetts v. EPA litigation and leaves to other CRS reports the numerous EPA actions taken as a result of the Supreme Court decision. On the merits, it found that the CAA gives EPA authority to regulate GHG emissions from new motor vehicles, and does not give EPA discretion to inject policy considerations into its decision whether to so regulate. As to the issue of EPA's discretion, the Court concluded that the phrase "in [the Administrator's] judgment" in CAA Section 202 should be read narrowly. Since the Supreme Court Decision

The Court's decision left EPA with three options for responding to the petition: (1) find that new motor vehicle GHG emissions may "endanger public health or welfare," the prerequisite to limiting them under Section 202, then issue emission standards; (2) find that they do not satisfy that prerequisite, or (3) decide that climate change science is so uncertain as to preclude making either finding (1) or (2). Given the state of climate change science by 2007, it was widely believed at the time that option (1) was the only legally defensible one for EPA. This is the option that EPA took. Under other sections of the CAA, EPA has regulated GHG emissions from various stationary sources. Its holding that the CAA authorizes EPA to regulate GHG emissions from new motor vehicles is the governing law, barring Supreme Court reversal or congressional amendment. Standing

So far, the finding of standing in Massachusetts generally has not proved helpful to non-state plaintiffs seeking to establish standing in other climate change litigation. Displacement of Federal Common Law

The holding of Massachusetts was used by a 2011 Supreme Court decision to bar federal common law claims (such as nuisance) against entities on the basis of their contribution to climate change. Regulation of GHG Emissions Under CAA Section 111

The Massachusetts ruling upholding CAA coverage of Section 202 GHG emissions contributed to a 2010 litigation settlement that committed EPA to establishing new source performance standards (NSPSs) for GHG emissions from new fossil fuel fired power plants, and emission guidelines for existing fossil fuel fired power plants, under CAA Section 111.
In 2007, the Supreme Court issued its decision in Massachusetts v. EPA, its first pronouncement on climate change and a singularly important environmental law decision. This report reviews that decision, but leaves coverage of the many EPA actions based on the decision to other CRS reports.
Massachusetts v. EPA was a case brought to challenge EPA's denial of a petition asking the agency to regulate greenhouse gas (GHG) emissions from new motor vehicles under the Clean Air Act (CAA). By a vote of 5-4, the Court held first that Massachusetts had standing to sue, an issue that took up most of the majority opinion. On the merits, the Court found that the CAA definition of "air pollutant" was unambiguously broad enough to include GHGs. That being so, the Court held, CAA Section 202 authorizes EPA to regulate emissions from new motor vehicles on the basis of their possible climate change impacts. Finally, the Court determined that the phrase "in [the Administrator's] judgment" in Section 202 did not authorize EPA to inject policy considerations into its decision whether to so regulate. For these reasons, the Court reversed the lower court decision upholding the petition denial.
The Court's decision left EPA with three options for responding to the petition: (1) find that new motor vehicle GHG emissions may "endanger public health or welfare," the prerequisite to limiting them under Section 202, then issue emission standards; (2) find that they do not satisfy that prerequisite, or (3) decide that climate change science is so uncertain as to preclude making either finding (1) or (2). Given the state of climate change science by 2007, it was widely believed at the time that option (1) was the only legally defensible one for EPA. This is the option that EPA took, starting with an "endangerment finding" issued in 2009.
Since 2007, the finding of standing in Massachusetts generally has not proved helpful to non-state plaintiffs in climate change litigation, leaving intact this considerable threshold hurdle for climate change plaintiffs. In addition, the Massachusetts holding was used, in part, by a 2011 Supreme Court decision to bar federal common law claims against entities based on their contribution to climate change. On the other hand, Massachusetts has been applied by EPA to support regulations not only of motor vehicles but also of stationary sources of GHG emissions. In particular, Massachusetts helped bring about a 2010 litigation settlement that committed EPA to restricting GHG emissions from certain stationary sources of emissions under Section 111 of the CAA. EPA issued two rules based in part on this settlement: New Source Performance Standards (NSPSs) for GHG emissions from new, modified, or reconstructed fossil fuel fired power plants, and emission guidelines (known as the "Clean Power Plan") for GHG emissions from existing fossil fuel fired power plants. Both rules are being challenged in litigation, and the Clean Power Plan was stayed by the Supreme Court in February 2016, as discussed in other CRS reports.
The Massachusetts decision remains judicially unquestioned. Its holding that the CAA authorizes EPA to regulate GHG emissions remains the governing law, barring Supreme Court reversal or congressional amendment of the CAA.