Does the Clean Air Act authorize the EPA to regulate greenhouse gas emissions from new motor vehicles, and may the EPA decline to do so for reasons unrelated to the statutory question whether those gases contribute to climate change, where the petitioning State has standing to challenge the denial of its rulemaking petition?

In 1999, nineteen 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. That provision directs the EPA Administrator to prescribe standards for emissions of any air pollutant from new motor vehicles that, in the Administrator's judgment, cause or contribute to air pollution reasonably anticipated to endanger public health or welfare. The petitioners alleged that carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons trap heat, that human emissions had accelerated climate change, and that climate change threatens human health and the environment. EPA's own General Counsels had earlier concluded that EPA had authority to regulate carbon dioxide. After receiving more than 50,000 public comments and a 2001 National Research Council report, EPA denied the petition in September 2003. It gave two reasons: the Clean Air Act does not authorize regulation of greenhouse gases to address global climate change, and even if it did, regulation would be unwise at present because of scientific uncertainty, the President's comprehensive approach, and foreign policy concerns. Massachusetts alleged that rising sea levels linked to global warming were already eroding its coastal land, much of which the Commonwealth owns.

The private organizations filed the rulemaking petition with EPA in October 1999, and EPA denied it on September 8, 2003. Massachusetts and other States, local governments, and private organizations petitioned for review in the United States Court of Appeals for the District of Columbia Circuit under 42 U.S.C. § 7607(b)(1). Ten States and several trade associations intervened to support EPA. Each of the three judges on the panel wrote separately. Judge Randolph, announcing the judgment, declined to rule definitively on standing, assumed without deciding that EPA had statutory authority, and held that EPA reasonably exercised its discretion in denying the petition. Judge Sentelle concluded that petitioners lacked standing but joined the judgment on the merits as the closest to his preferred outcome. Judge Tatel dissented, finding that Massachusetts had standing and that EPA had statutory authority and offered no valid reason for refusing to act. The court of appeals denied the petition for review. The Supreme Court granted certiorari.

(Stevens, J.)

Yes. Massachusetts has standing, the Clean Air Act authorizes EPA to regulate greenhouse gas emissions from new motor vehicles, and EPA's stated reasons for refusing to act were not grounded in the statute.

Standing. Only one petitioner needs standing, and Massachusetts has it. Congress gave litigants a procedural right to challenge EPA's denial of a rulemaking petition, § 7607(b)(1), and a litigant holding such a right need not meet the normal redressability and immediacy standards in full. As a sovereign State asserting quasi-sovereign interests, Massachusetts is entitled to special solicitude. Georgia v. Tennessee Copper Co., 206 U.S. 230 (1907). The State surrendered the power to protect its territory by other means, and Congress charged EPA with doing so.

Injury, causation, and redressability. Rising sea levels are swallowing Massachusetts' coastal land, which the State owns in substantial part, and this injury is actual and imminent. That the harm is widely shared does not defeat standing. Federal Election Comm'n v. Akins, 524 U.S. 11 (1998). EPA's failure to regulate contributes to the injury. U.S. motor vehicles emit over six percent of worldwide carbon dioxide, so regulation is a meaningful step. A remedy need not eliminate every injury; reducing domestic emissions would slow global increases whatever other nations do.

Statutory authority. Section 7602(g) defines "air pollutant" as "any" physical or chemical substance emitted into the ambient air. Greenhouse gases fit that sweeping text. Post-enactment congressional inaction and research programs do not show Congress withdrew authority, and FDA v. Brown & Williamson Tobacco Corp., 529 U.S. 120 (2000), is distinguishable. EPA's duty to protect public health and welfare is independent of the Department of Transportation's fuel economy mandate.

The denial. The statute conditions EPA's authority on a "judgment" whether an air pollutant endangers public health or welfare. That judgment must relate to that statutory question. Policy rationales such as voluntary programs, a piecemeal approach, and foreign policy are not a reasoned basis for declining to make that judgment. If scientific uncertainty is so profound that EPA cannot make a reasoned judgment, EPA must say so. The Court did not decide whether policy concerns can inform EPA's actions if it makes an endangerment finding. EPA's denial was arbitrary, capricious, and not in accordance with law. The Court does not decide whether EPA must make an endangerment finding on remand.

Dissent (Roberts, C.J., joined by Scalia, Thomas, and Alito, JJ.) The petitions are nonjustifiable and should be dismissed. No precedent supports relaxing Article III requirements because a State is the plaintiff. Tennessee Copper concerned available remedies, not standing, and parens patriae status is an additional hurdle, not a substitute for injury, causation, and redressability. The majority answers that Hart & Wechsler reads Tennessee Copper as a standing decision, and that Mellon does not bar a State from asserting its rights under federal law. Global warming is a harm to humanity at large, which is inconsistent with the requirement of particularized injury. Petitioners' loss-of-coastline allegations are conjectural: the declarations do not link actual land loss to global warming, and the predicted loss rests on century-long projections and a computer model with a conceded error of about 30 centimeters. Causation fails because domestic new-vehicle emissions are a small fraction of global emissions and the link to coastal loss runs through a complex web of factors. Redressability fails because emissions from China, India, and other nations will likely overwhelm any domestic reduction, and the Court never connects reduced emissions to prevention of the specific land loss. The decision revives the diluted standing of United States v. SCRAP, 412 U.S. 669 (1973), and intrudes on the political branches. The majority answers by quoting SCRAP for the point that standing is not denied merely because many people suffer the same injury.

Dissent (Scalia, J., joined by Roberts, C.J., Thomas, and Alito, JJ.) Beyond standing, the merits holding is wrong. Nothing in the statute obliges EPA to make an endangerment judgment whenever a rulemaking petition is filed, and the statute is silent about the permissible reasons for deferring judgment. The Court wrongly narrows those reasons to scientific uncertainty. EPA's policy reasons, including effects on other Executive Branch programs and foreign policy, are legitimate, and EPA's reading of its discretion deserves Chevron deference. Even on the Court's own terms, EPA explained at length, relying on the National Research Council report, that scientific uncertainty precluded a judgment. Finally, the definition of "air pollutant" has two parts: the substance must be an "air pollution agent," not merely a substance emitted into the air. EPA reasonably read "air pollution" to mean ground-level impurities, not global climate change, and the Court's reading would make everything airborne, from Frisbees to flatulence, an air pollutant. The majority answers that EPA's distinction finds no support in the statutory text and that Congress's definition of "air pollutant" was too broad to permit EPA to narrow it by calling a substance not an "agent."