MASSACHUSETTS et al. v. ENVIRONMENTAL PROTECTION AGENCY et al.

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497 OCTOBER TERM, 2006
Syllabus
MASSACHUSETTS et al. v. ENVIRONMENTAL
PROTECTION AGENCY et al.
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 concentra
tion 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 Adminis
trator’s] judgment cause[s], or contribute[s] to, air pollution . . . reason
ably . . . anticipated to endanger public health or welfare,” 42 U. S. C.
§ 7521(a)(1). The Act defines “air pollutant” to include “any air pollu
tion 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 comprehen
sive approach involving additional support for technological innovation,
the creation of nonregulatory programs to encourage voluntary private
sector 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 Ad
ministrator’s exercise of “judgment” as to whether a pollutant could
“reasonably be anticipated to endanger public health or welfare,”

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498 MASSACHUSETTS v. EPA
Syllabus
§ 7521(a)(1), could be based on scientific uncertainty as well as other
factors, including the concern that unilateral U. S. regulation of motor
vehicle emissions could weaken efforts to reduce other countries’ green
house 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 rule
making 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 argu
ment, standing doctrine presents no insuperable jurisdictional obstacle
here. To demonstrate standing, a litigant must show that it has suf
fered a concrete and particularized injury that is either actual or immi
nent, that the injury is fairly traceable to the defendant, and that a
favorable decision will likely redress that injury. See Lujan v. Defend
ers of Wildlife, 504 U. S. 555, 560–561. However, a litigant to whom
Congress has “accorded a procedural right to protect his concrete inter
ests,” id., at 573, n. 7—here, the right to challenge agency action unlaw
fully 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 negoti
ate emissions treaties with developing countries, and (in some circum
stances) to exercise the police power to reduce motor-vehicle emissions
are now lodged in the Federal Government. Because Congress has or
dered EPA to protect Massachusetts (among others) by prescribing ap
plicable standards, § 7521(a)(1), and has given Massachusetts a concomi
tant procedural right to challenge the rejection of its rulemaking
petition as arbitrary and capricious, § 7607(b)(1), petitioners’ submis
sions as they pertain to Massachusetts have satisfied the most demand
ing standards of the adversarial process. EPA’s steadfast refusal to

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Syllabus
regulate greenhouse gas emissions presents a risk of harm to Massachu
setts 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. Caro
lina 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 rele
vant science and a strong consensus among qualified experts indicate
that global warming threatens, inter alia, a precipitate rise in sea lev
els, severe and irreversible changes to natural ecosystems, a significant
reduction in winter snowpack with direct and important economic con
sequences, and increases in the spread of disease and the ferocity of
weather events. That these changes are widely shared does not mini
mize Massachusetts’ interest in the outcome of this litigation. See Fed
eral Election Comm’n v. Akins, 524 U. S. 11, 24. According to petition
ers’ 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. Remedia
tion 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 connec
tion 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’ in
juries 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 in
creases 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 mas
sive 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 nu
anced 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 automo
bile 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 re
verse 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.

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See Larson v. Valente, 456 U. S. 228, 243, n. 15. Because of the enor
mous 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 is
sues 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 nonenforce
ment 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 defi
nition of “air pollutant,” EPA has statutory authority to regulate emis
sion 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 what
ever 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 green
house 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 cur
tail 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 pol
lutant” that may endanger the public welfare. FDA v. Brown & Wil
liamson Tobacco Corp., 529 U. S. 120, 133, distinguished. Also unper

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suasive is EPA’s argument that its regulation of motor-vehicle carbon
dioxide emissions would require it to tighten mileage standards, a job
(according to EPA) that Congress has assigned to the Department of
Transportation. The fact that DOT’s mandate to promote energy effi
ciency by setting mileage standards may overlap with EPA’s envi
ronmental responsibilities in no way licenses EPA to shirk its duty to
protect the public “health” and “welfare,” § 7521(a)(1). Pp. 528–532.
4. EPA’s alternative basis for its decision—that even if it has statu
tory authority to regulate greenhouse gases, it would be unwise to do
so at this time—rests on reasoning divorced from the statutory text.
While the statute conditions EPA action on its formation of a “judg
ment,” that judgment must relate to whether an air pollutant “cause[s],
or contribute[s] to, air pollution which may reasonably be anticipated to
endanger public health or welfare.” § 7601(a)(1). Under the Act’s clear
terms, EPA can avoid promulgating regulations only if it determines
that greenhouse gases do not contribute to climate change or if it pro
vides some reasonable explanation as to why it cannot or will not exer
cise its discretion to determine whether they do. It has refused to do
so, offering instead a laundry list of reasons not to regulate, including
the existence of voluntary Executive Branch programs providing a re
sponse to global warming and impairment of the President’s ability to
negotiate with developing nations to reduce emissions. These policy
judgments have nothing to do with whether greenhouse gas emissions
contribute to climate change and do not amount to a reasoned justifica
tion for declining to form a scientific judgment. Nor can EPA avoid
its statutory obligation by noting the uncertainty surrounding various
features of climate change and concluding that it would therefore be
better not to regulate at this time. If the scientific uncertainty is so
profound that it precludes EPA from making a reasoned judgment, it
must say so. The statutory question is whether sufficient information
exists for it to make an endangerment finding. Instead, EPA rejected
the rulemaking petition based on impermissible considerations. Its ac
tion was therefore “arbitrary, capricious, or otherwise not in accordance
with law,” § 7607(d)(9). On remand, EPA must ground its reasons for
action or inaction in the statute. Pp. 532–535.
415 F. 3d 50, reversed and remanded.
Stevens, J., delivered the opinion of the Court, in which Kennedy,
Souter, Ginsburg, and Breyer, JJ., joined. Roberts, C. J., filed a dis
senting opinion, in which Scalia, Thomas, and Alito, JJ., joined, post,
p. 535. Scalia, J., filed a dissenting opinion, in which Roberts, C. J., and
Thomas and Alito, JJ., joined, post, p. 549.

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502 MASSACHUSETTS v. EPA
Counsel
James R. Milkey, Assistant Attorney General of Massa
chusetts, argued the cause for petitioners. With him on the
briefs were Thomas F. Reilly, Attorney General, Lisa
Heinzerling, Special Assistant Attorney General, and Wil
liam L. Pardee and Carol Iancu, Assistant Attorneys Gen
eral, Zulima V. Farber, Attorney General of New Jersey,
Michael Cardozo, Corporation Counsel of the City of New
York, and Scott Pasternack, Assistant Corporation Counsel,
Ralph S. Tyler, City Solicitor of Baltimore, and William
Phelan, Jr., Joseph Mendelson III, John M. Stanton, David
Doniger, David Bookbinder, and Howard Fox, and by the
Attorneys General and other officials for their respective ju
risdictions as follows: Bill Lockyer, Attorney General of Cal
ifornia, Marc N. Melnick and Nicholas Stern, Deputy Attor
neys General, Richard Blumenthal, Attorney General of
Connecticut, Kimberly Massicotte and Matthew Levin, As
sistant Attorneys General, Robert J. Spagnoletti, Attorney
General of the District of Columbia, Todd S. Kim, Solicitor
General, Donna Murasky, Senior Assistant Attorney Gen
eral, Lisa Madigan, Attorney General of Illinois, Matthew
J. Dunn and Gerald T. Karr, Assistant Attorneys Gen
eral, G. Steven Rowe, Attorney General of Maine, Gerald D.
Reid, Assistant Attorney General, Stuart Rabner, Attorney
General of New Jersey, Stefanie A. Brand, Kevin P. Auer
bacher, and Lisa Morelli, Deputy Attorneys General, Patri
cia A. Madrid, Attorney General of New Mexico, Stuart M.
Bluestone, Deputy Attorney General, Stephen R. Ferris and
Judith Ann Moore, Assistant Attorneys General, Eliot
Spitzer, Attorney General of New York, Caitlin J. Halligan,
Solicitor General, Peter Lehner and J. Jared Snyder, Assist
ant Attorneys General, Hardy Myers, Attorney General of
Oregon, Philip Schradle, Special Counsel to the Attorney
General, Richard Whitman, Assistant Attorney General,
Patrick C. Lynch, Attorney General of Rhode Island, Tricia
K. Jedele, Special Assistant Attorney General, William H.
Sorrell, Attorney General of Vermont, Kevin O. Leske, As

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Counsel
sistant Attorney General, Rob McKenna, Attorney General
of Washington, Leslie R. Seffern, Assistant Attorney Gen
eral, Jay D. Geck, Deputy Solicitor General, and Malaetasi
M. Togafau, Attorney General of American Samoa.
Deputy Solicitor General Garre argued the cause for re
spondents. With him on the brief for the federal respondent
were Solicitor General Clement, Assistant Attorney Gen
eral Wooldridge, Deputy Solicitor General Hungar, Mal
colm L. Stewart, Jon M. Lipshultz, and Carol S. Holmes.
Michael A. Cox, Attorney General of Michigan, filed a brief
for respondent State of Michigan. With him on the brief
were Thomas L. Casey, Solicitor General, Alan F. Hoffman
and Neil D. Gordon, Assistant Attorneys General, and the
Attorneys General and other officials for their respective
States as follows: David W. Ma´ rquez, Attorney General of
Alaska, Phil Kline, Attorney General of Kansas, David W.
Davies, Deputy Attorney General, Jon C. Bruning, Attorney
General of Nebraska, David D. Cookson, Special Counsel to
the Attorney General, Natalee J. Hart, Assistant Attor
ney General, Wayne Stenehjem, Attorney General of North
Dakota, Lyle Witham, Assistant Attorney General, Jim
Petro, Attorney General of Ohio, Dale T. Vitale, Senior Dep
uty Attorney General, Lawrence E. Long, Attorney General
of South Dakota, Greg Abbott, Attorney General of Texas,
Karen W. Kornell and Jane Atwood, Assistant Attorneys
General, and Mark L. Shurtleff, Attorney General of Utah,
and Fred G. Nelson, Assistant Attorney General. Theodore
B. Olson, Miguel A. Estrada, David Debold, Matthew D. Mc-
Gill, Kenneth W. Starr, Stuart A. C. Drake, Andrew B. Clu
bok, and Ashley C. Parrish filed a brief for respondent Alli
ance of Automobile Manufacturers et al. Russell S. Frye,
Leslie A. Hulse, Richard Wasserstrom, Harry M. Ng, Ralph
J. Colleli, Jr., Nick Goldstein, Jan S. Amundson, Quentin
Riegel, Robin S. Conrad, and John L. Wittenborn filed a
brief for respondent CO2 Litigation Group. Norman W.

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504 MASSACHUSETTS v. EPA
Opinion of the Court
Fichthorn and Allison D. Wood filed a brief for respondent
Utility Air Regulatory Group.*
Justice Stevens delivered the opinion of the Court.
A well-documented rise in global temperatures has coin
cided with a significant increase in the concentration of car
*Briefs of amici curiae urging reversal were filed for the State of Ari
zona et al. by Terry Goddard, Attorney General of Arizona, Paula S.
Bickett, Chief Counsel, Joseph P. Mikitish, Assistant Attorney General,
and Amy J. Wildermuth, and by Thomas J. Miller, Attorney General of
Iowa, J. Joseph Curran, Jr., Attorney General of Maryland, Mike Hatch,
Attorney General of Minnesota, and Peggy A. Lautenschlager, Attorney
General of Wisconsin, and Thomas J. Dawson, Assistant Attorney Gen
eral; for the Alaska Inter-Tribal Council et al. by Frances M. Raskin; for
Aspen Skiing Co. by Edward T. Ramey and Blain D. Myhre; for Calpine
Corp. by Richard E. Ayres; for the National Council of the Churches of
Christ in the U. S. A. et al. by Fran M. Layton; for Ocean and Coastal
Conservation Interests by Patrick A. Parenteau; for the U. S. Conference
of Mayors et al. by Timothy J. Dowling; for Wildlife Conservation Inter
ests by John F. Kostyack; for Madeleine K. Albright by Kathleen M. Sulli
van; for Climate Scientist David Battisti et al. by Robert B. McKinstry,
Jr., Stephanie Tai, and John C. Dernbach; and for Former EPA Adminis
trator Carol M. Browner et al. by Deborah A. Sivas, Michael C. Davis,
and Barry S. Neuman.
Briefs of amici curiae urging affirmance were filed for the Washington
Legal Foundation by Daniel J. Popeo, Paul D. Kamenar, and Peter S.
Glaser; for Climatologist and Scientist Sallie Baliunas et al. by Sam Kaz
man, Hans Bader, and Christopher C. Horner; for William J. Baumol et al.
by Timothy S. Bishop, Russell R. Eggert, and Erika Z. Jones; for Ernest
L. Daman et al. by Martin S. Kaufman; and for William H. Taft IV by
Arnold W. Reitze, Jr.
Briefs of amici curiae were filed for the State of Delaware by Carl C.
Danberg, Attorney General, Lawrence Lewis, State Solicitor, and Kevin
Maloney, Robert Phillips, and Valerie Csizmadia, Deputy Attorneys
General; for the Cato Institute et al. by Timothy Lynch; for Entergy Corp.
by Elise N. Zoli, U. Gwyn Williams, Kevin P. Martin, and Chuck D. Bar
low; for the North Coast Rivers Alliance et al. by Stephan C. Volker; for
the Pacific Legal Foundation by M. Reed Hopper; for the Union for Jobs
and the Environment by Scott H. Segal, Jason B. Hutt, and Shelby J.
Kelley; for Robert H. Bork et al. by David B. Rivkin, Jr., Lee A. Casey,
and Darin R. Bartram; and for Jerome B. Carr by Albert Auburn.

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Opinion of the Court
bon dioxide in the atmosphere. Respected scientists believe
the two trends are related. For when carbon dioxide is re
leased into the atmosphere, it acts like the ceiling of a green
house, trapping solar energy and retarding the escape of re
flected 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,” 1 a group of States,2 local govern
ments,3 and private organizations 4 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 consist
ent with the statute.
In response, EPA, supported by 10 intervening States 5
and six trade associations,6 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. Notwithstanding the serious character of
1 Pet. for Cert. 22.
2 California, Connecticut, Illinois, Maine, Massachusetts, New Jersey,
New Mexico, New York, Oregon, Rhode Island, Vermont, and Washington.
3 District of Columbia, American Samoa, New York City, and Baltimore.
4 Center for Biological Diversity, Center for Food Safety, Conserva
tion Law Foundation, Environmental Advocates, Environmental Defense,
Friends of the Earth, Greenpeace, International Center for Technology
Assessment, National Environmental Trust, Natural Resources Defense
Council, Sierra Club, Union of Concerned Scientists, and U. S. Public In
terest Research Group.
5 Alaska, Idaho, Kansas, Michigan, Nebraska, North Dakota, Ohio, South
Dakota, Texas, and Utah.
6 Alliance of Automobile Manufacturers, National Automobile Dealers
Association, Engine Manufacturers Association, Truck Manufacturers As
sociation, CO2 Litigation Group, and Utility Air Regulatory Group.

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that jurisdictional argument and the absence of any conflict
ing decisions construing § 202(a)(1), the unusual importance
of the underlying issue persuaded us to grant the writ. 548
U. S. 903 (2006).
I
Section 202(a)(1) of the Clean Air Act, as added by Pub. L.
89–272, § 101(8), 79 Stat. 992, and as amended by, inter alia,
84 Stat. 1690 and 91 Stat. 791, 42 U. S. C. § 7521(a)(1),
provides:
“The [EPA] Administrator shall by regulation pre
scribe (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 . . . .” 7
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).
7 The 1970 version of § 202(a)(1) used the phrase “which endangers the
public health or welfare” rather than the more protective “which may rea
sonably be anticipated to endanger public health or welfare.” See § 6(a)
of the Clean Air Amendments of 1970, 84 Stat. 1690. Congress amended
§ 202(a)(1) in 1977 to give its approval to the decision in Ethyl Corp. v.
EPA, 541 F. 2d 1, 25 (CADC 1976) (en banc), which held that the Clean
Air Act “and common sense . . . demand regulatory action to prevent harm,
even if the regulator is less than certain that harm is otherwise inevita
ble.” See § 401(d)(1) of the Clean Air Act Amendments of 1977, 91 Stat.
791; see also H. R. Rep. No. 95–294, p. 49 (1977).

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When Congress enacted these provisions, the study of cli
mate change was in its infancy.8 In 1959, shortly after the
U. S. Weather Bureau began monitoring atmospheric carbon
dioxide levels, an observatory in Mauna Loa, Hawaii, re
corded 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.9 By the time Congress drafted § 202(a)(1)
in 1970, carbon dioxide levels had reached 325 parts per
million.10
In the late 1970’s, the Federal Government began devoting
serious attention to the possibility that carbon dioxide emis
sions 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
8 The Council on Environmental Quality had issued a report in 1970 con
cluding that “[m]an may be changing his weather.” Environmental Qual
ity: The First Annual Report 93. Considerable uncertainty remained in
those early years, and the issue went largely unmentioned in the congres
sional debate over the enactment of the Clean Air Act. But see 116 Cong.
Rec. 32914 (1970) (statement of Sen. Boggs referring to Council’s conclu
sion that “[a]ir pollution alters the climate and may produce global changes
in temperature”).
9 See Intergovernmental Panel on Climate Change, Climate Change
2001: Synthesis Report, pp. 202–203 (2001). By drilling through thick
Antarctic ice sheets and extracting “cores,” scientists can examine ice
from long ago and extract small samples of ancient air. That air can then
be analyzed, yielding estimates of carbon dioxide levels. Ibid.
10 A more dramatic rise was yet to come: In 2006, carbon dioxide levels
reached 382 parts per million, see Dept. of Commerce, National Oceanic &
Atmospheric Administration, Mauna Loa CO2 Monthly Mean Data, http://
www.esrl.noaa.gov/gmd/ccgg/trends/co2_mm_mlo.dat (all Internet materi
als as visited Mar. 29, 2007, and available in Clerk of Court’s case file), a
level thought to exceed the concentration of carbon dioxide in the atmos
phere at any point over the past 20 million years. See Intergovernmental
Panel on Climate Change, Technical Summary of Working Group I Report
39 (2001).

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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 rea
son 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.” 11
Congress next addressed the issue in 1987, when it enacted
the Global Climate Protection Act, Title XI of Pub. L. 100–
204, 101 Stat. 1407, note following 15 U. S. C. § 2901. Find
ing that “manmade pollution—the release of carbon dioxide,
chlorofluorocarbons, methane, and other trace gases into the
atmosphere—may be producing a long-term and substantial
increase in the average temperature on Earth,” § 1102(1), 101
Stat. 1408, Congress directed EPA to propose to Congress
a “coordinated national policy on global climate change,”
§ 1103(b), and ordered the Secretary of State to work
“through the channels of multilateral diplomacy” and coordi
nate diplomatic efforts to combat global warming, § 1103(c).
Congress emphasized that “ongoing pollution and deforesta
tion may be contributing now to an irreversible process” and
that “[n]ecessary actions must be identified and implemented
in time to protect the climate.” § 1102(4).
Meanwhile, the scientific understanding of climate change
progressed. In 1990, the Intergovernmental Panel on Cli
mate Change (IPCC), a multinational scientific body orga
nized under the auspices of the United Nations, published its
first comprehensive report on the topic. Drawing on expert
opinions from across the globe, the IPCC concluded that
“emissions resulting from human activities are substantially
11 Climate Research Board, Carbon Dioxide and Climate: A Scientific
Assessment, p. viii (1979).

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increasing the atmospheric concentrations of . . . green
house gases [which] will enhance the greenhouse effect, re
sulting on average in an additional warming of the Earth’s
surface.” 12
Responding to the IPCC report, the United Nations con
vened the “Earth Summit” in 1992 in Rio de Janeiro. The
first President Bush attended and signed the United Nations
Framework Convention on Climate Change (UNFCCC), a
nonbinding agreement among 154 nations to reduce atmos
pheric concentrations of carbon dioxide and other green
house gases for the purpose of “prevent[ing] dangerous an
thropogenic [i. e., human-induced] interference with the
[Earth’s] climate system.” 13 S. Treaty Doc. No. 102–38, Art.
2, p. 5, 1771 U. N. T. S. 107 (1992). The Senate unanimously
ratified the treaty.
Some five years later—after the IPCC issued a second
comprehensive report in 1995 concluding that “[t]he balance
of evidence suggests there is a discernible human influence
on global climate” 14—the UNFCCC signatories met in
Kyoto, Japan, and adopted a protocol that assigned manda
tory targets for industrialized nations to reduce greenhouse
gas emissions. Because those targets did not apply to devel
oping and heavily polluting nations such as China and India,
the Senate unanimously passed a resolution expressing its
sense that the United States should not enter into the Kyoto
Protocol. See S. Res. 98, 105th Cong., 1st Sess. (July 25,
1997) (as passed). President Clinton did not submit the pro
tocol to the Senate for ratification.
12 IPCC, Climate Change: The IPCC Scientific Assessment, p. xi (J.
Houghton, G. Jenkins, & J. Ephraums eds. 1991).
13 The industrialized countries listed in Annex I to the UNFCCC under
took to reduce their emissions of greenhouse gases to 1990 levels by the
year 2000. No immediate restrictions were imposed on developing coun
tries, including China and India. They could choose to become Annex I
countries when sufficiently developed.
14 IPCC, Climate Change 1995, The Science of Climate Change, p. 4.

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II
On October 20, 1999, a group of 19 private organizations 15
filed a rulemaking petition asking EPA to regulate “green
house gas emissions from new motor vehicles under § 202 of
the Clean Air Act.” App. 5. 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 [manmade] forcing of climate
change.” Id., at 13 (internal quotation marks omitted).
The petition further alleged that climate change will have
serious adverse effects on human health and the environ
ment. Id., at 22–35. As to EPA’s statutory authority, the
petition observed that the Agency itself had already con
firmed that it had the power to regulate carbon dioxide.
See id., at 18, n. 21. In 1998, Jonathan Z. Cannon, then
EPA’s general counsel, prepared a legal opinion concluding
that “CO2 emissions are within the scope of EPA’s authority
to regulate,” even as he recognized that EPA had so far de
clined to exercise that authority. Id., at 54 (memorandum to
Carol M. Browner, Administrator (Apr. 10, 1998) (hereinafter
Cannon memorandum)). Cannon’s successor, Gary S. Guzy,
reiterated that opinion before a congressional committee just
15 Alliance for Sustainable Communities; Applied Power Technologies,
Inc.; Bio Fuels America; The California Solar Energy Industries Assn.;
Clements Environmental Corp.; Environmental Advocates; Environmental
and Energy Study Institute; Friends of the Earth; Full Circle Energy
Project, Inc.; The Green Party of Rhode Island; Greenpeace USA; Interna
tional Center for Technology Assessment; Network for Environmental and
Economic Responsibility of the United Church of Christ; New Jersey Envi
ronmental Watch; New Mexico Solar Energy Assn.; Oregon Environmen
tal Council; Public Citizen; Solar Energy Industries Assn.; The SUN DAY
Campaign. See App. 7–11.

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two weeks before the rulemaking petition was filed. See
id., at 61.
Fifteen months after the petition’s submission, EPA re
quested public comment on “all the issues raised in [the] peti
tion,” 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.” 66 Fed. Reg. 7486, 7487 (2001). EPA received
more than 50,000 comments over the next five months. See
68 Fed. Reg. 52924 (2003).
Before the close of the comment period, the White House
sought “assistance in identifying the areas in the science of
climate change where there are the greatest certainties and
uncertainties” from the National Research Council, asking
for a response “as soon as possible.” App. 213. The result
was a 2001 report titled Climate Change Science: An Analy
sis of Some Key Questions (NRC Report), which, drawing
heavily on the 1995 IPCC report, concluded that “[g]reen
house gases are accumulating in Earth’s atmosphere as a re
sult of human activities, causing surface air temperatures
and subsurface ocean temperatures to rise. Temperatures
are, in fact, rising.” NRC Report 1.
On September 8, 2003, EPA entered an order denying the
rulemaking petition. 68 Fed. Reg. 52922. 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, see id., at 52925–52929; and
(2) that even if the Agency had the authority to set green
house gas emission standards, it would be unwise to do so at
this time, id., at 52929–52931.
In concluding that it lacked statutory authority over
greenhouse gases, EPA observed that Congress “was well
aware of the global climate change issue when it last compre
hensively amended the [Clean Air Act] in 1990,” yet it de
clined to adopt a proposed amendment establishing binding

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emissions limitations. Id., at 52926. Congress instead
chose to authorize further investigation into climate change.
Ibid. (citing §§ 103(g) and 602(e) of the Clean Air Act Amend
ments of 1990, 104 Stat. 2652, 2703, 42 U. S. C. §§ 7403(g)(1)
and 7671a(e)). EPA further reasoned that Congress’ “spe
cially tailored solutions to global atmospheric issues,” 68
Fed. Reg. 52926—in particular, its 1990 enactment of a com
prehensive scheme to regulate pollutants that depleted the
ozone layer, see Title VI, 104 Stat. 2649, 42 U. S. C. §§ 7671–
7671q—counseled against reading the general authorization
of § 202(a)(1) to confer regulatory authority over green
house gases.
EPA stated that it was “urged on in this view,” 68 Fed.
Reg. 52928, by this Court’s decision in FDA v. Brown & Wil
liamson Tobacco Corp., 529 U. S. 120 (2000). In that case,
relying on “tobacco[’s] unique political history,” id., at 159,
we invalidated the Food and Drug Administration’s reliance
on its general authority to regulate drugs as a basis for as
serting jurisdiction over an “industry constituting a signifi
cant portion of the American economy,” ibid.
EPA reasoned that climate change had its own “political
history”: Congress designed the original Clean Air Act to
address local air pollutants rather than a substance that “is
fairly consistent in its concentration throughout the world’s
atmosphere,” 68 Fed. Reg. 52927; declined in 1990 to enact
proposed amendments to force EPA to set carbon dioxide
emission standards for motor vehicles, ibid. (citing H. R.
5966, 101st Cong., 2d Sess. (1990)); and addressed global cli
mate change in other legislation, 68 Fed. Reg. 52927. Be
cause of this political history, and because imposing emission
limitations on greenhouse gases would have even greater
economic and political repercussions than regulating tobacco,
EPA was persuaded that it lacked the power to do so. Id.,
at 52928. In essence, EPA concluded that climate change
was so important that unless Congress spoke with exacting
specificity, it could not have meant the Agency to address it.

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Having reached that conclusion, EPA believed it followed
that greenhouse gases cannot be “air pollutants” within the
meaning of the Act. See ibid. (“It follows from this conclu
sion, that [greenhouse gases], as such, are not air pollutants
under the [Clean Air Act’s] regulatory provisions . . . ”).
The Agency bolstered this conclusion by explaining that if
carbon dioxide were an air pollutant, the only feasible
method of reducing tailpipe emissions would be to improve
fuel economy. But because Congress has already created
detailed mandatory fuel economy standards subject to De
partment of Transportation (DOT) administration, the
Agency concluded that EPA regulation would either conflict
with those standards or be superfluous. Id., at 52929.
Even assuming that it had authority over greenhouse
gases, EPA explained in detail why it would refuse to exer
cise that authority. The Agency began by recognizing that
the concentration of greenhouse gases has dramatically in
creased as a result of human activities, and acknowledged
the attendant increase in global surface air temperatures.
Id., at 52930. EPA nevertheless gave controlling impor
tance to the NRC Report’s statement that a causal link
between the two “ ‘cannot be unequivocally established.’ ”
Ibid. (quoting NRC Report 17). Given that residual uncer
tainty, EPA concluded that regulating greenhouse gas emis
sions would be unwise. 68 Fed. Reg. 52930.
The Agency furthermore characterized any EPA regula
tion of motor-vehicle emissions as a “piecemeal approach”
to climate change, id., at 52931, and stated that such regula
tion would conflict with the President’s “comprehensive
approach” to the problem, ibid. That approach involves
additional support for technological innovation, the cre
ation of nonregulatory programs to encourage voluntary
private-sector reductions in greenhouse gas emissions, and
further research on climate change—not actual regulation.
Id., at 52932–52933. According to EPA, unilateral EPA reg
ulation of motor-vehicle greenhouse gas emissions might also

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hamper the President’s ability to persuade key developing
countries to reduce greenhouse gas emissions. Id., at 52931.
III
Petitioners, now joined by intervenor States and local gov
ernments, sought review of EPA’s order in the United States
Court of Appeals for the District of Columbia Circuit.16 Al
though each of the three judges on the panel wrote a sepa
rate opinion, two judges agreed “that the EPA Administra
tor properly exercised his discretion under § 202(a)(1) in
denying the petition for rule making.” 415 F. 3d 50, 58
(2005). 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’ stand
ing, id., at 56, reasoning that it was permissible to proceed
to the merits because the standing and the merits inquiries
“overlap[ped],” ibid. Assuming without deciding that the
statute authorized the EPA Administrator to regulate green
house gas emissions that “in his judgment” may “reasonably
be anticipated to endanger public health or welfare,” 42
U. S. C. § 7521(a)(1), Judge Randolph concluded that the exer
cise of that judgment need not be based solely on scientific
evidence, but may also be informed by the sort of policy
judgments that motivate congressional action. 415 F. 3d,
at 58. Given that framework, it was reasonable for EPA to
base its decision on scientific uncertainty as well as on other
factors, including the concern that unilateral regulation of
U. S. motor-vehicle emissions could weaken efforts to reduce
greenhouse gas emissions from other countries. Ibid.
Judge Sentelle wrote separately because he believed peti
tioners failed to “demonstrat[e] the element of injury neces
16 See 42 U. S. C. § 7607(b)(1) (“A petition for review of action of the
Administrator in promulgating any . . . standard under section 7521 of this
title . . . or final action taken, by the Administrator under this chapter
may be filed only in the United States Court of Appeals for the District
of Columbia”).

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sary to establish standing under Article III.” Id., at 59
(opinion dissenting in part and concurring in judgment). In
his view, they had alleged that global warming is “harmful
to humanity at large,” but could not allege “particularized
injuries” to themselves. Id., at 60 (citing Lujan v. Defend
ers of Wildlife, 504 U. S. 555, 562 (1992)). While he dis
sented on standing, however, he accepted the contrary view
as the law of the case and joined Judge Randolph’s judgment
on the merits as the closest to that which he preferred. 415
F. 3d, at 60–61.
Judge Tatel dissented. Emphasizing that EPA nowhere
challenged the factual basis of petitioners’ affidavits, id., at
66, he concluded that at least Massachusetts had “satisfied
each element of Article III standing—injury, causation, and
redressability,” id., at 64. In Judge Tatel’s view, the “ ‘sub
stantial probability,’ ” id., at 66, 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. Id., at 65. He found that petition
ers’ affidavits more than adequately supported the conclusion
that EPA’s failure to curb greenhouse gas emissions contrib
uted to the sea level changes that threatened Massachusetts’
coastal property. Ibid. 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.’ ” Ibid. (quoting declaration of Michael Mac-
Cracken, former Executive Director, U. S. Global Change
Research Program ¶ 5(e) (hereinafter MacCracken Decl.),
available in 2 Petitioners’ Standing Appendix in No. 03–1361
etc. (CADC), p. 209 (Stdg. App.)). He further noted that the
one-time director of EPA’s motor-vehicle pollution control ef
forts stated in an affidavit that enforceable emission stand
ards would lead to the development of new technologies that
“ ‘would gradually be mandated by other countries around

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the world.’ ” 415 F. 3d, at 66 (quoting declaration of Michael
Walsh ¶¶ 7–8, 10, Stdg. App. 309–310, 311). On the merits,
Judge Tatel explained at length why he believed the text of
the statute provided EPA with authority to regulate green
house gas emissions, and why its policy concerns did not
justify its refusal to exercise that authority. 415 F. 3d, at
67–82.
IV
Article III of the Constitution limits federal-court jurisdic
tion to “Cases” and “Controversies.” Those two words con
fine “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.” Flast v.
Cohen, 392 U. S. 83, 95 (1968). It is therefore familiar learn
ing that no justiciable “controversy” exists when parties seek
adjudication of a political question, Luther v. Borden, 7 How.
1 (1849), when they ask for an advisory opinion, Hayburn’s
Case, 2 Dall. 409 (1792), see also Clinton v. Jones, 520 U. S.
681, 700, n. 33 (1997), or when the question sought to be adju
dicated has been mooted by subsequent developments, Cali
fornia v. San Pablo & Tulare R. Co., 149 U. S. 308 (1893).
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 reso
lution in federal court. Congress has moreover authorized
this type of challenge to EPA action. See 42 U. S. C.
§ 7607(b)(1). That authorization is of critical importance to
the standing inquiry: “Congress has the power to define inju
ries and articulate chains of causation that will give rise to
a case or controversy where none existed before.” Lujan,
504 U. S., at 580 (Kennedy, J., concurring in part and concur
ring in judgment). “In exercising this power, however, Con
gress 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.” Ibid. We will not, therefore, “entertain citi

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zen suits to vindicate the public’s nonconcrete interest in the
proper administration of the laws.” Id., at 581.
EPA maintains that because greenhouse gas emissions in
flict 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.” Baker v. Carr, 369 U. S.
186, 204 (1962). As Justice Kennedy explained in his
Lujan concurrence:
“While it does not matter how many persons have been
injured by the challenged action, the party bringing suit
must show that the action injures him in a concrete and
personal way. This requirement is not just an empty
formality. It preserves the vitality of the adversarial
process by assuring both that the parties before the
court have an actual, as opposed to professed, stake in
the outcome, and that the legal questions presented . . .
will be resolved, not in the rarified atmosphere of a de
bating society, but in a concrete factual context condu
cive to a realistic appreciation of the consequences of
judicial action.” 504 U. S., at 581 (internal quotation
marks omitted).
To ensure the proper adversarial presentation, Lujan
holds that a litigant must demonstrate 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 it is likely that a favorable decision will redress that
injury. See id., at 560–561. However, a litigant to whom
Congress has “accorded a procedural right to protect his con
crete interests,” id., at 572, 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 re

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dressability and immediacy,” ibid. When a litigant is vested
with a procedural right, that litigant has standing if there is
some possibility that the requested relief will prompt the
injury-causing party to reconsider the decision that allegedly
harmed the litigant. Ibid.; see also Sugar Cane Growers
Cooperative of Fla. v. Veneman, 289 F. 3d 89, 94–95 (CADC
2002) (“A [litigant] who alleges a deprivation of a procedural
protection to which he is entitled never has to prove that if
he had received the procedure the substantive result would
have been altered. All that is necessary is to show that the
procedural step was connected to the substantive result”).
Only one of the petitioners needs to have standing to per
mit us to consider the petition for review. See Rumsfeld v.
Forum for Academic and Institutional Rights, Inc., 547
U. S. 47, 52, n. 2 (2006). 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 pri
vate 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 pro
tect 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 want
ing 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 in
terest independent of and behind the titles of its citizens,

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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. Cf. Alden v.
Maine, 527 U. S. 706, 715 (1999) (observing that in the federal
system, the States “are not relegated to the role of mere
provinces or political corporations, but retain the dignity,
though not the full authority, of sovereignty”). That Massa
chusetts does in fact own a great deal of the “territory al
leged 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 sov
ereign 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. See Alfred L. Snapp & Son, Inc. v. Puerto
Rico ex rel. Barez, 458 U. S. 592, 607 (1982) (“One helpful
indication in determining whether an alleged injury to the
health and welfare of its citizens suffices to give the State
standing to sue parens patriae is whether the injury is one
that the State, if it could, would likely attempt to address
through its sovereign lawmaking powers”).
These sovereign prerogatives are now lodged in the Fed
eral Government, and Congress has ordered EPA to protect
Massachusetts (among others) by prescribing standards ap
plicable to the “emission of any air pollutant from any class
or classes of new motor vehicle engines, which in [the Admin
istrator’s] judgment cause, or contribute to, air pollution
which may reasonably be anticipated to endanger public

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health or welfare.” 42 U. S. C. § 7521(a)(1). Congress has
moreover recognized a concomitant procedural right to chal
lenge the rejection of its rulemaking petition as arbitrary
and capricious. § 7607(b)(1). Given that procedural right
and Massachusetts’ stake in protecting its quasi-sovereign
interests, the Commonwealth is entitled to special solicitude
in our standing analysis.17
17 The Chief Justice accuses the Court of misreading Georgia v. Ten
nessee Copper Co., 206 U. S. 230 (1907), see post, at 537–538 (dissenting
opinion), and “devis[ing] a new doctrine of state standing,” post, at 548.
But no less an authority than Hart & Wechsler’s The Federal Courts and
the Federal System understands Tennessee Copper as a standing decision.
R. Fallon, D. Meltzer, & D. Shapiro, Hart & Wechsler’s The Federal Courts
and the Federal System 290 (5th ed. 2003). Indeed, it devotes an entire
section to chronicling the long development of cases permitting States “to
litigate as parens patriae to protect quasi-sovereign interests—i. e., public
or governmental interests that concern the state as a whole.” Id., at 289;
see, e. g., Missouri v. Illinois, 180 U. S. 208, 240–241 (1901) (finding federal
jurisdiction appropriate not only “in cases involving boundaries and juris
diction over lands and their inhabitants, and in cases directly affecting the
property rights and interests of a State,” but also when the “substantial
impairment of the health and prosperity of the towns and cities of the
state” are at stake).
Drawing on Massachusetts v. Mellon, 262 U. S. 447 (1923), and Alfred
L. Snapp & Son, Inc. v. Puerto Rico ex rel. Barez, 458 U. S. 592 (1982)
(citing Missouri v. Illinois, 180 U. S. 208 (1901)), The Chief Justice
claims that we “overloo[k] the fact that our cases cast significant doubt on
a State’s standing to assert a quasi-sovereign interest . . . against the
Federal Government.” Post, at 539. Not so. Mellon itself disavowed
any such broad reading when it noted that the Court had been “called
upon to adjudicate, not rights of person or property, not rights of dominion
over physical domain, [and] not quasi-sovereign rights actually invaded
or threatened.” 262 U. S., at 484–485 (emphasis added). In any event,
we held in Georgia v. Pennsylvania R. Co., 324 U. S. 439, 447 (1945), that
there is a critical difference between allowing a State “to protect her citi
zens from the operation of federal statutes” (which is what Mellon prohib
its) and allowing a State to assert its rights under federal law (which it
has standing to do). Massachusetts does not here dispute that the Clean
Air Act applies to its citizens; it rather seeks to assert its rights under
the Act. See also Nebraska v. Wyoming, 515 U. S. 1, 20 (1995) (holding
that Wyoming had standing to bring a cross-claim against the United
States to vindicate its “ ‘quasi-sovereign’ interests which are ‘independent

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With that in mind, it is clear that petitioners’ submissions
as they pertain to Massachusetts have satisfied the most de
manding standards of the adversarial process. EPA’s stead
fast refusal to regulate greenhouse gas emissions presents
a risk of harm to Massachusetts that is both “actual” and
“imminent.” Lujan, 504 U. S., at 560 (internal quotation
marks omitted). There is, moreover, a “substantial likeli
hood 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 (1978).
The Injury
The harms associated with climate change are serious and
well recognized. Indeed, the NRC Report itself—which
EPA regards as an “objective and independent assessment
of the relevant science,” 68 Fed. Reg. 52930—identifies a
number of environmental changes that have already inflicted
significant harms, including “the global retreat of mountain
glaciers, reduction in snow-cover extent, the earlier spring
melting of ice on rivers and lakes, [and] the accelerated rate
of rise of sea levels during the 20th century relative to the
past few thousand years . . . .” NRC Report 16.
Petitioners allege that this only hints at the environmental
damage yet to come. According to the climate scientist Mi
chael MacCracken, “qualified scientific experts involved in
climate change research” have reached a “strong consensus”
that global warming threatens (among other things) a pre
cipitate rise in sea levels by the end of the century, Mac-
Cracken Decl. ¶ 5, Stdg. App. 207, “severe and irreversible
changes to natural ecosystems,” id., ¶ 5(d), at 209, a “signifi
cant reduction in water storage in winter snowpack in moun
tainous regions with direct and important economic conse
quences,” ibid., and an increase in the spread of disease, id.,
¶ 28, at 218–219. He also observes that rising ocean temper
of and behind the titles of its citizens, in all the earth and air within its
domain’ ” (quoting Tennessee Copper, 206 U. S., at 237)).

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atures may contribute to the ferocity of hurricanes. Id.,
¶¶ 23–25, at 216–217.18
That these climate-change risks 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 (1998) (“[W]here a harm is concrete, though widely
shared, the Court has found ‘injury in fact’ ”). According
to petitioners’ unchallenged affidavits, global sea levels rose
somewhere between 10 and 20 centimeters over the 20th cen
tury as a result of global warming. MacCracken Decl. ¶ 5(c),
Stdg. App. 208. These rising seas have already begun to
swallow Massachusetts’ coastal land. Id., at 196 (declaration
of Paul H. Kirshen ¶ 5), 216 (MacCracken Decl. ¶ 23). Be
cause the Commonwealth “owns a substantial portion of the
state’s coastal property,” id., at 171 (declaration of Karst R.
Hoogeboom ¶ 4),19 it has alleged a particularized injury in its
capacity as a landowner. The severity of that injury will
18 In this regard, MacCracken’s 2004 affidavit—drafted more than a year
in advance of Hurricane Katrina—was eerily prescient. Immediately
after discussing the “particular concern” that climate change might cause
an “increase in the wind speed and peak rate of precipitation of major
tropical cyclones (i. e., hurricanes and typhoons),” MacCracken noted that
“[s]oil compaction, sea level rise and recurrent storms are destroying ap
proximately 20–30 square miles of Louisiana wetlands each year. These
wetlands serve as a ‘shock absorber’ for storm surges that could inundate
New Orleans, significantly enhancing the risk to a major urban popula
tion.” ¶¶ 24–25, Stdg. App. 217.
19 “For example, the [Massachusetts Department of Conservation and
Recreation] owns, operates and maintains approximately 53 coastal state
parks, beaches, reservations, and wildlife sanctuaries. [It] also owns, op
erates and maintains sporting and recreational facilities in coastal areas,
including numerous pools, skating rinks, playgrounds, playing fields, for
mer coastal fortifications, public stages, museums, bike trails, tennis
courts, boathouses and boat ramps and landings. Associated with these
coastal properties and facilities is a significant amount of infrastructure,
which the Commonwealth also owns, operates and maintains, including
roads, parkways, stormwater pump stations, pier[s], sea wal[l] revetments
and dams.” Hoogeboom Decl. ¶ 4, at 171.

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only increase over the course of the next century: If sea lev
els 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.” Id.,
¶ 6, at 172.20 Remediation costs alone, petitioners allege,
could run well into the hundreds of millions of dollars. Id.,
¶ 7, at 172; see also Kirshen Decl. ¶ 12, at 198.21
Causation
EPA does not dispute the existence of a causal connection
between manmade greenhouse gas emissions and global
warming. At a minimum, therefore, EPA’s refusal to regu
late such emissions “contributes” to Massachusetts’ injuries.
EPA nevertheless maintains that its decision not to regu
late greenhouse gas emissions from new motor vehicles con
tributes 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 miti
gate global climate change and remedy their injuries. That
is especially so because predicted increases in greenhouse
20 See also id., at 179 (declaration of Christian Jacqz) (discussing possible
loss of roughly 14 acres of land per miles of coastline by 2100); Kirshen
Decl. ¶ 10, at 198 (alleging that “[w]hen such a rise in sea level occurs, a
10-year flood will have the magnitude of the present 100-year flood and a
100-year flood will have the magnitude of the present 500-year flood”).
21 In dissent, The Chief Justice dismisses petitioners’ submissions as
“conclusory,” presumably because they do not quantify Massachusetts’
land loss with the exactitude he would prefer. Post, at 542. He therefore
asserts that the Commonwealth’s injury is “conjectur[al].” See ibid.
Yet the likelihood that Massachusetts’ coastline will recede has nothing to
do with whether petitioners have determined the precise metes and
bounds of their soon-to-be-flooded land. Petitioners maintain that the
seas are rising and will continue to rise, and have alleged that such a rise
will lead to the loss of Massachusetts’ sovereign territory. No one, save
perhaps the dissenters, disputes those allegations. Our cases require
nothing more.

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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 chal
lenges to regulatory action. Agencies, like legislatures, do
not generally resolve massive problems in one fell regulatory
swoop. See Williamson v. Lee Optical of Okla., Inc., 348
U. S. 483, 489 (1955) (“[A] reform may take one step at a time,
addressing itself to the phase of the problem which seems
most acute to the legislative mind”). They instead whittle
away at them over time, refining their preferred approach as
circumstances change and as they develop a more nuanced
understanding of how best to proceed. Cf. SEC v. Chenery
Corp., 332 U. S. 194, 202 (1947) (“Some principles must await
their own development, while others must be adjusted to
meet particular, unforeseeable situations”). That a first
step might be tentative does not by itself support the notion
that federal courts lack jurisdiction to determine whether
that step conforms to law.
And reducing domestic automobile emissions is hardly a
tentative step. Even leaving aside the other greenhouse
gases, the United States transportation sector emits an enor
mous quantity of carbon dioxide into the atmosphere—ac
cording to the MacCracken affidavit, more than 1.7 billion
metric tons in 1999 alone. ¶ 30, Stdg. App. 219. That ac
counts for more than 6% of worldwide carbon dioxide emis
sions. Id., at 232 (Oppenheimer Decl. ¶ 3); see also Mac-
Cracken Decl. ¶ 31, at 220. To put this in perspective:
Considering just emissions from the transportation sector,
which represent less than one-third of this country’s total
carbon dioxide emissions, the United States would still rank
as the third-largest emitter of carbon dioxide in the world,

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outpaced only by the European Union and China.22 Judged
by any standard, U. S. motor-vehicle emissions make a mean
ingful contribution to greenhouse gas concentrations and
hence, according to petitioners, to global warming.
The Remedy
While it may be true that regulating motor-vehicle emis
sions 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. See also
Larson v. Valente, 456 U. S. 228, 244, n. 15 (1982) (“[A] plain
tiff satisfies the redressability requirement when he shows
that a favorable decision will relieve a discrete injury to him
self. He need not show that a favorable decision will relieve
his every injury”). Because of the enormity of the potential
consequences associated with manmade climate change, the
fact that the effectiveness of a remedy might be delayed dur
ing the (relatively short) time it takes for a new motor
vehicle fleet to replace an older one is essentially irrelevant.23
Nor is it dispositive that developing countries such as China
and India are poised to increase greenhouse gas emissions
22 See UNFCCC, National Greenhouse Gas Inventory Data for the Pe
riod 1990–2004 and Status of Reporting 14 (2006) (reflecting emissions
from Annex I countries); UNFCCC, Sixth Compilation and Synthesis of
Initial National Communications from Parties not Included in Annex I to
the Convention 7–8 (2005) (reflecting emissions from non-Annex I coun
tries); see also Dept. of Energy, Energy Information Admin., International
Energy Annual 2004, H.1co2 World Carbon Dioxide Emissions from the
Consumption and Flaring of Fossil Fuels, 1980–2004 (Table), http://
www.eia.doe.gov/pub/international/iealf/tableh1co2.xls.
23 See also Mountain States Legal Foundation v. Glickman, 92 F. 3d
1228, 1234 (CADC 1996) (“The more drastic the injury that government
action makes more likely, the lesser the increment in probability to estab
lish standing”); Village of Elk Grove Village v. Evans, 997 F. 2d 328, 329
(CA7 1993) (“[E]ven a small probability of injury is sufficient to create a
case or controversy—to take a suit out of the category of the hypotheti
cal—provided of course that the relief sought would, if granted, reduce
the probability”).

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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,’ ” 68 Fed. Reg. 52929 (quoting
remarks announcing Clear Skies and Global Climate Initia
tives, 2002 Public Papers of George W. Bush, Vol. 1, Feb.
14, p. 227 (2004)), and to EPA’s ardent support for various
voluntary emission-reduction programs, 68 Fed. Reg. 52932.
As Judge Tatel observed in dissent below, “EPA would pre
sumably not bother with such efforts if it thought emissions
reductions would have no discernable impact on future
global warming.” 415 F. 3d, at 66.
In sum—at least according to petitioners’ uncontested af
fidavits—the rise in sea levels associated with global warm
ing has already harmed and will continue to harm Massachu
setts. The risk of catastrophic harm, though remote, is
nevertheless real. That risk would be reduced to some ex
tent if petitioners received the relief they seek. We there
fore hold that petitioners have standing to challenge EPA’s
denial of their rulemaking petition.24
24 In his dissent, The Chief Justice expresses disagreement with the
Court’s holding in United States v. Students Challenging Regulatory
Agency Procedures (SCRAP), 412 U. S. 669, 687–688 (1973). He does not,
however, disavow this portion of Justice Stewart’s opinion for the Court:
“Unlike the specific and geographically limited federal action of which the
petitioner complained in Sierra Club [v. Morton, 405 U. S. 727 (1972)], the
challenged agency action in this case is applicable to substantially all of
the Nation’s railroads, and thus allegedly has an adverse environmental
impact on all the natural resources of the country. Rather than a limited
group of persons who used a picturesque valley in California, all persons
who utilize the scenic resources of the country, and indeed all who breathe
its air, could claim harm similar to that alleged by the environmental
groups here. But we have already made it clear that standing is not to
be denied simply because many people suffer the same injury. Indeed
some of the cases on which we relied in Sierra Club demonstrated the
patent fact that persons across the Nation could be adversely affected by

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V
The scope of our review of the merits of the statutory is
sues is narrow. As we have repeated time and again, an
agency has broad discretion to choose how best to marshal
its limited resources and personnel to carry out its delegated
responsibilities. See Chevron U. S. A. Inc. v. Natural Re
sources Defense Council, Inc., 467 U. S. 837, 842–845 (1984).
That discretion is at its height when the agency decides not
to bring an enforcement action. Therefore, in Heckler v.
Chaney, 470 U. S. 821 (1985), we held that an agency’s refusal
to initiate enforcement proceedings is not ordinarily subject
to judicial review. Some debate remains, however, as to the
rigor with which we review an agency’s denial of a petition
for rulemaking.
There are key differences between a denial of a petition
for rulemaking and an agency’s decision not to initiate an
enforcement action. See American Horse Protection Assn.,
Inc. v. Lyng, 812 F. 2d 1, 3–4 (CADC 1987). In contrast to
nonenforcement decisions, agency refusals to initiate rule
making “are less frequent, more apt to involve legal as op
posed to factual analysis, and subject to special formalities,
including a public explanation.” Id., at 4; see also 5 U. S. C.
§ 555(e). They moreover arise out of denials of petitions for
rulemaking which (at least in the circumstances here) the
affected party had an undoubted procedural right to file in
the first instance. Refusals to promulgate rules are thus
susceptible to judicial review, though such review is “ex
major governmental actions. To deny standing to persons who are in
fact injured simply because many others are also injured, would mean
that the most injurious and widespread Government actions could be
questioned by nobody. We cannot accept that conclusion.” Ibid. (cita
tions omitted and emphasis added).
It is moreover quite wrong to analogize the legal claim advanced by Mas
sachusetts and the other public and private entities who challenge EPA’s
parsimonious construction of the Clean Air Act to a mere “lawyer’s game.”
See post, at 548.

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tremely limited” and “highly deferential.” National Cus
toms Brokers & Forwarders Assn. of America, Inc. v.
United States, 883 F. 2d 93, 96 (CADC 1989).
EPA concluded in its denial of the petition for rulemaking
that it lacked authority under 42 U. S. C. § 7521(a)(1) to regu
late new vehicle emissions because carbon dioxide is not an
“air pollutant” as that term is defined in § 7602. In the al
ternative, it concluded that even if it possessed authority, it
would decline to do so because regulation would conflict with
other administration priorities. As discussed earlier, the
Clean Air Act expressly permits review of such an action.
§ 7607(b)(1). We therefore “may reverse any such action
found to be . . . arbitrary, capricious, an abuse of discretion,
or otherwise not in accordance with law.” § 7607(d)(9).
VI
On the merits, the first question is whether § 202(a)(1) of
the Clean Air Act authorizes EPA to regulate greenhouse
gas emissions from new motor vehicles in the event that it
forms a “judgment” that such emissions contribute to climate
change. We have little trouble concluding that it does. In
relevant part, § 202(a)(1) provides that EPA “shall by regula
tion prescribe . . . 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 [the Administrator’s]
judgment cause, or contribute to, air pollution which may
reasonably be anticipated to endanger public health or wel
fare.” 42 U. S. C. § 7521(a)(1). Because EPA believes that
Congress did not intend it to regulate substances that con
tribute to climate change, the agency maintains that carbon
dioxide is not an “air pollutant” within the meaning of the
provision.
The statutory text forecloses EPA’s reading. The Clean
Air Act’s sweeping definition of “air pollutant” includes “any
air pollution agent or combination of such agents, including
any physical, chemical . . . substance or matter which is emit

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ted into or otherwise enters the ambient air . . . .” § 7602(g)
(emphasis added). On its face, the definition embraces all
airborne compounds of whatever stripe, and underscores that
intent through the repeated use of the word “any.” 25 Car
bon dioxide, methane, nitrous oxide, and hydrofluorocarbons
are without a doubt “physical [and] chemical . . . substance[s]
which [are] emitted into . . . the ambient air.” The statute
is unambiguous.26
Rather than relying on statutory text, EPA invokes post
enactment congressional actions and deliberations it views
as tantamount to a congressional command to refrain from
regulating greenhouse gas emissions. Even if such post
enactment legislative history could shed light on the mean
ing of an otherwise-unambiguous statute, EPA never identi
fies any action remotely suggesting that Congress meant to
curtail its power to treat greenhouse gases as air pollutants.
That subsequent Congresses have eschewed enacting bind
25 See Department of Housing and Urban Development v. Rucker, 535
U. S. 125, 131 (2002) (observing that “ ‘any’ . . . has an expansive meaning,
that is, one or some indiscriminately of whatever kind” (some internal
quotation marks omitted)).
26 In dissent, Justice Scalia maintains that because greenhouse gases
permeate the world’s atmosphere rather than a limited area near the
earth’s surface, EPA’s exclusion of greenhouse gases from the category of
air pollution “agent[s]” is entitled to deference under Chevron U. S. A. Inc.
v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984). See
post, at 558–560. EPA’s distinction, however, finds no support in the text
of the statute, which uses the phrase “the ambient air” without distin
guishing between atmospheric layers. Moreover, it is a plainly unreason
able reading of a sweeping statutory provision designed to capture “any
physical, chemical . . . substance or matter which is emitted into or other
wise enters the ambient air.” 42 U. S. C. § 7602(g). Justice Scalia does
not (and cannot) explain why Congress would define “air pollutant” so
carefully and so broadly, yet confer on EPA the authority to narrow that
definition whenever expedient by asserting that a particular substance is
not an “agent.” At any rate, no party to this dispute contests that green
house gases both “ente[r] the ambient air” and tend to warm the atmos
phere. They are therefore unquestionably “agent[s]” of air pollution.

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ing emissions limitations to combat global warming tells us
nothing about what Congress meant when it amended
§ 202(a)(1) in 1970 and 1977.27 And unlike EPA, we have no
difficulty reconciling Congress’ various efforts to promote in
teragency collaboration and research to better understand
climate change 28 with the Agency’s pre-existing mandate to
regulate “any air pollutant” that may endanger the public
welfare. See 42 U. S. C. § 7601(a)(1). Collaboration and re
search do not conflict with any thoughtful regulatory effort;
they complement it.29
EPA’s reliance on Brown & Williamson Tobacco Corp.,
529 U. S. 120, is similarly misplaced. In holding that tobacco
products are not “drugs” or “devices” subject to Food and
Drug Administration (FDA) regulation pursuant to the Food,
Drug and Cosmetic Act (FDCA), see 529 U. S., at 133, we
27 See United States v. Price, 361 U. S. 304, 313 (1960) (holding that “the
views of a subsequent Congress form a hazardous basis for inferring the
intent of an earlier one”); see also Cobell v. Norton, 428 F. 3d 1070, 1075
(CADC 2005) (“[P]ost-enactment legislative history is not only oxymoronic
but inherently entitled to little weight”).
28 See, e. g., National Climate Program Act, § 5, 92 Stat. 601, 15 U. S. C.
§ 2901 et seq. (calling for the establishment of a National Climate Program
and for additional climate-change research); Global Climate Protection Act
of 1987, § 1103, 101 Stat. 1408–1409, note following 15 U. S. C. § 2901 (di
recting EPA and the Secretary of State to “jointly” develop a “coordinated
national policy on global climate change” and report to Congress); Global
Change Research Act of 1990, Tit. I, 104 Stat. 3097, 15 U. S. C. §§ 2921–
2938 (establishing for the “development and coordination of a comprehen
sive and integrated United States research program” to aid in “under
stand[ing] . . . human-induced and natural processes of climate change”);
Global Climate Change Prevention Act of 1990, 104 Stat. 4058, 7 U. S. C.
§ 6701 et seq. (directing the Dept. of Agriculture to study the effects of
climate change on forestry and agriculture); Energy Policy Act of 1992,
§§ 1601–1609, 106 Stat. 2999, 42 U. S. C. §§ 13381–13388 (requiring the Sec
retary of Energy to report on information pertaining to climate change).
29 We are moreover puzzled by EPA’s roundabout argument that because
later Congresses chose to address stratospheric ozone pollution in a spe
cific legislative provision, it somehow follows that greenhouse gases cannot
be air pollutants within the meaning of the Clean Air Act.

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found critical at least two considerations that have no coun
terpart in this case.
First, we thought it unlikely that Congress meant to ban
tobacco products, which the FDCA would have required had
such products been classified as “drugs” or “devices.” Id.,
at 135–137. Here, in contrast, EPA jurisdiction would lead
to no such extreme measures. EPA would only regulate
emissions, and even then, it would have to delay any action
“to permit the development and application of the requisite
technology, giving appropriate consideration to the cost of
compliance,” § 7521(a)(2). However much a ban on tobacco
products clashed with the “common sense” intuition that
Congress never meant to remove those products from circu
lation, Brown & Williamson, 529 U. S., at 133, there is noth
ing counterintuitive to the notion that EPA can curtail the
emission of substances that are putting the global climate
out of kilter.
Second, in Brown & Williamson we pointed to an unbro
ken series of congressional enactments that made sense only
if adopted “against the backdrop of the FDA’s consistent and
repeated statements that it lacked authority under the
FDCA to regulate tobacco.” Id., at 144. We can point to
no such enactments here: EPA has not identified any con
gressional action that conflicts in any way with the regula
tion of greenhouse gases from new motor vehicles. Even if
it had, Congress could not have acted against a regulatory
“backdrop” of disclaimers of regulatory authority. Prior to
the order that provoked this litigation, EPA had never disa
vowed the authority to regulate greenhouse gases, and in
1998 it in fact affirmed that it had such authority. See App.
54 (Cannon memorandum). There is no reason, much less a
compelling reason, to accept EPA’s invitation to read ambi
guity into a clear statute.
EPA finally argues that it cannot regulate carbon dioxide
emissions from motor vehicles because doing so would re
quire it to tighten mileage standards, a job (according to

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EPA) that Congress has assigned to DOT. See 68 Fed. Reg.
52929. But that DOT sets mileage standards in no way
licenses EPA to shirk its environmental responsibilities.
EPA has been charged with protecting the public’s “health”
and “welfare,” 42 U. S. C. § 7521(a)(1), a statutory obliga
tion wholly independent of DOT’s mandate to promote en
ergy efficiency. See Energy Policy and Conservation Act,
§ 2(5), 89 Stat. 874, 42 U. S. C. § 6201(5). The two obligations
may overlap, but there is no reason to think the two agencies
cannot both administer their obligations and yet avoid
inconsistency.
While the Congresses that drafted § 202(a)(1) might not
have appreciated the possibility that burning fossil fuels
could lead to global warming, they did understand that with
out regulatory flexibility, changing circumstances and sci
entific developments would soon render the Clean Air Act
obsolete. The broad language of § 202(a)(1) reflects an inten
tional effort to confer the flexibility necessary to forestall
such obsolescence. See Pennsylvania Dept. of Corrections
v. Yeskey, 524 U. S. 206, 212 (1998) (“[T]he fact that a statute
can be applied in situations not expressly anticipated by Con
gress does not demonstrate ambiguity. It demonstrates
breadth” (internal quotation marks omitted)). Because
greenhouse gases fit well within the Clean Air Act’s capa
cious definition of “air pollutant,” we hold that EPA has the
statutory authority to regulate the emission of such gases
from new motor vehicles.
VII
The alternative basis for EPA’s decision—that even if it
does have statutory authority to regulate greenhouse gases,
it would be unwise to do so at this time—rests on reasoning
divorced from the statutory text. While the statute does
condition the exercise of EPA’s authority on its formation of
a “judgment,” 42 U. S. C. § 7521(a)(1), that judgment must
relate to whether an air pollutant “cause[s], or contribute[s]
to, air pollution which may reasonably be anticipated to en

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danger public health or welfare,” ibid. Put another way, the
use of the word “judgment” is not a roving license to ignore
the statutory text. It is but a direction to exercise discre
tion within defined statutory limits.
If EPA makes a finding of endangerment, the Clean Air
Act requires the Agency to regulate emissions of the delete
rious pollutant from new motor vehicles. Ibid. (stating that
“[EPA] shall by regulation prescribe . . . standards applicable
to the emission of any air pollutant from any class or classes
of new motor vehicles”). EPA no doubt has significant lati
tude as to the manner, timing, content, and coordination of
its regulations with those of other agencies. But once EPA
has responded to a petition for rulemaking, its reasons for
action or inaction must conform to the authorizing statute.
Under the clear terms of the Clean Air Act, EPA can avoid
taking further action only if it determines that greenhouse
gases do not contribute to climate change or if it provides
some reasonable explanation as to why it cannot or will not
exercise its discretion to determine whether they do. Ibid.
To the extent that this constrains agency discretion to pur
sue other priorities of the Administrator or the President,
this is the congressional design.
EPA has refused to comply with this clear statutory com
mand. Instead, it has offered a laundry list of reasons not
to regulate. For example, EPA said that a number of volun
tary Executive Branch programs already provide an effec
tive response to the threat of global warming, 68 Fed. Reg.
52932, that regulating greenhouse gases might impair the
President’s ability to negotiate with “key developing na
tions” to reduce emissions, id., at 52931, and that curtailing
motor-vehicle emissions would reflect “an inefficient, piece
meal approach to address the climate change issue,” ibid.
Although we have neither the expertise nor the authority
to evaluate these policy judgments, it is evident they have
nothing to do with whether greenhouse gas emissions con
tribute to climate change. Still less do they amount to a

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reasoned justification for declining to form a scientific judg
ment. In particular, while the President has broad author
ity in foreign affairs, that authority does not extend to the
refusal to execute domestic laws. In the Global Climate
Protection Act of 1987, Congress authorized the State De
partment—not EPA—to formulate United States foreign
policy with reference to environmental matters relating to
climate. See § 1103(c), 101 Stat. 1409. EPA has made no
showing that it issued the ruling in question here after con
sultation with the State Department. Congress did direct
EPA to consult with other agencies in the formulation of its
policies and rules, but the State Department is absent from
that list. § 1103(b).
Nor can EPA avoid its statutory obligation by noting the
uncertainty surrounding various features of climate change
and concluding that it would therefore be better not to regu
late at this time. See 68 Fed. Reg. 52930–52931. If the sci
entific uncertainty is so profound that it precludes EPA from
making a reasoned judgment as to whether greenhouse
gases contribute to global warming, EPA must say so. That
EPA would prefer not to regulate greenhouse gases because
of some residual uncertainty—which, contrary to Justice
Scalia’s apparent belief, post, at 553–555, is in fact all that
it said, see 68 Fed. Reg. 52929–52930 (“We do not believe . . .
that it would be either effective or appropriate for EPA to
establish [greenhouse gas] standards for motor vehicles at
this time” (emphasis added))—is irrelevant. The statutory
question is whether sufficient information exists to make an
endangerment finding.
In short, EPA has offered no reasoned explanation for its
refusal to decide whether greenhouse gases cause or contrib
ute to climate change. Its action was therefore “arbitrary,
capricious, . . . or otherwise not in accordance with law.”
42 U. S. C. § 7607(d)(9)(A). We need not and do not reach
the question whether on remand EPA must make an en
dangerment finding, or whether policy concerns can inform

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Roberts, C. J., dissenting
EPA’s actions in the event that it makes such a finding.
Cf. Chevron U. S. A. Inc. v. Natural Resources Defense
Council, Inc., 467 U. S., at 843–844. We hold only that EPA
must ground its reasons for action or inaction in the statute.
VIII
The judgment of the Court of Appeals is reversed, and
the case is remanded for further proceedings consistent with
this opinion.
It is so ordered.
Chief Justice Roberts, with whom Justice Scalia,
Justice Thomas, and Justice Alito join, dissenting.
Global warming may be a “crisis,” even “the most pressing
environmental problem of our time.” Pet. for Cert. 26, 22.
Indeed, it may ultimately affect nearly everyone on the
planet in some potentially adverse way, and it may be that
governments have done too little to address it. It is not a
problem, however, that has escaped the attention of policy
makers in the Executive and Legislative Branches of our
Government, who continue to consider regulatory, legisla
tive, and treaty-based means of addressing global climate
change.
Apparently dissatisfied with the pace of progress on this
issue in the elected branches, petitioners have come to the
courts claiming broad-ranging injury, and attempting to tie
that injury to the Government’s alleged failure to comply
with a rather narrow statutory provision. I would reject
these challenges as nonjusticiable. Such a conclusion in
volves no judgment on whether global warming exists, what
causes it, or the extent of the problem. Nor does it render
petitioners without recourse. This Court’s standing juris
prudence simply recognizes that redress of grievances of the
sort at issue here “is the function of Congress and the Chief
Executive,” not the federal courts. Lujan v. Defenders of
Wildlife, 504 U. S. 555, 576 (1992). I would vacate the judg

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ment below and remand for dismissal of the petitions for
review.
I
Article III, § 2, of the Constitution limits the federal judi
cial power to the adjudication of “Cases” and “Controver
sies.” “If a dispute is not a proper case or controversy, the
courts have no business deciding it, or expounding the law
in the course of doing so.” DaimlerChrysler Corp. v. Cuno,
547 U. S. 332, 341 (2006). “Standing to sue is part of the
common understanding of what it takes to make a justiciable
case,” Steel Co. v. Citizens for Better Environment, 523 U. S.
83, 102 (1998), and has been described as “an essential and
unchanging part of the case-or-controversy requirement of
Article III,” Defenders of Wildlife, supra, at 560.
Our modern framework for addressing standing is famil
iar: “A plaintiff must allege personal injury fairly traceable
to the defendant’s allegedly unlawful conduct and likely to
be redressed by the requested relief.” DaimlerChrysler,
supra, at 342 (quoting Allen v. Wright, 468 U. S. 737, 751
(1984); internal quotation marks omitted). Applying that
standard here, petitioners bear the burden of alleging an
injury that is fairly traceable to the Environmental Pro
tection Agency’s failure to promulgate new motor vehicle
greenhouse gas emission standards, and that is likely to be
redressed by the prospective issuance of such standards.
Before determining whether petitioners can meet this fa
miliar test, however, the Court changes the rules. It as
serts that “States are not normal litigants for the purposes
of invoking federal jurisdiction,” and that given “Massachu
setts’ stake in protecting its quasi-sovereign interests, the
Commonwealth is entitled to special solicitude in our stand
ing analysis.” Ante, at 518, 520 (emphasis added).
Relaxing Article III standing requirements because as
serted injuries are pressed by a State, however, has no basis
in our jurisprudence, and support for any such “special solici
tude” is conspicuously absent from the Court’s opinion. The
general judicial review provision cited by the Court, 42

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Roberts, C. J., dissenting
U. S. C. § 7607(b)(1), affords States no special rights or status.
The Court states that “Congress has ordered EPA to protect
Massachusetts (among others)” through the statutory provi
sion at issue, § 7521(a)(1), and that “Congress has . . . recog
nized a concomitant procedural right to challenge the rejec
tion of its rulemaking petition as arbitrary and capricious.”
Ante, at 519, 520. The reader might think from this unfor
tunate phrasing that Congress said something about the
rights of States in this particular provision of the statute.
Congress knows how to do that when it wants to, see, e. g.,
§ 7426(b) (affording States the right to petition EPA to di
rectly regulate certain sources of pollution), but it has done
nothing of the sort here. Under the law on which petition
ers rely, Congress treated public and private litigants ex
actly the same.
Nor does the case law cited by the Court provide any sup
port for the notion that Article III somehow implicitly treats
public and private litigants differently. The Court has to go
back a full century in an attempt to justify its novel standing
rule, but even there it comes up short. The Court’s analysis
hinges on Georgia v. Tennessee Copper Co., 206 U. S. 230
(1907)—a case that did indeed draw a distinction between a
State and private litigants, but solely with respect to avail
able remedies. The case had nothing to do with Article
III standing.
In Tennessee Copper, the State of Georgia sought to enjoin
copper companies in neighboring Tennessee from discharg
ing pollutants that were inflicting “a wholesale destruction
of forests, orchards and crops” in bordering Georgia counties.
Id., at 236. Although the State owned very little of the ter
ritory allegedly affected, the Court reasoned that Georgia—
in its capacity as a “quasi-sovereign”—“has an interest inde
pendent of and behind the titles of its citizens, in all the earth
and air within its domain.” Id., at 237. The Court ex
plained that while “[t]he very elements that would be relied
upon in a suit between fellow-citizens as a ground for equita
ble relief [were] wanting,” a State “is not lightly to be re

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quired to give up quasi-sovereign rights for pay.” Ibid.
Thus while a complaining private litigant would have to
make do with a legal remedy—one “for pay”—the State was
entitled to equitable relief. See id., at 237–238.
In contrast to the present case, there was no question in
Tennessee Copper about Article III injury. See id., at 238–
239. There was certainly no suggestion that the State could
show standing where the private parties could not; there was
no dispute, after all, that the private landowners had “an
action at law.” Id., at 238. Tennessee Copper has since
stood for nothing more than a State’s right, in an original
jurisdiction action, to sue in a representative capacity as pa
rens patriae. See, e. g., Maryland v. Louisiana, 451 U. S.
725, 737 (1981). Nothing about a State’s ability to sue in
that capacity dilutes the bedrock requirement of showing in
jury, causation, and redressability to satisfy Article III.
A claim of parens patriae standing is distinct from an alle
gation of direct injury. See Wyoming v. Oklahoma, 502
U. S. 437, 448–449, 451 (1992). Far from being a substitute
for Article III injury, parens patriae actions raise an addi
tional hurdle for a state litigant: the articulation of a “quasi
sovereign interest” “apart from the interests of particular
private parties.” Alfred L. Snapp & Son, Inc. v. Puerto
Rico ex rel. Barez, 458 U. S. 592, 607 (1982) (emphasis added)
(cited ante, at 519). Just as an association suing on behalf
of its members must show not only that it represents the
members but that at least one satisfies Article III require
ments, so too a State asserting quasi-sovereign interests as
parens patriae must still show that its citizens satisfy Arti
cle III. Focusing on Massachusetts’s interests as quasi
sovereign makes the required showing here harder, not eas
ier. The Court, in effect, takes what has always been
regarded as a necessary condition for parens patriae stand
ing—a quasi-sovereign interest—and converts it into a suf
ficient showing for purposes of Article III.

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Roberts, C. J., dissenting
What is more, the Court’s reasoning falters on its own
terms. The Court asserts that Massachusetts is entitled to
“special solicitude” due to its “quasi-sovereign interests,”
ante, at 520, but then applies our Article III standing test to
the asserted injury of the Commonwealth’s loss of coastal
property. See ante, at 522 (concluding that Massachusetts
“has alleged a particularized injury in its capacity as a land
owner” (emphasis added)). In the context of parens patriae
standing, however, we have characterized state ownership of
land as a “nonsovereign interes[t]” because a State “is likely
to have the same interests as other similarly situated propri
etors.” Alfred L. Snapp & Son, supra, at 601.
On top of everything else, the Court overlooks the fact
that our cases cast significant doubt on a State’s standing
to assert a quasi-sovereign interest—as opposed to a direct
injury—against the Federal Government. As a general
rule, we have held that while a State might assert a quasi
sovereign right as parens patriae “for the protection of its
citizens, it is no part of its duty or power to enforce their
rights in respect of their relations with the Federal Govern
ment. In that field it is the United States, and not the State,
which represents them.” Massachusetts v. Mellon, 262
U. S. 447, 485–486 (1923) (citation omitted); see also Alfred
L. Snapp & Son, supra, at 610, n. 16.
All of this presumably explains why petitioners never cited
Tennessee Copper in their briefs before this Court or the
D. C. Circuit. It presumably explains why not one of the
legion of amici supporting petitioners ever cited the case.
And it presumably explains why not one of the three judges
writing below ever cited the case either. Given that one
purpose of the standing requirement is “ ‘to assure that con
crete adverseness which sharpens the presentation of issues
upon which the court so largely depends for illumination,’ ”
ante, at 517 (quoting Baker v. Carr, 369 U. S. 186, 204
(1962)), it is ironic that the Court today adopts a new theory

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of Article III standing for States without the benefit of
briefing or argument on the point.1
II
It is not at all clear how the Court’s “special solicitude” for
Massachusetts plays out in the standing analysis, except as
an implicit concession that petitioners cannot establish
standing on traditional terms. But the status of Massachu
setts as a State cannot compensate for petitioners’ failure to
demonstrate injury in fact, causation, and redressability.
When the Court actually applies the three-part test, it fo
cuses, as did the dissent below, see 415 F. 3d 50, 64 (CADC
2005) (opinion of Tatel, J.), on the Commonwealth’s asserted
loss of coastal land as the injury in fact. If petitioners rely
on loss of land as the Article III injury, however, they must
ground the rest of the standing analysis in that specific in
jury. That alleged injury must be “concrete and particular
ized,” Defenders of Wildlife, 504 U. S., at 560, and “distinct
and palpable,” Allen, 468 U. S., at 751 (internal quotation
marks omitted). Central to this concept of “particularized”
injury is the requirement that a plaintiff be affected in a
“personal and individual way,” Defenders of Wildlife, 504
1 The Court seems to think we do not recognize that Tennessee Copper
is a case about parens patriae standing, ante, at 520–521, n. 17, but we
have no doubt about that. The point is that nothing in our cases (or
Hart & Wechsler) suggests that the prudential requirements for parens
patriae standing, see Republic of Venezuela v. Philip Morris Inc., 287
F. 3d 192, 199, n. (CADC 2002) (observing that “parens patriae is merely
a species of prudential standing” (internal quotation marks omitted)), can
somehow substitute for, or alter the content of, the “irreducible constitu
tional minimum” requirements of injury in fact, causation, and redressabil
ity under Article III. Lujan v. Defenders of Wildlife, 504 U. S. 555, 560
(1992).
Georgia v. Pennsylvania R. Co., 324 U. S. 439 (1945), is not to the con
trary. As the caption makes clear enough, the fact that a State may as
sert rights under a federal statute as parens patriae in no way refutes
our clear ruling that “[a] State does not have standing as parens patriae
to bring an action against the Federal Government.” Alfred L. Snapp &
Son, Inc. v. Puerto Rico ex rel. Barez, 458 U. S. 592, 610, n. 16 (1982).

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Roberts, C. J., dissenting
U. S., at 560, n. 1, and seek relief that “directly and tangibly
benefits him” in a manner distinct from its impact on “the
public at large,” id., at 573–574. Without “particularized in
jury, there can be no confidence of ‘a real need to exercise
the power of judicial review’ or that relief can be framed ‘no
broader than required by the precise facts to which the
court’s ruling would be applied.’ ” Warth v. Seldin, 422 U. S.
490, 508 (1975) (quoting Schlesinger v. Reservists Comm. to
Stop the War, 418 U. S. 208, 221–222 (1974)).
The very concept of global warming seems inconsistent
with this particularization requirement. Global warming is
a phenomenon “harmful to humanity at large,” 415 F. 3d, at
60 (Sentelle, J., dissenting in part and concurring in judg
ment), and the redress petitioners seek is focused no more
on them than on the public generally—it is literally to change
the atmosphere around the world.
If petitioners’ particularized injury is loss of coastal land,
it is also that injury that must be “actual or imminent, not
conjectural or hypothetical,” Defenders of Wildlife, supra,
at 560 (internal quotation marks omitted), “real and imme
diate,” Los Angeles v. Lyons, 461 U. S. 95, 102 (1983) (inter
nal quotation marks omitted), and “certainly impending,”
Whitmore v. Arkansas, 495 U. S. 149, 158 (1990) (internal
quotation marks omitted).
As to “actual” injury, the Court observes that “global sea
levels rose somewhere between 10 and 20 centimeters over
the 20th century as a result of global warming” and that
“[t]hese rising seas have already begun to swallow Massa
chusetts’ coastal land.” Ante, at 522. But none of petition
ers’ declarations supports that connection. One declaration
states that “a rise in sea level due to climate change is occur
ring on the coast of Massachusetts, in the metropolitan Bos
ton area,” but there is no elaboration. 2 Petitioners’ Stand
ing Appendix in No. 03–1361, etc. (CADC), p. 196 (Stdg.
App.). And the declarant goes on to identify a “significan[t]”
non-global-warming cause of Boston’s rising sea level: land

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subsidence. Id., at 197; see also id., at 216. Thus, aside
from a single conclusory statement, there is nothing in peti
tioners’ 43 standing declarations and accompanying exhibits
to support an inference of actual loss of Massachusetts
coastal land from 20th-century global sea level increases. It
is pure conjecture.
The Court’s attempts to identify “imminent” or “certainly
impending” loss of Massachusetts coastal land fares no bet
ter. See ante, at 522–523. One of petitioners’ declarants
predicts global warming will cause sea level to rise by 20 to
70 centimeters by the year 2100. Stdg. App. 216. Another
uses a computer modeling program to map the Common
wealth’s coastal land and its current elevation, and calculates
that the high-end estimate of sea level rise would result in
the loss of significant state-owned coastal land. Id., at 179.
But the computer modeling program has a conceded average
error of about 30 centimeters and a maximum observed error
of 70 centimeters. Id., at 177–178. As an initial matter, if
it is possible that the model underrepresents the elevation of
coastal land to an extent equal to or in excess of the pro
jected sea level rise, it is difficult to put much stock in the
predicted loss of land. But even placing that problem to the
side, accepting a century-long time horizon and a series of
compounded estimates renders requirements of imminence
and immediacy utterly toothless. See Defenders of Wild
life, supra, at 565, n. 2 (while the concept of “ ‘imminence’ ” in
standing doctrine is “somewhat elastic,” it can be “stretched
beyond the breaking point”). “Allegations of possible future
injury do not satisfy the requirements of Art. III. A threat
ened injury must be certainly impending to constitute in
jury in fact.” Whitmore, supra, at 158 (internal quotation
marks omitted; emphasis added).
III
Petitioners’ reliance on Massachusetts’s loss of coastal land
as their injury in fact for standing purposes creates insur

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mountable problems for them with respect to causation and
redressability. To establish standing, petitioners must show
a causal connection between that specific injury and the lack
of new motor vehicle greenhouse gas emission standards, and
that the promulgation of such standards would likely redress
that injury. As is often the case, the questions of causation
and redressability overlap. See Allen, 468 U. S., at 753,
n. 19 (observing that the two requirements were “initially
articulated by this Court as two facets of a single causation
requirement” (internal quotation marks omitted)). And im
portantly, when a party is challenging the Government’s al
legedly unlawful regulation, or lack of regulation, of a third
party, satisfying the causation and redressability require
ments becomes “substantially more difficult.” Defenders of
Wildlife, 504 U. S., at 562 (internal quotation marks omit
ted); see also Warth, supra, at 504–505.
Petitioners view the relationship between their injuries
and EPA’s failure to promulgate new motor vehicle green
house gas emission standards as simple and direct: Domestic
motor vehicles emit carbon dioxide and other greenhouse
gases. Worldwide emissions of greenhouse gases contribute
to global warming and therefore also to petitioners’ alleged
injuries. Without the new vehicle standards, greenhouse
gas emissions—and therefore global warming and its attend
ant harms—have been higher than they otherwise would
have been; once EPA changes course, the trend will be
reversed.
The Court ignores the complexities of global warming, and
does so by now disregarding the “particularized” injury it
relied on in step one, and using the dire nature of global
warming itself as a bootstrap for finding causation and re
dressability. First, it is important to recognize the extent
of the emissions at issue here. Because local greenhouse gas
emissions disperse throughout the atmosphere and remain
there for anywhere from 50 to 200 years, it is global emis
sions data that are relevant. See App. to Pet. for Cert.

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A–73. According to one of petitioners’ declarations, domes
tic motor vehicles contribute about 6 percent of global carbon
dioxide emissions and 4 percent of global greenhouse gas
emissions. Stdg. App. 232. The amount of global emissions
at issue here is smaller still; § 202(a)(1) of the Clean Air Act
covers only new motor vehicles and new motor vehicle en
gines, so petitioners’ desired emission standards might re
duce only a fraction of 4 percent of global emissions.
This gets us only to the relevant greenhouse gas emissions;
linking them to global warming and ultimately to petitioners’
alleged injuries next requires consideration of further com
plexities. As EPA explained in its denial of petitioners’ re
quest for rulemaking,
“predicting future climate change necessarily involves a
complex web of economic and physical factors including:
our ability to predict future global anthropogenic emis
sions of [greenhouse gases] and aerosols; the fate of
these emissions once they enter the atmosphere (e. g.,
what percentage are absorbed by vegetation or are
taken up by the oceans); the impact of those emissions
that remain in the atmosphere on the radiative proper
ties of the atmosphere; changes in critically important
climate feedbacks (e. g., changes in cloud cover and ocean
circulation); changes in temperature characteristics
(e. g., average temperatures, shifts in daytime and eve
ning temperatures); changes in other climatic parame
ters (e. g., shifts in precipitation, storms); and ultimately
the impact of such changes on human health and welfare
(e. g., increases or decreases in agricultural productivity,
human health impacts).” App. to Pet. for Cert. A–83
through A–84.
Petitioners are never able to trace their alleged injuries
back through this complex web to the fractional amount of
global emissions that might have been limited with EPA
standards. In light of the bit-part domestic new motor vehi

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Roberts, C. J., dissenting
cle greenhouse gas emissions have played in what petitioners
describe as a 150-year global phenomenon, and the myriad
additional factors bearing on petitioners’ alleged injury—the
loss of Massachusetts coastal land—the connection is far too
speculative to establish causation.
IV
Redressability is even more problematic. To the tenuous
link between petitioners’ alleged injury and the indetermi
nate fractional domestic emissions at issue here, add the fact
that petitioners cannot meaningfully predict what will come
of the 80 percent of global greenhouse gas emissions that
originate outside the United States. As the Court acknowl
edges, “developing countries such as China and India are
poised to increase greenhouse gas emissions substantially
over the next century,” ante, at 525–526, so the domestic
emissions at issue here may become an increasingly marginal
portion of global emissions, and any decreases produced by
petitioners’ desired standards are likely to be overwhelmed
many times over by emissions increases elsewhere in the
world.
Petitioners offer declarations attempting to address this
uncertainty, contending that “[i]f the U. S. takes steps to re
duce motor vehicle emissions, other countries are very likely
to take similar actions regarding their own motor vehicles
using technology developed in response to the U. S. pro
gram.” Stdg. App. 220; see also id., at 311–312. In other
words, do not worry that other countries will contribute far
more to global warming than will U. S. automobile emissions;
someone is bound to invent something, and places like the
People’s Republic of China or India will surely require use
of the new technology, regardless of cost. The Court pre
viously has explained that when the existence of an element
of standing “depends on the unfettered choices made by inde
pendent actors not before the courts and whose exercise of
broad and legitimate discretion the courts cannot presume

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Roberts, C. J., dissenting
either to control or to predict,” a party must present facts
supporting an assertion that the actor will proceed in such a
manner. Defenders of Wildlife, 504 U. S., at 562 (quoting
ASARCO Inc. v. Kadish, 490 U. S. 605, 615 (1989) (opinion of
Kennedy, J.); internal quotation marks omitted). The dec
larations’ conclusory (not to say fanciful) statements do not
even come close.
No matter, the Court reasons, because any decrease in do
mestic emissions will “slow the pace of global emissions in
creases, no matter what happens elsewhere.” Ante, at 526.
Every little bit helps, so Massachusetts can sue over any
little bit.
The Court’s sleight of hand is in failing to link up the dif
ferent elements of the three-part standing test. What must
be likely to be redressed is the particular injury in fact.
The injury the Court looks to is the asserted loss of land.
The Court contends that regulating domestic motor vehicle
emissions will reduce carbon dioxide in the atmosphere, and
therefore redress Massachusetts’s injury. But even if regu
lation does reduce emissions—to some indeterminate degree,
given events elsewhere in the world—the Court never ex
plains why that makes it likely that the injury in fact—the
loss of land—will be redressed. Schoolchildren know that a
kingdom might be lost “all for the want of a horseshoe nail,”
but “likely” redressability is a different matter. The reali
ties make it pure conjecture to suppose that EPA regulation
of new automobile emissions will likely prevent the loss of
Massachusetts coastal land.
V
Petitioners’ difficulty in demonstrating causation and re
dressability is not surprising given the evident mismatch be
tween the source of their alleged injury—catastrophic global
warming—and the narrow subject matter of the Clean Air
Act provision at issue in this suit. The mismatch suggests

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Roberts, C. J., dissenting
that petitioners’ true goal for this litigation may be more
symbolic than anything else. The constitutional role of the
courts, however, is to decide concrete cases—not to serve
as a convenient forum for policy debates. See Valley Forge
Christian College v. Americans United for Separation of
Church and State, Inc., 454 U. S. 464, 472 (1982) (“[Standing]
tends to assure that the legal questions presented to the
court will be resolved, not in the rarified atmosphere of a
debating society, but in a concrete factual context conducive
to a realistic appreciation of the consequences of judicial
action”).
When dealing with legal doctrine phrased in terms of what
is “fairly” traceable or “likely” to be redressed, it is perhaps
not surprising that the matter is subject to some debate.
But in considering how loosely or rigorously to define those
adverbs, it is vital to keep in mind the purpose of the inquiry.
The limitation of the judicial power to cases and controver
sies “is crucial in maintaining the tripartite allocation of
power set forth in the Constitution.” DaimlerChrysler, 547
U. S., at 341 (internal quotation marks omitted). In my
view, the Court today—addressing Article III’s “core compo
nent of standing,” Defenders of Wildlife, supra, at 560—fails
to take this limitation seriously.
To be fair, it is not the first time the Court has done so.
Today’s decision recalls the previous high-water mark of di
luted standing requirements, United States v. Students Chal
lenging Regulatory Agency Procedures (SCRAP), 412 U. S.
669 (1973). SCRAP involved “[p]robably the most attenu
ated injury conferring Art. III standing” and “surely went
to the very outer limit of the law”—until today. Whitmore,
495 U. S., at 158–159; see also Lujan v. National Wildlife
Federation, 497 U. S. 871, 889 (1990) (SCRAP “has never
since been emulated by this Court”). In SCRAP, the Court
based an environmental group’s standing to challenge a rail
road freight rate surcharge on the group’s allegation that

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increases in railroad rates would cause an increase in the use
of nonrecyclable goods, resulting in the increased need for
natural resources to produce such goods. According to the
group, some of these resources might be taken from the
Washington area, resulting in increased refuse that might
find its way into area parks, harming the group’s members.
412 U. S., at 688.
Over time, SCRAP became emblematic not of the loose
ness of Article III standing requirements, but of how utterly
manipulable they are if not taken seriously as a matter of
judicial self-restraint. SCRAP made standing seem a law
yer’s game, rather than a fundamental limitation ensuring
that courts function as courts and not intrude on the politi
cally accountable branches. Today’s decision is SCRAP for
a new generation.2
Perhaps the Court recognizes as much. How else to ex
plain its need to devise a new doctrine of state standing to
support its result? The good news is that the Court’s “spe
cial solicitude” for Massachusetts limits the future applicabil
ity of the diluted standing requirements applied in this case.
The bad news is that the Court’s self-professed relaxation of
those Article III requirements has caused us to transgress
“the proper—and properly limited—role of the courts in a
2 The difficulty with SCRAP, and the reason it has not been followed, is
not the portion cited by the Court. See ante, at 526–527, n. 24. Rather,
it is the attenuated nature of the injury there, and here, that is so trou
bling. Even in SCRAP, the Court noted that what was required was
“something more than an ingenious academic exercise in the conceivable,”
412 U. S., at 688, and we have since understood the allegation there to have
been “that the string of occurrences alleged would happen immediately,”
Whitmore v. Arkansas, 495 U. S. 149, 159 (1990) (emphasis added). That
is hardly the case here.
The Court says it is “quite wrong” to compare petitioners’ challenging
“EPA’s parsimonious construction of the Clean Air Act to a mere ‘lawyer’s
game.’ ” Ante, at 527, n. 24. Of course it is not the legal challenge that
is merely “an ingenious academic exercise in the conceivable,” SCRAP,
supra, at 688, but the assertions made in support of standing.

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Scalia, J., dissenting
democratic society.” Allen, 468 U. S., at 750 (internal quota
tion marks omitted).
I respectfully dissent.
Justice Scalia, with whom The Chief Justice, Justice
Thomas, and Justice Alito join, dissenting.
I join The Chief Justice’s opinion in full, and would hold
that this Court has no jurisdiction to decide this case because
petitioners lack standing. The Court having decided other
wise, it is appropriate for me to note my dissent on the
merits.
I
A
The provision of law at the heart of this case is § 202(a)(1)
of the Clean Air Act (CAA or Act), which provides that
the Administrator of the Environmental Protection Agency
(EPA) “shall by regulation prescribe . . . 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.” 42 U. S. C. § 7521(a)(1) (emphasis added). As the
Court recognizes, the statute “condition[s] the exercise of
EPA’s authority on its formation of a ‘judgment.’ ” Ante,
at 532. There is no dispute that the Administrator has made
no such judgment in this case. See ante, at 534 (“We need
not and do not reach the question whether on remand EPA
must make an endangerment finding”); 68 Fed. Reg. 52929
(2003) (“[N]o Administrator has made a finding under any of
the CAA’s regulatory provisions that CO2 meets the applica
ble statutory criteria for regulation”).
The question thus arises: Does anything require the Ad
ministrator to make a “judgment” whenever a petition for
rulemaking is filed? Without citation of the statute or any
other authority, the Court says yes. Why is that so? When

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Congress wishes to make private action force an agency’s
hand, it knows how to do so. See, e. g., Brock v. Pierce
County, 476 U. S. 253, 254–255 (1986) (discussing the Com
prehensive Employment and Training Act (CETA), 92 Stat.
1926, 29 U. S. C. § 816(b) (1976 ed., Supp. V), which “pro
vide[d] that the Secretary of Labor ‘shall’ issue a final deter
mination as to the misuse of CETA funds by a grant recipient
within 120 days after receiving a complaint alleging such
misuse”). Where does the CAA say that the EPA Adminis
trator is required to come to a decision on this question
whenever a rulemaking petition is filed? The Court points
to no such provision because none exists.
Instead, the Court invents a multiple-choice question that
the EPA Administrator must answer when a petition for
rulemaking is filed. The Administrator must exercise his
judgment in one of three ways: (a) by concluding that the
pollutant does cause, or contribute to, air pollution that en
dangers public welfare (in which case EPA is required to
regulate); (b) by concluding that the pollutant does not cause,
or contribute to, air pollution that endangers public welfare
(in which case EPA is not required to regulate); or (c) by
“provid[ing] some reasonable explanation as to why it cannot
or will not exercise its discretion to determine whether”
greenhouse gases endanger public welfare, ante, at 533 (in
which case EPA is not required to regulate).
I am willing to assume, for the sake of argument, that
the Administrator’s discretion in this regard is not entirely
unbounded—that if he has no reasonable basis for deferring
judgment he must grasp the nettle at once. The Court,
however, with no basis in text or precedent, rejects all of
EPA’s stated “policy judgments” as not “amount[ing] to a
reasoned justification,” ante, at 533–534, effectively narrow
ing the universe of potential reasonable bases to a single one:
Judgment can be delayed only if the Administrator concludes
that “the scientific uncertainty is [too] profound.” Ante, at
534. The Administrator is precluded from concluding for
other reasons “that it would . . . be better not to regulate

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at this time.” Ibid.1 Such other reasons—perfectly valid
reasons—were set forth in the Agency’s statement.
“We do not believe . . . that it would be either effective
or appropriate for EPA to establish [greenhouse gas]
standards for motor vehicles at this time. As described
in detail below, the President has laid out a comprehen
sive approach to climate change that calls for near-term
voluntary actions and incentives along with programs
aimed at reducing scientific uncertainties and encourag
ing technological development so that the government
may effectively and efficiently address the climate
change issue over the long term.
. . . . .
“[E]stablishing [greenhouse gas] emission standards for
U. S. motor vehicles at this time would . . . result in an
inefficient, piecemeal approach to addressing the climate
change issue. The U. S. motor vehicle fleet is one of
many sources of [greenhouse gas] emissions both here
and abroad, and different [greenhouse gas] emission
sources face different technological and financial chal
lenges in reducing emissions. A sensible regulatory
scheme would require that all significant sources and
sinks of [greenhouse gas] emissions be considered in
deciding how best to achieve any needed emission
reductions.
“Unilateral EPA regulation of motor vehicle [green
house gas] emissions could also weaken U. S. efforts to
persuade developing countries to reduce the [green
house gas] intensity of their economies. Considering
the large populations and growing economies of some
developing countries, increases in their [greenhouse gas]
emissions could quickly overwhelm the effects of [green
1 The Court’s way of putting it is, of course, not quite accurate. The
issue is whether it would be better to defer the decision about whether to
exercise judgment. This has the effect of deferring regulation but is quite
a different determination.

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house gas] reduction measures in developed countries.
Any potential benefit of EPA regulation could be lost to
the extent other nations decided to let their emissions
significantly increase in view of U. S. emissions reduc
tions. Unavoidably, climate change raises important
foreign policy issues, and it is the President’s preroga
tive to address them.” 68 Fed. Reg. 52929–52931 (foot
note omitted).
The Court dismisses this analysis as “rest[ing] on rea
soning divorced from the statutory text.” Ante, at 532.
“While the statute does condition the exercise of EPA’s au
thority on its formation of a ‘judgment,’ . . . that judgment
must relate to whether an air pollutant ‘cause[s], or contrib
ute[s] to, air pollution which may reasonably be anticipated
to endanger public health or welfare.’ ” Ante, at 532–533.
True but irrelevant. When the Administrator makes a
judgment whether to regulate greenhouse gases, that judg
ment must relate to whether they are air pollutants that
“cause, or contribute to, air pollution which may reasonably
be anticipated to endanger public health or welfare.” 42
U. S. C. § 7521(a)(1). But the statute says nothing at all
about the reasons for which the Administrator may defer
making a judgment—the permissible reasons for deciding
not to grapple with the issue at the present time. Thus,
the various “policy” rationales, ante, at 533, that the Court
criticizes are not “divorced from the statutory text,” ante, at
532, except in the sense that the statutory text is silent,
as texts are often silent about permissible reasons for the
exercise of agency discretion. The reasons EPA gave are
surely considerations executive agencies regularly take into
account (and ought to take into account) when deciding
whether to consider entering a new field: the impact such
entry would have on other Executive Branch programs and
on foreign policy. There is no basis in law for the Court’s
imposed limitation.
EPA’s interpretation of the discretion conferred by the
statutory reference to “its judgment” is not only reasonable,

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it is the most natural reading of the text. The Court no
where explains why this interpretation is incorrect, let alone
why it is not entitled to deference under Chevron U. S. A.
Inc. v. Natural Resources Defense Council, Inc., 467 U. S.
837 (1984). As the Administrator acted within the law in
declining to make a “judgment” for the policy reasons above
set forth, I would uphold the decision to deny the rulemaking
petition on that ground alone.
B
Even on the Court’s own terms, however, the same conclu
sion follows. As mentioned above, the Court gives EPA the
option of determining that the science is too uncertain to
allow it to form a “judgment” as to whether greenhouse
gases endanger public welfare. Attached to this option (on
what basis is unclear) is an essay requirement: “If,” the
Court says, “the scientific uncertainty is so profound that it
precludes EPA from making a reasoned judgment as to
whether greenhouse gases contribute to global warming,
EPA must say so.” Ante, at 534. But EPA has said pre
cisely that—and at great length, based on information con
tained in a 2001 report by the National Research Council
(NRC) entitled Climate Change Science: An Analysis of
Some Key Questions:
“As the NRC noted in its report, concentrations of
[greenhouse gases (GHGs)] are increasing in the atmos
phere as a result of human activities (pp. 9–12). It also
noted that ‘[a] diverse array of evidence points to a
warming of global surface air temperatures’ (p. 16).
The report goes on to state, however, that ‘[b]ecause of
the large and still uncertain level of natural variability
inherent in the climate record and the uncertainties
in the time histories of the various forcing agents (and
particularly aerosols), a [causal] linkage between the
buildup of [GHGs] in the atmosphere and the ob
served climate changes during the 20th century can
not be unequivocally established. The fact that the

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magnitude of the observed warming is large in compari
son to natural variability as simulated in climate models
is suggestive of such a linkage, but it does not constitute
proof of one because the model simulations could be de
ficient in natural variability on the decadal to century
time scale’ (p. 17).
“The NRC also observed that ‘there is considerable
uncertainty in current understanding of how the cli
mate system varies naturally and reacts to emissions of
[GHGs] and aerosols’ (p. 1). As a result of that uncer
tainty, the NRC cautioned that ‘current estimate of the
magnitude of future warming should be regarded as ten
tative and subject to future adjustments (either upward
or downward).’ Id. It further advised that ‘[r]educing
the wide range of uncertainty inherent in current model
predictions of global climate change will require major
advances in understanding and modeling of both (1) the
factors that determine atmospheric concentrations of
[GHGs] and aerosols and (2) the so-called “feedbacks”
that determine the sensitivity of the climate system to
a prescribed increase in [GHGs].’ Id.
“The science of climate change is extraordinarily com
plex and still evolving. Although there have been sub
stantial advances in climate change science, there con
tinue to be important uncertainties in our understanding
of the factors that may affect future climate change and
how it should be addressed. As the NRC explained,
predicting future climate change necessarily involves a
complex web of economic and physical factors including:
Our ability to predict future global anthropogenic emis
sions of GHGs and aerosols; the fate of these emissions
once they enter the atmosphere (e. g., what percentage
are absorbed by vegetation or are taken up by the
oceans); the impact of those emissions that remain in the
atmosphere on the radiative properties of the atmos

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phere; changes in critically important climate feedbacks
(e. g., changes in cloud cover and ocean circulation);
changes in temperature characteristics (e. g., average
temperatures, shifts in daytime and evening tempera
tures); changes in other climatic parameters (e. g., shifts
in precipitation, storms); and ultimately the impact of
such changes on human health and welfare (e. g., in
creases or decreases in agricultural productivity, human
health impacts). The NRC noted, in particular, that
‘[t]he understanding of the relationships between
weather/climate and human health is in its infancy and
therefore the health consequences of climate change are
poorly understood’ (p. 20). Substantial scientific uncer
tainties limit our ability to assess each of these factors
and to separate out those changes resulting from natural
variability from those that are directly the result of in
creases in anthropogenic GHGs.
“Reducing the wide range of uncertainty inherent in
current model predictions will require major advances
in understanding and modeling of the factors that deter
mine atmospheric concentrations of [GHGs] and aero
sols, and the processes that determine the sensitivity of
the climate system.” 68 Fed. Reg. 52930.
I simply cannot conceive of what else the Court would like
EPA to say.
II
A
Even before reaching its discussion of the word “judg
ment,” the Court makes another significant error when it
concludes that Ҥ 202(a)(1) of the Clean Air Act authorizes
EPA to regulate greenhouse gas emissions from new motor
vehicles in the event that it forms a ‘judgment’ that such
emissions contribute to climate change.” Ante, at 528 (em
phasis added). For such authorization, the Court relies on

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what it calls “the Clean Air Act’s capacious definition of ‘air
pollutant.’ ” Ante, at 532.
“Air pollutant” is defined by the Act as “any air pollution
agent or combination of such agents, including any physical,
chemical, . . . substance or matter which is emitted into or
otherwise enters the ambient air.” 42 U. S. C. § 7602(g).
The Court is correct that “[c]arbon dioxide, methane, nitrous
oxide, and hydrofluorocarbons,” ante, at 529, fit within
the second half of that definition: They are “physical,
chemical, . . . substance[s] or matter which [are] emitted into
or otherwise ente[r] the ambient air.” But the Court mis
takenly believes this to be the end of the analysis. In order
to be an “air pollutant” under the Act’s definition, the “sub
stance or matter [being] emitted into . . . the ambient air”
must also meet the first half of the definition—namely, it
must be an “air pollution agent or combination of such
agents.” The Court simply pretends this half of the defini
tion does not exist.
The Court’s analysis faithfully follows the argument ad
vanced by petitioners, which focuses on the word “including”
in the statutory definition of “air pollutant.” See Brief for
Petitioners 13–14. As that argument goes, anything that
follows the word “including” must necessarily be a subset of
whatever precedes it. Thus, if greenhouse gases qualify
under the phrase following the word “including,” they must
qualify under the phrase preceding it. Since greenhouse
gases come within the capacious phrase “any physical, chemi
cal, . . . substance or matter which is emitted into or other
wise enters the ambient air,” they must also be “air pollution
agent[s] or combination[s] of such agents,” and therefore
meet the definition of “air pollutant[s].”
That is certainly one possible interpretation of the statu
tory definition. The word “including” can indeed indicate
that what follows will be an “illustrative” sampling of the
general category that precedes the word. Federal Land
Bank of St. Paul v. Bismarck Lumber Co., 314 U. S. 95, 100

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(1941). Often, however, the examples standing alone are
broader than the general category, and must be viewed as
limited in light of that category. The Government provides
a helpful (and unanswered) example: “The phrase ‘any Amer
ican automobile, including any truck or minivan,’ would not
naturally be construed to encompass a foreign-manufactured
[truck or] minivan.” Brief for Federal Respondent 34. The
general principle enunciated—that the speaker is talking
about American automobiles—carries forward to the illus
trative examples (trucks and minivans), and limits them
accordingly, even though in isolation they are broader. Con
gress often uses the word “including” in this manner. In
28 U. S. C. § 1782(a), for example, it refers to “a proceeding
in a foreign or international tribunal, including criminal
investigations conducted before formal accusation.” Cer
tainly this provision would not encompass criminal inves
tigations underway in a domestic tribunal. See also, e. g., 2
U. S. C. § 54(a) (“The Clerk of the House of Representatives
shall, at the request of a Member of the House of Repre
sentatives, furnish to the Member, for official use only, one
set of a privately published annotated version of the United
States Code, including supplements and pocket parts”);
22 U. S. C. § 2304(b)(1) (“the relevant findings of appropri
ate international organizations, including nongovernmental
organizations”).
In short, the word “including” does not require the Court’s
(or the petitioners’) result. It is perfectly reasonable to
view the definition of “air pollutant” in its entirety: An air
pollutant can be “any physical, chemical, . . . substance or
matter which is emitted into or otherwise enters the ambient
air,” but only if it retains the general characteristic of being
an “air pollution agent or combination of such agents.” This
is precisely the conclusion EPA reached: “[A] substance does
not meet the CAA definition of ‘air pollutant’ simply because
it is a ‘physical, chemical, . . . substance or matter which is
emitted into or otherwise enters the ambient air.’ It must

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also be an ‘air pollution agent.’ ” 68 Fed. Reg. 52929, n. 3.
See also id., at 52928 (“The root of the definition indicates
that for a substance to be an ‘air pollutant,’ it must be an
‘agent’ of ‘air pollution’ ”). Once again, in the face of textual
ambiguity, the Court’s application of Chevron deference to
EPA’s interpretation of the word “including” is nowhere to
be found.2 Evidently, the Court defers only to those reason
able interpretations that it favors.
B
Using (as we ought to) EPA’s interpretation of the defini
tion of “air pollutant,” we must next determine whether
greenhouse gases are “agent[s]” of “air pollution.” If so, the
statute would authorize regulation; if not, EPA would lack
authority.
Unlike “air pollutants,” the term “air pollution” is not itself
defined by the CAA; thus, once again we must accept EPA’s
interpretation of that ambiguous term, provided its interpre
tation is a “permissible construction of the statute.” Chev
ron, 467 U. S., at 843. In this case, the petition for rule
making asked EPA for “regulation of [greenhouse gas]
emissions from motor vehicles to reduce the risk of global
climate change.” 68 Fed. Reg. 52925. Thus, in deciding
whether it had authority to regulate, EPA had to determine
whether the concentration of greenhouse gases assertedly
responsible for “global climate change” qualifies as “air pollu
tion.” EPA began with the commonsense observation that
the “[p]roblems associated with atmospheric concentrations
2 Not only is EPA’s interpretation reasonable, it is far more plausible
than the Court’s alternative. As the Court correctly points out, “all air
borne compounds of whatever stripe,” ante, at 529, would qualify as
“physical, chemical, . . . substance[s] or matter which [are] emitted into or
otherwise ente[r] the ambient air,” 42 U. S. C. § 7602(g). It follows that
everything airborne, from Frisbees to flatulence, qualifies as an “air pollut
ant.” This reading of the statute defies common sense.

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of CO2 ,” id., at 52927, bear little resemblance to what would
naturally be termed “air pollution”:
“EPA’s prior use of the CAA’s general regulatory pro
visions provides an important context. Since the in
ception of the Act, EPA has used these provisions to
address air pollution problems that occur primarily at
ground level or near the surface of the earth. For ex
ample, national ambient air quality standards (NAAQS)
established under CAA section 109 address concentra
tions of substances in the ambient air and the related
public health and welfare problems. This has meant
setting NAAQS for concentrations of ozone, carbon mon
oxide, particulate matter and other substances in the
air near the surface of the earth, not higher in the
atmosphere. . . . CO2 , by contrast, is fairly consistent
in concentration throughout the world’s atmosphere
up to approximately the lower stratosphere.” Id., at
52926–52927.
In other words, regulating the buildup of CO2 and other
greenhouse gases in the upper reaches of the atmosphere,
which is alleged to be causing global climate change, is not
akin to regulating the concentration of some substance that
is polluting the air.
We need look no further than the dictionary for confirma
tion that this interpretation of “air pollution” is eminently
reasonable. The definition of “pollute,” of course, is “[t]o
make or render impure or unclean.” Webster’s New Inter
national Dictionary 1910 (2d ed. 1949). And the first three
definitions of “air” are as follows: (1) “[t]he invisible, odorless,
and tasteless mixture of gases which surrounds the earth”;
(2) “[t]he body of the earth’s atmosphere; esp., the part of
it near the earth, as distinguished from the upper rar
efied part”; (3) “[a] portion of air or of the air considered
with respect to physical characteristics or as affecting the

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senses.” Id., at 54. EPA’s conception of “air pollution”—
focusing on impurities in the “ambient air” “at ground level
or near the surface of the earth”—is perfectly consistent
with the natural meaning of that term.
In the end, EPA concluded that since “CAA authorization
to regulate is generally based on a finding that an air pollut
ant causes or contributes to air pollution,” 68 Fed. Reg.
52928, the concentrations of CO2 and other greenhouse gases
allegedly affecting the global climate are beyond the scope
of CAA’s authorization to regulate. “[T]he term ‘air pollu
tion’ as used in the regulatory provisions cannot be inter
preted to encompass global climate change.” Ibid. Once
again, the Court utterly fails to explain why this interpreta
tion is incorrect, let alone so unreasonable as to be unworthy
of Chevron deference.
* * *
The Court’s alarm over global warming may or may not
be justified, but it ought not distort the outcome of this litiga
tion. This is a straightforward administrative-law case, in
which Congress has passed a malleable statute giving broad
discretion, not to us but to an executive agency. No matter
how important the underlying policy issues at stake, this
Court has no business substituting its own desired outcome
for the reasoned judgment of the responsible agency.