Amicus Curiae Brief — Suncor Energy (U.S.A.) Inc., et al., Petitioners v. County Commissioners of Boulder County, et al.
Supreme Court briefMay 21, 2026
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No. 25-170
In the Supreme Court of the United States
SUNCOR ENERGY (U.S.A.) INC.; SUNCOR ENERGY
SALES INC.; EXXON MOBIL CORPORATION,
Petitioners,
v.
COUNTY COMMISSIONERS OF BOULDER COUNTY;
CITY OF BOULDER,
Respondents.
ON WRIT OF CERTIORARI TO THE
SUPREME COURT OF COLORADO
BRIEF FOR THE AMERICAN PETROLEUM
INSTITUTE AS AMICUS CURIAE
IN SUPPORT OF PETITIONERS
MARK A. PERRY
Counsel of Record
BRADY D. MORRIS
WEIL, GOTSHAL & MANGES LLP
2001 M Street NW
Suite 600
Washington, D.C. 20036
(202) 682-7000
Mark.Perry@weil.com
SARAH M. STERNLIEB
WEIL, GOTSHAL & MANGES LLP
1395 Brickell Avenue
Suite 1200
Miami, FL 33131
Counsel for Amicus Curiae
American Petroleum Institute
May 21, 2026
WILSON-E PES PRINTING CO., INC. – (202) 789-0096 – WASHINGTON, D.C. 20002
i
TABLE OF CONTENTS
Page
TABLE OF AUTHORITIES ...........................................ii
INTERESTS OF THE AMICUS CURIAE ................... 1
QUESTION ADDRESSED BY THE AMICUS ............ 3
SUMMARY OF ARGUMENT ........................................ 3
ARGUMENT .................................................................... 7
I. This case is symptomatic of a rash of statelaw climate change litigation ................................ 7
A. Climate litigation trends post-American
Electric Power illuminate the problem ........... 8
B. State statutes and private rights of action
compound the problem, subjecting energy
companies to innumerable different
liability regimes ............................................ 12
II. Climate change litigation cannot proceed
under state law ..................................................... 15
A. Respondents’ claims are premised on outof-state greenhouse gas emissions ................. 15
B. The regulation of interstate emissions is
an inherently federal domain ........................ 18
C. Allowing Respondents’ claims would
interfere with federal energy, economic,
and foreign policy ............................................ 23
1. Expansive extraterritorial
regulation is untenable .............................. 23
2. Blessing Respondents’ theories
would likely have dire economic
consequences ............................................... 26
3. Foreign affairs and national security
require exclusive federal control ............... 28
CONCLUSION ........................................................... 31
(i)
ii
TABLE OF AUTHORITIES
CASES ................................................................................Page(s)
Alabama v. California, No. 158 (Original)
(U.S., filed May 22, 2024), motion for
leave to file a bill of complaint denied,
145 S. Ct. 757 (2025) ......................................... 11
Am. Elec. Power Co. v. Connecticut,
564 U.S. 410 (2011) ....... 5, 8, 9, 10, 18, 19, 22, 23
Am. Ins. Ass’n v. Garamendi,
539 U.S. 396 (2003) ........................................... 28
Anne Arundel County v. BP p.l.c., No. C-02CV-21-000565 (Md. Cir. Ct.) ............................... 7
Bucks County v. BP P.L.C.,
No. 2024-01836 (Pa. Ct. C.P. May 16,
2025) .............................................................. 8, 11
California v. Exxon Mobil Corp., No.
CGC23609134 (Cal. Super. Ct.) .......................... 7
California v. Gen. Motors Corp.,
No. C06-05755 MJJ, 2007 WL 2726871
(N.D. Cal. Sept. 17, 2007) ................................... 9
California ex rel. Herrera v. BP p.l.c., No.
CGC-17-561370 (Cal. Super. Ct.) ....................... 8
California ex rel. Oakland City Att’y v. BP
p.l.c., No. RG17875889 (Cal. Super. Ct.) ............ 8
Chevron USA Inc. v. Plaquemines Par.,
Louisiana,
146 S. Ct. 1052 (2026) ....................................... 29
City & County of Honolulu v. Sunoco LP,
537 P.3d 1173 (Haw. 2023) ......................... 10, 11
iii
TABLE OF AUTHORITIES — Continued
Page(s)
City and County of Honolulu v. Sunoco LP,
No. 1CCV-20-0000380 (JPC), 2022 WL
22866746 (Haw. Cir. Ct. Mar. 29, 2022)............. 8
City and County of Honolulu v. Sunoco LP,
No. 1CCV-20-0000380 (JPC), 2022 WL
22866745 (Haw. Cir. Ct. Mar. 31, 2022)............. 8
City of Annapolis v. BP p.l.c., No. C-02-CV21-000250 (Md. Cir. Ct.) ..................................... 7
City of Charleston v. Brabham Oil Co., Inc.,
No. 2020-CP-10-03975, 2025 WL
2269770 (S.C. Ct. C.P. Aug. 6, 2025) ............ 7, 11
City of Chicago v. BP p.l.c., No.
2024CH01024 (Ill. Cir. Ct.) ................................. 7
City of Hoboken v. Exxon Mobil Corp., No.
HUD-L-003179-20 (N.J. Super. Ct.) ................... 7
City of Imperial Beach v. Chevron Corp.,
No. C17-01227 (Cal. Super. Ct.) ......................... 8
City of Milwaukee v. Illinois & Michigan,
451 U.S. 304 (1981) ........................... 5, 19, 23, 25
City of New York v. Chevron Corp.,
993 F.3d 81 (2d Cir. 2021) ................. 5, 10, 18, 29
City of Richmond v. Chevron Corp., No.
C18-00055 (Cal. Super. Ct.) ................................ 7
City of Santa Cruz v. Chevron Corp., No.
17CV03243 (Cal. Super. Ct.) ............................... 8
Comer v. Murphy Oil USA, Inc.,
718 F.3d 460 (5th Cir. 2013) ............................... 9
iv
TABLE OF AUTHORITIES — Continued
Page(s)
Comer v. Murphy Oil USA, Inc.,
839 F. Supp. 2d 849 (S.D. Miss. 2012),
aff’d, 718 F.3d 460 (5th Cir. 2013) ...................... 9
Connecticut v. Am. Elec. Power Co.,
406 F. Supp. 2d 265 (S.D.N.Y. 2005),
vacated and remanded, 582 F.3d 309
(2d Cir. 2009), rev’d, 564 U.S. 410 (2011) ........... 9
County of Marin v. Chevron Corp., No.
CIV1702586 (Cal. Super. Ct.) ............................. 8
County of Multnomah v. Exxon Mobil
Corp., No. 23CV25164 (Or. Cir. Ct. June
22, 2023) ........................................................ 7, 26
County of San Mateo v. Chevron Corp., No.
17CIV03222 (Cal. Super. Ct.) ............................. 8
County of Santa Cruz v. Chevron Corp., No.
17CV03242 (Cal. Super. Ct.) ............................... 8
Delaware ex rel. Jennings v. BP Am. Inc.,
No. N20C-09-097, 2024 WL 98888 (Del.
Super. Ct. Jan. 9, 2024)................................. 1, 10
Estado Libre Asociado de Puerto Rico v. Exxon Mobil Corp., No. SJ2024CV06512
(P.R. Super. Ct.) .................................................. 8
Fuel Industry Climate Cases, No. CJC-24005310 (Cal. Super. Ct. Apr. 14, 2026) ............. 11
Illinois v. City of Milwaukee,
406 U.S. 91 (1972) ................. 5, 18, 19, 20, 21, 25
Illinois v. City of Milwaukee,
731 F.2d 403 (7th Cir. 1984), cert.
denied, 469 U.S. 1196 (1985) ............................ 19
v
TABLE OF AUTHORITIES — Continued
Page(s)
Int’l Paper Co. v. Ouellette,
479 U.S. 481 (1987) ............... 8, 19, 20, 22, 23, 25
Leon v. Exxon Mobil Corp., No. 25-2-159868 (Wash. Super. Ct.) ............................................ 7
Makah Indian Tribe v. Exxon Mobil Corp.,
No. 23-2-25216-1 (Wash. Super. Ct.) .................. 7
Mayor & City Council of Balt. v. BP p.l.c.,
No. 24-C-18-004219 (Md. Cir. Ct.) ...................... 8
Mayor & City Council of Baltimore v. B.P.
P.L.C.,
353 A.3d 1142 (Md. 2026) ............................. 5, 10
Minnesota v. Am. Petroleum Inst.,
63 F.4th 703 (8th Cir. 2023).................. 16, 17, 25
Minnesota v. Am. Petroleum Inst.,
No. 62-CV-20-3837 (Minn. Dist. Ct.) .............. 1, 8
Native Village of Kivalina v. ExxonMobil
Corp.,
696 F.3d 849 (9th Cir. 2012) ............................... 9
Platkin v. Exxon Mobil Corp.,
No. MER-L-001797-22, 2025 WL 604846
(N.J. Super. Ct. Law Div. Feb. 5, 2025).......... 7, 0
Rhode Island v. Chevron Corp., No. PC2018-4716 (R.I. Super. Ct.) ................................. 7
Texas v. Pankey,
441 F.2d 236 (10th Cir. 1971) ........................... 19
United States v. Hawaii,
No. CV 25-00179 HG-WRP, 2026 WL
1021227 (D. Haw. Apr. 15, 2026) ...................... 12
vi
TABLE OF AUTHORITIES — Continued
Page(s)
United States v. Michigan,
817 F. Supp. 3d 630 (W.D. Mich. 2026) ............ 12
United States v. Minnesota,
No. 26-cv-2456 (D. Minn. May 4, 2026) ............ 11
West Virginia v. EPA,
597 U.S. 697 (2022) ........................................... 21
STATUTES, BILLS, & LEGISLATIVE MATERIALS
10 V.S.A. §§ 596-599c ............................................. 13
42 U.S.C. §§ 7401 et seq. ......................................... 25
Cal S.B. 982, 2025-2026 Reg. Sess. ........................ 14
Haw. S.B. 3000, 33d Leg., Reg. Sess. (2026) ......... 14
N.Y. Env’t Conserv. Law art. 76 ............................ 12
N.Y. Env’t Conserv. Law § 76-0103 ....................... 13
S.824, 2025-2026 Leg., Reg. Sess. (N.Y.
2025) .................................................................. 12
2024 Vt. Acts & Resolves No. 122 .......................... 13
OTHER AUTHORITIES
Bill History, SB-982 Climate disasters: civil
actions, Cal. Legis. Info. (Apr. 23, 2026) .......... 14
Clifford Krauss, Europe and the U.S. Make
Ambitious Plans to Reduce Reliance on
Russian Gas, N.Y. Times, Mar. 25, 2022 ......... 30
Energy’s Vital Role in World War II Offers
Lessons For Today, Am. Oil & Gas Rep.
(Oct. 2023) ......................................................... 30
vii
TABLE OF AUTHORITIES — Continued
Page(s)
Establishing Accountability for Climate
Change Damages: Lessons from Tobacco
Control, Summary of the Workshop on
Climate Accountability, Public Opinion,
and Legal Strategies, Union of Concerned Scientists & Climate Accountability Inst. (Oct. 2012) ....................................... 10
Iran War Energy Cost Tracker, Climate Solutions Lab at Brown University ...................... 28
Michael Froman, Iran, the Strait of Hormuz, and an Unprecedented Energy
Crunch, Council on Foreign Relations
(Mar. 13, 2026) .................................................. 31
Nat’l Petroleum Council, A National Oil
Policy for the United States (1949) ................... 30
Restatement (Second) of Torts § 821B
(1979) ................................................................. 21
Sources of Greenhouse Gas Emissions, U.S.
Env’t Prot. Agency ............................................. 20
U.S. Dep’t of Agric., Impacts of Higher Energy Prices on Agriculture and Rural
Economies (Aug. 2011) ...................................... 27
U.S. Dep’t of Energy, U.S. Oil and Natural
Gas: Providing Energy Security and
Supporting Our Quality of Life (Sept.
2020) .................................................................. 28
U.S. Dep’t of Transp., Bureau of Transp.
Stats., Inflation and Transportation ................ 27
viii
TABLE OF AUTHORITIES — Continued
Page(s)
U.S. Energy Info. Admin., Natural gas explained, Use of natural gas ............................... 26
U.S. Energy Info. Admin., Use of energy explained ............................................................... 26
U.S. Energy Info. Admin., Use of energy explained, Energy use for transportation ............. 27
What are the trends in greenhouse gas emissions and concentrations and their impacts on human health and the environment?, U.S. Env’t Prot. Agency ......................... 20
William Brangham & Dorothy Hastings,
California Sues Oil Companies for Exacerbating Climate Change, PBS News
Hour (Sept. 20, 2023) (comments of Rob
Bonta, Attorney General of Cal.) ...................... 26
World Bank, Commodity Markets Outlook
(Apr. 2022) ......................................................... 28
INTERESTS OF THE AMICUS CURIAE1
The American Petroleum Institute (“API”) is a nationwide, non-profit trade association that represents
approximately 600 companies involved in every aspect
of the petroleum and natural-gas industry. Its members
range from the largest integrated companies to the
smallest independent oil and gas producers. API’s
members include producers, refiners, suppliers, marketers, pipeline operators, and marine transporters, as well
as service and supply companies that support the industry. API is also the leading body for establishing standards that govern the oil and natural-gas industry.
This case is one of many that have been brought
against petroleum and natural-gas companies ostensibly on behalf of state and local governments, often represented by the same private counsel. Although API is
not a party to this case, API has been named as a defendant in other cases, in which the plaintiffs contend
that API’s exercise of its First Amendment rights to advocate and petition the government on behalf of its
members is a basis for tort liability. See, e.g., Minnesota
v. Am. Petroleum Inst., No. 62-CV-20-3837 (Minn. Dist.
Ct.); Delaware ex rel. Jennings v. BP Am. Inc., No.
N20C-09-097 (Del. Super. Ct.). More broadly, the
Court’s resolution of this case will have implications for
the entire petroleum and natural-gas industry, including API’s members, and thus API has a concrete interest
1 Pursuant to Supreme Court Rule 37.6, amicus states that no
counsel for a party authored this brief in whole or in part and that
no person other than amicus, its members, or its counsel made any
monetary contributions intended to fund the preparation or submission of this brief.
(1)
2
in ensuring that state tort law is not misused to target
its members for extraterritorial conduct that is properly
subject only to federal regulation.
This suit, and others like it, is an effort to impose
policy preferences and regulatory control, at the state
and local level, over a small subset of the alleged contributors to the global phenomenon of climate change.
At bottom, Respondents seek money damages under
state tort law based on greenhouse gas emissions. Interstate emissions, however, have long been governed
exclusively by federal law because they occupy an inherently federal domain that states and municipalities do
not have the authority to regulate. In API’s view, the
contrary decision of the Colorado Supreme Court in this
case conflicts with a century of this Court’s precedent,
and it should be rejected.
In response to increasing concerns about climate
change, API has advocated for considered and evidencebased policies at the national level that support research and the ongoing transition to cleaner energy.
API knows from long experience that policymakers
must strike a delicate balance between reducing greenhouse gas emissions and maintaining the consistent energy supply on which the world economy depends. Tort
claims like this one permit no such balance; rather, individual plaintiffs seek to recover maximal damages,
while leaving the hard work of reducing greenhouse gas
emissions to others. If anything, Respondents’ suit
would make it more difficult to address climate change
by inviting 50 states and countless cities, counties, and
territories to differentially regulate beyond their boundaries.
3
Ad hoc sanctioning and extraterritorial regulation of
energy companies through the state tort system would
destabilize the whole sector. API is uniquely situated to
explain the likely effects on the industry, national security, and the world economy if the threat of future liability under varying state-court judgments undercuts
American energy production. As API explains below,
even small changes to costs and prices in the energy industry can have ripple effects throughout the global infrastructure. This Court should make clear that this
suit, and others like it, may not proceed under state tort
law, thereby safeguarding principles of federalism and
leaving the global issue of greenhouse gas emissions to
policymakers at the federal level.
QUESTION ADDRESSED BY THE AMICUS
This brief addresses the first question presented in
the Brief for Petitioners: Whether federal law precludes
state-law claims seeking relief for injuries allegedly
caused by the effects of interstate and international
greenhouse-gas emissions on the global climate.
SUMMARY OF ARGUMENT
The Colorado Supreme Court erred in ruling that
Respondents could bring state-law tort claims seeking
damages for injuries allegedly caused by global greenhouse gas emissions and global climate change. For
over a century, this Court has held that interstate air
and water pollution are inherently federal domains,
governed exclusively by federal common law or statute.
Accordingly, claims alleging that out-of-state emissions
cause injury within a state have always been governed
by federal law. Yet the court below found that Congress’s enactment of the Clean Air Act (“CAA”) somehow
4
“revived” state-law claims that, under this Court’s precedent, never existed.
This case is emblematic of the concerted effort litigants have made to repackage their climate litigation
claims to avoid application of federal law. The Colorado
Supreme Court endorsed this effort, finding that Respondents’ state tort claims were viable because (1) the
tortious conduct was not the emission of greenhouse
gases, and (2) federal common law no longer precludes
state-law claims. Pet. App. 18a, 20a. But Respondents
necessarily allege that the tortious conduct at issue is
causing the emission of greenhouse gases, and the decision below erred in concluding otherwise.
Allowing Respondents’ claims to proceed would trigger a surge of similar suits, subjecting Petitioners and
other participants in the energy industry to an impossible web of disparate judgments and multi-billion-dollar
claims for the same conduct. This would undermine the
federal government’s ability to set nationwide policy, instead creating piecemeal standards and chaos in the industry and world economy more broadly.
This problem is compounded by a disparate array of
enacted and proposed state so-called climate change
“superfund” statutes, insurance recovery statutes, and
private rights of action that would subject energy companies to even more liability regimes. In short, Respondents’ suit is not a workable means by which to address climate change, and indeed would destabilize sectors vital to the American economy and national security.
Respondents’ effort to plead around the exclusivity of
federal law, by portraying their claims as related only to
the marketing, sale, and production of fossil fuels—
5
rather than the emission of greenhouse gases—should
be rejected. All of Respondents’ asserted injuries were
allegedly caused by global climate change, which is
caused largely by the emission of greenhouse gases. Petitioners’ “upstream” marketing, sale, and production of
fossil fuels are at best several times removed from Respondents’ alleged injury. The complaint’s focus on a
narrow set of remote activities is not controlling because
Respondents ultimately seek to recover for the effects of
interstate greenhouse gas emissions. But “[n]o amount
of creative pleading can masquerade the fact that the
local governments are attempting to utilize state law to
regulate global conduct that is purportedly causing
global harm.” Mayor & City Council of Baltimore v. B.P.
P.L.C., 353 A.3d 1142, 1173 (Md. 2026).
Federal law has always applied to disputes arising
from interstate emissions, because the regulation of interstate emissions is an inherently federal domain. Am.
Elec. Power Co. v. Connecticut, 564 U.S. 410, 421, 422
(2011) (“air and water in their ambient or interstate aspects” are “meet for federal law governance”). For decades, this Court applied federal common law to disputes
arising from interstate emissions. See Illinois v. City of
Milwaukee, 406 U.S. 91, 103 (1972) (hereinafter “Milwaukee I”); see also City of New York v. Chevron Corp.,
993 F.3d 81, 91 (2d Cir. 2021) (collecting cases). After
the CAA and Clean Water Act (“CWA”) were enacted,
this Court held that Congress had displaced federal
common law in the realm of interstate emissions. Am.
Elec. Power, 564 U.S. at 420-24; City of Milwaukee v. Illinois & Michigan, 451 U.S. 304, 313-14 (1981) (hereinafter “Milwaukee II ”). Disputes arising from interstate
emissions were thereafter governed by the CAA, which
6
is a comprehensive statutory scheme for the regulation
of air quality across the United States. It leaves no room
for the application of state law to interstate emissions.
Extraterritorial state regulation in this area would
not only be unprecedented, but likely devastatingly
costly. The multi-billion-dollar judgments that may flow
from these claims could cause major economic disruption. Fossil fuels still power large swaths of the American and world economies—from transportation and logistics to agriculture and healthcare—and a judgmentfueled increase in energy costs could create volatility in
the energy markets and broader economic uncertainty.
Fossil fuels not only drive the world economy, they
also play a key role in U.S. national security and diplomacy. The Constitution vests exclusive control over
matters related to foreign affairs in the federal government, and state law must not interfere with this exclusive federal domain. Respondents’ suit threatens to interfere with the United States’ ability to conduct foreign
affairs, shifting regulatory power over a strategically
important industry from the federal government to the
states. Furthermore, Respondents’ suit and the likely
follow-on suits, if successful, threaten the United States’
ability to manage energy resources in global conflicts
and weaken national security.
The question presented in this case is not whether
climate change is serious. It is. The question is what
law applies to decisions that directly affect how to balance emissions reduction, energy reliability, consumer
cost, infrastructure investment, foreign relations, and
national security. Fossil fuels provide the majority of
the world’s energy, with no replacement yet viable at
scale. Regulation must be carefully targeted to avoid
7
destabilizing the energy supply that underlies the world
economy. A federal regulatory determination, rather
than extraterritorial state laws and lawsuits, is better
suited for a coordinated, effective policy. Respondents’
suit bluntly targets fossil fuel companies and attempts
to recover localized damages, without regard to the effects on the rest of the country or the world. Allowing it
to proceed would impair federal action by inviting a
complex and inconsistent web of state-court rules.
ARGUMENT
I. This Case Is Symptomatic Of A Rash Of State-Law
Climate Change Litigation
Respondents’ case is part of a movement that
stretches far beyond Boulder County, Colorado. If Respondents’ claims are allowed to proceed, an onslaught
of similar claims will follow in state courts across the
country. Dozens of lawsuits bringing extraterritorial
state-law tort claims have already been filed in different
state jurisdictions.2 Inevitably, state courts around the
2 Leon v. Exxon Mobil Corp., No. 25-2-15986-8 (Wash. Super. Ct.);
City of Chicago v. BP p.l.c., No. 2024CH01024 (Ill. Cir. Ct.); County
of Multnomah v. Exxon Mobil Corp., No. 23CV25164 (Or. Cir. Ct.);
California v. Exxon Mobil Corp., No. CGC23609134 (Cal. Super.
Ct.); Makah Indian Tribe v. Exxon Mobil Corp., No. 23-2-25216-1
(Wash. Super. Ct.); Platkin v. Exxon Mobil Corp., No. MER-L001797-22 (N.J. Super. Ct.); City of Annapolis v. BP p.l.c., No. C-02CV-21-000250 (Md. Cir. Ct.); Anne Arundel County v. BP p.l.c., No.
C-02-CV-21-000565 (Md. Cir. Ct.); City of Hoboken v. Exxon Mobil
Corp., No. HUD-L-003179-20 (N.J. Super. Ct.); Delaware v. BP Am.
Inc., No. N20C-09-097 (Del. Super. Ct.); City of Charleston v. Brabham Oil Co., No. 2020-CP-10-03975 (S.C. Ct. Com.); Minnesota v.
Am. Petroleum Inst., No. 62-CV-20-3837 (Minn. Dist. Ct.); Rhode Island v. Chevron Corp., No. PC-2018-4716 (R.I. Super. Ct.); City of
Richmond v. Chevron Corp., No. C18-00055 (Cal. Super. Ct.); Mayor
8
country will reach contradictory conclusions, and the oil
and natural gas industry could well be subject to inconsistent laws and judgments. Int’l Paper Co. v. Ouellette,
479 U.S. 481, 496 (1987) (allowing “a number of different states to have independent and plenary regulatory
authority over a single discharge would lead to chaotic
confrontation between sovereign states.” (citation omitted)). Respondents seek to hijack the formulation of national policymaking to their exclusive benefit, at the expense of every other state and locality in the nation—all
of which are affected by climate change.
A.
Climate Litigation Trends Post-American Electric
Power Illuminate The Problem
The use of strategic litigation to influence climate
policy has evolved over the past two decades. American
Electric Power, the first major case addressing an attempt to hold companies liable for greenhouse gas emissions and alleged climate change harms, dealt with common-law public nuisance claims against power
& City Council of Balt. v. BP p.l.c., No. 24-C-18-004219 (Md. Cir.
Ct.); City of Imperial Beach v. Chevron Corp., No. C17-01227 (Cal.
Super. Ct.); County of Marin v. Chevron Corp., No. CIV1702586
(Cal. Super. Ct.); County of San Mateo v. Chevron Corp., No.
17CIV03222 (Cal. Super. Ct.); City of Santa Cruz v. Chevron Corp.,
No. 17CV03243 (Cal. Super. Ct.); County of Santa Cruz v. Chevron
Corp., No. 17CV03242 (Cal. Super. Ct.); California ex rel. Herrera v.
BP p.l.c., No. CGC-17-561370 (Cal. Super. Ct.); California ex rel.
Oakland City Att’y v. BP p.l.c., No. RG17875889 (Cal. Super. Ct.);
City & County of Honolulu v. Sunoco LP, No. 1CCV-20-0000380
(JPC), 2022 WL 22866746 (Haw. Cir. Ct. Mar. 29, 2022); City &
County of Honolulu v. Sunoco LP, No. 1CCV-20-0000380 (JPC),
2022 WL 22866745 (Haw. Cir. Ct. Mar. 31, 2022); Bucks County v.
BP p.l.c., No. 2024-01836 (Pa. Ct. C.P.); Estado Libre Asociado de
Puerto Rico v. Exxon Mobil Corp., No. SJ2024CV06512 (P.R. Super.
Ct.).
9
companies for emitting greenhouse gases. Connecticut
v. Am. Elec. Power Co., 406 F. Supp. 2d 265 (S.D.N.Y.
2005), vacated and remanded, 582 F.3d 309 (2d Cir.
2009), rev’d, 564 U.S. 410 (2011). During this early
phase of strategic climate litigation, cases were also
filed against auto manufacturers for allegedly making
products that emit greenhouse gases that contribute to
global warming, California v. Gen. Motors Corp., No.
C06-05755 MJJ, 2007 WL 2726871 (N.D. Cal. Sept. 17,
2007) (claims dismissed as non-justiciable), oil and gas
producers for emitting greenhouse gases that contribute
to rising sea levels, Native Village of Kivalina v. ExxonMobil Corp., 696 F.3d 849 (9th Cir. 2012), and energy
producers for emitting greenhouse gases that made
Hurricane Katrina more intense, Comer v. Murphy Oil
USA, Inc., 718 F.3d 460 (5th Cir. 2013).
In the wake of this Court’s decision in American
Electric Power, the Ninth and Fifth Circuits affirmed
the dismissal of both the state and federal law climate
change claims brought in Kivalina and Comer. In Kivalina, the Ninth Circuit concluded that federal statutory law precluded plaintiffs’ federal common law
claims. 696 F.3d at 856-58. And in Comer, the undisturbed district court decision held that the plaintiffs’
state-law claims were preempted by the Clean Air Act.
Comer v. Murphy Oil USA, Inc., 839 F. Supp. 2d 849, 865
(S.D. Miss. 2012), aff’d, 718 F.3d 460 (5th Cir. 2013).
After the Court’s decision in American Electric
Power and plaintiffs’ losses in Kivalina and Comer,
there was a concerted effort to repackage climate litigation claims in an attempt to skirt the clear implication
of American Electric Power’s holding: that state-law
claims seeking redress for alleged climate change
10
injuries are available only under the laws of the state in
which the pollution-emitting defendants are located.
See, e.g., Establishing Accountability for Climate
Change Damages: Lessons from Tobacco Control, Summary of the Workshop on Climate Accountability, Public
Opinion, and Legal Strategies, Union of Concerned Scientists & Climate Accountability Inst. (Oct. 2012), at 1114, 18-19.3
As the first appellate court to rule on the merits of
this reframing, the Second Circuit in City of New York
v. Chevron Corp. held that municipalities were precluded from holding multinational oil companies liable
for climate change damages under state tort law. 993
F.3d at 100. As here, the City argued that its suit concerned “‘the production, promotion, and sale of fossil
fuels,’ not the regulation of emissions.” Id. at 91 (quoting City Br. at 40). The Second Circuit rejected this,
stating: “Artful pleading cannot transform the City’s
complaint into anything other than a suit over global
greenhouse gas emissions. It is precisely because fossil
fuels emit greenhouse gases – which collectively ‘exacerbate global warming’ – that the City is seeking damages.” Id.
State courts have not uniformly followed the Second
Circuit’s lead.4 Although the Colorado Supreme Court’s
3 https://www.ucs.org/sites/default/files/attach/2016/04/establishing-accountability-climate-change-damages-lessons-tobacco-control.pdf.
4 Contrast Pet. App. A (the Colorado Supreme Court’s opinion below) and City & County of Honolulu v. Sunoco LP, 537 P.3d 1173
(Haw. 2023) (permitting state claims to proceed) with Mayor & City
Council of Baltimore v. B.P. P.L.C., 353 A.3d 1142 (Md. 2026); Delaware ex rel. Jennings v. BP Am., Inc., No. N20C-09-097, 2024 WL
11
opinion below was not the first to depart from the Second Circuit’s conclusion, it is in the minority. The Colorado Supreme Court largely adopted the analysis employed by the Hawaii Supreme Court’s earlier conclusion that federal law did not preempt state tort claims
seeking climate change damages from oil and gas producers. See Pet. App. at 8a, 15a-16a, 19a, 25a-26a; City
& County of Honolulu v. Sunoco LP, 537 P.3d 1173 (Haw.
2023).
Efforts to stem the tide of this form of litigation have
also been undertaken by other states and the federal
government. In 2024, Alabama, joined by 18 states, unsuccessfully sought to file a bill of complaint in this
Court to stop these suits. See Alabama v. California,
No. 158 (Original) (U.S., filed May 22, 2024), motion for
leave to file a bill of complaint denied, 145 S. Ct. 757
(2025). In the past year, the federal government has
filed lawsuits in Hawaii, Michigan, and Minnesota to
prevent their climate litigation from proceeding, arguing the states are “thwarting the United States’ exclusive authority to regulate interstate air pollution, administer federal law, and conduct foreign affairs.”
Compl. ¶ 2, United States v. Minnesota, No. 26-cv-2456
(D. Minn. May 4, 2026). District courts have since
98888 (Del. Super. Ct. Jan. 9, 2024); Platkin v. Exxon Mobil Corp.,
No. MER-L-001797-22, 2025 WL 604846 (N.J. Super. Ct. Law Div.
Feb. 5, 2025); Bucks County v. BP P.L.C., No. 2024-01836 (Pa. Ct.
C.P. May 16, 2025); City of Charleston v. Brabham Oil Co., Inc., No.
2020-CP-10-03975, 2025 WL 2269770 (S.C. Ct. C.P. Aug. 6, 2025)
(dismissing state claims). Many more suits remain pending, with
some stayed in anticipation of the Court’s resolution of this case.
See, e.g., Fuel Industry Climate Cases, No. CJC-24-005310 (Cal. Super. Ct. Apr. 14, 2026) (“Order Staying Litigation Pending Final Decision by U.S. Supreme Court”).
12
dismissed the Michigan and Hawaii lawsuits, ruling
they lacked Article III jurisdiction to hear the cases due
to standing and ripeness issues. See United States v.
Michigan, 817 F. Supp. 3d 630 (W.D. Mich. 2026);
United States v. Hawaii, No. CV 25-00179 HG-WRP,
2026 WL 1021227 (D. Haw. Apr. 15, 2026).
B. State Statutes And Private Rights Of Action
Compound The Problem, Subjecting Energy
Companies To Innumerable Different Liability
Regimes
The patchwork problem is not limited to Boulderlike lawsuits by state and local governments. Colorado’s
rule would bless a broader state-by-state campaign to
impose liability on energy companies for interstate
emissions through state statutes, administrative programs, insurance-recovery laws, and newly created private rights of action. If a city or state may impose liability for alleged local injuries attributed to interstate
and international greenhouse-gas emissions in an area
covered by the Clean Air Act, the other 49 states (and
innumerable municipalities) may do the same. This
may be through whatever mix of tort law, statutory
strict liability, cost-recovery funds, attorney-general actions, insurer subrogation rights, and private causes of
action its legislature or courts choose to create.
Climate “superfund” programs, like those in New
York and Vermont, illustrate the point. New York’s Climate Change Superfund Act directs state officials to collect $75 billion from selected energy companies over a
25-year period for climate-adaptation projects. N.Y.
Env’t Conserv. Law art. 76; see also S.824, 2025-2026
Leg., Reg. Sess. (N.Y. 2025). The law does not, however,
impose liability based on a defendant’s emissions in
13
New York; instead, it assigns liability based on historical, worldwide fossil-fuel activity and the emissions allegedly attributable to that activity for the covered period of January 1, 2000 to December 31, 2024. A “responsible party” is strictly liable for a share of New York
State’s selected climate-adaptation costs. N.Y. Env’t
Conserv. Law § 76-0103.
Vermont’s Climate Superfund Cost Recovery Program (Vermont Act 122) follows the same model, but
with somewhat different rules. Vermont’s program covers an expanded period (January 1, 1995 to December
31, 2024), directs the State to identify “responsible
part[ies],” and mandates cost-recovery demands tied to
alleged greenhouse-gas emissions associated with fossil
fuels extracted or refined over those 30 years. 10 V.S.A.
§§ 596-599c; 2024 Vt. Acts & Resolves No. 122. Like
New York, Vermont imposes strict liability on climaterelated costs and preserves other remedies. 10 V.S.A.
§§ 598, 599c.
The result here is not a single national rule of decision. It is a state-by-state, overlapping regime in which
different states may choose different periods, different
emissions thresholds, different attribution methodologies, different defenses, different remedies, and different administrative processes—all for the same molecules in the same atmosphere. For example, energy
companies who sold fossil-fuel products to consumers in
California would by definition be liable to both New York
and Vermont for the same emissions resulting from the
use of those same products in California—and would be
subject to money damages for those emissions even if
the sale and use of those products was entirely lawful as
a matter of both federal and California law. There
14
would be no reason why dozens of other states could not
jump into the fray, each assigning its own standards of
liability and damages for those same lawful activities
taking place outside of its state. The resulting quagmire
of conflicting and duplicative state laws, all seeking to
regulate the same out-of-state conduct, is easy to predict.
Insurance-recovery measures and private rights of
action compound the problem. The California legislature has considered authorizing its Attorney General to
sue selected fossil-fuel companies to recover insurancerelated losses allegedly arising from climate disasters,
including losses suffered by the California FAIR Plan
Association and policyholders. Cal S.B. 982, 2025-2026
Reg. Sess. Thus far, that legislation has been rejected.
Bill History, SB-982 Climate disasters: civil actions, Cal.
Legis. Info. (Apr. 23, 2026).5 Hawaii, too, has considered
legislation authorizing its Attorney General, the Hawaii
Property Insurance Association, the Hawaii hurricane
relief fund, and private insurers to bring civil actions
against “responsible parties” to recover costs and losses
resulting from “climate attributable harm,” including
increased premiums, insurer withdrawals, and reduced
insurance availability. Haw. S.B. 3000, 33d Leg., Reg.
Sess. (2026).
These enactments and proposals are the predictable
consequence of the rule Respondents defend. The premise of Respondents’ theory is that each state may use its
own law to allocate the costs of global climate change to
energy producers and sellers beyond its borders. If state
5 https://leginfo.legislature.ca.gov/faces/billHistoryCli-
ent.xhtml?bill_id=202520260SB982.
15
law is not preempted, and Boulder County may seek relief under Colorado law for alleged local injuries caused
by interstate and international emissions, states will
rush to pursue their own attempts for relief. New York
may seek to impose a $75 billion statutory assessment;
Vermont may seek to impose its own retroactive cost-recovery program; California may seek to create an insurance-recovery cause of action; Hawaii may seek to authorize insurers and state funds to sue; and every other
state might experiment with other policy variations, including their own private rights of action. There is no
limiting principle in Boulder County’s theory.
A single barrel of oil, cubic foot of natural gas, or ton
of coal may be counted again and again by different
states, under different formulas, for different time periods, as the basis for fifty different states to impose liability. An energy company may face strict liability in
one state, negligence-based liability in another, publicnuisance remedies in a third, insurer-subrogation
claims in a fourth, and private damages actions in a
fifth. And because climate change results from cumulative global emissions over time, each State’s asserted
“local” injury necessarily depends on emissions and energy consumption far outside that State’s borders, accumulated in the global atmosphere over decades. Fifty
competing liability systems reaching extraterritorially
for the same underlying emissions is simply untenable.
II. Climate Change Litigation Cannot Proceed Under State
Law
A. Respondents’ Claims Are Premised On Out-Of-State
Greenhouse Gas Emissions
For over a hundred years, disputes over interstate
pollution have been resolved exclusively under federal
16
law. See infra Section II.B. The opinion below upends
that consistent history by authorizing state regulation
of interstate and international emissions of greenhouse
gases. The Colorado Supreme Court held that the Clean
Air Act, having displaced the federal common law governing interstate greenhouse gas emissions, did not
preempt Respondents’ state-law tort claims—interpreting Congress’s silence on state-law claims as an implicit
license. See Pet. App. at 14a-16a (holding “the CAA
does not completely occupy the field of emissions regulation[s],” nor does “state tort liability…frustrate the
CAA’s purposes” or “upset any balance set by Congress
because Boulder’s claims do not seek to impose liability
for activities that the CAA regulates”). However, “even
if the federal common law in this area still existed,” the
court held, “it would not appear to apply here” because,
according to the court, Boulder’s suit does not seek to
regulate greenhouse gas emissions. Id. at 17a.
Respondents argue their claims are premised only
on the marketing, sale, and production of fossil fuels—
purportedly bringing their claims within the ambit of
state law. In fact, Respondents’ claims seek to remedy
alleged injuries from interstate greenhouse gas emissions—bringing them within an inherently federal domain. The Colorado Supreme Court accepted Respondents’ arguments at face value. Finding that the complaint’s allegations had everything to do with “tortious
conduct that [federal law] does not address,” and nothing to do with “[greenhouse gas] emissions by defendants themselves,” the court held that Respondents’
claims did not implicate the regulation of interstate
emissions. Pet. App. at 21a.
Respondents’ assertion that their claims relate only
to the marketing, sale, and production of fossil fuels
17
does not withstand scrutiny, and the Court should not
indulge their sleight of hand pleading. Minn. v. Am. Petroleum Inst., 63 F.4th 703, 717 (8th Cir. 2023) (Stras, J.,
concurring) (describing Minnesota’s purported “state
law consumer-protection claims” as “artful pleading,”
“tak[ing] aim at the production and sale of fossil fuels
worldwide”).
The majority below reasoned that “[Respondents’]
claims do not seek compensation for any [greenhouse
gas] emissions by defendants themselves but rather focus on [Petitioners’] upstream production activities.”
Pet. App. at 21a. But the distinction between greenhouse gas emissions and “upstream activities” is illusory. Respondents demand compensation from Petitioners for the effects of worldwide greenhouse gas emissions. The “upstream activities” Respondents identify
are only relevant to the extent they allegedly caused the
emission of greenhouse gases. See, e.g., J.A. 35-36,
¶¶ 127-29 (alleging that production of fossil fuels resulted in higher levels of CO2); see also Pet. App. at 32a
(Samour, J., dissenting) (“[A] closer look at the substance of [Respondents’] claims’ allegations reveals that
Boulder seeks to effectively abate or regulate interstate
emissions.”).
There is no question that all of Respondents’ injuries
are alleged to have been directly caused by the accumulation of greenhouse gas emissions. See, e.g., J.A. 36,
¶ 129. The emissions themselves are therefore a necessary causal link, without which Respondents cannot establish that Petitioners’ marketing, sale, and production
of fossil fuels was an actual or proximate cause of injuries in Colorado. That these emissions—emitted from
many sources since the beginning of the industrial
18
revolution—are the direct cause of Respondents’ alleged
injuries and a necessary element of Respondents’ claims
elides Respondents’ assertions that the case does not involve the regulation of interstate greenhouse gases.
The decision below sidestepped the central issue in
the complaint by concluding that Respondents’ claims
do not “involve uniquely federal areas of regulation” because “nuisance abatement issues and the other torts
that Boulder has alleged in this case have been deemed
traditional state law matters implicating important
state interests.” Pet. App. at 15a (emphasis omitted).
The court failed to acknowledge, however, that the “nuisance abatement issues” are not standard local disputes, but rather concern atmospheric changes with
global impact. Putting state-law labels on plainly interstate activities does not suffice to sustain state-law
claims in the inherently federal domain of interstate
emissions.
B. The Regulation Of Interstate Emissions Is An
Inherently Federal Domain
This Court has recognized that “air and water in
their ambient or interstate aspects” are “meet for federal law governance.” Am. Elec. Power, 564 U.S. at 421,
422. “[A] mostly unbroken string of cases” going back
more than a century “has applied federal law to disputes
involving” claims arising out of interstate emissions.
City of New York, 993 F.3d at 91 (collecting cases); see
Milwaukee I, 406 U.S. at 103. It is because of the inherently federal nature of interstate emissions and discharges that this Court long held that suits related to
air and water pollution are governed by federal common
law. See Am. Elec. Power, 564 U.S. at 420-24; Milwaukee I, 406 U.S. at 103. After the enactment of the CAA
19
and CWA, this Court held that the federal statutory
schemes had displaced federal common law. Milwaukee
II, 451 U.S. at 313-14; Ouellette, 479 U.S. at 492; Am.
Elec. Power, 564 U.S. at 420-23. In holding that the
CWA preempted most state-law claims, this Court relied
not only on the statute itself, but also on “the fact that
the control of interstate pollution is primarily a matter
of federal law.” Ouellette, 479 U.S. at 492.
That a comprehensive statutory scheme displaced
federal common law does not render this area of law any
less inherently federal. The “demands for applying federal law”—which may implicate federal common law or
a federal statute—implicate an “overriding federal interest in the need for a uniform rule of decision” in the
field of interstate emissions. Milwaukee I, 406 U.S. at
105 n.6. “[F]ederal common law and not the varying
common law of the individual States” must apply when
a controversy invokes “the environmental rights of a
State against improper impairment by sources outside
its domain.” Id. at 107 n.9 (quoting Texas v. Pankey, 441
F.2d 236 (10th Cir. 1971)). If state law was permitted to
resolve such disputes, “more conflicting disputes, increasing assertions and proliferating contentions would
seem to be inevitable.” Pankey, 441 F.2d at 241.
The justifications for precluding state-law claims in
interstate emissions cases are not “undermine[d]” by
the CAA or the CWA. Illinois v. City of Milwaukee, 731
F.2d 403, 410 (7th Cir. 1984), cert. denied, 469 U.S. 1196
(1985). Nor are they any less applicable to the emissions
that cause global climate change. That global climate
change inherently requires a federal solution is perhaps
more evident than with respect to the other forms of pollution that this Court has previously addressed. In
20
particular, this Court’s decisions emphasize that the location of the source of an emission or discharge is a dispositive factor in determining whether federal law provides the exclusive remedy. See, e.g., Milwaukee I, 406
U.S. at 93, 103 (federal common law applied to pollution
in Wisconsin caused by sewage discharge originating in
Illinois); Ouellette, 479 U.S. at 488-89 (state-law claims
permitted only where water pollution is caused by an instate source).
Although Respondents try to avoid saying so in their
complaint, it cannot seriously be disputed that emissions throughout the United States and the world contribute to climate change, and that CO2, methane, and
other greenhouse gases from countless sources intermix
in the atmosphere. See What are the trends in greenhouse gas emissions and concentrations and their impacts on human health and the environment?, U.S. Environmental Protection Agency.6 Importantly, not all of
these emissions originate in petroleum products, or indeed from energy consumption at all. Sources of Greenhouse Gas Emissions, U.S. Environmental Protection
Agency.7 Given the breadth and scale of the causes of
climate change, any solutions that are to be effective
must be uniform and comprehensive, whether by federal statute or federal common law.
State-law tort claims that aim to regulate emissions
not only violate the “overriding federal interest in the
need for a uniform rule of decision,” Milwaukee I, 406
6 https://web.ar-
chive.org/web/20250830015710/https://www.epa.gov/report-environment/greenhouse-gases (last visited May 21, 2026).
7 https://www.epa.gov/ghgemissions/sources-greenhouse-gasemissions (last visited May 21, 2026).
21
U.S. at 105 n.6, they also impinge on the rights of other
states by making determinations that will have an impact well beyond the borders of the state in which the
claims are brought. For example, by asking a Colorado
court to determine whether fossil fuel production “unreasonabl[y] interfere[s]” with a public right such that it
amounts to a public nuisance, Restatement (Second) of
Torts § 821B (1979), Respondents are necessarily asking
the court to determine whether fuel producers’ conduct
was reasonable. Making that determination requires
considering not only the risks of fossil fuel use to the
planet, but also how well those risks have been weighed
against the world’s gargantuan need for energy and the
difficulty of developing an alternative at scale. See infra
Section II.C.2. Furthermore, the Colorado court would
need to apportion liability and damages for climate
change as a whole, not merely alleged harms felt in Colorado, which cannot possibly be traced to specific
sources. The single state court would thus take on the
role of quantifying the contribution of whole industries
to global climate change, including the many fuel producers and unrelated industries not before the court
(not to mention other states that might do the same).
This Court has affirmed on multiple occasions that
weighty determinations affecting the entire nation must
be made by Congress or its designated federal agency.
West Virginia v. EPA, 597 U.S. 697, 735 (2022) (concluding that “[c]apping carbon dioxide emissions at a level
that will force a nationwide transition” is a “decision of
such magnitude and consequence [that it] rests with
Congress itself, or an agency acting pursuant to a clear
delegation from that representative body”); Am. Elec.
Power, 564 U.S. at 428 ( “Congress designated an expert
22
agency, here, EPA, as best suited to serve as primary
regulator of greenhouse gas emissions”).
In American Electric Power, the Court held that the
Clean Air Act “displaces federal common law” climate
change claims. 564 U.S. at 429. Although the Court did
not decide whether federal law preempted claims pursuant to the law of a state other than the source state
(because that question was not briefed), the Court did
explain that “the availability vel non of a state lawsuit
depends, inter alia, on the preemptive effect of the federal Act.” Id. Citing Ouellette, the Court reiterated that
“the Clean Water Act does not preclude aggrieved individuals from bringing a ‘nuisance claim pursuant to the
law of the source State.’” Id.
In an attempt to distinguish the repeated declarations of this Court regarding the inherently federal nature of claims premised on interstate emissions, the decision below asserted that the enactment of the CAA
rendered the Court’s prior holdings inapplicable. Specifically, the Colorado Supreme Court reasoned that “the
CAA displaced federal common law governing interstate
pollution damages suits and, thereafter, federal common law did not preempt state law.” Pet. App. 16a. The
court thus appeared to posit that if federal common law
no longer applies, state law must apply.
As an initial matter, the decision below rests on the
dubious suggestion that the enactment of a broad federal air pollution and emissions scheme reduced the
scope of federal authority in that very field. Id. at 17a
(noting Petitioners cited “no applicable authority supporting the proposition that once federal common law
exists, the structure of the Constitution precludes the
application of state law even when that common law no
23
longer exists”). This proposition has no basis in this
Court’s precedents, which teach that the CWA’s (and, by
extension, the CAA’s) displacement of federal common
law leaves no room for the types of state-law claims at
issue here. See, e.g., Milwaukee II, 451 U.S. at 313 n.7
(“[I]f federal common law exists, it is because state law
cannot be used.”); Ouellette, 479 U.S. at 488-89; Am.
Elec. Power, 564 U.S. at 429 (citing Ouellette, opining on
“the availability vel non” of state-law claims). Furthermore, even assuming that the displacement of federal
common law by a federal statute could theoretically resurrect state-law claims, the court’s reasoning would
nevertheless run up against the basic fact that interstate emissions have never been governed by state law.
In short, the CAA’s displacement of federal common law
could not have resurrected state-law claims that never
existed.
C. Allowing Respondents’ Claims Would Interfere With
Federal Energy, Economic, and Foreign Policy
The inherently federal nature of emissions regulation is grounded not only in abstract constitutional principles of federalism, but also in the practical impossibility of effectively regulating interstate (and international) environmental matters at the state level. Allowing state law to regulate interstate emissions would
compromise any uniform regulatory scheme and risk serious disruption to the national economy and undermine the United States’ ability to conduct foreign affairs.
1. Expansive
Untenable
Extraterritorial
Regulation
Is
The CAA leaves room for states to impose unique
regulations on intrastate emissions, but it does not
24
permit extraterritorial, conflicting regulatory schemes
governing interstate and international emissions. The
practical implications of expansive extraterritorial regulation are well known to API and its members, who operate across the world and comply with the laws of many
different jurisdictions. Because of the need to standardize fuel production methods, changes in the law of one
jurisdiction affect companies’ behavior in other jurisdictions. Climate change is undisputedly a global phenomenon that requires a coordinated response at the national and international level. Crafting policy to adequately address global climate change—while balancing
energy availability, national security, and other concerns—is one of the great challenges of our age. The solutions require significant coordination, research, scientific innovation, and carefully targeted regulation. Any
solution also requires coordination with other sovereign
nations. Federal authorities—the President, Congress,
and the expert agency to which it has delegated authority (the EPA)—are the bodies capable of undertaking
this task.
In contrast, state courts are not in a position to effectively regulate interstate and global greenhouse gas
emissions and are barred from doing so in our federal
system. Regulating greenhouse gas emissions via a litany of state-law tort actions would create a sprawling
patchwork of regulations across all 50 states that would
both undermine any attempt at uniform, federal regulation and result in equally sovereign states treading on
each other. “[W]hen interstate disputes are litigated
through the surrogate of a private party as the defendant, fifty state courts get to handle them” in a myriad of
25
ways. Minnesota v. Am. Petroleum Inst., 63 F.4th 703,
717-19 (8th Cir. 2023) (Stras, J., concurring).
Our federal system of laws has never tolerated a Balkanized approach to regulating interstate air pollution.
Instead, disputes over pollution crossing state lines require a “uniform” federal rule, Milwaukee I, 406 U.S. at
105 n.6, not “vague and indeterminate” standards
drawn from the laws of multiple states over extraterritorial emissions. Milwaukee II, 451 U.S. at 317; see also
Ouellette, 479 U.S. at 496-97 (recognizing that permitting individual state nuisance law to apply to out-ofstate pollution sources would result in a “variety of common-law rules”). Yet, this case is emblematic of the conscious efforts by some state and local governments to depart from federal policy.
At bottom, the CAA provides federal mechanisms for
regulating air emissions, including cooperative federalism rules that preserve state authority over in-state
sources while preventing one State from dictating the
emissions policy of others. See 42 U.S.C. §§ 7401 et seq.;
Ouellette, 479 U.S. at 497-500. Respondents’ rule would
invert that structure, allowing each state to impose retroactive liability on interstate and international energy
activity, not through source-specific standards approved
under federal law, but through open-ended damages actions and cost-recovery programs untethered to any federal emissions standard. “[T]hese liabilities would attach even though the source had fully complied” with
federal obligations. Ouellette, 479 U.S. at 495. That result would offend both vertical and horizontal federalism, and is precisely what federal law forbids.
26
2.
Blessing Respondents’ Theories Would Likely
Have Dire Economic Consequences
The damages requested by Respondents and other
plaintiffs across the country could severely impact the
energy industry and cause ripple effects throughout the
American economy. Respondents seek extensive monetary relief to compensate for alleged property damage
and to maintain basic municipal functions, such as repairing bridges and containing wildfires. J.A. 136-37, ¶
532. Other states have signaled that they will seek
damages on an even larger scale. For example, California is seeking “tens of billions to hundreds of billions of
dollars in ongoing damage going forward.” William
Brangham & Dorothy Hastings, California Sues Oil
Companies for Exacerbating Climate Change, PBS
News Hour (Sept. 20, 2023) (comments of Rob Bonta,
Attorney General of California). 8 Multnomah, Oregon
is seeking over $1.5 billion in damages and an abatement fund of over $50 billion paid for by the defendants.
Compl. at 174-75, County of Multnomah, No.
23CV25164 (Or. Cir. Ct. June 22, 2023).
If these suits succeed in obtaining billion-dollar judgments, the costs—payouts made to individual states
and localities—will likely impact the energy supply
chain. This could have sweeping effects on the U.S.
economy and international trade. About 60% of U.S.
households rely on natural gas as their primary source
of energy. U.S. Energy Info. Admin., Natural gas explained, Use of natural gas 9; U.S. Energy Info. Admin.,
https://www.pbs.org/newshour/show/california-sues-oil-companies-for-exacerbating-climate-change.
9
https://www.eia.gov/energyexplained/natural-gas/use-of-natural-gas.php (last visited May 21, 2026).
8
27
Use of energy explained.10 Nearly the entire transportation sector depends on energy derived from fossil fuels.
U.S. Energy Info. Admin., Use of energy explained, Energy use for transportation.11 Inflated fossil fuel prices
affect not only the cost of gas for individuals, but also
the cost of logistics and shipping. Within these vital sectors, even modest increases in core energy prices can
have ripple effects that disrupt the entire economy.
Dep’t of Transp., Bureau of Transp. Stats., Inflation and
Transportation (showing that, in April 2026, transportation was responsible for 31.1% of the year-over-year
change in the price for all goods and services).12
The value of petroleum to the economy also extends
well beyond fuel. Petroleum-based products such as
plastic are ubiquitous in basic consumer products and
essential to nearly every major industry. An increase in
the cost of petroleum-based products would likely be immediately felt in the agricultural industry, U.S. Dep’t of
Agric., Impacts of Higher Energy Prices on Agriculture
and Rural Economies (Aug. 2011),13 the manufacturing
industry, U.S. Energy Info. Admin., Use of energy explained,14 and the healthcare industry, U.S. Dep’t of
10 https://www.eia.gov/energyexplained/use-of-energy/ (last visited
May 21, 2026).
11 https://www.eia.gov/energyexplained/use-of-energy/transportation.php (last visited May 21, 2026).
12 https://data.bts.gov/stories/s/Transportation-and-Inflation/f9jmcqwe/ (last visited May 21, 2026).
13
https://ers.usda.gov/sites/default/files/_laserfiche/publications/44894/6806_err123_reportsummary.pdf.
14 https://www.eia.gov/energyexplained/use-of-energy/ (last visited
May 21, 2026).
28
Energy, U.S. Oil and Natural Gas: Providing Energy
Security and Supporting Our Quality of Life (Sept.
2020).15
The economy-wide impacts of increased fuel costs
are not hypothetical, nor are they borne solely by energy
companies. When global events cause a temporary price
shock in energy markets, it affects the whole economy.
In the wake of Russia’s 2022 expanded invasion of
Ukraine, markets were rocked by “the largest 23-month
increase in energy prices since the 1973 oil price hike.”
World Bank, Commodity Markets Outlook, 1-2, 9 (Apr.
2022).16 More recently, the Iran conflict has also impacted energy costs. See, e.g., Iran War Energy Cost
Tracker, Climate Solutions Lab at Brown University.17
The potential consequences of Respondents’ suit
have serious implications for the national economy. It is
for good reason that federal policymakers, and not individual states, have the exclusive authority to regulate
interstate emissions. Allowing states to bypass federal
supremacy would impose ad hoc, localized solutions on
a problem that requires a broad and careful review in
which all interested parties are represented.
3.
Foreign Affairs And National Security Require
Exclusive Federal Control
Allowing state tort law to govern worldwide emissions would also intrude on the federal government’s
https://www.energy.gov/sites/prod/files/2020/10/f79/Natural%20Gas%20Benefits%20Report.pdf.
16
https://openknowledge.worldbank.org/server/api/core/bitstreams/da0196b9-6f9c-5d28-b77c-31a936d5098f/content.
17 https://iranwarcost.watson.brown.edu/ (last visited May 21,
2026).
15
29
exclusive control over foreign affairs. Am. Ins. Ass’n v.
Garamendi, 539 U.S. 396, 421 (2003) (“[t]he exercise of
the federal executive authority,” particularly in the area
of foreign affairs, “means that state law must give way
where, as here, there is evidence of clear conflict between the policies adopted by the two”). Based on its
(incorrect) understanding that Respondents’ claims do
not seek to regulate greenhouse-gas emissions and instead “involve areas of traditional state responsibility,”
the Colorado Supreme Court held that neither “principles of conflict preemption” nor field preemption relating to foreign affairs bar Respondents’ claims. Pet. App.
at 22a-24a. But any climate solution demands international cooperation, and the federal government must retain authority to decide energy policy on behalf of the
nation as a whole. The federal government cannot effectively do so if the states have already imposed their
own extraterritorial standards that may conflict with
those under negotiation. City of New York, 993 F.3d at
103 (state-law tort suit “would not only risk jeopardizing
our nation’s foreign policy goals but would also seem to
circumvent Congress’s own expectations and carefully
balanced scheme of international cooperation on a topic
of global concern.”).
More generally, the strategic importance of fossil
fuels has been demonstrated by their crucial role in foreign affairs. “When the United States entered the Second World War, aviation gasoline—or “avgas”—became
critical for the military.”
Chevron USA Inc. v.
Plaquemines Par., Louisiana, 146 S. Ct. 1052, 1058
(2026). The United States’ reserves of oil became “[a]
prime weapon of victory in two world wars” and “a bulwark of our national security.” Nat’l Petroleum Council,
30
A National Oil Policy for the United States 1 (1949).18
At the time the United States entered the war, it had
the world’s largest petroleum reserves, and President
Franklin Roosevelt wielded the industry as an instrument of foreign affairs. Energy’s Vital Role in World
War II Offers Lessons For Today, Am. Oil & Gas Rep.
(Oct. 2023).19 In 1941, the United States embargoed oil
shipments to Japan while accelerating shipments of
high-octane fuel for aircraft, as well as oil for ships, lubricants, and synthetic rubber to the Allies. Id. During
the span of the conflict, the oil industry increased production by nearly 30% to meet the enormous demand.
Id. U.S. oil and petroleum-based products were necessary for the Allies to continue fighting, and the United
States’ wealth of petroleum resources emerged as one of
its most powerful tools in foreign affairs. Id.; Nat’l Petroleum Council, A National Oil Policy for the United
States 1.20
The petroleum industry is no less a part of foreign
affairs today. In 2022, following Russia’s invasion of
Ukraine, the European Union sought to reduce its dependence on natural gas from Russia. President Biden
agreed to increase shipments of natural gas and dramatically increase the United States’ export capacity.
Clifford Krauss, Europe and the U.S. Make Ambitious
Plans to Reduce Reliance on Russian Gas, N.Y. Times,
https://www.energy.gov/sites/default/files/2022-11/1949-National_Oil_Policy_for_United_States.pdf.
19 https://www.aogr.com/web-exclusives/exclusive-story/energysvital-role-in-world-war-ii-offers-lessons-for-today.
20
https://www.energy.gov/sites/default/files/2022-11/1949-National_Oil_Policy_for_United_States.pdf.
18
31
Mar. 25, 2022.21 This year, the petroleum industry’s role
in national security once again came to the fore due to
the conflict with Iran. See, e.g., Michael Froman, Iran,
the Strait of Hormuz, and an Unprecedented Energy
Crunch, Council on Foreign Relations (Mar. 13, 2026).22
Given the vital role that fossil fuels continue to play
in foreign affairs and national security, the need to reduce emissions and combat climate change must be
carefully weighed against the need to increase production when it is in the interest of national security. State
courts are not the proper authority to conduct this balancing of environmental and national security interests,
and their attempt to do so would violate the federal government’s exclusive control over foreign affairs. Statecourt suits like Respondents’ and their attendant risk of
future liability for purported climate-related damages
could well impact fuel production. This would severely
hinder the federal government’s ability to use the
United States’ natural resources as a tool to advance the
nation’s strategic interests.
CONCLUSION
Global climate change is a serious issue that deserves serious attention. The competing interests at
stake require that the federal government must maintain its exclusive discretion in setting national standards for interstate and international greenhouse gas
emissions, leaving other States the authority to regulate
emissions within their own borders. Americans depend
https://www.nytimes.com/2022/03/25/business/energy-environment/biden-eu-liquefied-natural-gas-deal-russia.html.
22
https://www.cfr.org/articles/iran-the-strait-of-hormuz-and-anunprecedented-energy-crunch.
21
32
on a stable energy supply and the economy that it powers, and these energy needs must be carefully balanced.
The judgment below should be reversed.
Respectfully submitted,
SARAH M. STERNLIEB
WEIL, GOTSHAL & MANGES LLP
1395 Brickell Avenue
Suite 1200
Miami, FL 33131
MARK A. PERRY
Counsel of Record
BRADY D. MORRIS
WEIL, GOTSHAL & MANGES LLP
2001 M Street NW
Suite 600
Washington, D.C. 20036
(202) 682-7000
Mark.Perry@weil.com
Counsel for Amicus Curiae
American Petroleum Institute
May 21, 2026
This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.