Opinion of SOUTER, J. ing as debt piles up, I know of no independent suggestion that the debt limit was designed to operate as a political discouragement, not as a hard cap. It would, after all, have been strange for Congress to set a debt cap to constrain the Guam Legislature, only to leave the limiting figure subject to easy manipulation by the legislature. While I know that actual valuation can be manipulated, too, manipulation of that figure could only be done by officials acting in bad faith and subject to an obvious political or judicial challenge. The Court's approach, by contrast, gives the legislature a green light to subvert its own stated limit with a clear conscience.6 The more practical understanding of what must have been intended is a statute tying the debt limitation to Guam's capacity to tax property. The actual, market value of property is the only economic index of Guam's ability to collect property taxes to pay its bills, the only figure under consideration that is fixed in the real world, and the only figure that provides a genuine limitation. This was the figure employed or required by Congress in each of the other Territories mentioned above, see n. 3, supra, and I presume that its practical significance was in Congress's mind when it set the debt caps for each of them. I see no reason not to attribute the same practical assessment to Congress in this instance. I would affirm. 6 The attorney general's position would be strengthened if the assessment rate appeared in the Organic Act itself, for then the legislature would lack the power to change it. This state of affairs would be analogous to an assessment rate appearing in a state constitution. See, e. g., Colo. Const., Art. X, §3(1)(b); La. Const., Art. VII, § 18(B). But the Organic Act set no assessment rate, leaving that up to the Guam Legislature. 7 It is not, of course, the only index of Guam's capacity to pay its bills; income taxation is an obvious source of revenue, see 48 U. S. C. §§ 1421i(a)– (b) (authorizing Guam to collect income tax). Syllabus MASSACHUSETTS ET AL. v. ENVIRONMENTAL CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE DISTRICT OF COLUMBIA CIRCUIT No. 05-1120. Argued November 29, 2006-Decided April 2, 2007 Based on respected scientific opinion that a well-documented rise in global temperatures and attendant climatological and environmental changes have resulted from a significant increase in the atmospheric concentration of "greenhouse gases," a group of private organizations petitioned the Environmental Protection Agency (EPA) to begin regulating the emissions of four such gases, including carbon dioxide, under § 202(a)(1) of the Clean Air Act, which requires that EPA "shall by regulation prescribe... standards applicable to the emission of any air pollutant from any class... of new motor vehicles... which in [the EPA Administrator's] judgment cause[s], or contribute[s] to, air pollution... reasonably . . . anticipated to endanger public health or welfare," 42 U. S. C. § 7521(a)(1). The Act defines "air pollutant" to include "any air pollution agent . . ., including any physical, chemical . . . substance. emitted into . . . the ambient air." §7602(g). EPA ultimately denied the petition, reasoning that (1) the Act does not authorize it to issue mandatory regulations to address global climate change, and (2) even if it had the authority to set greenhouse gas emission standards, it would have been unwise to do so at that time because a causal link between greenhouse gases and the increase in global surface air temperatures was not unequivocally established. The Agency further characterized any EPA regulation of motor-vehicle emissions as a piecemeal approach to climate change that would conflict with the President's comprehensive approach involving additional support for technological innovation, the creation of nonregulatory programs to encourage voluntary privatesector reductions in greenhouse gas emissions, and further research on climate change, and might hamper the President's ability to persuade key developing nations to reduce emissions. Petitioners, now joined by intervenor Massachusetts and other state and local governments, sought review in the D. C. Circuit. Although each of the three judges on the panel wrote separately, two of them agreed that the EPA Administrator properly exercised his discretion in denying the rulemaking petition. One judge concluded that the Administrator's exercise of "judgment" as to whether a pollutant could "reasonably be anticipated to endanger public health or welfare," Syllabus § 7521(a)(1), could be based on scientific uncertainty as well as other factors, including the concern that unilateral U. S. regulation of motorvehicle emissions could weaken efforts to reduce other countries' greenhouse gas emissions. The second judge opined that petitioners had failed to demonstrate the particularized injury to them that is necessary to establish standing under Article III, but accepted the contrary view as the law of the case and joined the judgment on the merits as the closest to that which he preferred. The court therefore denied review. Held: 1. Petitioners have standing to challenge EPA's denial of their rulemaking petition. Pp. 516-526. (a) This case suffers from none of the defects that would preclude it from being a justiciable Article III "Controvers[y]." See, e. g., Luther v. Borden, 7 How. 1. Moreover, the proper construction of a congressional statute is an eminently suitable question for federal-court resolution, and Congress has authorized precisely this type of challenge to EPA action, see 42 U. S. C. § 7607(b)(1). Contrary to EPA's argument, standing doctrine presents no insuperable jurisdictional obstacle here. To demonstrate standing, a litigant must show that it has suffered a concrete and particularized injury that is either actual or imminent, that the injury is fairly traceable to the defendant, and that a favorable decision will likely redress that injury. See Lujan v. Defenders of Wildlife, 504 U. S. 555, 560-561. However, a litigant to whom Congress has "accorded a procedural right to protect his concrete interests," id., at 573, n. 7-here, the right to challenge agency action unlawfully withheld, § 7607(b)(1)—"can assert that right without meeting all the normal standards for redressability and immediacy," ibid. Only one petitioner needs to have standing to authorize review. See Rumsfeld v. Forum for Academic and Institutional Rights, Inc., 547 U. S. 47, 52, n. 2. Massachusetts has a special position and interest here. It is a sovereign State and not, as in Lujan, a private individual, and it actually owns a great deal of the territory alleged to be affected. The sovereign prerogatives to force reductions in greenhouse gas emissions, to negotiate emissions treaties with developing countries, and (in some circumstances) to exercise the police power to reduce motor-vehicle emissions are now lodged in the Federal Government. Because Congress has ordered EPA to protect Massachusetts (among others) by prescribing applicable standards, § 7521(a)(1), and has given Massachusetts a concomitant procedural right to challenge the rejection of its rulemaking petition as arbitrary and capricious, § 7607(b)(1), petitioners' submissions as they pertain to Massachusetts have satisfied the most demanding standards of the adversarial process. EPA's steadfast refusal to Syllabus regulate greenhouse gas emissions presents a risk of harm to Massachusetts that is both "actual" and "imminent," Lujan, 504 U. S., at 560, and there is a "substantial likelihood that the judicial relief requested" will prompt EPA to take steps to reduce that risk, Duke Power Co. v. Carolina Environmental Study Group, Inc., 438 U. S. 59, 79. Pp. 516–521. (b) The harms associated with climate change are serious and well recognized. The Government's own objective assessment of the relevant science and a strong consensus among qualified experts indicate that global warming threatens, inter alia, a precipitate rise in sea levels, severe and irreversible changes to natural ecosystems, a significant reduction in winter snowpack with direct and important economic consequences, and increases in the spread of disease and the ferocity of weather events. That these changes are widely shared does not minimize Massachusetts' interest in the outcome of this litigation. See Federal Election Comm'n v. Akins, 524 U. S. 11, 24. According to petitioners' uncontested affidavits, global sea levels rose between 10 and 20 centimeters over the 20th century as a result of global warming and have already begun to swallow Massachusetts' coastal land. Remediation costs alone, moreover, could reach hundreds of millions of dollars. Pp. 521-523. (c) Given EPA's failure to dispute the existence of a causal connection between manmade greenhouse gas emissions and global warming, its refusal to regulate such emissions, at a minimum, "contributes" to Massachusetts' injuries. EPA overstates its case in arguing that its decision not to regulate contributes so insignificantly to petitioners' injuries that it cannot be haled into federal court, and that there is no realistic possibility that the relief sought would mitigate global climate change and remedy petitioners' injuries, especially since predicted increases in emissions from China, India, and other developing nations will likely offset any marginal domestic decrease EPA regulation could bring about. Agencies, like legislatures, do not generally resolve massive problems in one fell swoop, see Williamson v. Lee Optical of Okla., Inc., 348 U. S. 483, 489, but instead whittle away over time, refining their approach as circumstances change and they develop a more nuanced understanding of how best to proceed, cf. SEC v. Chenery Corp., 332 U. S. 194, 202-203. That a first step might be tentative does not by itself negate federal-court jurisdiction. And reducing domestic automobile emissions is hardly tentative. Leaving aside the other greenhouse gases, the record indicates that the U. S. transportation sector emits an enormous quantity of carbon dioxide into the atmosphere. Pp. 523–525. (d) While regulating motor-vehicle emissions may not by itself reverse global warming, it does not follow that the Court lacks jurisdiction to decide whether EPA has a duty to take steps to slow or reduce it. Syllabus See Larson v. Valente, 456 U. S. 228, 243, n. 15. Because of the enormous potential consequences, the fact that a remedy's effectiveness 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 are poised to substantially increase greenhouse gas emissions: A reduction in domestic emissions would slow the pace of global emissions increases, no matter what happens elsewhere. The Court attaches considerable significance to EPA's espoused belief that global climate change must be addressed. Pp. 525-526. 2. The scope of the Court's review of the merits of the statutory issues is narrow. Although an agency's refusal to initiate enforcement proceedings is not ordinarily subject to judicial review, Heckler v. Chaney, 470 U. S. 821, there are key differences between nonenforcement and denials of rulemaking petitions that are, as in the present circumstances, expressly authorized. EPA concluded alternatively in its petition denial that it lacked authority under § 7521(a)(1) to regulate new vehicle emissions because carbon dioxide is not an "air pollutant" under § 7602, and that, even if it possessed authority, it would decline to exercise it because regulation would conflict with other administration priorities. Because the Act expressly permits review of such an action, § 7607(b)(1), this Court "may reverse [it if it finds it to be] arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law," § 7607(d)(9). Pp. 527-528. 3. Because greenhouse gases fit well within the Act's capacious definition of "air pollutant," EPA has statutory authority to regulate emission of such gases from new motor vehicles. That definition—which includes "any air pollution agent including any physical, chemical, . . . substance . . . emitted into . . . the ambient air § 7602(g) (emphasis added)-embraces all airborne compounds of whatever stripe. Moreover, carbon dioxide and other greenhouse gases are undoubtedly "physical [and] chemical . . . substance[s]." Ibid. EPA's reliance on postenactment congressional actions and deliberations it views as tantamount to a command to refrain from regulating greenhouse gas emissions is unavailing. Even if postenactment legislative history could shed light on the meaning of an otherwise-unambiguous statute, EPA identifies nothing suggesting that Congress meant to curtail EPA's power to treat greenhouse gases as air pollutants. The Court has no difficulty reconciling Congress' various efforts to promote interagency collaboration and research to better understand climate change with the Agency's pre-existing mandate to regulate "any air pollutant" that may endanger the public welfare. FDA v. Brown & Williamson Tobacco Corp., 529 U. S. 120, 133, distinguished. Also unper |