Petitioners Brief — Suncor Energy (U.S.A.) Inc., et al., Petitioners v. County Commissioners of Boulder County, et al.

Supreme Court briefMay 14, 2026

Ask Donna

What actually matters in this document.

Text

No. 25-170

In the Supreme Court of the United States

SUNCOR ENERGY (U.S.A.) INC., ET AL., PETITIONERS

COUNTY COMMISSIONERS OF BOULDER COUNTY, ET AL.

ON WRIT OF CERTIORARI

TO THE SUPREME COURT OF COLORADO

BRIEF FOR THE PETITIONERS

THEODORE V. WELLS, JR.

DANIEL J. TOAL

YAHONNES CLEARY

PAUL, WEISS, RIFKIND,

WHARTON & GARRISON LLP

1285 Avenue of the Americas

New York, NY 10019

KANNON K. SHANMUGAM

Counsel of Record

JAKE L. KRAMER

ELEANOR K. RITTER

DAVIS POLK & WARDWELL LLP

1050 17th Street, N.W.

Washington, DC 20036

(202) 962-7000

kshanmugam@davispolk.com

WILLIAM T. MARKS

ANNA J. LUCARDI

DAVID T. WONG

HUGH QUAN GOTTSCHALK

PAUL, WEISS, RIFKIND,

ERIC L. ROBERTSON

WHARTON & GARRISON LLP WHEELER TRIGG

2001 K Street, N.W.

O’DONNELL LLP

Washington, DC 20006

370 Seventeenth Street,

Suite 4500

Denver, CO 80202

QUESTIONS PRESENTED

1. 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.

2. Whether the Court has statutory and Article III

jurisdiction to hear this case.

(I)

PARTIES TO THE PROCEEDING

AND CORPORATE DISCLOSURE STATEMENT

Petitioners are Suncor Energy (U.S.A.) Inc.; Suncor

Energy Sales Inc.; and Exxon Mobil Corporation. Respondents are the County Commissioners of Boulder

County and the City of Boulder.

Petitioner Suncor Energy (U.S.A.) Inc. is a wholly

owned subsidiary of Suncor Energy (U.S.A.) Holdings

Inc., which is a wholly owned subsidiary of Suncor Energy

Inc. Suncor Energy Inc. has no parent corporation, and

no publicly traded company owns 10% or more of its stock.

Its stock ticker symbol is SU.

Petitioner Suncor Energy Sales Inc. is a wholly owned

subsidiary of Suncor Energy (U.S.A.) Inc.

Petitioner Exxon Mobil Corporation has no parent

corporation, and no publicly held company owns 10% or

more of its stock. Its stock ticker symbol is XOM.

(II)

TABLE OF CONTENTS

Page

Opinions below ................................................................................ 1

Jurisdiction ...................................................................................... 1

Constitutional and statutory provisions involved....................... 2

Statement ......................................................................................... 2

A. Background ........................................................................ 5

B. Procedural history ............................................................. 6

Summary of argument ................................................................. 11

Argument ....................................................................................... 15

I. The Court has statutory and constitutional

jurisdiction over this case ............................................... 15

A. The Court has jurisdiction

under 28 U.S.C. 1257(a) ........................................... 15

B. The Court has jurisdiction

under Article III of the Constitution ..................... 19

II. The Constitution precludes state-law claims

seeking relief for injuries allegedly caused

by interstate greenhouse-gas emissions ...................... 21

A. The structure of the Constitution does not allow

the law of a single State to govern claims

concerning interstate emissions ............................. 22

B. The Clean Air Act reinforces the constitutional

rule that States lack authority to regulate

out-of-state emissions............................................... 29

C. Respondents’ state-law claims seek relief

for injuries allegedly caused by interstate

emissions .................................................................... 34

III. The Constitution precludes state-law claims

seeking relief for injuries allegedly caused

by international greenhouse-gas emissions ............... 39

IV. The Clean Air Act preempts state-law claims

seeking relief for injuries allegedly caused

by emissions from another State ................................. 43

(III)

Page

Table of contents—continued:

Conclusion ...................................................................................... 48

TABLE OF AUTHORITIES

Cases:

American Electric Power Co.

v. Connecticut, 564 U.S. 410 (2011) ......... 6, 10, 22, 26-29,

31, 32, 44-46

American Insurance Association

v. Garamendi, 539 U.S. 396 (2003) ........................... 40, 42

Arizona v. United States, 567 U.S. 387 (2012) ................... 44

ASARCO Inc. v. Kadish, 490 U.S. 605 (1989) .................... 20

Atlantic Richfield Co. v. Christian,

590 U.S. 1 (2020) .................................................... 12, 16, 18

Atlantic Richfield Co. v. Montana Second

Judicial District Court,

408 P.3d 515 (Mont. 2017) ................................................ 16

Banco Nacional de Cuba v. Sabbatino,

376 U.S. 398 (1964) ............................................................ 40

Bandini Petroleum Co. v. Superior Court,

284 U.S. 8 (1931) ................................................................ 18

BMW of North America, Inc. v. Gore,

517 U.S. 559 (1996) ............................................................ 24

Bonaparte v. Tax Court, 104 U.S. 592 (1882) ..................... 24

Boyle v. United Technologies Corp.,

487 U.S. 500 (1988) ............................................................ 44

BP p.l.c. v. Mayor & City Council of Baltimore,

593 U.S. 230 (2021) .............................................................. 9

Brown v. Fletcher’s Estate, 210 U.S. 82 (1908) .................. 24

Buckman Co. v. Plaintiffs’ Legal Committee,

531 U.S. 341 (2001) ...................................................... 30, 44

Burnet v. Brooks, 288 U.S. 378 (1933) ................................. 24

California v. General Motors Corp.,

Civ. No. 06-5755, 2007 WL 2726871

(N.D. Cal. Sept. 17, 2007) ................................................... 6

Page

Cases—continued:

Cameron v. District Court, 565 P.2d 925 (Colo. 1977) ...... 18

Camreta v. Greene, 563 U.S. 692 (2011) .............................. 20

Chicago & Southern Air Lines v. Waterman S.S.

Corp., 333 U.S. 103 (1948) ................................................ 43

Chy Lung v. Freeman, 92 U.S. 275 (1875) .......................... 40

City of Milwaukee v. Illinois, 451 U.S. 304 (1981) ........... 26

City of New York v. Chevron,

993 F.3d 81 (2d Cir. 2021) .............................. 31, 35, 41-43

Coventry Health Care of Missouri, Inc.

v. Nevils, 581 U.S. 87 (2017) ............................................ 19

Cox Broadcasting Corp. v. Cohn,

420 U.S. 469 (1975) ................................................ 12, 16, 19

Coyle v. Smith, 221 U.S. 559 (1911) ..................................... 23

Crosby v. National Foreign Trade Council,

530 U.S. 363 (2000) ...................................................... 31, 46

Dan’s City Used Cars, Inc. v. Pelkey,

569 U.S. 251 (2013) ............................................................ 19

Detroit & Mackinac Railway Co. v. Michigan

Railroad Commission, 240 U.S. 564 (1916) .................. 16

Egbert v. Boule, 596 U.S. 482 (2022) .................................... 43

EPA v. EME Homer City Generation, L.P.,

572 U.S. 489 (2014) ................................................ 27, 33, 46

Erie Railroad Co. v. Tompkins,

304 U.S. 64 (1938) ........................................................ 25, 26

Fisher v. District Court, 424 U.S. 382 (1976) ..................... 16

Fognani v. Young, 115 P.3d 1268 (Colo. 2005) ................... 18

Food Marketing Institute v. Argus Leader Media,

588 U.S. 427 (2019) ...................................................... 19, 20

Fort Wayne Books, Inc. v. Indiana,

489 U.S. 46 (1989) .............................................................. 19

Franchise Tax Board v. Hyatt,

587 U.S. 230 (2019) .......................................... 22-24, 28, 29

Fuld v. Palestine Liberation Organization,

606 U.S. 1 (2025) .................................................... 24, 40, 42

Page

Cases—continued:

Georgia v. Tennessee Copper Co.,

206 U.S. 230 (1907) ...................................................... 25, 27

Gibbons v. Ogden, 22 U.S. (9 Wheat.) 1 (1824) ................... 23

Goodyear Atomic Corp. v. Miller, 486 U.S. 174 (1988)..... 30

Hawaii v. Office of Hawaiian Affairs,

556 U.S. 163 (2009) ............................................................ 15

Health & Hospital Corp. of Marion County

v. Talevski, 599 U.S. 166 (2023) ...................................... 21

Hencely v. Fluor Corp., 146 S. Ct. 1086 (2026) .................. 32

Hines v. Davidowitz, 312 U.S. 52 (1941) ............................. 40

Hoery v. United States, 64 P.3d 214 (Colo. 2003) .............. 36

Houston Community College System v. Wilson,

595 U.S. 468 (2022) ............................................................ 21

Illinois v. City of Milwaukee, 406 U.S. 91 (1972) ........ 25, 29

Illinois v. City of Milwaukee,

731 F.2d 403 (7th Cir. 1984) ............................................. 29

International Paper Co. v. Ouellette,

479 U.S. 481 (1987) ......................................... 26, 31, 32, 34,

39, 44-46

Kansas v. Colorado, 206 U.S. 46 (1907) .............................. 23

Kurns v. Railroad Friction Products Corp.,

565 U.S. 625 (2012) ...................................................... 38, 39

Lamps Plus, Inc. v. Varela, 587 U.S. 176 (2019) ............... 20

McKinney v. Arizona, 589 U.S. 139 (2020) ........................ 18

Missouri v. Illinois, 200 U.S. 496 (1906) ...................... 24, 25

Monsanto Co. v. Geertson Seed Farms,

561 U.S. 139 (2010) ............................................................ 21

National Pork Producers Council v. Ross,

598 U.S. 356 (2023) ............................................................ 22

New Jersey v. New York, 283 U.S. 473 (1931).................... 25

New York v. New Jersey, 256 U.S. 296 (1921).................... 25

North Dakota v. Minnesota, 263 U.S. 365 (1923) .............. 25

Parker Drilling Management Services, Ltd.

v. Newton, 587 U.S. 601 (2019) ........................................ 30

People v. District Court, 664 P.2d 247 (Colo. 1983) ........... 18

VII

Page

Cases—continued:

People ex rel. T.T., 442 P.3d 851 (Colo. 2019) ..................... 18

Public Service Co. v. Van Wyk,

27 P.3d 377 (Colo. 2001) ................................................... 36

Rhode Island v. Massachusetts,

37 U.S. (12 Pet.) 657 (1838) .............................................. 22

Robinson v. Colorado State Lottery Division,

179 P.3d 998 (Colo. 2008) ................................................. 36

Saint John’s Church in Wilderness v. Scott,

194 P.3d 475 (Colo. App. 2008) ........................................ 36

Shelby County v. Holder, 570 U.S. 529 (2013) ................... 23

State Farm Mutual Automobile Insurance Co.

v. Campbell, 538 U.S. 408 (2003) ..................................... 24

Sturges v. Crowninshield,

17 U.S. (4 Wheat.) 122 (1819) .......................................... 28

Texas Industries, Inc. v. Radcliff Materials, Inc.,

451 U.S. 630 (1981) ...................................................... 22, 28

Tyler v. Hennepin County, 598 U.S. 631 (2023) ................ 20

U.S. Term Limits, Inc. v. Thornton,

514 U.S. 779 (1995) ............................................................ 23

United States Forest Service v. Cowpasture River

Preservation Association, 590 U.S. 604 (2020) ............ 30

United States v. Bevans,

16 U.S. (3 Wheat.) 336 (1818) .......................................... 24

United States v. Curtiss-Wright Export Corp.,

299 U.S. 304 (1936) ............................................................ 40

United States v. Locke, 529 U.S. 89 (2000) ............. 30, 44, 46

United States v. Pink, 315 U.S. 203 (1942) ............. 40, 42, 43

United States v. Standard Oil Co.,

332 U.S. 301 (1947) ............................................................ 30

Warner Chappell Music, Inc. v. Nealy,

601 U.S. 366 (2024) ............................................................ 21

Watson v. Employers Liability Assurance Corp.,

348 U.S. 66 (1954) .............................................................. 24

Williams v. Lee, 358 U.S. 217 (1959) ................................... 30

Zschernig v. Miller, 389 U.S. 429 (1968) ............................. 40

VIII

Page

Constitutions, treaties, statutes, and rules:

U.S. Const.:

Art. I, § 10 .......................................................................... 23

Art. III.................................................................... 12, 19-21

Art. VI, cl. 2 ....................................................................... 23

Kigali Amendment to the Montreal Protocol

on Substances That Deplete the Ozone Layers,

Oct. 15, 2016, S. Treaty Doc. No. 117-1,

C.N.730.2017 ...................................................................... 41

United Nations Framework Convention on Climate

Change, May 9, 1992, S. Treaty Doc. No. 102-38,

1771 U.N.T.S. 107. ............................................................ 41

Clean Air Act, 42 U.S.C. 7401-7675:

42 U.S.C. 7410(a)(2)(H)(ii) ............................................... 41

42 U.S.C. 7411(b)............................................................... 33

42 U.S.C. 7411(d)............................................................... 33

42 U.S.C. 7415 ................................................................... 41

42 U.S.C. 7416 ................................................................... 33

42 U.S.C. 7426(b)............................................................... 33

42 U.S.C. 7521(a)(1) .......................................................... 33

42 U.S.C. 7521(a)(2) .......................................................... 33

42 U.S.C. 7521(a)(3)(E) .................................................... 33

42 U.S.C. 7547(a)(1) .......................................................... 33

42 U.S.C. 7547(a)(5) .......................................................... 33

42 U.S.C. 7571(a)(2)(A) .................................................... 33

42 U.S.C. 7604(e) ............................................................... 33

Clean Water Act, 33 U.S.C. 1251-1389 .................... 31-33, 45

Global Climate Protection Act, Pub. L. No. 100-204,

tit. 11, § 1103, 101 Stat. 1407 (1987) ................................ 41

Locomotive Inspection Act, 49 U.S.C. 20701-20703 .......... 38

28 U.S.C. 1257(a) ..............................................1, 12, 15, 16, 18

28 U.S.C. 1331(a) .................................................................... 25

Colo. Const. Art. VI:

§ 2 ........................................................................................ 17

§ 3 ........................................................................................ 17

Colorado Consumer Protection Act,

Colo. Rev. Stat. § 6-1-105(1) .............................................. 8

Page

Statute and rules—continued:

Iowa Code § 673B.2 (2026) .................................................... 28

Colo. App. R.:

Rule 21 .......................................................................... 17, 18

Rule 21(a)(1) .................................................................. 9, 17

Rule 21(a)(2) ...................................................................... 18

Rule 21(b) ........................................................................... 17

Rule 21(e)(1) ...................................................................... 17

Rule 21(h)(2) ...................................................................... 17

Rule 21(o) ........................................................................... 18

Miscellaneous:

Declaration of Independence (1776) ................................... 22

European Commission, GHG Emissions

of All World Countries (2025)

<tinyurl.com/worldemissions> ...................................... 39

Exec. Order 14,162 (Jan. 20, 2025)....................................... 41

Exxon Mobil Corp.,

2026 Advancing Climate Solutions Report

<tinyurl.com/emclimatesolutions2026> ......................... 6

Exxon Mobil Corp., Corporate Plan Update

(Dec. 9, 2025) <tinyurl.com/em-update>........................ 6

91 Fed. Reg. 7,723 (Feb. 18, 2026) ....................................... 33

Federalist Society, Can State Courts Set Global

Climate Policy? (Oct. 8, 2025)

<tinyurl.com/federalistsocietypanel> .......................... 38

Henry J. Friendly, In Praise of ‘Erie’—

And of the New Federal Common Law,

39 N.Y.U. L. Rev. 383 (1964) ........................................... 26

Anne Whale Gill, Colorado Appellate Law &

Practice (3d ed. 2018) ....................................................... 18

Okla. S.B. 1439 (2026 Reg. Sess.) ......................................... 28

Stephen M. Shapiro et al., Supreme Court Practice

(11th ed. 2019) ................................................................... 17

Joseph Story, Commentaries on the Constitution of

the United States (4th ed. 1873) ...................................... 23

Page

Miscellaneous—continued:

Suncor, Response to Recent Changes

to the Competition Act (June 2024)

<tinyurl.com/suncorresponse> ....................................... 6

Utah H.B. 222 (2026 Gen. Sess.) .......................................... 28

The White House, American Energy Dominance Is

Back Under President Trump (Feb. 24, 2026)

<tinyurl.com/americanenergydominance> ................. 41

In the Supreme Court of the United States

No. 25-170

SUNCOR ENERGY (U.S.A.) INC., ET AL., PETITIONERS

COUNTY COMMISSIONERS OF BOULDER COUNTY, ET AL.

ON WRIT OF CERTIORARI

TO THE SUPREME COURT OF COLORADO

BRIEF FOR THE PETITIONERS

OPINIONS BELOW

The opinion of the Colorado Supreme Court (Pet. App.

1a-47a) is reported at 586 P.3d 161. The opinion of the

trial court (Pet. App. 48a-139a) is unreported but is available at 2024 WL 3204275.

JURISDICTION

The judgment of the Colorado Supreme Court was entered on May 12, 2025. The petition for a writ of certiorari

was filed on August 8, 2025, and was granted on February

23, 2026. The jurisdiction of this Court rests on 28 U.S.C.

1257(a). See pp. 15-21, infra.

(1)

CONSTITUTIONAL AND

STATUTORY PROVISIONS INVOLVED

Pertinent constitutional and statutory provisions are

reproduced in an appendix to this brief. See App., infra,

1a-4a.

STATEMENT

Global climate change is one of the most complex public-policy challenges of our time. It results from the accumulation of greenhouse gases emitted from every State in

the Nation and every nation in the world—emissions that

cannot be unmixed and traced to their individual sources.

Yet respondents—the city of Boulder, Colorado, and the

surrounding county—are attempting to address that inherently interstate and international challenge by seeking

to impose massive monetary liability through the mechanism of state tort law.

Respondents have brought suit against two of the

world’s countless fossil-fuel producers seeking to recover

damages for past and future harms allegedly caused by

global climate change. Respondents’ claims are avowedly

interstate and international in scope: they contend that

petitioners’ worldwide production and allegedly deceptive

marketing of fossil fuels resulted in consumers’ use of fossil fuels around the world, which released interstate and

international greenhouse-gas emissions, which combined

with all other greenhouse gases in the atmosphere to alter

the global climate, which then resulted in localized physical harms in Boulder. According to respondents, state law

is competent to regulate the inherently interstate and international issue of global climate change because the

combined effect of all of humanity’s emissions—only a

tiny fraction of which resulted from petitioners’ fossil-fuel

products—allegedly caused in-state harm.

Respondents are not alone in pursuing that dubious

theory. Scores of other state and local governments have

brought similar suits, claiming that the production and allegedly deceptive marketing of fossil fuels violated state

tort law. As a member of respondents’ legal team openly

avowed, this coordinated nationwide litigation aims to impose an enormous “carbon tax” that could “bankrupt[]”

the energy industry. The requested damages in any one

case could reach into the billions. And if claims such as

Boulder’s are allowed to proceed, every political jurisdiction in the Nation could bring a similar suit against any

subset of the world’s fossil-fuel producers (with the defendants carefully selected, as here, to keep the suit in

state court).

The question presented in this case is whether state

law is competent within our federal system to impose potentially crushing monetary liability on a subset of energy

producers for localized harms allegedly caused by the effects of interstate and international greenhouse-gas emissions on the global climate. The answer to that question

is no.

Respondents’ audacious attempt to use state tort law

to address the effects of global climate change is incompatible with the structure of the Constitution. The States

surrendered their ability to redress inherently transboundary issues such as global climate change when they

agreed to enter the Union. As a consequence, for over a

century, the Court fashioned federal rules of decision to

resolve claims seeking relief from the effects of interstate

air and water pollution, until Congress stepped in to address those issues by statute. The application of federal

law to such claims stems from the principles that the

States are coequal sovereigns with competing claims to

regulate shared natural resources and that States lack the

power to regulate conduct beyond their borders. As this

Court has consistently recognized, resorting to a single

State’s law to resolve an inherently interstate dispute contradicts the basic scheme of the Constitution.

Under the foregoing principles, respondents’ statelaw claims cannot proceed. Respondents concededly seek

relief for injuries allegedly caused by interstate greenhouse-gas emissions. And although Congress displaced

the federal common-law rules of decision that formerly

governed interstate-pollution claims by enacting the

Clean Air Act, that did not invite state law to apply in this

area for the first time. Instead, the structure of our constitutional system continues to foreclose resort to state

law unless Congress affirmatively authorizes its application. States have no residual or inherent power under our

Constitution to regulate in this area, and no federal law

authorizes state common-law claims for harms caused by

diffuse interstate and international emissions. For those

reasons, respondents’ claims fail.

The Constitution further forecloses respondents’

claims because they necessarily seek relief for harms allegedly caused by greenhouse-gas emissions occurring

outside the United States. Claims seeking relief from the

effects of international greenhouse-gas emissions interfere with the federal government’s extensive diplomatic

efforts, which balance the need to address climate change

on the international level with other competing foreign

and domestic interests. Under the Constitution, the federal government is the Nation’s exclusive voice in foreign

affairs. State tort law cannot stand in its way.

Finally, by its own force, the Clean Air Act also

preempts respondents’ claims. The Act establishes a comprehensive statutory scheme for the regulation of air

quality across the United States. Respondents’ state-law

claims undermine that scheme by subverting the primacy

of federal regulation and aggrandizing the limited and defined role afforded to the States.

In short, the Colorado Supreme Court’s decision allowing respondents’ state-law claims to proceed is incompatible with the structure of our constitutional system, the

Clean Air Act, and this Court’s precedents. And if the rule

in that decision were adopted on a national scale, it would

authorize all fifty States, the tens of thousands of municipalities, and even the hundreds of millions of individuals

in our country to ask local courts to establish countless,

conflicting climate policies for the Nation. Giving even a

single jury the power to impose ruinous liability on selected members of the energy industry is a recipe for

chaos. Unleashing juries nationwide is a recipe for disaster.

This misuse of the legal system cannot stand. State

tort law is not the solution to global climate change. The

Colorado Supreme Court’s decision should be reversed.

A. Background

1. Petitioner Exxon Mobil Corporation is the Nation’s largest energy company; its primary business includes the production and sale of fossil fuels around the

world. Petitioners Suncor Energy (U.S.A.) Inc. and Suncor Energy Sales Inc. are indirect subsidiaries of Suncor

Energy Inc., a leading Canadian energy company; Suncor

operates Colorado’s only two oil refineries.

ExxonMobil and Suncor recognize that greenhousegas emissions contribute to global climate change; that

global climate change is one of society’s biggest challenges; and that comprehensive policy responses, balancing risk reduction with affordable energy, are necessary

to address those risks. As ExxonMobil has stated, global

climate change is “real,” and “the challenge is more complex—and the range of solutions more broad—than most

conversations acknowledge.” Exxon Mobil Corp., 2026

Advancing Climate Solutions Report 2 <tinyurl.com/emclimatesolutions2026>. ExxonMobil thus aims to provide

“reliable, affordable energy even as [it] lower[s] [greenhouse-gas] emissions.” Ibid. To that end, ExxonMobil

has supported legislation addressing the issue of global

climate change, see id. at 15; has advocated for innovative,

practical policies such as carbon-emissions accounting

and product-level carbon-intensity standards, see id. at 9,

44-52; and is pursuing approximately $20 billion in loweremission investments between 2025 and 2030, see Exxon

Mobil Corp., Corporate Plan Update 18 (Dec. 9, 2025) <tinyurl.com/em-update>.

Like ExxonMobil, Suncor is “fully committed” to “environmental performance,” “sustainable development,”

and “reduc[ing] greenhouse gas emissions.” Suncor, Response to Recent Changes to the Competition Act (June

2024) <tinyurl.com/suncorresponse>. Suncor believes

that it has a “key role to play in helping Canada reduce its

greenhouse gas emissions and meet its climate ambitions,

while also supporting a vibrant economy, improving

environmental performance and providing Canadians

with secure access to affordable energy.” Ibid.

2. Dissatisfied with the climate policy set by the federal government, state and local governments have resorted to the courts in an effort to bring about reductions

of greenhouse-gas emissions. They initially focused primarily on car manufacturers and electric-power producers, pursuing claims under federal law for public nuisance

resulting from climate change; those claims were uniformly dismissed as not cognizable under federal law.

See, e.g., American Electric Power Co. v. Connecticut, 564

U.S. 410, 429 (2011); California v. General Motors Corp.,

Civ. No. 06-5755, 2007 WL 2726871, at *17 (N.D. Cal.

Sept. 17, 2007). In recent years, state and local governments have shifted their strategy. They are now targeting private fossil-fuel producers, and they are bringing

their claims under state law (rather than federal law) for

monetary relief for past and future harms allegedly

caused by climate change. And rather than bringing suit

in federal court, those governments are now doing so in

state court instead, selecting their defendants carefully in

a bid to avoid federal diversity jurisdiction. Nearly 60

state and local governments have filed lawsuits such as

this one, and more are continuing to do so.

B. Procedural History

1. The plaintiffs in this case (respondents here) are

the City of Boulder, Colorado, and the surrounding

county. On April 27, 2018, they filed the underlying lawsuit against petitioners in Colorado state court. Respondents claim that petitioners’ worldwide conduct has contributed to global climate change, which in turn has

caused a variety of harms in Boulder. Specifically, respondents allege that petitioners have “supplied a substantial portion of all fossil fuels used worldwide” and are

“the largest sources of [greenhouse-gas] emissions both

globally and historically.” J.A. 23, 98, 102. According to

respondents, petitioners’ “unchecked production, promotion, refining, marketing and sale of fossil fuels” throughout the world, “while concealing and/or misrepresenting

the dangers associated with fossil fuels’ intended use,” has

“led to unchecked fossil fuel use,” resulting in an “unprecedented rapid rise in the concentration of [greenhouse

gases] in the atmosphere.” J.A. 3. Respondents further

allege that petitioners are “continuing their efforts and increasing fossil fuel activities” instead of “bringing emissions under control.” J.A. 97-98. The resulting increasing

concentration of greenhouse gases, according to respondents, leads to “warming [of] the atmosphere and oceans”

and “alteration of the climate,” including rising “global average temperatures.” J.A. 3, 34-35, 37.

Respondents allege that the effects of global climate

change manifest in “increases in extreme hot summer

days and increases in minimum nighttime temperatures,

precipitation changes, larger and more frequent wildfires,

increased concentrations of ground-level ozone, higher

transmission of viruses and disease from insects, altered

streamflows, bark beetle outbreaks, ecosystem damage,

forest die-off, reduced snowpack, and drought.” J.A. 39.

Respondents allege that, as a result of the effects of global

climate change, they have incurred, and will incur, billions

of dollars in property damage, in addition to costs related

to mitigation measures and repairs, emergency services,

and public-health measures. J.A. 53-83.

Respondents assert state-law claims for public nuisance, private nuisance, trespass, and unjust enrichment,

as well as consumer deception in violation of the Colorado

Consumer Protection Act, Colo. Rev. Stat. § 6-1-105(1),

and a derivative claim for civil conspiracy. J.A. 112-136.

Each of respondents’ claims is premised on the same basic

theory of liability: petitioners “altered the climate by selling fossil fuels at levels [they] knew would bring numerous and catastrophic injuries to Colorado, and by misleading the public about the consequences of unfettered fossil

fuel use to maintain demand for their products.” Resp.

Colo. S. Ct. Br. 1. Respondents seek to recoup “billions of

dollars” from petitioners for past and future climatechange harms. J.A. 1-3, 114, 136-137.

2. Petitioners removed this case to federal court, but

the district court granted respondents’ motion to remand.

405 F. Supp. 3d 947 (D. Colo. 2019). On appeal, the Tenth

Circuit initially affirmed. 965 F.3d 792 (2020). After this

Court’s decision in BP p.l.c. v. Mayor & City Council of

Baltimore, 593 U.S. 230 (2021), the Court granted certiorari, vacated the Tenth Circuit’s decision, and remanded

for further consideration. 141 S. Ct. 2667 (2021). The

Tenth Circuit again affirmed, 25 F.4th 1238 (2022), and

this Court denied certiorari, 143 S. Ct. 1795 (2023).

3. Petitioners moved to dismiss the amended complaint, arguing in relevant part that federal law forecloses

state-law claims seeking relief for injuries allegedly

caused by the effects of global greenhouse-gas emissions

on the global climate. The trial court denied petitioners’

motion in relevant part, holding that federal law did not

foreclose respondents’ claims. Pet. App. 87a-115a. (The

trial court did dismiss respondents’ statutory consumerdeception claim for failure to state a claim, id. at 133a136a, and that claim is no longer in the case.)

4. ExxonMobil then petitioned the Colorado Supreme Court for “an order to show cause,” Pet. App. 7a,

invoking that court’s “original jurisdiction” to exercise

“general superintending authority” over the trial court.

Colo. App. R. 21(a)(1). Suncor joined that request.

The Colorado Supreme Court granted the petition and

issued the order to show cause. J.A. 141-142. In the order, the Colorado Supreme Court directed respondents

and the state trial court to answer “[w]hether the district

court erroneously concluded that [Boulder’s] claims could

proceed under state law.” Ibid. Respondents and the trial

court answered the order to show cause independently

and were represented by separate counsel.

5. Following briefing and oral argument, the Colorado Supreme Court discharged the order to show cause

and remanded to the trial court for further proceedings,

holding that federal law did not foreclose respondents’

claims. Pet. App. 1a-25a.

a. The Colorado Supreme Court first concluded that,

because the Clean Air Act displaced the federal common

law that previously governed claims concerning interstate

air pollution, federal common law played no role in assessing whether federal law forecloses respondents’

claims. Pet. App. 9a-11a. The Colorado Supreme Court

acknowledged this Court’s holding that federal common

law governs “interstate and international disputes implicating the conflicting rights of states or the United

States’s relations with foreign nations.” Id. at 9a (citing

American Electric Power, 564 U.S. at 421). But because

the Clean Air Act displaced federal common law, the court

conducted a more limited inquiry into “whether the [Clean

Air Act] preempts [respondents’] claims.” Id. at 11a.

The Colorado Supreme Court added that federal common law would not have applied even if it had not been

displaced. Pet. App. 18a. The court reasoned that, because respondents have not “brought an action against a

pollution emitter to abate pollution” and instead “seek[]

damages from upstream producers for harms stemming

from the production and sale of fossil fuels,” respondents’

claims “do not seek to regulate [greenhouse-gas] emissions.” Id. at 17a, 21a.

The Colorado Supreme Court proceeded to hold that

the Clean Air Act did not preempt respondents’ claims.

Pet. App. 11a-16a. Applying the presumption against

preemption, the court reasoned that respondents’ claims

were not subject to either field preemption or conflict

preemption. Id. at 13a-15a.

Finally, the Colorado Supreme Court concluded that

respondents’ claims could proceed despite their reliance

on international emissions. Pet. App. 22a-24a. Because

the court determined that respondents’ claims “involve

areas of traditional state responsibility” and do not seek

to regulate greenhouse-gas emissions, it held that respondents’ claims did not intrude on or conflict with any

federal power over foreign policy and accordingly were

not preempted. Id. at 24a.

b. Justice Samour, joined by Justice Boatright, dissented. Pet. App. 25a-47a. In his view, before the Clean

Air Act, “federal common law conflicted with[] and precluded state-law claims to redress interstate pollution,”

id. at 31a, and respondents’ claims closely resembled

those precluded claims, id. at 34a. As a result, rather than

applying “ordinary statutory preemption,” Justice

Samour explained that “the appropriate inquiry with respect to the interstate aspect of [respondents’] claims is

whether the [Clean Air Act] affirmatively authorizes

them,” which “it does not.” Id. at 26a-27a. Finally, because respondents’ claims implicate greenhouse-gas

emissions occurring outside the United States, Justice

Samour concluded that the claims were preempted under

the doctrine of foreign-affairs preemption, because the

claims would “imped[e]” the federal government’s judgment on addressing air pollution “in the international

sphere.” Id. at 43a, 45a.

SUMMARY OF ARGUMENT

The question presented in the petition for certiorari is

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. When granting certiorari, the Court directed the parties to brief the additional question whether

the Court has jurisdiction to hear this case. The answer

to both questions is yes.

I. The Court has statutory and constitutional jurisdiction to hear this case.

A. The Colorado Supreme Court’s decision constitutes a final judgment reviewable under 28 U.S.C. 1257(a)

because it terminated a self-contained original proceeding

in Colorado’s court of last resort. In Atlantic Richfield

Co. v. Christian, 590 U.S. 1 (2020), the Court held that

such a self-contained proceeding is “final” for purposes of

Section 1257(a). Colorado law makes clear that the showcause proceeding before the Colorado Supreme Court

was an original proceeding. In the alternative, the Colorado Supreme Court’s decision should be treated as “final” for purposes of Section 1257(a) because it falls within

the fourth category of cases identified in Cox Broadcasting Corp. v. Cohn, 420 U.S. 469 (1975).

B. This Court also has Article III jurisdiction over the

case because petitioners have Article III standing to invoke the Court’s authority. The decision below rejected

petitioners’ federal defense and will constitute binding

precedent in climate lawsuits pending in Colorado state

courts; as a result, it finally determines petitioners’ federal rights and subjects them to the risk of adverse consequences that would not occur if petitioners had prevailed.

The decision below will also force petitioners to incur

monetary costs as a result of being forced to continue defending these lawsuits. Such consequences, flowing from

the adverse decision below and redressable by a favorable

decision from this Court, easily provide petitioners with

Article III standing to seek this Court’s review.

II. On the merits, federal law precludes state-law

claims seeking relief for injuries allegedly caused by the

effects of interstate greenhouse-gas emissions on the

global climate.

A. As the Court has long recognized, there are certain

areas in which state law cannot apply to resolve contro-

versies in our Nation’s federal system. Claims seeking relief for the effects of global climate change fall within one

of those areas.

The application of federal law to those claims results

from our constitutional structure. Under the foundational

principle of equal sovereignty, the Constitution limits the

powers that the States previously enjoyed as independent

sovereigns. As a result of that principle, States cannot apply their laws in certain areas. A closely related principle

is that a State cannot extend its law to regulate conduct

beyond its borders.

Consistent with those principles, this Court has long

held that federal law governs disputes over the regulation

of air and water in their ambient or interstate aspects.

And the structure of the Constitution explains those decisions. Because air and water are shared natural resources

that flow without concern for political borders, the States

each have their own potentially conflicting interests. By

joining the Union, the States surrendered their right to

resolve those conflicts by resort to their own law in lieu of

a neutral, uniform federal law. The need for uniform federal law is even greater in the context of global climate

change, where any claim necessarily implicates emissions

released from countless sources spread across every

State in the Nation—and indeed every nation in the world.

B. The enactment of the Clean Air Act reinforces that

federal-state balance. In the absence of an applicable act

of Congress, this Court applied federal common law to

disputes over interstate pollution. Congress’s enactment

of the Clean Air Act, which replaced that federal common

law with a comprehensive statutory scheme, did not authorize state law to reach interstate emissions. Those controversies remain inherently federal. If state law could

not constitutionally apply before the enactment of the

Clean Air Act, it necessarily follows that state law remains

inapplicable unless Congress expressly authorizes it. But

nothing in the Clean Air Act authorizes state common-law

claims seeking relief for the effects of emissions emanating from other States.

C. Respondents seek to apply Colorado law to the inherently federal area of interstate emissions. Respondents’ claims are premised on greenhouse-gas emissions

occurring worldwide. The fact that the claims target producers of fossil fuels, rather than emitters of greenhouse

gases, does not allow them to sidestep the application of

federal law. Regardless of the choice of defendant, the

gravamen of respondents’ claims is that some marginal increase in global greenhouse-gas emissions attributable to

petitioners’ conduct caused them harm. Those claims

thus fall squarely within the inherently federal area of interstate-pollution disputes and are presumptively foreclosed by federal law.

III. Respondents’ state-law claims also cannot proceed for the independent reason that such claims would

undermine the federal government’s exclusive control

over foreign affairs. For decades, the federal government

has addressed climate change by carefully balancing mitigating the risks of climate change with satisfying domestic and global energy needs. Allowing state and local governments to seek liability for greenhouse-gas emissions

released abroad would directly undermine the federal

government’s efforts to handle this quintessentially

global challenge. Such lawsuits would create an end-run

around the United States’ existing diplomatic channels for

addressing climate change in favor of innumerable state

judicial ones. And the imposition of potentially devastating liability on fossil-fuel producers will undercut the government’s pursuit of primacy in global energy production.

The Constitution’s allocation of foreign-affairs powers exclusively to the federal government thus forecloses respondents’ claims.

IV. Independent of the Constitution’s structural division of powers between the state and federal governments, the Clean Air Act preempts respondents’ state-law

claims of its own accord. The Clean Air Act establishes a

comprehensive statutory scheme for the regulation of air

quality across the United States. That scheme directs the

Environmental Protection Agency to be the first decider

of the Nation’s emissions standards and defines a circumscribed role for the States. Respondents’ state-law claims

thus intrude upon a field dominated by Congress and undermine the Act’s regulatory structure and purpose by

seeking to apply Colorado law to redress harms caused by

out-of-state emissions.

The Colorado Supreme Court’s determination that respondents’ state-law claims could proceed was erroneous.

Its judgment should be reversed.

ARGUMENT

THE COURT HAS STATUTORY AND CONSTITUTIONAL JURISDICTION OVER THIS CASE

A. The Court Has Jurisdiction Under 28 U.S.C. 1257(a)

Section 1257(a) provides that the Court may review by

writ of certiorari “[f]inal judgments or decrees rendered

by the highest court of a State in which a decision could be

had,” where the state-court judgment sufficiently depends on the resolution of a question of federal law. See

Hawaii v. Office of Hawaiian Affairs, 556 U.S. 163, 171172 (2009). Respondents concede that the decision below

was issued by Colorado’s highest court on an issue of federal law. See Br. in Opp. 6-7. The only question is

whether the decision below was “final” for purposes of

Section 1257(a). It was, for two independent reasons.

First, this case arises from a final determination of the

Colorado Supreme Court in an original proceeding. Second, this case falls within the fourth category of cases

identified in Cox Broadcasting Corp. v. Cohn, 420 U.S. 469

(1975).

1. The Colorado Supreme Court’s decision was “final” for purposes of Section 1257(a) because it terminated

a self-contained original proceeding in Colorado’s court of

last resort.

a. The Court’s decision in Atlantic Richfield Co. v.

Christian, 590 U.S. 1 (2020), is directly on point. In that

case, the Montana Supreme Court granted a supervisory

writ to review a trial court’s order denying summary judgment; it ultimately affirmed the order and remanded for

the case to continue. See Atlantic Richfield Co. v. Montana Second Judicial District Court, 408 P.3d 515, 517,

523 (Mont. 2017). This Court held that the Montana Supreme Court’s decision was “final” for purposes of Section

1257(a) because, “[u]nder Montana law, a supervisory writ

proceeding is a self-contained case, not an interlocutory

appeal.” Atlantic Richfield, 590 U.S. at 12. That was true

even though the Montana Supreme Court conducted de

novo review of the denial of summary judgment and disposed of the action by remanding to the trial court for further proceedings. See 408 P.3d at 518, 523. The Court

emphasized that finality is determined by “the nature of

the [state-court] proceeding, not the issues the state court

reviewed.” 590 U.S. at 12.

Atlantic Richfield does not stand alone. In numerous

cases, the Court has held that, when a state’s highest

court entertains an original writ proceeding, the petition

initiates a separate case, and the court’s ensuing decision

is final for purposes of this Court’s review. See, e.g.,

Fisher v. District Court, 424 U.S. 382, 385 n.7 (1976); Detroit & Mackinac Railway Co. v. Michigan Railroad

Commission, 240 U.S. 564, 570-571 (1916); Stephen M.

Shapiro et al., Supreme Court Practice § 3.8 (11th ed.

2019) (collecting additional cases).

b. The foregoing precedents confirm the Court’s statutory jurisdiction over this case. In the proceeding below,

petitioners filed a petition in the Colorado Supreme Court

for an order to show cause under Colorado Appellate Rule

21, seeking, as is relevant here, an order reversing the district court’s determination that federal law did not foreclose respondents’ claims. See Colo. S. Ct. Pet. 5. The

Colorado Supreme Court issued an order and rule to show

cause to respondents and the state trial court why the relief in the petition should not be granted. See J.A. 141142. And after holding that federal law did not foreclose

respondents’ claims, the Colorado Supreme Court discharged the order to show cause. See Pet. App. 24a.

Under Colorado law, a proceeding under Colorado Appellate Rule 21 constitutes a self-contained original proceeding before the Colorado Supreme Court. Rule 21 is

entitled “Original Proceedings in the Supreme Court,”

and the filing of a petition under Rule 21 “[i]nitiat[es] an

original proceeding” in the Colorado Supreme Court.

Colo. App. R. 21(b). The rule applies where the Colorado

Supreme Court is exercising its constitutional authority

to issue “original and remedial writs,” such as writs of

mandamus, and its “general superintending control over

all inferior courts” in Colorado. Colo. Const. Art. VI, §§ 23; see Colo. App. R. 21(a)(1).

Other aspects of Rule 21 support the conclusion that a

proceeding under that rule is a self-contained original proceeding. The trial court itself may be named as a respondent—as occurred here. Colo. App. R. 21(e)(1); see J.A.

141-142. Upon the issuance of an order to show cause, any

related proceedings are stayed “until final determination

of the original proceeding in the supreme court.” Colo.

App. R. 21(h)(2). And at the end of a Rule 21 proceeding,

the Colorado Supreme Court “in its discretion may discharge the order or make it absolute, in whole or in part.”

Colo. App. R. 21(o). An order to show cause is thus “extraordinary in nature,” Colo. App. R. 21(a)(2); is available

only when an “appeal” is not, ibid.; and, “if granted, takes

the form of a special mandate from the court,” Anne

Whalen Gill, Colorado Appellate Law & Practice § 15:1,

at 246 (3d ed. 2018).

Unsurprisingly, the Colorado Supreme Court has repeatedly characterized proceedings under Rule 21 as

“original proceedings”—including in the decision below.

See, e.g., Pet. App. 7a; People ex rel. T.T., 442 P.3d 851,

853, 855-856 (2019); Fognani v. Young, 115 P.3d 1268,

1271 (2005); People v. District Court, 664 P.2d 247, 251

(1983). And it has explained that it can properly invoke

“its supervisory powers by means of [its] original jurisdiction” even where “an error by the trial court, acting within

its jurisdiction, may later be corrected on appeal.” Cameron v. District Court, 565 P.2d 925, 928 (Colo. 1977).

It is well settled that this Court will not “secondguess” a state court’s “characterization of state law” regarding the nature of a state-court proceeding. McKinney v. Arizona, 589 U.S. 139, 146 (2020); see Atlantic

Richfield, 590 U.S. at 12; Bandini Petroleum Co. v. Superior Court, 284 U.S. 8, 14-15 (1931). There is no question

under Colorado law that a Rule 21 proceeding is a selfcontained original proceeding before the Colorado Supreme Court. Accordingly, the decision below discharging the order to show cause constitutes a “final judgment”

reviewable by this Court under Section 1257(a). See Atlantic Richfield, 590 U.S. at 12.

2. In the alternative, the Colorado Supreme Court’s

decision should be treated as “final” for purposes of Section 1257(a) because it falls within the fourth category of

cases identified in Cox Broadcasting Corp. v. Cohn, 420

U.S. 469 (1975). The Colorado Supreme Court finally decided the question of federal preclusion; reversal of that

decision would terminate the underlying litigation; and

the failure to review the decision now would seriously

erode federal policies. See id. at 482-483. Indeed, the

Court has routinely exercised its statutory jurisdiction to

review cases arising in a similar posture presenting ordinary questions of federal preemption. See, e.g., Coventry

Health Care of Missouri, Inc. v. Nevils, 581 U.S. 87, 9294 (2017); Dan’s City Used Cars, Inc. v. Pelkey, 569 U.S.

251, 259 (2013).

Jurisdiction under Cox is appropriate even though petitioners raised additional federal defenses below. This

Court has never treated the possibility of additional federal defenses as a bar to jurisdiction under Cox’s fourth

category. See Fort Wayne Books, Inc. v. Indiana, 489

U.S. 46, 54-57 (1989); id. at 69 (O’Connor, J., concurring in

part and dissenting in part). Instead, the Court requires

that the petitioner “might prevail on the merits on nonfederal grounds,” such that future review of the federal

issue by the Court would be “render[ed] unnecessary.”

Cox, 420 U.S. at 482 (emphasis added). That is the case

here, and jurisdiction thus exists under Cox as well.

B. The Court Has Jurisdiction Under Article III Of The

Constitution

When a party seeks this Court’s review of a lower

court’s decision, the Court’s Article III jurisdiction depends on the petitioner’s standing to invoke the Court’s

authority. See, e.g., Food Marketing Institute v. Argus

Leader Media, 588 U.S. 427, 432-433 (2019). The Court

can thus review a lower court’s judgment whenever the

petitioner suffered an “actual or imminent injury” that is

“fairly traceable” to the judgment and that could be “redress[ed] by a favorable ruling.” Ibid. (citation omitted).

That remains true even in a case arising from state court

in which the plaintiff would have lacked Article III standing to file suit in federal court in the first instance. See

ASARCO Inc. v. Kadish, 490 U.S. 605, 618 (1989).

Here, petitioners plainly have Article III standing to

invoke the Court’s jurisdiction. In the original proceeding

below, the Colorado Supreme Court issued a decision

holding that federal law did not foreclose state-law claims

against petitioners seeking redress for injuries allegedly

caused by global climate change. See Pet. App. 24a. That

decision constitutes binding precedent in Colorado state

court that will preclude petitioners’ federal defense both

in the underlying case and in other climate lawsuits pending in Colorado. See Board of County Commissioners of

San Miguel County v. Suncor Energy (U.S.A.) Inc., No.

21-CV-150 (Colo. Dist. Ct. Denver Cnty.). The decision

below thus finally determines petitioners’ federal rights

and subjects petitioners to adverse consequences that

would not occur if petitioners had prevailed. Such an adverse “adjudication of legal rights” constitutes the “kind

of injury cognizable in this Court.” ASARCO, 490 U.S. at

618; see Lamps Plus, Inc. v. Varela, 587 U.S. 176, 182

(2019); Camreta v. Greene, 563 U.S. 692, 701-702 (2011).

The decision below will also force petitioners to incur

monetary costs that would not have arisen if petitioners

had prevailed. As a result of the decision below, petitioners will be forced to continue litigating in Colorado state

court, rather than having those lawsuits dismissed. That

will cause petitioners to suffer a classic pocketbook injury.

See Tyler v. Hennepin County, 598 U.S. 631, 636 (2023).

Those forms of injury explain why this Court has routinely heard cases to decide a purely legal question on an

interlocutory basis where the losing party could still have

prevailed on some other ground later in litigation. See,

e.g., Warner Chappell Music, Inc. v. Nealy, 601 U.S. 366,

370-371 (2024); Health & Hospital Corp. of Marion

County v. Talevski, 599 U.S. 166, 174 (2023); Houston

Community College System v. Wilson, 595 U.S. 468, 473

(2022). The litigation consequences that flow from an

adverse ruling on a legal question constitute an injury sufficient for the losing party to seek appellate review.

The causation and redressability requirements for Article III standing are readily satisfied as well. Petitioners’

injuries were caused by the Colorado Supreme Court’s

adverse decision. And because that decision is what petitioners “challenge on appeal,” petitioners’ injuries “would

be redressed by a favorable ruling from this Court.”

Monsanto Co. v. Geertson Seed Farms, 561 U.S. 139, 150

(2010). Petitioners thus have Article III standing to seek

the Court’s review.

II. THE CONSTITUTION PRECLUDES STATE-LAW

CLAIMS SEEKING RELIEF FOR INJURIES ALLEGEDLY CAUSED BY INTERSTATE GREENHOUSE-GAS

EMISSIONS

Respondents are attempting to impose liability on petitioners under state law for injuries allegedly caused by

the effects of interstate greenhouse-gas emissions on the

global climate. State law is not competent to govern those

claims. The Court has long held that interstate pollution

is an inherently federal area in which state law cannot

govern. That rule arises from the fundamental structure

of the Constitution, which limits a State’s ability to regulate air and water in their ambient aspects. Although the

Clean Air Act displaced the federal common law that formerly governed claims seeking relief for injuries from interstate emissions, Congress did not thereby authorize

state law to provide relief in its place. Respondents’ statelaw claims thus cannot proceed.

A. The Structure Of The Constitution Does Not Allow

The Law Of A Single State To Govern Claims Concerning Interstate Emissions

Although state law is presumptively competent to govern most issues in our federal system, there are certain

areas in which “our federal system does not permit the

controversy to be resolved under state law.” Texas Industries, Inc. v. Radcliff Materials, Inc., 451 U.S. 630, 641

(1981). For more than a century, this Court has recognized that disputes arising from injuries caused by interstate pollution are “meet for federal law governance” and

that applying “the law of a particular State would be inappropriate.” American Electric Power Co. v. Connecticut,

564 U.S. 410, 422 (2011). That rule follows from “the Constitution’s structure and the principles of sovereignty and

comity it embraces.” National Pork Producers Council

v. Ross, 598 U.S. 356, 376 (2023) (internal quotation marks

and citation omitted).

1. On July 4, 1776, the Colonies declared themselves

to be “Free and Independent States.” Declaration of Independence ¶ 4. And after independence, the States initially “considered themselves fully sovereign nations.”

Franchise Tax Board v. Hyatt, 587 U.S. 230, 237 (2019).

Under international law, the States were “entitled” to “all

the rights and powers of sovereign states,” id. at 328 (citation omitted), including the powers to “declare war,

make peace, [and] contract alliances” to resolve disputes

among themselves and with foreign nations, Rhode Island

v. Massachusetts, 37 U.S. (12 Pet.) 657, 737, 743 (1838).

Upon ratification of the Constitution, however, the

States were “no longer fully independent nations” and “no

longer relate[d] to each other solely as foreign sovereigns.” Hyatt, 587 U.S. at 245-246. Instead, the Framers

created a new “perpetual Union,” id. at 246, in which the

States operated within a single federal system governed

by a “new National Government,” U.S. Term Limits, Inc.

v. Thornton, 514 U.S. 779, 803 (1995). The Constitution

was intended to provide a framework for the maintenance

of good relations among the various states of the Union

and their competing interests—a framework the Articles

of Confederation did not supply. See 1 Joseph Story,

Commentaries on the Constitution of the United States

179-180 (4th ed. 1873).

2. Under the structure of the Constitution, the States

surrendered certain powers that they previously enjoyed

as independent sovereigns. For example, the Constitution limited state power to enter into treaties, coin money,

or engage in war. See U.S. Const. Art. I, § 10. The Constitution also expressly mandated that federal law would

reign supreme over state law in the event of a conflict. See

U.S. Const. Art. VI, cl. 2; Gibbons v. Ogden, 22 U.S. (9

Wheat.) 1, 82 (1824).

Other limitations were “not spelled out in the Constitution” but were “nevertheless implicit in its structure.”

Hyatt, 587 U.S. at 247. Many of those limits arise from

the “fundamental principle of equal sovereignty among

the States.” Id. at 246 (quoting Shelby County v. Holder,

570 U.S. 529, 544 (2013)) (emphasis omitted). As the

Court has explained, our Nation “was and is a union of

States, equal in power, dignity and authority.” Coyle v.

Smith, 221 U.S. 559, 567 (1911). “The Constitution affirmatively altered the relationships between the States,” Hyatt, 587 U.S. at 245, ensuring that each State would

“stand[] on the same level with all the rest,” Kansas v.

Colorado, 206 U.S. 46, 97 (1907), with no State having

more sovereign power than another, see Coyle, 221 U.S.

at 573.

Flowing from each State’s equal sovereignty are “certain constitutional limitations on the sovereignty of all of

its sister States.” Hyatt, 587 U.S. at 245 (internal quotation marks and citation omitted). Put differently, the “relation of the [S]tates to each other in the Federal Union”

creates certain “limits” on “state power.” Burnet v.

Brooks, 288 U.S. 378, 401 (1933). Recently, for example,

the Court has held that, as a matter of “constitutional design,” every State is shielded from private suits not only

in its own courts but also in the courts of other States.

Hyatt, 587 U.S. at 245, 249.

Closely related to the principle of equal sovereignty is

the principle that a State is “without power to exercise ‘extra territorial jurisdiction,’ that is, to regulate and control

activities wholly beyond its boundaries.” Watson v. Employers Liability Assurance Corp., 348 U.S. 66, 70 (1954);

see Bonaparte v. Tax Court, 104 U.S. 592, 594 (1882);

United States v. Bevans, 16 U.S. (3 Wheat.) 336, 387

(1818). While each State has “exclusive jurisdiction and

sovereignty over persons and property within its territory,” Brown v. Fletcher’s Estate, 210 U.S. 82, 89 (1908),

that authority is “bounded by the States’ respective borders,” Fuld v. Palestine Liberation Organization, 606

U.S. 1, 14 (2025). Under the extraterritoriality principle,

“each State alone” can determine what conduct to permit

or punish within its borders. State Farm Mutual Automobile Insurance Co. v. Campbell, 538 U.S. 408, 422

(2003). And no State can “impose its own policy choice[s]

on other States.” BMW of North America, Inc. v. Gore,

517 U.S. 559, 571 & n.16 (1996).

3. For over a century, this Court has applied federal

rules of decision to disputes concerning injuries allegedly

caused by interstate air and water pollution.

The first such case was Missouri v. Illinois, 200 U.S.

496 (1906). There, the Court considered an action against

the State of Illinois to enjoin the City of Chicago from discharging untreated sewage into an interstate river. See

id. at 519. Since Congress had not created law to govern

such claims, the Court concluded that it must craft a federal rule of decision, explaining that it “must follow and

apply [federal] rules even if legislation of one or both of

the states seems to stand in the way.” Id. at 520.

Shortly after Missouri, the Court applied federal common law to a claim seeking abatement of the discharge of

noxious gases in Tennessee that were causing damage in

Georgia. See Georgia v. Tennessee Copper Co., 206 U.S.

230, 236 (1907). Other early cases concerning harms from

interstate pollution followed the same pattern. See New

York v. New Jersey, 256 U.S. 296, 301-302 (1921); North

Dakota v. Minnesota, 263 U.S. 365, 373-374 (1923); New

Jersey v. New York, 283 U.S. 473, 483 (1931).

The Court again addressed the source of law governing interstate-pollution disputes—and made clear that the

principle extended beyond original-jurisdiction disputes

between States—in Illinois v. City of Milwaukee, 406

U.S. 91 (1972) (Milwaukee I). There, the Court held that

an action to abate the discharge of the City of Milwaukee’s

sewage into Lake Michigan arose under the “laws of the

United States” within the meaning of a federal district

court’s jurisdiction under 28 U.S.C. 1331(a). See id. at 99100. Relying on Tennessee Copper, the Court explained

that federal law applies because “the States by their union

made the forcible abatement of outside nuisances impossible to each.” Id. at 104 (quoting 206 U.S. at 237). Consistent with that constitutional design, federal common

law applied not because any act of Congress governed the

issue, but because there was “an overriding federal interest in the need for a uniform rule of decision” and “the

controversy touche[d] basic interests of federalism.” Id.

at 105 n.6. The Court reiterated the point nearly a decade

later, stating that the only reason the federal common law

of interstate pollution existed after Erie Railroad Co. v.

Tompkins, 304 U.S. 64 (1938), was “because state law cannot be used.” City of Milwaukee v. Illinois, 451 U.S. 304

313 n.7 (1981). As the Court stated in International Paper Co. v. Ouellette, 479 U.S. 481 (1987), “the regulation of

interstate water pollution is a matter of federal, not state

law.” Id. at 488. Applying varying state laws would result

in “an irrational system of regulation” and “lead to chaotic

confrontation between sovereign states.” Id. at 496-497

(citation omitted).

Most recently, in American Electric Power, the Court

reaffirmed the principle that federal law applies to disputes involving interstate pollution. There, the plaintiffs

asserted nuisance claims under federal common law seeking the abatement of carbon-dioxide emissions by fossilfuel-fired powerplants located in other States. See 564

U.S. at 418. In deciding whether those claims could proceed, the Court reiterated that “borrowing the law of a

particular State” to govern climate-change disputes concerning interstate air pollution would be “inappropriate.”

Id. at 422. Instead, “air and water in their ambient or interstate aspects” are “meet for federal law governance.”

Id. at 421-422 (citation omitted). In the absence of a federal statutory rule of decision, the Court explained, the

“specialized federal common law” that remains after Erie

governs such disputes. Id. at 421. That “ ‘new’ federal

common law addresses ‘subjects within national legislative power where Congress has so directed’ or where the

basic scheme of the Constitution so demands.” Ibid.

(quoting Henry J. Friendly, In Praise of ‘Erie’—And of

the New Federal Common Law, 39 N.Y.U. L. Rev. 383,

408 n.119, 421-422 (1964)).

4. The structure of the Constitution explains why the

Court has long held that federal law necessarily and exclusively governs interstate-pollution disputes.

Air and water are “ambient,” American Electric

Power, 564 U.S. at 422, in the sense that they exist in nature and flow based on natural forces, without human intervention and without concern for political boundaries.

As a result, pollution from a single source can readily flow

from one State to another. See EPA v. EME Homer City

Generation, L.P., 572 U.S. 489, 495 (2014).

The ambient nature of air and water gives rise to

equal-sovereignty and extraterritoriality problems if one

particular State’s law is allowed to govern disputes concerning injuries from interstate air and water pollution.

In the context of air pollution, the “downwind” State—the

one where the alleged injury occurred—cannot apply its

law beyond its borders to regulate a source of pollution in

the “upwind” State. The emitting source is simply releasing emissions inside the upwind State that are naturally

carried downwind; it does not engage in any conduct in, or

directed toward, the second State. At the same time, it is

“fair and reasonable” for the downwind State to demand

that “the air over its territory should not be polluted on a

great scale.” Tennessee Copper, 206 U.S. at 238. To allow

the upwind State’s law to dictate the downwind State’s

remedy would infringe the downwind State’s legitimate

sovereign interest.

Considered in light of the constitutional principles discussed above, the cases applying federal law to disputes

concerning harms from interstate air and water pollution

make perfect sense. By joining the Union, the States surrendered many of their traditional tools to address the

problem of interstate pollution. The Constitution prohibits a State from applying its law beyond its borders, and

federal law provides a neutral source of law under which

to resolve the controversy. Under the Constitution,

therefore, States have always lacked the authority to regulate interstate pollution.

5. The need for the application of uniform federal law

is especially acute in the context of global climate change.

As the Court has explained, “[g]reenhouse gases once

emitted become well mixed in the atmosphere,” such that

“emissions in New Jersey may contribute no more to

[climate-related effects] in New York than emissions in

China.” American Electric Power, 564 U.S. at 422 (internal quotation marks and citation omitted). As a result,

any claim seeking relief for injuries allegedly caused by

the effects of greenhouse-gas emissions on the global climate necessarily implicates emissions released from

countless sources spread across every State and indeed

every jurisdiction around the world. Greenhouse gases in

the atmosphere cannot be unmixed and traced to their

sources in particular States or countries. And if all fifty

States were permitted to apply their divergent laws to

global greenhouse-gas emissions and their concentration

in the atmosphere, “[t]he confusion resulting from such a

practice would be endless.” Sturges v. Crowninshield, 17

U.S. (4 Wheat.) 122, 193 (1819). Indeed, this confusion is

already occurring: while some States and municipalities

(like respondents) are seeking to use state law to pursue

climate-change claims, other States are seeking to protect

fossil-fuel producers from those claims. See, e.g., Iowa

Code § 673B.2 (2026); Okla. S.B. 1439, § 1(C)(1), (D)(1)

(2026 Reg. Sess.); Utah H.B. 222, § 1(2)(a) (2026 Gen.

Sess.).

In disputes stemming from climate change, where

States have “conflicting rights,” no State is permitted to

“supply [the] rules of decision.” Hyatt, 587 U.S. at 246

(citation omitted). Put simply, “our federal system does

not permit the controversy to be resolved under state

law,” because “the interstate or international nature of

the controversy makes it inappropriate for state law to

control.” Texas Industries, 451 U.S. at 641. Instead,

“[f]ederal rules of law” must govern. Hyatt, 587 U.S. at

246 (internal quotation marks and citation omitted). The

“need for a uniform rule of decision” is all the greater because climate change affects every State—not just an

“upwind” and a “downwind” State, as in a classic case of

interstate pollution. Milwaukee I, 406 U.S. at 105 n.6.

B. The Clean Air Act Reinforces The Constitutional Rule

That States Lack Authority To Regulate Out-Of-State

Emissions

In American Electric Power, the Court held that Congress’s enactment of the Clean Air Act displaced the federal common-law rules of decision that formerly governed

disputes concerning harm from interstate air pollution.

See 564 U.S. at 424. The Clean Air Act does not authorize

the application of state law to disputes concerning interstate pollution. It is a comprehensive statutory scheme

that is consistent with the allocation of federal-state authority under the structure of the Constitution.

1. By displacing the federal common law of interstate

pollution, Congress did not authorize state law to apply in

its place.

a. As just explained, the Court’s precedents applying

federal common law to interstate-pollution disputes are

rooted in structural constitutional principles. See pp. 2229, supra. Even where Congress has acted to displace the

federal-common-law rules of decision that previously applied to those disputes, those controversies remain interstate conflicts to which the application of an affected

State’s law would be inappropriate. Put simply, congressional displacement of federal common law “does nothing

to undermine” the “reasons * * * for resorting to federal common law” in the first place. Illinois v. City of Milwaukee, 731 F.2d 403, 410 (7th Cir. 1984).

If state law could not be applied before the enactment

of the Clean Air Act, it thus follows that state law remains

inapplicable unless the Clean Air Act affirmatively authorizes it. Both before and after the Clean Air Act’s

enactment, the Constitution rendered state law inapplicable to interstate air-pollution disputes.

That conclusion is not a novel one. The Court has repeatedly recognized that there is no need to apply the presumption against preemption when state law seeks to operate in areas of inherent federal authority. See Parker

Drilling Management Services, Ltd. v. Newton, 587 U.S.

601, 610 (2019); Buckman Co. v. Plaintiffs’ Legal Committee, 531 U.S. 341, 347-348 (2001); United States v.

Locke, 529 U.S. 89, 108 (2000). A traditional preemption

analysis—one that looks for affirmative congressional intent to preempt state law, rather than affirmative congressional intent to authorize it—is applicable “only

where the overlapping, dual jurisdiction of the [f]ederal

and [s]tate [g]overnments makes it necessary to decide

which law takes precedence.” Parker Drilling, 587 U.S.

at 610. But where the issue is “distinctively federal in

character,” there is no need for “affirmative action” from

Congress to foreclose the application of state law. United

States v. Standard Oil Co., 332 U.S. 301, 305-306, 306 n.8

(1947). Such matters are “neither primarily one of state

interest nor exclusively for determination by state law,”

“quite apart from any positive action by Congress.” Id. at

307.

If Congress wishes to disturb the application of federal law to interstate-pollution disputes, it must clearly

express its intention to do so. As this Court has repeatedly reiterated, when Congress “significantly alter[s] the

balance between federal and state power,” it must do so

with “exceedingly clear language.” United States Forest

Service v. Cowpasture River Preservation Association,

590 U.S. 604, 621-622 (2020); see Goodyear Atomic Corp.

v. Miller, 486 U.S. 174, 180 (1988); Williams v. Lee, 358

U.S. 217, 220-221 (1959). The lack of any affirmative action to preempt state law reflects the settled principle that

States already lacked the authority to apply their laws to

interstate-pollution disputes. See Crosby v. National

Foreign Trade Council, 530 U.S. 363, 387-388 (2000).

A contrary rule would make little sense. Before the

enactment of the Clean Air Act, Colorado had no power to

regulate interstate emissions. In the Clean Air Act, Congress decided to fill the void by enacting a scheme that

places exclusive responsibility with EPA and upwind

States to control sources of emissions. Respondents’ position is that, because Congress stepped in to fill that void,

every State and municipality in the country suddenly obtained power that they never previously possessed to regulate interstate emissions—even though Congress took

no affirmative action to authorize state law to govern. As

one court has aptly put it, that result is “too strange to

seriously contemplate.” City of New York v. Chevron, 993

F.3d 81, 98-99 (2d Cir. 2021).

b. This Court’s decisions in Ouellette and American

Electric Power confirm that state-law claims seeking relief for injuries allegedly caused by interstate emissions

are available only to the extent authorized by Congress.

Ouellette demonstrates that, to the extent state law

can apply in an area formerly governed by federal common law, it is only to the extent affirmatively authorized

by Congress. There, a group of lakefront property owners in Vermont sued a paper mill operating on the opposite side of Lake Champlain in New York. See 479 U.S. at

483-484. The property owners asserted a nuisance claim

under Vermont law for the alleged effects of pollution

dumped into the lake by the New York paper mill. See id.

at 484. In light of the “pervasive regulation” of the Clean

Water Act and “the fact that the control of interstate pollution is primarily a matter of federal law,” the Court held

that the only permissible state-law actions seeking relief

for interstate water pollution are “those specifically preserved by the [Clean Water] Act.” Id. at 492 (citation

omitted). The Court proceeded to analyze the Clean Water Act and concluded that it did not authorize resort to

any State’s law except the law of the State in which the

source of the pollution was located. See id. at 487-498.

The Vermont plaintiffs thus could not seek relief under

Vermont law for alleged harms caused by the New York

mill.

American Electric Power confirms that the same

framework should apply under the Clean Air Act. There,

the Court addressed the effect of the Clean Air Act on

preexisting federal common law governing air pollution.

The Court held that the Act displaced those claims, because the Act authorized EPA to regulate carbon-dioxide

emissions from stationary sources such as powerplants.

See 564 U.S. at 424-425. Critically, the Court then remanded the case for consideration of the remaining statelaw claims not before the Court, which were based on the

law of the source State. See id. at 429. The Court stated

that “the availability vel non of a state lawsuit depends,

inter alia, on the preemptive effect of the federal act.”

Ibid. In so stating, the Court cited Ouellette, confirming

that the same analysis should apply under the Clean Air

Act. See ibid.

2. The Clean Air Act does not authorize state common-law claims seeking relief for the effects of emissions

emanating from every State in the Nation. To the contrary, the Act provides “disclosure of a purpose” by Congress to prevent a State from applying its common law to

claims arising from emissions in another State. Hencely

v. Fluor Corp., 146 S. Ct. 1086, 1099 (2026) (citation omitted).

The Clean Air Act grants EPA authority to regulate

emissions from stationary sources, see 42 U.S.C. 7411(b),

(d), and to set emissions standards for cars, trains, airplanes, and other equipment, see 42 U.S.C. 7521(a)(1)-(2),

(a)(3)(E), 7547(a)(1), (a)(5), 7571(a)(2)(A).* States are responsible for regulating emissions within their own borders in accordance with federally approved plans, but

they “lack authority to control” any “out-of-state pollution.” EME Homer City Generation, 572 U.S. at 495. In

particular, the Act’s “Good Neighbor Provision” directly

addresses the problem of interstate pollution by vesting

regulatory responsibility exclusively with EPA and upwind States and limiting downwind States to petition EPA

to intervene if that regulation is insufficient. See 42

U.S.C. 7426(b). Nowhere does the Act authorize States to

regulate—through tort law or otherwise—emissions emanating from other States.

The Clean Air Act contains two saving clauses, but neither authorizes state common-law claims for harms allegedly caused by out-of-state emissions. The saving clauses

preserve a State’s right to adopt and enforce emissions

standards that are stricter than national requirements,

see 42 U.S.C. 7416, and any person’s right to seek enforcement of any emission standard or limitation or to seek any

other relief, see 42 U.S.C. 7604(e). Those provisions are

materially identical to provisions in the Clean Water Act,

EPA recently determined that it would no longer regulate emissions of greenhouse gases from new motor vehicles and rescinded its

existing regulations. See 91 Fed. Reg. 7,723 (Feb. 18, 2026). Petitioners’ argument here—that the Constitution forecloses the application

of state law to claims for injuries allegedly caused by interstate emissions—does not depend on whether EPA believes the pollutant at issue meets the standard for regulation under a particular provision of

the Clean Air Act. The salient point is that the Clean Air Act does not

authorize the application of state law to control out-of-state sources

of emissions under any circumstances.

see pp. 31-32, supra, which the Court has held not to permit state-law claims seeking to “regulate the conduct of

out-of-state sources,” but instead to permit only claims

brought “pursuant to the law of the source State.” Ouellette, 479 U.S. at 495, 497.

The Clean Air Act thus does not authorize state-law

tort claims seeking relief from harms allegedly caused by

out-of-state emissions—including greenhouse-gas emissions. Indeed, the Act codifies the constitutional limits on

state authority and evinces a congressional purpose to

prevent such claims from proceeding. Federal law thus

forecloses respondents’ state-law claims.

C. Respondents’ State-Law Claims Seek Relief For Injuries Allegedly Caused By Interstate Emissions

Respondents’ state-law tort claims, which seek relief

for the alleged effects of global climate change in Boulder,

Colorado, are premised on greenhouse-gas emissions occurring worldwide. Those claims fall within the exclusively federal area of interstate pollution and “far exceed

the territorial limits on Colorado’s authority.” U.S. Cert.

Br. 13.

1. Respondents assert state-law claims against petitioners for public nuisance, private nuisance, trespass,

and unjust enrichment. Respondents’ theory of liability is

that petitioners have “caused billions of tons of excess CO2

emissions” by “producing, promoting, refining, marketing

and selling fossil fuels at levels that have caused and continue to cause climate change, while concealing and/or

misrepresenting the dangers associated with fossil fuels’

intended use.” J.A. 3, 97.

Respondents allege that petitioners’ worldwide conduct is responsible for a “substantial percentage of all the

fossil fuels” that further the effects of climate change.

J.A. 5-6; Pet. App. 135a. As respondents have explained,

“fossil fuels sold and burned outside Colorado are part of

the chain of causation linking [petitioners’] tortious conduct to [respondents’] injuries.” Resp. Colo. S. Ct. Br. 25.

Respondents’ claims are thus “based on [petitioners’] total fossil fuel sales,” Resp. C.A. Br. 16 (No. 19-1330). And

based on petitioners’ challenged conduct, respondents are

seeking “[m]onetary relief to compensate” for “past and

future damages and costs to mitigate the impacts of climate change,” including wildfires, pests, droughts, extreme heat, and flooding. J.A. 116, 136.

Given the nature of climate change, respondents’

claims necessarily implicate not only emissions traceable

to petitioners, but also emissions released by every emitter of greenhouse gases worldwide. Indeed, respondents

admit that their claims are based in part on “fossil fuel use

by non-parties and the resulting emissions.” Resp. C.A.

Supp. Br. 7 (No. 19-1330).

The thrust of respondents’ complaint is thus that petitioners’ global conduct increased the global use of fossil

fuels, resulting in increased global greenhouse-gas emissions, which accumulated with emissions from countless

other sources worldwide and contributed to global climate

change and resulted in global harms—including harms in

Boulder, Colorado, for which respondents seek to recover.

See City of New York, 993 F.3d at 91. Respondents’

claims thus necessarily seek to regulate activities outside

Colorado that are contributing to global climate change.

Resolution of respondents’ claims also inherently involves interstate emissions. In particular, to prove the element of causation for its tort claims, respondents must

show that, absent petitioners’ production and marketing

of their products, fewer fossil fuels would have been used,

which would have resulted in decreased global greenhouse-gas emissions, which would have minimized the ef-

fects of global climate change enough to alleviate the alleged harms. Interstate emissions are thus a critical step

in the causal chain between petitioners’ alleged conduct

and respondents’ alleged injuries.

What is more, each of respondents’ claims also requires a policy determination of the appropriate level of

greenhouse-gas emissions. The nuisance claims would require a jury to determine whether the level of emissions

petitioners allegedly caused in other States was “reasonable” relative to that baseline. See Public Service Co. v.

Van Wyk, 27 P.3d 377, 391 (Colo. 2001); Saint John’s

Church in Wilderness v. Scott, 194 P.3d 475, 479 (Colo.

App. 2008). The unjust-enrichment claim would similarly

require a determination of whether petitioners’ emissions-causing conduct outside Colorado was “unjust.” See

Robinson v. Colorado State Lottery Division, 179 P.3d

998, 1007 (Colo. 2008). And the trespass claim would permit a Colorado court to decide on the level of acceptable

global emissions in order to assess whether a “physical intrusion” has occurred. Hoery v. United States, 64 P.3d

214, 217 (Colo. 2003). There is thus no escaping the fact

that respondents’ claims seek relief for injuries allegedly

caused by interstate emissions resulting from conduct

outside Colorado—making it inappropriate to apply one

State’s law to resolve them.

To be sure, respondents contend that the alleged outof-state conduct caused injury in Colorado. But to put it

mildly, the chain of causation between that conduct and

the asserted in-state injuries here is attenuated. Specifically, respondents contend that their in-state injuries occurred because petitioners’ production and allegedly deceptive marketing of fossil fuels resulted in the combustion of fossil fuels by countless entities around the world,

which resulted in the release of molecules of greenhouse

gases around the world, which then mixed with other molecules of greenhouse gases in the atmosphere from other

human and natural causes, which combined to create a

warming effect on the global climate, which then altered

local weather patterns, which then caused harmful effects

in respondents’ jurisdictions. See J.A. 1-6, 34-53, 58-84,

97-105, 112-123. Respondents’ claims thus comfortably

fall within the exclusively federal area of interstate pollution and cannot be justified as a permissible regulation of

conduct in, or directed toward, Colorado.

2. In an effort to avoid foreclosure, respondents’

state-law claims target fossil-fuel producers, rather than

the emitters of greenhouse gases. But the source of the

injury indisputably remains interstate (and international)

emissions. Respondents allege harms only from the effects of increased greenhouse-gas emissions on the global

climate.

Respondents cannot avoid foreclosure simply by moving one step up the causal chain. Regardless of their

choice of defendant, respondents are still seeking relief

for injuries allegedly caused by interstate emissions. And

resolution of the elements of respondents’ claims inherently requires the consideration of interstate emissions.

Indeed, there can be no serious dispute that the relief respondents are seeking here constitutes an effort to limit

interstate greenhouse-gas emissions. The complaint targets not just past conduct, but also future conduct: specifically, petitioners’ “continuing their efforts and increasing their fossil fuel activities.” J.A. 97. Respondents are

seeking relief because petitioners allegedly are not

“bringing emissions under control” or “helping to mitigate the impacts of climate change.” J.A. 98.

Should respondents’ claims succeed, a Colorado jury,

applying Colorado law, will set a legal standard to which

petitioners (and other fossil-fuel producers) must conform. As a member of respondents’ legal team has freely

admitted, the liability being sought here is designed to

serve as a nationwide “carbon tax” on fossil-fuel producers, in order to “bankrupt[]” the energy industry. See

Federalist Society, Can State Courts Set Global Climate

Policy?, at 32:55-35:05 (Oct. 8, 2025) (Federalist Society

Panel) <tinyurl.com/federalistsocietypanel> (comments

of David Bookbinder). The stated intent and obvious effect of respondents’ claims are to impose respondents’

preferred policy of limiting emissions across the Nation.

Respondents cannot plead around the application of federal law simply by limiting their claimed recovery to localized harms.

Notably, the Court rejected a similar attempt at artful

pleading to avoid federal preemption in Kurns v. Railroad Friction Products Corp., 565 U.S. 625 (2012). There,

a railroad worker and his wife brought state-law claims

alleging that the equipment he had worked on was defectively designed because it contained asbestos and that the

defendants had failed to warn about the dangers of asbestos or to provide instructions about its safe use. See id. at

628-629. The Court first held that the Locomotive Inspection Act “occup[ies] the entire field of regulating locomotive equipment” and thus preempted state-law claims that

the equipment was defectively designed. Id. at 634. The

plaintiffs argued, however, that their failure-to-warn

claims could still survive because they did not target the

“design or manufacture” of locomotive equipment. Id. at

635.

The Court rejected that argument. Because the “gravamen” of the plaintiffs’ failure-to-warn claim was still

that the railroad worker “suffered harmful consequences

as a result of his exposure to asbestos contained in locomotive parts and appurtenances,” the claim was “directed

at the equipment of locomotives” and fell within the

preempted field. Kurns, 565 U.S. at 635. As the Court

explained, the state-law duty would “inevitably influence

a manufacturer’s choice whether to use [a] particular design” for locomotive equipment. Id. at 635 n.4.

The same reasoning applies here. Respondents seek

to escape the federal field of interstate emissions by moving up the causal chain to assert a theory of liability based

on the excessive production or deceptive marketing of fossil fuels. But no matter the theory of liability, the “gravamen” of their claims is that some marginal increase in

global greenhouse-gas emissions attributable to petitioners’ conduct caused them harm. The claims are inherently

premised on the notion that fewer greenhouse-gas emissions should have occurred. And the threat of liability is

designed to force petitioners to reduce the sale of fossil

fuels and thereby limit global greenhouse-gas emissions.

Cf. Ouellette, 479 U.S. at 495 (explaining that the “threat

of ongoing liability” can cause a source of emissions to

“change its methods of doing business and controlling pollution”). Respondents’ state-law claims thus fall squarely

within the inherently federal area of interstate-pollution

disputes that are foreclosed by the Constitution.

III. THE CONSTITUTION PRECLUDES STATE-LAW

CLAIMS SEEKING RELIEF FOR INJURIES ALLEGEDLY CAUSED BY INTERNATIONAL GREENHOUSE-GAS EMISSIONS

Respondents’ claims fail for the additional reason that,

by seeking redress for the effects of international emissions, they infringe on the federal government’s exclusive

authority over foreign affairs.

Petitioners consist of energy companies that sell fossil-fuel products within the United States and around the

world. See J.A. 14-24. And international emissions dwarf

domestic emissions. See, e.g., European Commission,

GHG Emissions of All World Countries (2025) <tinyurl.com/worldemissions>. Respondents have thus

never disputed that, under their theory of liability, their

harms for which they are seeking relief were allegedly

caused in large part by greenhouse-gas emissions occurring outside the United States.

Because States lack constitutional authority over interstate emissions, it necessarily follows that they also

lack authority over international emissions. Indeed, the

case for state authority over international emissions is especially weak, because “the [S]tates severally never possessed international powers.” United States v. CurtissWright Export Corp., 299 U.S. 304, 316 (1936) (emphasis

added). The Constitution insists that the “supremacy of

the national power in the general field of foreign affairs”

is absolute and “entirely free from local interference.”

Hines v. Davidowitz, 312 U.S. 52, 62-63 (1941). In other

words, “[p]ower over external affairs is not shared by the

States; it is vested in the national government exclusively.” United States v. Pink, 315 U.S. 203, 233 (1942);

see Fuld, 606 U.S. at 15; Banco Nacional de Cuba v. Sabbatino, 376 U.S. 398, 427 n.25 (1964).

As a corollary to that rule, state laws “give way” if they

“impair the effective exercise of the Nation’s foreign policy.” Zschernig v. Miller, 389 U.S. 429, 440 (1968). The

“likelihood” that “state [action] will produce something

more than incidental effect in conflict with express foreign

policy of the National Government” is sufficient for the

Constitution to foreclose the application of state law.

American Insurance Association v. Garamendi, 539 U.S.

396, 420 (2003) (citation omitted). Such a rule ensures

“uniformity in this country’s dealings with foreign nations,” id. at 413, and prevents a single State from “embroil[ing] us in disastrous quarrels with other nations,”

Chy Lung v. Freeman, 92 U.S. 275, 280 (1875).

Climate change poses a “global problem” that the

United States “cannot confront alone.” City of New York,

993 F.3d at 88. And for decades, the federal government

has coordinated and refined its foreign-policy strategy

with respect to climate change. In 1987, Congress directed the executive branch to develop a “coordinated national policy on global climate change.” Global Climate

Protection Act, Pub. L. No. 100-204, tit. 11, § 1103, 101

Stat. 1407-1409 (1987). The United States has since entered into numerous multilateral treaties addressing climate change. See, e.g., United Nations Framework Convention on Climate Change, May 9, 1992, S. Treaty Doc.

No. 102-38, 1771 U.N.T.S. 107; Kigali Amendment to the

Montreal Protocol on Substances That Deplete the Ozone

Layer, Oct. 15, 2016, S. Treaty Doc. No. 117-1, C.N.

730.2017. And through the Clean Air Act, Congress authorized EPA to require an individual State to address

emissions within its borders which harm another nation

on the condition of reciprocity from the foreign nation.

See 42 U.S.C. 7415; see also 42 U.S.C. 7410(a)(2)(H)(ii).

The federal government has also made strategic decisions to participate (and not to participate) in international protocols and restrictions on greenhouse-gas emissions. See, e.g., Exec. Order 14,162 (Jan. 20, 2025). And

across administrations, the United States has consistently

“oppose[d] the establishment of liability and compensation schemes at the international level.” City of New York,

993 F.3d at 103 n.11 (citation omitted).

Addressing international greenhouse-gas emissions

implicates the complex balance of risk reduction with energy needs. For example, affordable energy is a linchpin

of this Administration’s geopolitical strategy, underpinning its objective to be “the world’s leading energy producer and exporter.” The White House, American Energy Dominance Is Back Under President Trump (Feb.

24, 2026) <tinyurl.com/americanenergydominance>.

Supplying the world with affordable energy generates

significant revenue for the United States and its energy

producers. It also ensures continued global demand for

the United States dollar (which is used to trade oil), bolstering the dollar as a key tool of American foreign policy.

And it is critical to the Nation’s national security.

Allowing state and local governments to seek liability

for greenhouse-gas emissions released abroad would interfere with the United States’ foreign policy on climate

and energy issues and thus undermine the federal government’s “exclusive authority in international relations.”

Fuld, 606 U.S. at 15 (internal quotation marks, alterations, and citation omitted). State and local governments

seeking liability for injuries caused by international emissions would “bypass the various diplomatic channels that

the United States uses to address” climate change. City

of New York, 993 F.3d at 103. And although the claims

here involve the liability of private companies, the “legitimate scope of the Executive’s international negotiations”

can encompass “private acts.” Garamendi, 539 U.S. at

416.

Worse yet, such claims could foment hostility between

nations whose fossil-fuel producers are targeted or that

will suffer from higher energy prices. Notably, two of the

three petitioners here are subsidiaries of a Canadian energy company. State-law climate-change actions have

also been brought against foreign fossil-fuel producers

such as BP and Shell (British companies), and Total Energies (a French company), and those actions could spark

tit-for-tat litigation by foreign governments against

American producers. See Pink, 315 U.S. at 232.

The specter of state and local governments seeking exorbitant awards for harms allegedly caused by interna-

tional emissions would also undermine the Administration’s foreign-policy goal of affordable energy by substantially “affect[ing] the price and production of fossil fuels

abroad.” City of New York, 993 F.3d at 103. To defend

against such lawsuits, fossil-fuel producers may have to

increase prices, raising costs for both American and

global consumers. That would impede the Administration’s pursuit of global leadership in energy production.

No State can “rewrite our foreign policy to conform to

its own domestic policies,” even through “judicial decrees.” Pink, 315 U.S. at 233. Yet the climate tort suits

“risk[] impeding our federal government’s judgment as to

how to approach air pollution in the international sphere.”

Pet. App. 45a (Samour, J., dissenting). It is inconceivable

that state courts and juries would be entrusted with that

authority. Even in the federal courts, “[m]atters intimately related to foreign policy and national security are

rarely proper subjects for judicial intervention.” Egbert

v. Boule, 596 U.S. 482, 494 (2022) (citation omitted); see

Chicago & Southern Air Lines v. Waterman S.S. Corp.,

333 U.S. 103, 111 (1948). Because they are based in part

on international emissions, respondents’ claims cannot

proceed under Colorado law for this independent reason.

IV. THE CLEAN AIR ACT PREEMPTS STATE-LAW

CLAIMS SEEKING RELIEF FOR INJURIES ALLEGEDLY CAUSED BY EMISSIONS FROM ANOTHER

STATE

In the decision below, the Colorado Supreme Court

applied a statutory preemption framework to determine

that respondents’ claims could proceed under state law.

See Pet. App. 11a-16a. That decision was incorrect on its

own terms: even if the Constitution did not already foreclose respondents’ claims, the Clean Air Act would preempt them as well.

Under a statutory preemption framework, no presumption against preemption applies, because the regulation of interstate emissions is an inherently federal area.

See p. 30, supra. The question should instead be whether

the state law at issue is “consistent with the federal statutory structure.” Locke, 529 U.S. at 108. And the “conflict

with federal policy need not be as sharp as that which

must exist for ordinary pre-emption” in areas of traditional state authority. Boyle v. United Technologies

Corp., 487 U.S. 500, 507 (1988). But even applying a presumption against preemption, respondents’ state-law

claims would still fail. That presumption is overcome

where, as here, Congress has occupied the entire relevant

field of regulation or state law conflicts with the text,

structure, or objectives of federal law. See Arizona v.

United States, 567 U.S. 387, 399 (2012).

A. As already explained, the Clean Air Act establishes

a comprehensive statutory scheme for the regulation of

air quality across the United States. See pp. 32-34, supra.

The Act comprehensively directs EPA to set emissions

standards for stationary sources and vehicles, and it more

broadly authorizes the promulgation of national ambient

air quality standards. See American Electric Power, 564

U.S. at 424-428. The Act includes “multiple avenues for

enforcement,” and it authorizes States and private parties

to petition for rulemaking if EPA does not set appropriate

emissions limits. Id. at 425. The Clean Air Act thus sets

forth a pervasive statutory scheme clearly intended to

“dominate the field” of interstate pollution regulation.

Ouellette, 479 U.S. at 492. Application of state tort law in

that area would thus “exert an extraneous pull on the

scheme established by Congress” and thus be inconsistent with the Act. Buckman, 531 U.S. at 353. And the

same result would obtain even if a presumption against

preemption applied. See Arizona, 567 U.S. at 401-402.

B. In addition, respondents’ state-law claims “interfere[] with the methods by which the federal statute”—

here, the Clean Air Act—“was designed to reach [its]

goal[s].” Ouellette, 479 U.S. at 494. Under the Clean Air

Act, the “first decider” is EPA. American Electric Power,

564 U.S. at 427. EPA is tasked with establishing nationwide air quality standards, and States play circumscribed

roles enforcing standards “within [their] domain[s]” subject to EPA oversight. Id. at 428. For example, Congress

has delegated to EPA authority to decide “whether and

how to regulate” particular air pollutants from various

categories of sources. Id. at 426. And EPA, in turn, “may

delegate implementation and enforcement authority to

the States,” but it “retains the power to inspect and monitor regulated sources, to impose administrative penalties

for noncompliance, and to commence civil actions against

polluters in federal court.” Id. at 425-426. And as just

noted, if States disagree with the standards established

by EPA, their remedy is to petition EPA for rulemaking

and, ultimately, seek review in court. See ibid. When enacting this statutory scheme, Congress provided downwind States with limited avenues to voice their concerns

over upwind sources of pollution and placed primary responsibility for controlling interstate pollution with EPA

and the upwind States. See ibid.

In Ouellette, the Court addressed the analogous

scheme of regulation under the Clean Water Act and held

that state-law nuisance claims seeking relief for emissions

from another State would “circumvent” the Clean Water

Act’s statutory framework, “thereby upsetting the balance of public and private interests so carefully addressed

by the Act.” 479 U.S. at 494-496. Any contrary interpretation of the Act, the Court explained, would “subject

[regulated entities] to an indeterminate number of poten-

tial regulations”; “undermine the important goals of efficiency and predictability in the permit system”; and “undermine” the statute’s comprehensive “regulatory structure.” Id. at 496-497, 499.

So too here. Respondents’ claims conflict with the

Clean Air Act’s decisionmaking scheme and undermine

the Act’s regulatory structure and purpose by seeking to

apply Colorado law to redress harms caused by out-ofstate emissions. The Clean Air Act broadly contains the

same statutory features highlighted in Ouellette and, as

noted above, directly addresses the “complex problem” of

interstate pollution. EME Homer City Generation, 572

U.S. at 495. If respondents’ claims are allowed to proceed,

every State and municipality across the country will be

able to set and enforce its own emissions standards

against anyone emitting or causing another to emit greenhouse gases—which is to say, virtually every company

and person in the Nation. See American Electric Power,

564 U.S. at 428-429. That would eviscerate the federal

government’s discretion in setting national standards for

air quality and pollution control, as well as other States’

authority over emissions within their own borders, ultimately disrupting the entire system of cooperative federalism established by the Clean Air Act. See pp. 32-34, supra. Indeed, if the delegation of this discretion to federal

judges “cannot be reconciled with the decisionmaking

scheme Congress enacted,” American Electric Power,

564 U.S. at 429, it is implausible that Congress intended

state common-law claims to proceed. Respondents’

claims are therefore not “consistent with the federal statutory structure.” Locke, 529 U.S. at 108. And even with

a presumption against preemption, they are a “sufficient

obstacle” to the Act to mandate preemption. Crosby, 530

U.S. at 373.

The Constitution and the Clean Air Act independently

prohibit state law from governing claims seeking relief for

the effects of interstate and international greenhouse-gas

emissions. That outcome leaves the political branches on

the federal level in charge of the Nation’s climate-change

policy and avoids the prospect of each State, and each of

the country’s tens of thousands of local governments, imposing its own standard for what constitutes a “reasonable” amount of greenhouse-gas emissions. Only the federal government has the power, capability, and institutional expertise to effectuate meaningful, long-lasting

change across the United States and the world on the issue of global climate change.

Our Nation’s climate policy should not be left in the

hands of six jurors in Boulder, Colorado. The Colorado

Supreme Court’s decision to allow Boulder’s claims to

proceed should be reversed.

CONCLUSION

The judgment of the Colorado Supreme Court should

be reversed.

Respectfully submitted.

HUGH QUAN GOTTSCHALK

ERIC L. ROBERTSON

WHEELER TRIGG

O’DONNELL LLP

370 Seventeenth Street,

Suite 4500

Denver, CO 80202

KANNON K. SHANMUGAM

JAKE L. KRAMER

ELEANOR K. RITTER

DAVIS POLK & WARDWELL LLP

1050 17th Street, N.W.

Washington, DC 20036

(202) 962-7000

kshanmugam@davispolk.com

Counsel for Petitioners

THEODORE V. WELLS, JR.

Suncor Energy (U.S.A.) Inc.

and Suncor Energy Sales Inc. DANIEL J. TOAL

YAHONNES CLEARY

PAUL, WEISS, RIFKIND,

WHARTON & GARRISON LLP

1285 Avenue of the Americas

New York, NY 10019

WILLIAM T. MARKS

ANNA J. LUCARDI

DAVID T. WONG

PAUL, WEISS, RIFKIND,

WHARTON & GARRISON LLP

2001 K Street, N.W.

Washington, DC 20006

Counsel for Petitioner

Exxon Mobil Corporation

MAY 2026

APPENDIX

TABLE OF CONTENTS

Page

U.S. Const. Art. VI, cl. 2................................................................... 1a

28 U.S.C. 1257(a) ............................................................................... 1a

Colo. Const. Art. VI, § 2 ................................................................... 1a

Colo. Const. Art. VI, § 3 ................................................................... 2a

Colo. App. R. 21 ................................................................................. 2a

1. U.S. Const. Art. VI, cl. 2, provides:

This Constitution, and the laws of the United States

which shall be made in pursuance thereof; and all

treaties made, or which shall be made, under the authority of the United States, shall be the supreme law

of the land; and the judges in every state shall be

bound thereby, anything in the Constitution or laws

of any State to the contrary notwithstanding.

2. 28 U.S.C. 1257(a) provides:

Final judgments or decrees rendered by the highest

court of a State in which a decision could be had, may

be reviewed by the Supreme Court by writ of certiorari where the validity of a treaty or statute of the

United States is drawn in question or where the validity of a statute of any State is drawn in question on

the ground of its being repugnant to the Constitution,

treaties, or laws of the United States, or where any

title, right, privilege, or immunity is specially set up

or claimed under the Constitution or the treaties or

statutes of, or any commission held or authority exercised under, the United States.

3. Colo. Const. Art. VI, § 2, provides in relevant part:

The supreme court, except as otherwise provided in

this constitution, shall have appellate jurisdiction

only, which shall be coextensive with the state, and

shall have a general superintending control over all

inferior courts, under such regulations and limitations as may be prescribed by law. * * *

(1a)

4. Colo. Const. Art. VI, § 3, provides in relevant part:

The supreme court shall have power to issue writs of

habeas corpus, mandamus, quo warranto, certiorari,

injunction, and such other original and remedial writs

as may be provided by rule of court with authority to

hear and determine the same; and each judge of the

supreme court shall have like power and authority as

to writs of habeas corpus. * * *

5. Colo. App. R. 21 provides in relevant part:

(a) In General.

(1) Original Jurisdiction Under the Constitution.

This rule applies only to the original jurisdiction of

the supreme court to issue writs as provided in

Section 3 of Article VI of the Colorado Constitution

and to the exercise of the supreme court’s general

superintending authority over all courts as provided in Section 2 of Article VI of the Colorado

Constitution.

(2) Extraordinary Nature and Availability of Relief. Relief under this rule is extraordinary in nature and is a matter wholly within the discretion of

the supreme court. Such relief will be granted only

when no other adequate remedy is available, including relief available by appeal, under C.R.C.P.

106, or under Crim. P. 35.

(3) Forms of Writs Subject to This Rule. Petitions

for writs of habeas corpus, mandamus, quo warranto, injunction, prohibition, and other forms of

writs cognizable under the common law are subject

to this rule. The petitioner need not designate a

specific form of writ when seeking relief under this

rule.

(b) Initiating an Original Proceeding. The petitioner must file a petition for an order to show cause

specifying the relief sought and requesting the court

to issue to one or more proposed respondents, as set

forth in subsection (e)(1), an order to show cause why

the relief requested should not be granted.

* * *

(e) Contents of the Petition. The petitioner has the

burden of showing that the court should issue an order

to show cause. To enable the court to determine

whether to issue an order to show cause, the petition

must set forth in sufficient detail the following:

(1) the identity of the petitioner and of the proposed respondent(s), together with, if applicable,

their party status in the underlying proceeding

(e.g., plaintiff, defendant, etc.). The proposed respondent(s) must be the real party (or parties) in

interest against whom relief is sought. When a petition seeks a writ of mandamus or prohibition directed to a court or tribunal, the proposed respondents must be the lower court or tribunal, if appropriate, and all parties to the underlying proceeding

other than the petitioner[.]

* * *

(h) Stay.

* * *

(2) Upon Issuance of an Order to Show Cause. Issuance of an order to show cause by the supreme

court automatically stays all underlying proceed-

ings until final determination of the original proceeding in the supreme court unless the court, acting on its own, or upon motion, lifts the stay in

whole or in part.

* * *

(j) Ruling on the Petition.

(1) Denial. The court may deny the petition without explanation and without an answer by any respondent.

(2) Issuance of an Order to Show Cause. The court

may issue an order to show cause. The clerk will

serve the order on all persons ordered or invited

by the court to respond and on the lower court or

tribunal in the underlying proceeding.

* * *

(o) Disposition of an Order to Show Cause. The

court in its discretion may discharge the order or

make it absolute, in whole or in part, with or without

opinion. * * *

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.