Master The Supreme Court held that greenhouse gases are air pollutants under the Clean Air Act, granted states standing to challenge EPA inaction, and required EPA to ground any decision not to regulate in the statute’s endangerment criteria. with this comprehensive case brief.
Massachusetts v. EPA is a landmark Supreme Court decision that reshaped federal environmental regulation by recognizing greenhouse gases as pollutants subject to the Clean Air Act. The case compelled the Environmental Protection Agency to confront climate change within the statutory framework Congress enacted, rather than deferring to broad policy considerations unrelated to the statute. In doing so, the Court clarified both the scope of EPA’s authority and the limits of its discretion when faced with a petition for rulemaking.
The decision is equally significant for administrative and constitutional law. It recognized state plaintiffs’ standing to challenge agency inaction based on concrete, incremental injuries from climate change, and it reaffirmed that agencies must act or explain their inaction in terms Congress specified. The ruling set in motion modern federal greenhouse gas regulation and continues to influence litigation over agency authority and climate policy.
Massachusetts v. Environmental Protection Agency, 549 U.S. 497 (2007)
In 1999, a coalition of private organizations petitioned the Environmental Protection Agency (EPA) to regulate greenhouse gas emissions from new motor vehicles under Section 202(a)(1) of the Clean Air Act (CAA), 42 U.S.C. § 7521(a)(1). That provision directs EPA to prescribe standards for motor-vehicle emissions of any air pollutant that, in EPA’s judgment, causes or contributes to air pollution which may reasonably be anticipated to endanger public health or welfare. The CAA broadly defines air pollutant to include any physical or chemical substance emitted into the ambient air, 42 U.S.C. § 7602(g), and defines welfare to include effects on weather and climate, 42 U.S.C. § 7602(h). In 2003, EPA denied the petition, asserting that it lacked statutory authority to regulate greenhouse gases for climate change purposes and, alternatively, that even if it had authority, it would be unwise to regulate at that time due to scientific uncertainty and potential interference with the President’s comprehensive, nonregulatory climate policy. Several states, local governments, and environmental organizations petitioned for review. The D.C. Circuit denied relief in a split decision. The Supreme Court granted certiorari to address standing, EPA’s statutory authority, and the lawfulness of EPA’s denial.
1) Do petitioners, including the Commonwealth of Massachusetts, have Article III standing to challenge EPA’s denial of the rulemaking petition? 2) Does the Clean Air Act authorize EPA to regulate greenhouse gases from new motor vehicles? 3) Did EPA lawfully decline to regulate based on policy considerations and scientific uncertainty unrelated to the statutory endangerment inquiry?
Article III standing requires a concrete and particularized injury that is fairly traceable to the challenged conduct and likely to be redressed by a favorable decision; states receive special solicitude where Congress has afforded a procedural right to challenge agency action or inaction. Under CAA § 202(a)(1), EPA must regulate emissions of any air pollutant from new motor vehicles that, in its judgment, cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. The definitions of air pollutant and welfare are broad and encompass greenhouse gases and climate effects. An agency’s denial of a rulemaking petition is reviewable under the Administrative Procedure Act and must be grounded in the statute; an agency may not rely on extraneous policy preferences to avoid making the judgment Congress required, and its decision must not be arbitrary and capricious, 5 U.S.C. § 706(2)(A).
Yes, Massachusetts and other petitioners have standing to challenge EPA’s denial. Yes, the Clean Air Act authorizes EPA to regulate greenhouse gases as air pollutants under § 202(a)(1). EPA’s denial of the petition was unlawful because it rested on reasons not permitted by the statute; EPA must either make an endangerment finding or explain, based on the scientific record, why it cannot make such a judgment. The Court reversed and remanded.
Standing: The Court found that Massachusetts demonstrated a concrete injury in the form of loss of coastal land due to rising sea levels exacerbated by climate change. The injury was particularized to the state’s quasi-sovereign interests in its territory. Causation and redressability were satisfied because motor-vehicle greenhouse gas emissions are a meaningful contributor to atmospheric concentrations, and incremental reductions can slow or reduce the risk of harm. Congress provided a procedural right to challenge EPA’s inaction, and states are entitled to special solicitude in the standing analysis, lowering the redressability and imminence hurdles. Statutory authority: The Court turned to the CAA’s text. The definition of air pollutant includes any chemical substance emitted into the ambient air, a capacious definition that, read with the Act’s reference to effects on climate within the definition of welfare, plainly covers greenhouse gases. EPA’s argument that greenhouse gases were categorically excluded because Congress did not design the CAA specifically for climate change failed in light of the broad, technology-forcing nature of the statute and Congress’s choice of expansive terms like any air pollutant. Agency discretion: Although § 202(a)(1) grants EPA judgment about endangerment, that judgment must be exercised within statutory bounds. EPA cannot decline to regulate based on foreign policy considerations, voluntary programs, or general policy preferences unrelated to whether emissions may reasonably be anticipated to endanger public health or welfare. Scientific uncertainty alone does not justify refusing to decide; EPA must either make an endangerment finding or provide a reasoned explanation, tied to the record, that the evidence is insufficient to form a judgment. EPA’s denial invoked factors outside the statute, rendering it arbitrary and capricious. Deference: Because the statutory terms are unambiguous in covering greenhouse gases, EPA was not entitled to Chevron deference for its contrary interpretation. Even if ambiguity existed, the agency’s reliance on nonstatutory reasons would still be unlawful under the APA.
Massachusetts v. EPA is the foundation of federal climate regulation. It confirmed that greenhouse gases are pollutants under the CAA, required EPA to evaluate endangerment based on science, and spurred the 2009 endangerment finding and subsequent motor-vehicle greenhouse gas standards. The decision also reshaped standing doctrine by recognizing states’ special solicitude and the sufficiency of incremental, risk-reducing relief. For administrative law, it underscores that agencies must adhere to statutory directives and cannot invoke broad policy or uncertainty to avoid making required judgments. The case has influenced later climate and administrative decisions, including American Electric Power v. Connecticut (displacement of federal common law by the CAA) and Utility Air Regulatory Group v. EPA (limits on permitting for greenhouse gases).
No. The Court did not mandate immediate regulation. It held that greenhouse gases are air pollutants under the CAA and that EPA’s reasons for refusing to regulate were impermissible. On remand, EPA had to either make an endangerment finding under § 202(a)(1) and proceed to regulate, or explain, based on the scientific record, why it could not make such a judgment. EPA later issued a positive endangerment finding in 2009 and promulgated motor-vehicle greenhouse gas standards.
The Court recognized states’ special solicitude in the standing inquiry when Congress provides a procedural right to challenge agency inaction. Massachusetts established injury (loss of coastal land), causation (vehicle emissions contribute to greenhouse gas concentrations), and redressability (regulation would incrementally slow or reduce the risk of harm). This framework facilitates state challenges to federal agency decisions affecting environmental and public health interests.
The Court read the definition broadly to include any physical or chemical substance emitted into the ambient air, which encompasses greenhouse gases. It also emphasized that the CAA’s definition of welfare includes climate and weather effects. This textual analysis foreclosed EPA’s attempt to carve greenhouse gases out of the statute’s reach.
The Court applied arbitrary-and-capricious review under the APA and held that EPA must ground its decision in the statutory endangerment criteria. Policy preferences such as foreign affairs concerns or voluntary programs cannot substitute for the judgment Congress required. The decision reinforces that agencies must offer a reasoned explanation tied to statutory factors and the administrative record.
EPA argued for deference to its view that the CAA did not authorize regulation of greenhouse gases. The Court found the statute unambiguous on this point and therefore did not defer. Even if there were ambiguity, EPA’s denial rested on factors outside the statute, which would not merit Chevron deference and would fail under the APA’s requirement for reasoned decision-making.
Massachusetts v. EPA stands as a turning point in environmental and administrative law. By affirming that greenhouse gases fall within the Clean Air Act and by compelling EPA to evaluate endangerment based on scientific evidence, the Court ensured that federal climate policy would proceed through statutory channels rather than discretionary policy preferences.
For law students, the case illustrates how textual interpretation, standing doctrine, and arbitrary-and-capricious review interact in high-stakes regulatory disputes. It continues to influence climate litigation and agency rulemaking, serving as a template for how courts assess agency authority and discretion in the face of emerging environmental challenges.