(Slip Opinion)              OCTOBER TERM, 2010                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 

, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

    AMERICAN ELECTRIC POWER CO., INC., ET AL. v. 

              CONNECTICUT ET AL. 


CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                 THE SECOND CIRCUIT

       No. 10–174.      Argued April 19, 2011—Decided June 20, 2011
In Massachusetts v. EPA, 

, this Court held that the Clean
  Air Act authorizes federal regulation of emissions of carbon dioxide
  and other greenhouse gases, and that the Environmental Protection
  Agency (EPA) had misread that Act when it denied a rulemaking pe
  tition seeking controls on greenhouse gas emissions from new motor
  vehicles. In response, EPA commenced a rulemaking under §111 of
  the Act, 

. §7411, to set limits on greenhouse gas emissions
  from new, modified, and existing fossil-fuel fired power plants. Pur
  suant to a settlement finalized in March 2011, EPA has committed to
  issuing a final rule by May 2012.
     The lawsuits considered here began well before EPA initiated ef
  forts to regulate greenhouse gases. Two groups of plaintiffs, respon
  dents here, filed separate complaints in a Federal District Court
  against the same five major electric power companies, petitioners
  here. One group of plaintiffs included eight States and New York
  City; the second joined three nonprofit land trusts. According to the
  complaint, the defendants are the largest emitters of carbon dioxide
  in the Nation. By contributing to global warming, the plaintiffs as
  serted, the defendants’ emissions substantially and unreasonably in
  terfered with public rights, in violation of the federal common law of
  interstate nuisance, or, in the alternative, of state tort law. All plain
  tiffs ask for a decree setting carbon-dioxide emissions for each defen
  dant at an initial cap, to be further reduced annually.
     The District Court dismissed both suits as presenting nonjusticia
  ble political questions, but the Second Circuit reversed. On the
  threshold questions, the Circuit held that the suits were not barred
  by the political question doctrine and that the plaintiffs had ade
2          AMERICAN ELEC. POWER CO. v. CONNECTICUT

                                  Syllabus

    quately alleged Article III standing. On the merits, the court held
    that the plaintiffs had stated a claim under the “federal common law
    of nuisance,” relying on this Court’s decisions holding that States
    may maintain suits to abate air and water pollution produced by
    other States or by out-of-state industry, see, e.g., Illinois v. Milwau
    kee, 

, 93 (Milwaukee I). The court further determined
    that the Clean Air Act did not “displace” federal common law.
Held:
    1. The Second Circuit’s exercise of jurisdiction is affirmed by an
 equally divided Court. P. 6.
    2. The Clean Air Act and the EPA action the Act authorizes dis
 place any federal common-law right to seek abatement of carbon
 dioxide emissions from fossil-fuel fired power plants. Pp. 6–16.
       (a) Since Erie R. Co. v. Tompkins, 

, 78, recognized
 that there “is no federal general common law,” a new federal common
 law has emerged for subjects of national concern. When dealing
 “with air and water in their ambient or interstate aspects, there is a
 federal common law.” Milwaukee 

. Decisions of
 this Court predating Erie, but compatible with the emerging distinc
 tion between general common law and the new federal common law,
 have approved federal common-law suits brought by one State to
 abate pollution emanating from another State. See, e.g., Missouri v.
 Illinois, 

, 241–243. The plaintiffs contend that their
 right to maintain this suit follows from such cases. But recognition
 that a subject is meet for federal law governance does not necessarily
 mean that federal courts should create the controlling law. The
 Court need not address the question whether, absent the Clean Air
 Act and the EPA actions it authorizes, the plaintiffs could state a
 federal common-law claim for curtailment of greenhouse gas emis
 sions because of their contribution to global warming. Any such
 claim would be displaced by the federal legislation authorizing EPA
 to regulate carbon-dioxide emissions. Pp. 6–9.
       (b) “[W]hen Congress addresses a question previously governed
 by a decision rested on federal common law the need for such an un
 usual exercise of law-making by federal courts disappears.” Milwau
 kee v. Illinois, 

, 314 (Milwaukee II). Legislative dis
 placement of federal common law does not require the “same sort of
 evidence of a clear and manifest [congressional] purpose” demanded
 for preemption of state law. 

Rather, the test is simply
 whether the statute “speak[s] directly to [the] question” at issue.
 Mobil Oil Corp. v. Higginbotham, 

, 625. Here, Massa
 chusetts made plain that emissions of carbon dioxide qualify as air
 pollution subject to regulation under the Clean Air 

–529. And it is equally plain that the Act “speaks directly” to
                   Cite as: 564 U. S. ____ (2011)                    3

                              Syllabus

emissions of carbon dioxide from the defendants’ plants. The Act di
rects EPA to establish emissions standards for categories of station
ary sources that, “in [the Administrator’s] judgment,” “caus[e], or
contribut[e] significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.” §7411(b)(1)(A).
Once EPA lists a category, it must establish performance standards
for emission of pollutants from new or modified sources within that
category, §7411(b)(1)(B), and, most relevant here, must regulate ex
isting sources within the same category, §7411(d). The Act also pro
vides multiple avenues for enforcement. If EPA does not set emis
sions limits for a particular pollutant or source of pollution, States
and private parties may petition for a rulemaking on the matter, and
EPA’s response will be reviewable in federal court. See §7607(b)(1).
The Act itself thus provides a means to seek limits on emissions of
carbon dioxide from domestic power plants—the same relief the
plaintiffs seek by invoking federal common law. There is no room for
a parallel track. Pp. 9–11.
     (c) The Court rejects the plaintiffs’ argument, and the Second
Circuit’s holding, that federal common law is not displaced until EPA
actually exercises its regulatory authority by setting emissions stan
dards for the defendants’ plants. The relevant question for displace
ment purposes is “whether the field has been occupied, not whether it
has been occupied in a particular manner.” Milwaukee 

. The Clean Air Act is no less an exercise of the Legislature’s
“considered judgment” concerning air pollution regulation because it
permits emissions until EPA acts. The critical point is that Congress
delegated to EPA the decision whether and how to regulate carbon
dioxide emissions from power plants; the delegation displaces federal
common law. If the plaintiffs in this case are dissatisfied with the
outcome of EPA’s forthcoming rulemaking, their recourse is to seek
Court of Appeals review, and, ultimately, to petition for certiorari.
   The Act’s prescribed order of decisionmaking—first by the expert
agency, and then by federal judges—is yet another reason to resist
setting emissions standards by judicial decree under federal tort law.
The appropriate amount of regulation in a particular greenhouse gas
producing sector requires informed assessment of competing inter
ests. The Clean Air Act entrusts such complex balancing to EPA in
the first instance, in combination with state regulators. The expert
agency is surely better equipped to do the job than federal judges,
who lack the scientific, economic, and technological resources an
agency can utilize in coping with issues of this order. The plaintiffs’
proposal to have federal judges determine, in the first instance, what
amount of carbon-dioxide emissions is “unreasonable” and what level
of reduction is necessary cannot be reconciled with Congress’ scheme.
4          AMERICAN ELEC. POWER CO. v. CONNECTICUT

                                  Syllabus

    Pp. 12–15.
         (d) The plaintiffs also sought relief under state nuisance law.
    The Second Circuit did not reach those claims because it held that
    federal common law governed. In light of the holding here that the
    Clean Air Act displaces federal common law, the availability vel non
    of a state lawsuit depends, inter alia, on the preemptive effect of the
    federal Act. Because none of the parties have briefed preemption or
    otherwise addressed the availability of a claim under state nuisance
    law, the matter is left for consideration on remand. Pp. 15–16.

, reversed and remanded.

   GINSBURG, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and SCALIA, KENNEDY, BREYER, and KAGAN, JJ., joined. ALITO, J.,
filed an opinion concurring in part and concurring in the judgment, in
which THOMAS, J., joined. SOTOMAYOR, J., took no part in the considera
tion or decision of the case.
                        Cite as: 564 U. S. ____ (2011)                              1

                             Opinion of the Court

     NOTICE: This opinion is subject to formal revision before publication in the
     preliminary print of the United States Reports. Readers are requested to
     notify the Reporter of Decisions, Supreme Court of the United States, Wash
     ington, D. C. 20543, of any typographical or other formal errors, in order
     that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                                   No. 10–174
                                   _________________


   AMERICAN ELECTRIC POWER COMPANY, INC., 

    ET AL., PETITIONERS v. CONNECTICUT ET AL. 


 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

           APPEALS FOR THE SECOND CIRCUIT

                                 [June 20, 2011] 


   JUSTICE GINSBURG delivered the opinion of the Court.
   We address in this opinion the question whether the
plaintiffs (several States, the city of New York, and three
private land trusts) can maintain federal common law
public nuisance claims against carbon-dioxide emitters
(four private power companies and the federal Tennessee
Valley Authority). As relief, the plaintiffs ask for a decree
setting carbon-dioxide emissions for each defendant at an
initial cap, to be further reduced annually. The Clean Air
Act and the Environmental Protection Agency action the
Act authorizes, we hold, displace the claims the plaintiffs
seek to pursue.
                             I
    In Massachusetts v. EPA, 

(2007), this
Court held that the Clean Air Act, 

. §7401 et
seq., authorizes federal regulation of emissions of carbon
dioxide and other greenhouse gases. “[N]aturally present
in the atmosphere and . . . also emitted by human activi
ties,” greenhouse gases are so named because they “trap
. . . heat that would otherwise escape from the [Earth’s]
atmosphere, and thus form the greenhouse effect that
2        AMERICAN ELEC. POWER CO. v. CONNECTICUT

                         Opinion of the Court

helps keep the Earth warm enough for life.” 74 Fed. Reg.
66499 (2009).1 Massachusetts held that the Environ
mental Protection Agency (EPA) had misread the Clean
Air Act when it denied a rulemaking petition seeking
controls on greenhouse gas emissions from new motor

–511. Greenhouse gases, we
determined, qualify as “air pollutant[s]” within the mean
ing of the governing Clean Air Act provision, 

529 (quoting §7602(g)); they are therefore within EPA’s
regulatory ken. Because EPA had authority to set green
house gas emission standards and had offered no “rea
soned explanation” for failing to do so, we concluded that
the agency had not acted “in accordance with law” when it
denied the requested rulemaking. 

(quot
ing §7607(d)(9)(A)).
   Responding to our decision in Massachusetts, EPA un
dertook greenhouse gas regulation. In December 2009,
the agency concluded that greenhouse gas emissions from
motor vehicles “cause, or contribute to, air pollution which
may reasonably be anticipated to endanger public health
or welfare,” the Act’s regulatory trigger. §7521(a)(1); 74
Fed. Reg. 66496. The agency observed that “atmospheric
greenhouse gas concentrations are now at elevated and
essentially unprecedented levels,” almost entirely “due to
anthropogenic emissions,” 

mean global
temperatures, the agency continued, demonstrate an
“unambiguous warming trend over the last 100 years,”
and particularly “over the past 30 years,” 

not all scientists agreed on the causes and
consequences of the rise in global temperatures, 

66518, 66523–66524, EPA concluded that “compel
ling” evidence supported the “attribution of observed
——————
  1 In addition to carbon dioxide, the primary greenhouse gases emitted

by human activities include methane, nitrous oxide, hydrofluorocar
bons, perfluorocarbons, and sulfur hexafluoride. 74 Fed. Reg. 66499.
                    Cite as: 564 U. S. ____ (2011)                   3

                         Opinion of the Court

climate change to anthropogenic” emissions of greenhouse
gases, 

Consequent dangers of greenhouse
gas emissions, EPA determined, included increases in
heat-related deaths; coastal inundation and erosion
caused by melting icecaps and rising sea levels; more
frequent and intense hurricanes, floods, and other “ex
treme weather events” that cause death and destroy infra
structure; drought due to reductions in mountain snow
pack and shifting precipitation patterns; destruction of
ecosystems supporting animals and plants; and potentially
“significant disruptions” of food production. 

66535.2
   EPA and the Department of Transportation subse
quently issued a joint final rule regulating emissions from
light-duty vehicles, see 75 Fed. Reg. 25324 (2010), and
initiated a joint rulemaking covering medium- and heavy
duty vehicles, see 

EPA also began phasing
in requirements that new or modified “[m]ajor [greenhouse
gas] emitting facilities” use the “best available control
technology.” §7475(a)(4); 75 Fed. Reg. 31520–31521. Fin
ally, EPA commenced a rulemaking under §111 of the Act,

. §7411, to set limits on greenhouse gas emis
sions from new, modified, and existing fossil-fuel fired
power plants. Pursuant to a settlement finalized in March
2011, EPA has committed to issuing a proposed rule by
July 2011, and a final rule by May 2012. See 75 Fed. Reg.
82392; Reply Brief for Tennessee Valley Authority 18.
                            II
  The lawsuits we consider here began well before EPA
initiated the efforts to regulate greenhouse gases just
described. In July 2004, two groups of plaintiffs filed
——————
  2 For views opposing EPA’s, see, e.g., Dawidoff, The Civil Heretic,
N. Y. Times Magazine 32 (March 29, 2009). The Court, we caution,
endorses no particular view of the complicated issues related to carbon
dioxide emissions and climate change.
4        AMERICAN ELEC. POWER CO. v. CONNECTICUT

                         Opinion of the Court

separate complaints in the Southern District of New York
against the same five major electric power companies.
The first group of plaintiffs included eight States3 and
New York City, the second joined three nonprofit land
trusts4; both groups are respondents here. The defen
dants, now petitioners, are four private companies5 and
the Tennessee Valley Authority, a federally owned corpo
ration that operates fossil-fuel fired power plants in sev
eral States. According to the complaints, the defendants
“are the five largest emitters of carbon dioxide in the
United States.” App. 57, 118. Their collective annual
emissions of 650 million tons constitute 25 percent of
emissions from the domestic electric power sector, 10
percent of emissions from all domestic human activities,
ibid., and 2.5 percent of all anthropogenic emissions
worldwide, App. to Pet. for Cert. 72a.
  By contributing to global warming, the plaintiffs as
serted, the defendants’ carbon-dioxide emissions created
a “substantial and unreasonable interference with public
rights,” in violation of the federal common law of inter
state nuisance, or, in the alternative, of state tort law.
App. 103–105, 145–147. The States and New York City
alleged that public lands, infrastructure, and health were
at risk from climate change. App. 88–93. The trusts
urged that climate change would destroy habitats for
animals and rare species of trees and plants on land the
trusts owned and conserved. App. 139–145. All plaintiffs
sought injunctive relief requiring each defendant “to cap

——————
  3 California, Connecticut, Iowa, New Jersey, New York, Rhode Island,

Vermont, and Wisconsin, although New Jersey and Wisconsin are no
longer participating. Brief for Respondents Connecticut et al. 3, n. 1.
  4 Open Space Institute, Inc., Open Space Conservancy, Inc., and

Audubon Society of New Hampshire.
  5 American Electric Power Company, Inc. (and a wholly owned subsidi

ary), Southern Company, Xcel Energy Inc., and Cinergy Corporation.
                 Cite as: 564 U. S. ____ (2011)           5

                     Opinion of the Court

 its carbon dioxide emissions and then reduce them by a
specified percentage each year for at least a decade.” App.
110, 153.
   The District Court dismissed both suits as presenting
non-justiciable political questions, citing Baker v. Carr,

(1962), but the Second Circuit reversed, 

(2009). On the threshold questions, the Court of
Appeals held that the suits were not barred by the politi
cal question doctrine, 

and that the plaintiffs
had adequately alleged Article III standing, 

   Turning to the merits, the Second Circuit held that all
plaintiffs had stated a claim under the “federal common
law of nuisance.” 

371. For this determination,
the court relied dominantly on a series of this Court’s
decisions holding that States may maintain suits to abate
air and water pollution produced by other States or by out
of-state industry. 

see, e.g., Illinois v.
Milwaukee, 

, 93, (1972) (Milwaukee I) (recog
nizing right of Illinois to sue in federal district court to
abate discharge of sewage into Lake Michigan).
   The Court of Appeals further determined that the Clean
Air Act did not “displace” federal common law. In Mil
waukee v. Illinois, 

, 316–319 (1981) (Milwau
kee II), this Court held that Congress had displaced the
federal common law right of action recognized in Milwau
kee I by adopting amendments to the Clean Water Act, 

. §1251 et seq. That legislation installed an all
encompassing regulatory program, supervised by an ex
pert administrative agency, to deal comprehensively with
interstate water pollution. The legislation itself prohib
ited the discharge of pollutants into the waters of the
United States without a permit from a proper permitting
authority. Milwaukee 

–311 (citing
§1311). At the time of the Second Circuit’s decision, by
contrast, EPA had not yet promulgated any rule regulat
ing greenhouse gases, a fact the court thought dispositive.
6        AMERICAN ELEC. POWER CO. v. CONNECTICUT

                         Opinion of the 

–381. “Until EPA completes the rulemak
ing process,” the court reasoned, “we cannot speculate
as to whether the hypothetical regulation of greenhouse
gases under the Clean Air Act would in fact ‘spea[k] di
rectly’ to the ‘particular issue’ raised here by Plaintiffs.”

  We granted certiorari. 562 U. S. ___ (2010).
                              III
  The petitioners contend that the federal courts lack au
thority to adjudicate this case. Four members of the
Court would hold that at least some plaintiffs have Article
III standing under Massachusetts, which permitted a
State to challenge EPA’s refusal to regulate greenhouse
gas 

–526; and, further, that no
other threshold obstacle bars review.6 Four members of
the Court, adhering to a dissenting opinion in Massachu

, or regarding that decision as dis
tinguishable, would hold that none of the plaintiffs have
Article III standing. We therefore affirm, by an equally
divided Court, the Second Circuit’s exercise of jurisdiction
and proceed to the merits. See Nye v. United States, 

, 44 (1941).
                            IV 

                             A

  “There is no federal general common law,” Erie R. Co. v.
Tompkins, 

, 78 (1938), famously recognized.
In the wake of Erie, however, a keener understanding
developed. See generally Friendly, In Praise of Erie—And
of the New Federal Common Law, 39 N. Y. U. L. Rev. 383
——————
  6 In addition to renewing the political question argument made below,

the petitioners now assert an additional threshold obstacle: They seek
dismissal because of a “prudential” bar to the adjudication of general
ized grievances, purportedly distinct from Article III’s bar. See Brief
for Tennessee Valley Authority 14–24; Brief for Petitioners 30–31.
                 Cite as: 564 U. S. ____ (2011)            7

                     Opinion of the Court

(1964). Erie “le[ft] to the states what ought be left to
them,” 

and thus required “federal courts [to]
follow state decisions on matters of substantive law ap
propriately cognizable by the states,” 

Erie also
sparked “the emergence of a federal decisional law in
areas of national concern.” 

The “new” federal
common law addresses “subjects within national legisla
tive power where Congress has so directed” or where the
basic scheme of the Constitution so demands. 

n. 119, 421–422. Environmental protection is undoubtedly
an area “within national legislative power,” one in which
federal courts may fill in “statutory interstices,” and, if
necessary, even “fashion federal law.” 

As
the Court stated in Milwaukee I: “When we deal with air
and water in their ambient or interstate aspects, there is a
federal common 

.
   Decisions of this Court predating Erie, but compatible
with the distinction emerging from that decision between
“general common law” and “specialized federal common
law,” 

, have approved federal com
mon law suits brought by one State to abate pollution
emanating from another State. See, e.g., Missouri v.
Illinois, 

, 241–243 (1901) (permitting suit by
Missouri to enjoin Chicago from discharging untreated
sewage into interstate waters); New Jersey v. City of
New York, 

, 477, 481–483 (1931) (ordering
New York City to stop dumping garbage off New Jersey
coast); Georgia v. Tennessee Copper Co., 

(1916)
(ordering private copper companies to curtail sulfur
dioxide discharges in Tennessee that caused harm in
Georgia). See also Milwaukee 

(post-
Erie decision upholding suit by Illinois to abate sewage
discharges into Lake Michigan). The plaintiffs contend
that their right to maintain this suit follows inexorably
from that line of decisions.
   Recognition that a subject is meet for federal law gov
8      AMERICAN ELEC. POWER CO. v. CONNECTICUT

                     Opinion of the Court

ernance, however, does not necessarily mean that federal
courts should create the controlling law. Absent a demon
strated need for a federal rule of decision, the Court has
taken “the prudent course” of “adopt[ing] the readymade
body of state law as the federal rule of decision until Con
gress strikes a different accommodation.” United States v.
Kimbell Foods, Inc., 

, 740 (1979); see Bank of
America Nat. Trust & Sav. Assn. v. Parnell, 

,
32–34 (1956). And where, as here, borrowing the law of a
particular State would be inappropriate, the Court re
mains mindful that it does not have creative power akin to
that vested in Congress. See Missouri v. Illinois, 

, 519 (1906) (“fact that this court must decide does not
mean, of course, that it takes the place of a legislature”);
cf. United States v. Standard Oil Co. of Cal., 

,
308, 314 (1947) (holding that federal law determines
whether Government could secure indemnity from a com
pany whose truck injured a United States soldier, but
declining to impose such an indemnity absent action by
Congress, “the primary and most often the exclusive arbi
ter of federal fiscal affairs”).
   In the cases on which the plaintiffs heavily rely, States
were permitted to sue to challenge activity harmful to
their citizens’ health and welfare. We have not yet de
cided whether private citizens (here, the land trusts) or
political subdivisions (New York City) of a State may
invoke the federal common law of nuisance to abate out-of
state pollution. Nor have we ever held that a State may
sue to abate any and all manner of pollution originating
outside its borders.
   The defendants argue that considerations of scale and
complexity distinguish global warming from the more
bounded pollution giving rise to past federal nuisance
suits. Greenhouse gases once emitted “become well mixed
in the atmosphere,” 74 Fed. Reg. 66514; emissions in New
Jersey may contribute no more to flooding in New York
                 Cite as: 564 U. S. ____ (2011)            9

                     Opinion of the Court

than emissions in China. Cf. Brief for Petitioners 18–19.
The plaintiffs, on the other hand, contend that an equita
ble remedy against the largest emitters of carbon dioxide
in the United States is in order and not beyond judicial
competence. See Brief for Respondents Open Space In
stitute et al. 32–35. And we have recognized that public
nuisance law, like common law generally, adapts to chang
ing scientific and factual circumstances. 

(adjudicating claim though it did not concern
“nuisance of the simple kind that was known to the older
common law”); see also D’Oench, Duhme & Co. v. FDIC,

, 472 (1942) (Jackson, J., concurring) (“fed
eral courts are free to apply the traditional common-law
technique of decision” when fashioning federal common
law).
  We need not address the parties’ dispute in this regard.
For it is an academic question whether, in the absence of
the Clean Air Act and the EPA actions the Act authorizes,
the plaintiffs could state a federal common law claim for
curtailment of greenhouse gas emissions because of their
contribution to global warming. Any such claim would be
displaced by the federal legislation authorizing EPA to
regulate carbon-dioxide emissions.
                             B
   “[W]hen Congress addresses a question previously gov
erned by a decision rested on federal common law,” the
Court has explained, “the need for such an unusual exer
cise of law-making by federal courts disappears.” Mil
waukee 

(holding that amendments to
the Clean Water Act displaced the nuisance claim recog
nized in Milwaukee I). Legislative displacement of federal
common law does not require the “same sort of evidence of
a clear and manifest [congressional] purpose” demanded
for preemption of state law. 

“ ‘[D]ue regard for
the presuppositions of our embracing federal system . . . as
10          AMERICAN ELEC. POWER CO. v. CONNECTICUT

                         Opinion of the Court

a promoter of democracy,’ ” 

(quoting San Diego
Building Trades Council v. Garmon, 

, 243
(1959)), does not enter the calculus, for it is primarily
the office of Congress, not the federal courts, to prescribe
national policy in areas of special federal interest. TVA v.
Hill, 

, 194 (1978). The test for whether
congressional legislation excludes the declaration of fed
eral common law is simply whether the statute “speak[s]
directly to [the] question” at issue. Mobil Oil Corp. v.
Higginbotham, 

, 625 (1978); see Milwaukee

; County of Oneida v. Oneida Indian
Nation of N. Y., 

, 236–237 (1985).
   We hold that the Clean Air Act and the EPA actions it
authorizes displace any federal common law right to seek
abatement of carbon-dioxide emissions from fossil-fuel
fired power plants. Massachusetts made plain that emis
sions of carbon dioxide qualify as air pollution subject to
regulation under the 

–529. And we
think it equally plain that the Act “speaks directly” to
emissions of carbon dioxide from the defendants’ plants.
   Section 111 of the Act directs the EPA Administrator to
list “categories of stationary sources” that “in [her] judg
ment . . . caus[e], or contribut[e] significantly to, air pol
lution which may reasonably be anticipated to endanger
public health or welfare.” §7411(b)(1)(A). Once EPA lists
a category, the agency must establish standards of per
formance for emission of pollutants from new or modified
sources within that category. §7411(b)(1)(B); see also
§7411(a)(2). And, most relevant here, §7411(d) then re
quires regulation of existing sources within the same
category.7 For existing sources, EPA issues emissions

——————
  7 There is an exception: EPA may not employ §7411(d) if existing
stationary sources of the pollutant in question are regulated under the
national ambient air quality standard program, §§7408–7410, or the
“hazardous air pollutants” program, §7412. See §7411(d)(1).
                 Cite as: 564 U. S. ____ (2011)          11

                     Opinion of the Court

guidelines, see 40 C. F. R. §60.22, .23 (2009); in compli
ance with those guidelines and subject to federal over
sight, the States then issue performance standards for
stationary sources within their jurisdiction, §7411(d)(1).
   The Act provides multiple avenues for enforcement. See
County of 

–239 (reach of remedial
provisions is important to determination whether statute
displaces federal common law). EPA may delegate im
plementation and enforcement authority to the States,
§7411(c)(1), (d)(1), but the agency retains the power to in
spect and monitor regulated sources, to impose adminis
trative penalties for noncompliance, and to commence civil
actions against polluters in federal court. §§7411(c)(2),
(d)(2), 7413, 7414. In specified circumstances, the Act im
poses criminal penalties on any person who knowingly
violates emissions standards issued under §7411. See
§7413(c). And the Act provides for private enforcement. If
States (or EPA) fail to enforce emissions limits against
regulated sources, the Act permits “any person” to bring a
civil enforcement action in federal court. §7604(a).
   If EPA does not set emissions limits for a particular pol
lutant or source of pollution, States and private parties
may petition for a rulemaking on the matter, and EPA’s
response will be reviewable in federal court.            See
§7607(b)(1); 

–517, 529. As
earlier noted, 

, EPA is currently engaged in
a §7411 rulemaking to set standards for greenhouse gas
emissions from fossil-fuel fired power plants. To settle
litigation brought under §7607(b) by a group that included
the majority of the plaintiffs in this very case, the agency
agreed to complete that rulemaking by May 2012. 75 Fed.
Reg. 82392. The Act itself thus provides a means to seek
limits on emissions of carbon dioxide from domestic power
plants—the same relief the plaintiffs seek by invoking
federal common law. We see no room for a parallel track.
12     AMERICAN ELEC. POWER CO. v. CONNECTICUT

                     Opinion of the Court

                             C
   The plaintiffs argue, as the Second Circuit held, that
federal common law is not displaced until EPA actually
exercises its regulatory authority, i.e., until it sets stan
dards governing emissions from the defendants’ plants.
We disagree.
   The sewage discharges at issue in Milwaukee II, we do
not overlook, were subject to effluent limits set by EPA;
under the displacing statute, “[e]very point source dis
charge” of water pollution was “prohibited unless covered
by a 

–320 (emphasis deleted).
As Milwaukee II made clear, however, the relevant ques
tion for purposes of displacement is “whether the field
has been occupied, not whether it has been occupied in a
particular manner.” 

Of necessity, Congress se
lects different regulatory regimes to address different
problems. Congress could hardly preemptively prohibit
every discharge of carbon dioxide unless covered by a
permit. After all, we each emit carbon dioxide merely by
breathing.
   The Clean Air Act is no less an exercise of the legisla
ture’s “considered judgment” concerning the regulation of
air pollution because it permits emissions until EPA
acts. See Middlesex County Sewerage Authority v. National
Sea Clammers Assn., 

, 22, n. 32 (1981) (finding
displacement although Congress “allowed some continued
dumping of sludge” prior to a certain date). The critical
point is that Congress delegated to EPA the decision
whether and how to regulate carbon-dioxide emissions
from power plants; the delegation is what displaces federal
common law. Indeed, were EPA to decline to regulate
carbon-dioxide emissions altogether at the conclusion of its
ongoing §7411 rulemaking, the federal courts would have
no warrant to employ the federal common law of nuisance
to upset the agency’s expert determination.
   EPA’s judgment, we hasten to add, would not escape
                 Cite as: 564 U. S. ____ (2011)          13

                     Opinion of the Court

judicial review. Federal courts, we earlier observed, 

, can review agency action (or a final rule
declining to take action) to ensure compliance with the
statute Congress enacted. As we have noted, 

, the Clean Air Act directs EPA to establish emis-
sions standards for categories of stationary sources that,
“in [the Administrator’s] judgment,” “caus[e], or contri
but[e] significantly to, air pollution which may reasonably
be anticipated to endanger public health or welfare.”
§7411(b)(1)(A). “[T]he use of the word ‘judgment,’ ” we
explained in Massachusetts, “is not a roving license to
ignore the statutory 

. “It is but a
direction to exercise discretion within defined statutory
limits.” 

decline to regulate carbon
dioxide emissions from power plants if refusal to act would
be “arbitrary, capricious, an abuse of discretion, or other
wise not in accordance with law.” §7607(d)(9)(A). If the
plaintiffs in this case are dissatisfied with the outcome
of EPA’s forthcoming rulemaking, their recourse under
federal law is to seek Court of Appeals review, and, ulti
mately, to petition for certiorari in this Court.
   Indeed, this prescribed order of decisionmaking—the
first decider under the Act is the expert administrative
agency, the second, federal judges—is yet another reason
to resist setting emissions standards by judicial decree
under federal tort law. The appropriate amount of regula
tion in any particular greenhouse gas-producing sector
cannot be prescribed in a vacuum: as with other questions
of national or international policy, informed assessment of
competing interests is required. Along with the environ
mental benefit potentially achievable, our Nation’s energy
needs and the possibility of economic disruption must
weigh in the balance.
   The Clean Air Act entrusts such complex balancing to
EPA in the first instance, in combination with state regu
lators. Each “standard of performance” EPA sets must
14     AMERICAN ELEC. POWER CO. v. CONNECTICUT

                     Opinion of the Court

“tak[e] into account the cost of achieving [emissions] re
duction and any nonair quality health and environmental
impact and energy requirements.” §7411(a)(1), (b)(1)(B),
(d)(1); see also 40 C. F. R. §60.24(f) (EPA may permit
state plans to deviate from generally applicable emissions
standards upon demonstration that costs are “[u]n
reasonable”).     EPA may “distinguish among classes,
types, and sizes” of stationary sources in apportioning
responsibility for emissions reductions. §7411(b)(2), (d);
see also 40 C. F. R. §60.22(b)(5). And the agency may
waive compliance with emission limits to permit a facility
to test drive an “innovative technological system” that has
“not [yet] been adequately demonstrated.” §7411(j)(1)(A).
The Act envisions extensive cooperation between federal
and state authorities, see §7401(a), (b), generally permit
ting each State to take the first cut at determining how
best to achieve EPA emissions standards within its do
main, see §7411(c)(1), (d)(1)–(2).
   It is altogether fitting that Congress designated an ex
pert agency, here, EPA, as best suited to serve as pri-
mary regulator of greenhouse gas emissions. The expert
agency is surely better equipped to do the job than indi
vidual district judges issuing ad hoc, case-by-case injunc
tions. Federal judges lack the scientific, economic, and
technological resources an agency can utilize in coping
with issues of this order. See generally Chevron U. S. A.
Inc. v. Natural Resources Defense Council, Inc., 

, 865–866 (1984). Judges may not commission scien
tific studies or convene groups of experts for advice, or
issue rules under notice-and-comment procedures inviting
input by any interested person, or seek the counsel of
regulators in the States where the defendants are located.
Rather, judges are confined by a record comprising the
evidence the parties present. Moreover, federal district
judges, sitting as sole adjudicators, lack authority to ren
der precedential decisions binding other judges, even
                 Cite as: 564 U. S. ____ (2011)           15

                     Opinion of the Court

members of the same court.
  Notwithstanding these disabilities, the plaintiffs pro
pose that individual federal judges determine, in the first
instance, what amount of carbon-dioxide emissions is
“unreasonable,” App. 103, 145, and then decide what level
of reduction is “practical, feasible and economically vi
able,” App. 58, 119. These determinations would be made
for the defendants named in the two lawsuits launched by
the plaintiffs. Similar suits could be mounted, counsel for
the States and New York City estimated, against “thou
sands or hundreds or tens” of other defendants fitting the
description “large contributors” to carbon-dioxide emis
sions. Tr. of Oral Arg. 57.
  The judgments the plaintiffs would commit to federal
judges, in suits that could be filed in any federal district,
cannot be reconciled with the decisionmaking scheme
Congress enacted. The Second Circuit erred, we hold, in
ruling that federal judges may set limits on greenhouse
gas emissions in face of a law empowering EPA to set the
same limits, subject to judicial review only to ensure
against action “arbitrary, capricious, . . . or otherwise not
in accordance with law.” §7607(d)(9).
                              V
   The plaintiffs also sought relief under state law, in
particular, the law of each State where the defendants
operate power plants. See App. 105, 147. The Second
Circuit did not reach the state law claims because it held
that federal common law 

; see
International Paper Co. v. Ouellette, 

, 488
(1987) (if a case “should be resolved by reference to federal
common law[,] . . . state common law [is] preempted”). In
light of our holding that the Clean Air Act displaces fed
eral common law, the availability vel non of a state law
suit depends, inter alia, on the preemptive effect of the
federal Act. 

491, 497 (holding that the Clean
16     AMERICAN ELEC. POWER CO. v. CONNECTICUT

                     Opinion of the Court

Water Act does not preclude aggrieved individuals from
bringing a “nuisance claim pursuant to the law of the
source State”). None of the parties have briefed preemp
tion or otherwise addressed the availability of a claim
under state nuisance law. We therefore leave the matter
open for consideration on remand.
                        *     *    *
  For the reasons stated, we reverse the judgment of the
Second Circuit and remand the case for further proceed
ings consistent with this opinion.
                                          It is so ordered.

  JUSTICE SOTOMAYOR took no part in the consideration
or decision of this case.
                Cite as: 564 U. S. ____ (2011)         1

                     Opinion of ALITO, J.

SUPREME COURT OF THE UNITED STATES
                        _________________

                         No. 10–174
                        _________________


   AMERICAN ELECTRIC POWER COMPANY, INC., 

    ET AL., PETITIONERS v. CONNECTICUT ET AL. 


 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

           APPEALS FOR THE SECOND CIRCUIT

                       [June 20, 2011] 


  JUSTICE ALITO, with whom JUSTICE THOMAS joins,
concurring in part and concurring in the judgment.
  I concur in the judgment, and I agree with the Court’s
displacement analysis on the assumption (which I make
for the sake of argument because no party contends oth
erwise) that the interpretation of the Clean Air Act, 

. §7401 et seq., adopted by the majority in Massa
chusetts v. EPA, 

(2007), is correct.