The State of Massachusetts, joined by various other States,[1] local governments[2] and organizations[3] (Petitioners), 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).[4] The agency denied the petition, contending that (1) the CAA does not authorize EPA to issue binding regulations dealing with global climate change, and (2) even if the CAA did give the agency the authority to set greenhouse gas emissions standards, it would decline to exercise that authority for a number of political and scientific reasons. In 2005, the Court of Appeals for the District of Columbia held that EPA properly exercised its discretion in denying the petition for rulemaking and dismissed the petitions. The Supreme Court reversed the D.C. Circuit's decision, determining: (1) Petitioners had standing to challenge EPA's denial of their petition to regulate green house gas emissions from new motor vehicles under the CAA, (2) EPA has the authority to regulate green house gas emissions from new motor vehicles under the CAA, and (3) should EPA decline to exercise that authority, its reasons must be grounded in the statute.

Section 202(a)(1) of the CAA mandates that EPA set standards for emissions of air pollutants from motor vehicles where those pollutants "may reasonably be anticipated to endanger public health or welfare."[5] The CAA's definition of "welfare" includes effects on the climate.[6] In response to growing scientific evidence concerning the impact of carbon dioxide emissions on the climate and inaction on the part of the Federal Government to regulate the emission of greenhouse gases, a group of organizations filed a rulemaking petition with EPA in 1999. The groups petitioned EPA to regulate greenhouse gas emissions from new motor vehicles. In 2003, EPA denied the petition, stating first that the CAA does not give EPA the authority to regulate greenhouse gas emissions, and second, that even if EPA did possess that authority, it would not exercise the authority at that time. The agency turned to FDA v. Brown & Williamson Tobacco Corp. (Brown & Williamson)[7] to support its position that it lacked authority under the CAA to regulate greenhouse gases. In Brown & Williamson, the Court held that the Federal Drug Administration (FDA) lacked the authority to regulate tobacco products as drugs, relying in part on the political history of tobacco.[8] EPA contended that like the situation in Brown & Williamson, the regulation of greenhouse gas emissions had a unique political history. As a consequence, EPA stated that it lacked authority to regulate greenhouse gas emissions. Additionally, EPA stated that because greenhouse gases would be regulated by increasing fuel efficiency, and fuel efficiency is regulated by the Department of Transportation (DOT), EPA regulations would either conflict with DOT regulations or do nothing at all. Third, EPA asserted even if it possessed the authority to regulate greenhouses gases, it declined to exercise that authority because the connection between greenhouse gases and global climate change was not clearly established. Finally, EPA claimed that any attempt on its part to regulate greenhouse gas emissions would interfere with the President's "comprehensive approach" and compromise his negotiating position in convincing developing nations to reduce greenhouse gas emissions.

The Supreme Court first addressed the issue of standing. Standing requires that the plaintiff "suffer[] a concrete and particularized injury that is either actual or imminent, that the injury is fairly traceable to the defendant, and that it is likely that a favorable decision will redress that injury."[9] The Court noted that where, like here, an action is brought to assert a procedural right, the party is held to a more relaxed standard of immediacy and redressability,[10] and noted that only one petitioner needs to meet the standing requirements. The Court also stated that States are "entitled to a special solicitude in [the] standing analysis"[11] when seeking review of a procedural right because of their interest in protecting their territory.[12] Thus, the Court determined that Massachusetts demonstrated sufficient injury by alleging loss of state coastline. On the causation prong, the Court determined that despite EPA's assertion that any contribution of greenhouse gases from new motor vehicles was an insignificant contributor to Massachusetts' injury, emissions from new motor vehicles did increase greenhouse gas concentrations. Though the agency's action would be merely a "small incremental step" in alleviating this harm, the Court held the action significant enough to warrant judicial review. Otherwise, the Court noted, most challenges to regulatory action would fail because agencies "do not generally resolve massive problems in one fell regulatory swoop."[13] As to redressability, the Court noted that even though regulating emissions from new motor vehicles will not necessarily reverse global climate change, for standing purposes the remedy is only required to lessen the impact of the injury; regulating green house gas emissions from new motor vehicles would achieve this. Thus, Petitioners had standing to challenge EPA's denial of their rulemaking petition.

Turning to the merits, the Court began by noting that its review of an agency's denial of a rulemaking petition is "extremely limited" and "highly deferential,"[14] and is reviewed under the "arbitrary and capricious . . . abuse of discretion, or otherwise not in accordance with law"[15] standard of review. The Court first addressed whether EPA has the authority under the CAA to regulate greenhouse gas emissions from new motor vehicles, and concluded that EPA does possess such authority. The Court looked to the broad definition of "air pollutant" to support its determination, stating that "the definition embraces all airborne compounds of whatever stripe,"[16] which unambiguously included greenhouse gases. In making its determination, the Court rejected EPA's reliance on post-enactment legislative history and congressional actions indicating that the CAA was not intended to regulate greenhouse gases. The Court discerned no clear congressional action indicating a desire to exempt greenhouse gases from regulation under the CAA. The Court also rejected EPA's position that Brown & Williamson was controlling, distinguishing the instant case because there was no extreme, counterintuitive measure in the CAA similar to banning tobacco, and also no consistent congressional enactments indicating that EPA was not intended to regulate greenhouse gases. The Court rejected EPA's final argument that regulating greenhouse gases would require an increase in mileage standards, intruding on DOT authority to set mileage standards. The Court noted that just because DOT regulates mileage standards does not give EPA "license[] . . . to shirk its environmental responsibilities."[17] While the Court acknowledged that the agencies' obligations and regulations may overlap, the Court opined that it would be possible for both agencies to administer their respective regulations successfully.

The Court next considered EPA's argument that even if it had the authority to regulate greenhouse gases from new motor vehicles, it declined to do so at the present time. The Court began by noting that while the CAA gave EPA the discretion to determine if an air pollutant "cause[s], or contribute[s] to, air pollution which may reasonably be anticipated to endanger public health or welfare,"[18] if the agency determines that greenhouse gases do endanger public health or welfare then it is obligated to regulate green houses gases. The agency's discretion, the Court held, is constrained by the statute--EPA's justifications for action or inaction must be grounded in the CAA. The Court observed that instead of complying with the statutory mandate to make an endangerment finding about the impact of greenhouse gases and proceeding accordingly under the statute, EPA simply provided reasons why it did not have to regulate. That, the Court held, violated the CAA. The Court stated that if EPA felt that it was inappropriate to regulate greenhouse gas emissions from new motor vehicles at this time, the agency was required to give a "reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change."[19] Having failed to do this, the Court deemed EPA's action arbitrary and capricious, and not in accordance with the CAA. The Court made clear that its holding was limited to requiring EPA to "ground its reasons for action or inaction in the statute."[20]

Thus, the Supreme Court reversed the D.C. Circuit's decision, determining: (1) that Petitioners had standing to challenge EPA's denial of the rulemaking petition, (2) that EPA has the authority to regulate greenhouse gases from new motor vehicles under the CAA, and (3) should EPA decline to exercise that authority, its reasons must be grounded in the statute.

Chief Justice Roberts, joined by Justice Scalia, Justice Thomas, and Justice Alito, dissented, arguing that the Petitioners lacked standing. The Chief Justice was careful to note that he passed no judgment on whether the issue of global climate change was occurring, or to what extent. Instead, he argued that the Court's determination that States are treated differently in the standing analysis was not grounded in prior jurisprudence, and the majority's reliance on Georgia v. Tennessee Copper Co.[21] was misplaced because although that case did distinguish between States and private citizens in terms of remedies, it "had nothing to do with Article III standing."[22] Further, Chief Justice Roberts argued that Massachusetts' loss of coastline was not a particularized injury because, by its very nature, global climate change is injurious to all of humanity. Further, all predicted losses will occur over the course of many years; therefore the injury is not imminent. The Chief Justice also argued that the Petitioners failed to show causation because they were "never able to trace their alleged injuries back through th[e] complex web [of economic and physical factors influencing global warming] to the fractional amount of global emissions that might have been limited with EPA standards."[23] Thus, Petitioners failed to show that their injury was caused by the failure of EPA to regulate greenhouse gas emissions from new motor vehicles. The Chief Justice also argued that Petitioners failed to demonstrate redressability, as it was never shown that the regulation of the small percentage of greenhouse gases emitted from new motor vehicles was likely to redress Massachusetts' loss of coastline. The Chief Justice stated that this case represented the furthest attenuation of the standing analysis ever committed by the Court, and has "caused [the Court] to transgress 'the proper--and properly limited--role of the courts in a democratic society.'"[24]

Justice Scalia, joined by Chief Justice Roberts, Justice Thomas, and Justice Alito, also dissented. Justice Scalia argued that the CAA does not require the Administrator of EPA to make an endangerment finding each time a rulemaking petition is filed. To the contrary, he asserted, section 202(a)(1) gives the Administrator discretion as to when to exercise this authority. Justice Scalia argued that the Administrator properly exercised that authority when he declined to regulate greenhouse gas emissions from new motor vehicles, and he complied with the CAA by listing the policy reasons for deferring to make a judgment. Additionally, Justice Scalia argued that EPA has already done what the Court told the agency it needs to do on remand--the agency has already said that it lacks the scientific knowledge to make the decision. Further, Justice Scalia argued that greenhouse gases are not "air pollutants" under the statute because they are not an "air pollution agent or combination of such agents."[25] He stated that merely because greenhouses gases conform to the second half of the definition of air pollutant--"physical, chemical, . . . substance[s] or matter which are emitted into or otherwise ente[r] the ambient air"[26]--does not mean that greenhouse gases do not have to meet the first half--"air pollution agent of combinations of such agents." The EPA determined that the definition of air pollutant did not apply to greenhouse gases because they do not lower ambient air quality. Thus, Justice Scalia argued that because EPA's interpretations of the CAA are reasonable, the agency is entitled to Chevron deference,[27] and its denial of the rulemaking petition should be upheld on the merits.