MASSACHUSETTS, et al., PETITIONERS v. ENVIRON-
MENTAL PROTECTION AGENCY et al.

    Justice Stevens delivered the opinion of the Court.

    A well-documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related. For when carbon dioxide is released into the atmosphere, it acts like the ceiling of a greenhouse, trapping solar energy and retarding the escape of reflected heat. It is therefore a species—the most important species—of a “greenhouse gas.”

    Calling global warming “the most pressing environmental challenge of our time,” a group of States, local governments, and private organizations, alleged in a petition for certiorari that the Environmental Protection Agency (EPA) has abdicated its responsibility under the Clean Air Act to regulate the emissions of four greenhouse gases, including carbon dioxide. Specifically, petitioners asked us to answer two questions concerning the meaning of §202(a)(1) of the Act: whether EPA has the statutory authority to regulate greenhouse gas emissions from new motor vehicles; and if so, whether its stated reasons for refusing to do so are consistent with the statute.

    In response, EPA, supported by 10 intervening States and six trade associations, correctly argued that we may not address those two questions unless at least one petitioner has standing to invoke our jurisdiction under Article III of the Constitution....

I

    Section 202(a)(1) of the Clean Air Act provides:

“The [EPA] Administrator shall by regulation prescribe (and from time to time revise) in accordance with the provisions of this section, standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare … .”

The Act defines “air pollutant” to include “any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive … substance or matter which is emitted into or otherwise enters the ambient air.” §7602(g). “Welfare” is also defined broadly: among other things, it includes “effects on … weather … and climate.” §7602(h).

    When Congress enacted these provisions, the study of climate change was in its infancy. In 1959, shortly after the U. S. Weather Bureau began monitoring atmospheric carbon dioxide levels, an observatory in Mauna Loa, Hawaii, recorded a mean level of 316 parts per million. This was well above the highest carbon dioxide concentration—no more than 300 parts per million—revealed in the 420,000-year-old ice-core record. By the time Congress drafted §202(a)(1) in 1970, carbon dioxide levels had reached 325 parts per million.

    In the late 1970’s, the Federal Government began devoting serious attention to the possibility that carbon dioxide emissions associated with human activity could provoke climate change. In 1978, Congress enacted the National Climate Program Act, 92 Stat. 601, which required the President to establish a program to “assist the Nation and the world to understand and respond to natural and man-induced climate processes and their implications,” id., §3. President Carter, in turn, asked the National Research Council, the working arm of the National Academy of Sciences, to investigate the subject. The Council’s response was unequivocal: “If carbon dioxide continues to increase, the study group finds no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible… . A wait-and-see policy may mean waiting until it is too late....”

    On October 20, 1999, a group of 19 private organizations filed a rulemaking petition asking EPA to regulate “greenhouse gas emissions from new motor vehicles under §202 of the Clean Air Act.” Petitioners maintained that 1998 was the “warmest year on record”; that carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons are “heat trapping greenhouse gases”; that greenhouse gas emissions have significantly accelerated climate change; and that the IPCC’s 1995 report warned that “carbon dioxide remains the most important contributor to [man-made] forcing of climate change.” The petition further alleged that climate change will have serious adverse effects on human health and the environment. As to EPA’s statutory authority, the petition observed that the agency itself had already confirmed that it had the power to regulate carbon dioxide.

    Fifteen months after the petition’s submission, EPA requested public comment on “all the issues raised in [the] petition,” adding a “particular” request for comments on “any scientific, technical, legal, economic or other aspect of these issues that may be relevant to EPA’s consideration of this petition.” EPA received more than 50,000 comments over the next five months....

   On September 8, 2003, EPA entered an order denying the rulemaking petition. The agency gave two reasons for its decision: (1) that contrary to the opinions of its former general counsels, the Clean Air Act does not authorize EPA to issue mandatory regulations to address global climate change, and (2) that even if the agency had the authority to set greenhouse gas emission standards, it would be unwise to do so at this time.....

    Petitioners, now joined by intervenor States and local governments, sought review of EPA’s order in the United States Court of Appeals for the District of Columbia Circuit. Although each of the three judges on the panel wrote a separate opinion, two judges agreed “that the EPA Administrator properly exercised his discretion under §202(a)(1) in denying the petition for rule making.” The court therefore denied the petition for review.

    In his opinion announcing the court’s judgment, Judge Randolph avoided a definitive ruling as to petitioners’ standing, reasoning that it was permissible to proceed to the merits because the standing and the merits inquiries “overlap[ped].” 

    Judge Sentelle wrote separately because he believed petitioners failed to “demonstrat[e] the element of injury necessary to establish standing under Article III.” In his view, they had alleged that global warming is “harmful to humanity at large,” but could not allege “particularized injuries” to themselves. 

    Judge Tatel dissented. Emphasizing that EPA nowhere challenged the factual basis of petitioners’ affidavits, he concluded that at least Massachusetts had “satisfied each element of Article III standing—injury, causation, and redressability.” In Judge Tatel’s view, the “ ‘substantial probability,’ ”that projected rises in sea level would lead to serious loss of coastal property was a “far cry” from the kind of generalized harm insufficient to ground Article III jurisdiction. He found that petitioners’ affidavits more than adequately supported the conclusion that EPA’s failure to curb greenhouse gas emissions contributed to the sea level changes that threatened Massachusetts’ coastal property. As to redressability, he observed that one of petitioners’ experts, a former EPA climatologist, stated that “ ‘[a]chievable reductions in emissions of CO2 and other [greenhouse gases] from U. S. motor vehicles would … delay and moderate many of the adverse impacts of global warming.’ ” 

IV

    Article III of the Constitution limits federal-court jurisdiction to “Cases” and “Controversies.” Those two words confine “the business of federal courts to questions presented in an adversary context and in a form historically viewed as capable of resolution through the judicial process.”  It is therefore familiar learning that no justiciable “controversy” exists when parties seek adjudication of a political question, when they ask for an advisory opinion, or when the question sought to be adjudicated has been mooted by subsequent developments. This case suffers from none of these defects.

    The parties’ dispute turns on the proper construction of a congressional statute, a question eminently suitable to resolution in federal court. Congress has moreover authorized this type of challenge to EPA action. That authorization is of critical importance to the standing inquiry: “Congress has the power to define injuries and articulate chains of causation that will give rise to a case or controversy where none existed before.” In exercising this power, however, Congress must at the very least identify the injury it seeks to vindicate and relate the injury to the class of persons entitled to bring suit.. We will not, therefore, “entertain citizen suits to vindicate the public’s nonconcrete interest in the proper administration of the laws.” 

    EPA maintains that because greenhouse gas emissions inflict widespread harm, the doctrine of standing presents an insuperable jurisdictional obstacle. We do not agree. At bottom, “the gist of the question of standing” is whether petitioners have “such a personal stake in the outcome of the controversy as to assure that concrete adverseness which sharpens the presentation of issues upon which the court so largely depends for illumination....” 

    Only one of the petitioners needs to have standing to permit us to consider the petition for review.  We stress here, as did Judge Tatel below, the special position and interest of Massachusetts. It is of considerable relevance that the party seeking review here is a sovereign State and not, as it was in Lujan, a private individual.

    Well before the creation of the modern administrative state, we recognized that States are not normal litigants for the purposes of invoking federal jurisdiction. As Justice Holmes explained in Georgia v. Tennessee Copper Co., 206 U. S. 230, 237 (1907) , a case in which Georgia sought to protect its citizens from air pollution originating outside its borders:

    “The case has been argued largely as if it were one between two private parties; but it is not. The very elements that would be relied upon in a suit between fellow-citizens as a ground for equitable relief are wanting here. The State owns very little of the territory alleged to be affected, and the damage to it capable of estimate in money, possibly, at least, is small. This is a suit by a State for an injury to it in its capacity of quasi-sovereign. In that capacity the State has an interest independent of and behind the titles of its citizens, in all the earth and air within its domain. It has the last word as to whether its mountains shall be stripped of their forests and its inhabitants shall breathe pure air.”

Just as Georgia’s “independent interest … in all the earth and air within its domain” supported federal jurisdiction a century ago, so too does Massachusetts’ well-founded desire to preserve its sovereign territory today. That Massachusetts does in fact own a great deal of the “territory alleged to be affected” only reinforces the conclusion that its stake in the outcome of this case is sufficiently concrete to warrant the exercise of federal judicial power.

    When a State enters the Union, it surrenders certain sovereign prerogatives. Massachusetts cannot invade Rhode Island to force reductions in greenhouse gas emissions, it cannot negotiate an emissions treaty with China or India, and in some circumstances the exercise of its police powers to reduce in-state motor-vehicle emissions might well be pre-empted.

    These sovereign prerogatives are now lodged in the Federal Government, and Congress has ordered EPA to protect Massachusetts (among others) by prescribing standards applicable to the “emission of any air pollutant from any class or classes of new motor vehicle engines, which in [the Administrator’s] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Congress has moreover recognized a concomitant procedural right to challenge the rejection of its rulemaking petition as arbitrary and capricious. Given that procedural right and Massachusetts’ stake in protecting its quasi-sovereign interests, the Commonwealth is entitled to special solicitude in our standing analysis.

    With that in mind, it is clear that petitioners’ submissions as they pertain to Massachusetts have satisfied the most demanding standards of the adversarial process. EPA’s steadfast refusal to regulate greenhouse gas emissions presents a risk of harm to Massachusetts that is both “actual” and “imminent.” There is, moreover, a “substantial likelihood that the judicial relief requested” will prompt EPA to take steps to reduce that risk. 

The Injury

    The harms associated with climate change are serious and well recognized....

    Petitioners allege that this only hints at the environmental damage yet to come. According to the climate scientist Michael MacCracken, “qualified scientific experts involved in climate change research” have reached a “strong consensus” that global warming threatens (among other things) a precipitate rise in sea levels by the end of the century, “severe and irreversible changes to natural ecosystems,”  a “significant reduction in water storage in winter snowpack in mountainous regions with direct and important economic consequences,”and an increase in the spread of disease....

    That these climate-change risks are “widely shared” does not minimize Massachusetts’ interest in the outcome of this litigation. According to petitioners’ unchallenged affidavits, global sea levels rose somewhere between 10 and 20 centimeters over the 20th century as a result of global warming.  These rising seas have already begun to swallow Massachusetts’ coastal land.  Because the Commonwealth “owns a substantial portion of the state’s coastal property,” it has alleged a particularized injury in its capacity as a landowner. The severity of that injury will only increase over the course of the next century: If sea levels continue to rise as predicted, one Massachusetts official believes that a significant fraction of coastal property will be “either permanently lost through inundation or temporarily lost through periodic storm surge and flooding events.” Remediation costs alone, petitioners allege, could run well into the hundreds of millions of dollars.

Causation

    EPA does not dispute the existence of a causal connection between man-made greenhouse gas emissions and global warming. At a minimum, therefore, EPA’s refusal to regulate such emissions “contributes” to Massachusetts’ injuries.

    EPA nevertheless maintains that its decision not to regulate greenhouse gas emissions from new motor vehicles contributes so insignificantly to petitioners’ injuries that the agency cannot be haled into federal court to answer for them. For the same reason, EPA does not believe that any realistic possibility exists that the relief petitioners seek would mitigate global climate change and remedy their injuries. That is especially so because predicted increases in greenhouse gas emissions from developing nations, particularly China and India, are likely to offset any marginal domestic decrease.

    But EPA overstates its case. Its argument rests on the erroneous assumption that a small incremental step, because it is incremental, can never be attacked in a federal judicial forum. Yet accepting that premise would doom most challenges to regulatory action. Agencies, like legislatures, do not generally resolve massive problems in one fell regulatory swoop....

    The Remedy

    While it may be true that regulating motor-vehicle emissions will not by itself reverse global warming, it by no means follows that we lack jurisdiction to decide whether EPA has a duty to take steps to slow or reduce it.  Because of the enormity of the potential consequences associated with man-made climate change, the fact that the effectiveness of a remedy might be delayed during the (relatively short) time it takes for a new motor-vehicle fleet to replace an older one is essentially irrelevant. Nor is it dispositive that developing countries such as China and India are poised to increase greenhouse gas emissions substantially over the next century: A reduction in domestic emissions would slow the pace of global emissions increases, no matter what happens elsewhere.

    We moreover attach considerable significance to EPA’s “agree[ment] with the President that ‘we must address the issue of global climate change.’ ” As Judge Tatel observed in dissent below, “EPA would presumably not bother with such efforts if it thought emissions reductions would have no discernable impact on future global warming.”

    In sum—at least according to petitioners’ uncontested affidavits—the rise in sea levels associated with global warming has already harmed and will continue to harm Massachusetts. The risk of catastrophic harm, though remote, is nevertheless real. That risk would be reduced to some extent if petitioners received the relief they seek. We therefore hold that petitioners have standing to challenge the EPA’s denial of their rulemaking petition....