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

No. 25-170

IN THE

Supreme Court of the United States

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

Petitioners,

v.

COUNTY COMMISSIONERS OF BOULDER COUNTY, ET AL.,

Respondents.

On Petition for a Writ of Certiorari

to the Supreme Court of Colorado

BRIEF FOR THE CHAMBER OF COMMERCE

OF THE UNITED STATES OF AMERICA

AS AMICUS CURIAE

SUPPORTING PETITIONERS

ANDREW R. VARCOE

STEPHANIE A. MALONEY

U.S. CHAMBER

LITIGATION CENTER

1615 H Street, NW

Washington, DC 20062

JESSE LEMPEL

GOODWIN PROCTER LLP

100 Northern Avenue

Boston, MA 02210

October 9, 2025

WILLIAM M. JAY

Counsel of Record

GOODWIN PROCTER LLP

1900 N Street, NW

Washington, DC 20036

wjay@goodwinlaw.com

(202) 346-4000

TABLE OF CONTENTS

Page

INTEREST OF THE AMICUS CURIAE.................... 1

SUMMARY OF ARGUMENT ..................................... 3

ARGUMENT ............................................................... 5

I.

II.

Under our federal structure and the

Clean Air Act, state law may not impose

liability for the global climate effects of

emissions that originate all over the

world.................................................................. 5

A.

Only federal law can govern

disputes like this one, which

implicates interstate and

international interests. .......................... 6

B.

Respondents’ packaging of their

claims makes no difference to the

conclusion that the claims are

preempted by federal law. ................... 13

C.

The displacement of federal

common law by federal statute

does not authorize state law to

regulate a uniquely federal area. ........ 15

D.

The CAA also preempts

respondents’ state law claims.............. 18

This Court should grant certiorari now. ........ 20

CONCLUSION .......................................................... 23

i

TABLE OF AUTHORITIES

Page(s)

Cases:

Am. Elec. Power Co. v. Connecticut,

564 U.S. 410 (2011) ...... 7, 8, 9, 10, 11, 15, 16, 18, 19

Banco Nacional de Cuba v. Sabbatino,

376 U.S. 398 (1964) .................................................. 8

Bd. of Cnty. Comm’rs of Boulder Cnty. v. Suncor

Energy (U.S.A.) Inc.,

25 F.4th 1238 (10th Cir. 2022) .............................. 14

Bonaparte v. Tax Court,

104 U.S. 592 (1881) ................................................ 13

City & Cnty. of Honolulu v. Sunoco LP,

537 P.3d 1173 (Haw. 2023) .............................. 15, 16

City of Milwaukee v. Illinois (Milwaukee II),

451 U.S. 304 (1981) .......................................... 16, 21

City of N.Y. v. Chevron Corp.,

993 F.3d 81 (2d Cir. 2021) ... 4, 10, 12, 14, 15, 17, 19

Cnty. of Oneida v. Oneida Indian Nation of N.Y.,

470 U.S. 226 (1985) .................................................. 7

Fuld v. Palestine Liberation Org.,

606 U.S. 1 (2025).................................................... 13

Gerling Glob. Reins. Corp. v. Gallagher,

267 F.3d 1228 (11th Cir. 2001).............................. 13

ii

Hinderlider v. La Plata River & Cherry Creek Ditch

Co.,

304 U.S. 92 (1938) .................................................... 7

Home Ins. Co. v. Dick,

281 U.S. 397 (1930) ................................................ 13

Illinois v. City of Milwaukee (Milwaukee I),

406 U.S. 91 (1972) ............................ 3, 7, 8, 9, 12, 21

Illinois v. City of Milwaukee (Milwaukee III),

731 F.2d 403 (7th Cir. 1984)............................ 16, 17

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987) ................................ 8, 12, 18, 19

Kansas v. Colorado,

206 U.S. 46 (1907) .................................................... 7

Kurns v. R.R. Friction Prods. Corp.,

565 U.S. 625 (2012) ................................................ 14

Minnesota v. Am. Petroleum Inst.,

63 F.4th 703 (8th Cir. 2023) .................................. 14

Nat’l Pork Producers Council v. Ross,

598 U.S. 356 (2023) ................................................ 13

Provincial Gov’t of Marinduque v. Placer Dome, Inc.,

582 F.3d 1083 (9th Cir. 2009)..................................8

Sam L. Majors Jewelers v. ABX, Inc.,

117 F.3d 922 (5th Cir. 1997)....................................7

San Diego Bldg. Trades Council v. Garmon,

359 U.S. 236 (1959) ................................................ 14

iii

Tex. Indus., Inc. v. Radcliff Materials, Inc.,

451 U.S. 630 (1981) ............................ 6, 8, 10, 14, 16

Treiber & Straub, Inc. v. UPS, Inc.,

474 F.3d 379 (7th Cir. 2007)....................................7

Ungaro-Benages v. Dresdner Bank AG,

379 F.3d 1227 (11th Cir. 2004)................................8

Statutes and treaty:

42 U.S.C. § 7411(b)(1)(A) .......................................... 18

42 U.S.C. § 7411(b)(1)(B) .......................................... 18

42 U.S.C. § 7411(d) .................................................... 18

42 U.S.C. § 7521(a)(1) ............................................... 18

42 U.S.C. § 7521(a)(2) ............................................... 18

42 U.S.C. § 7521(a)(3)(E) .......................................... 18

42 U.S.C. § 7547(a)(1) ............................................... 18

42 U.S.C. § 7547(a)(5) ............................................... 18

42 U.S.C. § 7571(a)(2)(A) .......................................... 18

42 U.S.C. § 7604(e) .................................................... 19

43 U.S.C. § 1802(1) .................................................... 11

Inflation Reduction Act of 2022,

Pub. L. No. 117-169, 136 Stat. 1818 ..................... 11

iv

Infrastructure Investment and Jobs Act,

Pub. L. No. 117-58, 135 Stat. 429 (2021) .............. 11

One Big Beautiful Bill Act,

Pub. L. No. 119-21, 139 Stat. 72 (2025) ................ 11

United Nations Framework Convention on Climate

Change, May 9, 1992,

S. Treaty Doc. No. 102-38, 1771 U.N.T.S. 107...... 11

Regulatory materials:

Reconsideration of 2009 Endangerment Finding &

Greenhouse Gas Vehicle Standards,

90 Fed. Reg. 36,288 (Aug. 1, 2025) ........................ 19

Other authorities:

Henry J. Friendly, In Praise of Erie—and of the New

Federal Common Law,

39 N.Y.U. L. Rev. 383 (1964) ................................... 7

Mary Shelley, Frankenstein (Penguin Classics rev.

ed. 2003) ................................................................. 17

19 Wright & Miller, Fed. Prac. & Proc., Juris. (4th

ed. 2022) ...................................................................8

v

INTEREST OF THE AMICUS CURIAE1

The Chamber of Commerce of the United States of

America is the world’s largest business federation. It

represents approximately 300,000 direct members and

indirectly represents the interests of more than three

million companies and professional organizations of

every size, in every industry sector, and from every

region of the country. An important function of the

Chamber is to represent the interests of its members in

matters before Congress, the Executive Branch, and

the courts. To that end, the Chamber regularly files

amicus curiae briefs in cases, like this one, that raise

issues of concern to the nation’s business community.

The Chamber has a strong interest in the legal and

policy issues that underlie this case, including issues

relating to climate change. The global climate is

changing, and human activities contribute to these

changes. There is much common ground on which all

sides could come together to address climate change

with policies that are practical, flexible, predictable,

and durable, maintaining the national and

international competitiveness of U.S. industry and

ensuring consistency with free enterprise and free

trade principles. See U.S. Chamber of Commerce, Our

Approach to Climate Change (Apr. 19, 2020),

https://www.uschamber.com/climate-change/ourapproach-to-climate-change. Durable climate policy

must be made by the federal government, which should

encourage innovation and investment to reduce

emissions and improve economic resilience and clean

1 Amicus curiae timely provided notice of intent to file this brief to

all parties. No counsel for any party authored this brief in whole

or in part, and no entity or person, aside from amicus curiae, its

members, or its counsel, made any monetary contribution

intended to fund the preparation or submission of this brief.

1

2

energy deployment across the globe. Governmental

policies aimed at achieving these goals should not be

made by the courts, much less by a patchwork of

actions under state law that would do more harm than

good.

Climate change is an interstate and international

challenge, and putative state-law claims that would

impose liability for climate change must necessarily be

resolved by federal law. The cross-border nature of

climate change implicates “uniquely federal interests”

for which a uniform federal policy and the application

of federal law are essential.

In the limited range of circumstances in which such

uniquely federal interests arise, the relevant legal

questions often intersect with the interests of many of

the Chamber’s members, who rely on the predictability

and uniformity of federal policy. This case falls within

that limited range: the Chamber and its members

have a strong interest in ensuring that claims for

which a uniform federal standard is necessary are

governed by federal law, and not by a patchwork of

state laws applied in piecemeal fashion.

3

SUMMARY OF ARGUMENT

I. In a case implicating “uniquely federal interests,”

there is no room for state law to apply. This is such a

case. Respondents’ lawsuit is fundamentally about

global climate change. A phenomenon of this nature,

which affects (and is affected by) not just every State

but every nation in the world, requires a solution that

the best efforts of individual States simply cannot

provide. The law of a single State, or an order from a

single state court, simply cannot address the effects on

every State and every nation from greenhouse gas

emissions emanating from all States and all nations,

which routinely cross interstate and international

borders.

Any possible solution to climate change can be

achieved only on a national and international basis—

which, within the United States, means through

federal law and the federal government acting on

behalf of the country as a whole. That is a consequence

of our constitutional structure, which ensures that only

federal law governs interstate disputes where the law

of a single State cannot apply. Reinforcing that

limitation, the Due Process Clause prohibits States

from regulating transactions or behavior with which

they have insufficient contact to support legislative

jurisdiction.

The need for a uniform federal standard in cases

concerning cross-border emissions is why this Court

has long recognized that state law cannot supply a rule

of decision for disputes about “air and water in their

ambient or interstate aspects.” Illinois v. City of

Milwaukee, 406 U.S. 91, 103 (1972) (Milwaukee I)

(citation omitted). Those disputes must be resolved by

federal law; indeed, where there is no federal statute,

4

federal common law has governed such disputes.

Congress may displace federal common law by statute,

which then serves as the exclusive source of remedies

for the claim; if Congress displaces federal common law

but provides no private remedy, then there is none.

Whether the federal law governing these matters is

common law or statutory law, federal law governs.

Displacement of federal common law remedies does not

mean that federal law disappears from the field—much

less that it allows fifty States and their associated

municipalities to rush into a uniquely federal arena.

The Second Circuit recognized as much in City of

New York v. Chevron Corp., 993 F.3d 81 (2021), holding

that congressional displacement of federal common law

through the Clean Air Act (CAA) does not open the

door to state law rules, since this federal area demands

a uniform solution. And the Seventh Circuit has long

held the same regarding displacement through the

Clean Water Act. Yet the Colorado Supreme Court

explicitly disagreed with both the Second and Seventh

Circuits on this crucial point, opting instead to follow

the contrary reasoning of the Hawaii Supreme Court.

This Court should grant certiorari to resolve this split.

II. Unless the Court intervenes now, a patchwork

of disparate state law decisions will quickly grow.

Disagreeing with the Second Circuit, the highest courts

of two States, Colorado and Hawaii, have now held

that municipalities may bring claims under state law

imposing liability for climate change. Those two cases

are just the tip of the iceberg: there are approximately

30 similar lawsuits currently making their way

through state courts. Companies like petitioners thus

face potentially overlapping and conflicting decisions in

dozens of state courts regarding the same fundamental

conduct—with possible remedies ranging from

5

injunctions of various stripes to many millions or

billions in damages. Compliance with such a regime

emanating from dozens of county courthouses would be

expensive, uncertain, and quite likely impossible.

Similar problems arise from the so-called “superfund”

laws that New York and Vermont have already enacted

based on the same impermissible and preempted

theory of liability as these cases. Even more

fundamentally, the emergence of these disparate

regimes of liability and regulation will disrupt the

federal government’s own efforts to direct and

implement uniform national policies on climate

change, as the United States itself has emphasized.

The Court should return this interstate and

international issue to the national government’s

domain, where it belongs under our constitutional

system.

For these reasons, and those set forth below, this

Court should grant the petition.

ARGUMENT

I. Under our federal structure and the Clean

Air Act, state law may not impose liability

for the global climate effects of emissions

that originate all over the world.

The question presented is whether federal law

precludes state law claims for relief for harm to the

Earth’s climate that is attributed to interstate and

international greenhouse-gas emissions. The answer is

yes: federal law alone controls. Because greenhouse

gas emissions originate all over the world, intermix in

the global atmosphere, and cross state and national

borders, the laws of a single state cannot possibly

resolve a dispute like this one.

6

The Colorado Supreme Court incorrectly held that

respondents can pursue state-law claims arising from

harms to the world’s climate that are allegedly caused

by global greenhouse gas emissions. To the extent that

federal law would ordinarily control in this area, the

court reasoned, the Clean Air Act displaced federal

common law without providing any federal statutory

cause of action, and thus somehow opened the door for

state law to apply.

As the court recognized, its holding deepens a

binary disagreement in the lower courts, and that

disagreement concerns an issue of fundamental

national importance—one threatening the federal

government’s authority and ability to respond to a

global challenge on behalf of the nation. In a very

similar case brought by New York City, the Second

Circuit held that federal law preempts such state law

claims, and that the Clean Air Act does not authorize

them. And the Seventh Circuit confirmed that a

similar federal antipollution statute, the Clean Water

Act, displaces common-law remedies but does not

authorize state remedies, because it does not make the

interstate dispute any less uniquely federal in nature.

This Court should grant certiorari to resolve the

conflict and reverse the deeply flawed decision below.

A. Only federal law can govern disputes like

this one, which implicates interstate and

international interests.

There are certain controversies that “our federal

system does not permit … to be resolved under state

law,” where “the interstate or international nature of

the controversy makes it inappropriate for state law to

control.” Tex. Indus., Inc. v. Radcliff Materials, Inc.,

451 U.S. 630, 641 (1981). Disputes over interstate air

7

pollution or air quality are exactly that type of controversy. The state supreme court erred in refusing to

recognize that it was therefore “inappropriate for state

law to control.”

1. This Court has made clear that federal common

law, in its modern form, “addresses ‘subjects within national legislative power where Congress has so directed’ or where the basic scheme of the Constitution so

demands.” Am. Elec. Power Co. v. Connecticut (AEP),

564 U.S. 410, 421 (2011) (quoting Henry J. Friendly, In

Praise of Erie—and of the New Federal Common Law,

39 N.Y.U. L. Rev. 383, 408, 421-22 (1964)). In particular, this Court has held that federal law must govern

when “there is an overriding federal interest in the

need for a uniform rule of decision or where the controversy touches basic interests of federalism.” Milwaukee I, 406 U.S. at 105 n.6. Federal common law can

supply such a “uniform rule of decision” in those areas;

state law cannot.

Courts have applied federal common law in cases

involving interstate water disputes, 2 tribal land

rights,3 interstate air carrier liability,4 and foreign relations.5 In such cases, federal law must govern be-

2 Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U.S.

92, 109-10 (1938); Kansas v. Colorado, 206 U.S. 46, 95-96 (1907).

3 Cnty. of Oneida v. Oneida Indian Nation of N.Y., 470 U.S. 226,

235-36 (1985).

4 Treiber & Straub, Inc. v. UPS, Inc., 474 F.3d 379, 384 (7th Cir.

2007) (discussing the Fifth Circuit’s “extensive analysis of the history of federal common law liability of common carriers” in Sam L.

Majors Jewelers v. ABX, Inc., 117 F.3d 922, 925-29 (1997)).

8

cause “local law will not be sufficiently sensitive to federal concerns, it is not likely to be uniform across state

lines, and it will develop at various rates of speed in

different states.” 19 Wright & Miller, Fed. Prac. &

Proc., Juris. § 4514 (4th ed. 2022). Moreover, the

structure of the Constitution does not allow States to

engage in such cross-border regulation. See Tex. Indus., 451 U.S. at 641.

One archetypal area in which the basic scheme of

the Constitution requires a federal rule concerns “the

environmental rights of a State against improper impairment by sources outside its domain.” Milwaukee I,

406 U.S. at 107 n.9 (citation omitted). In such cases,

“[f]ederal common law and not the varying common

law of the individual States is . . . necessary” to provide

a “uniform standard” for such disputes. Id. (citation

omitted). Accordingly, this Court has held that “[w]hen

we deal with air and water in their ambient or interstate aspects, there is a federal common law.” AEP,

564 U.S. at 421 (quoting Milwaukee I, 406 U.S. at 103).

Claims regarding transboundary emissions implicate “uniquely federal interests.” Accordingly, when

Milwaukee I held that cases regarding interstate air

and water emissions “should be resolved by reference

to federal common law[,] the implicit corollary of this

ruling was that state common law was preempted.”

Int’l Paper Co. v. Ouellette, 479 U.S. 481, 488 (1987);

see Milwaukee I, 406 U.S. at 107 n.9.

5 Banco Nacional de Cuba v. Sabbatino, 376 U.S. 398, 425-27

(1964); Provincial Gov’t of Marinduque v. Placer Dome, Inc., 582

F.3d 1083, 1088-89 (9th Cir. 2009); Ungaro-Benages v. Dresdner

Bank AG, 379 F.3d 1227, 1233 (11th Cir. 2004).

9

2. Climate change is an international and interstate phenomenon. Greenhouse gas emissions are released into the Earth’s atmosphere, where they intermix, from all over the world, and their effects are just

as global.

The Amended Complaint in this case does not

mince words about the scope of its allegations. It repeatedly states that it seeks to hold the oil companies

responsible for their worldwide “fossil fuel products”

that “release CO2 and other GHGs into the atmosphere, and contribute to changes in the planet’s climate.” Am. Compl. ¶¶ 70, 85 (emphases added); id.

¶ 123 (alleging that “the emission of GHGs into the

atmosphere … has increased the concentration of those

gases in the atmosphere, trapping heat in the climate

system, and warming the planet”); id. ¶ 383 (“Exxon is

one of the largest sources of GHG emissions both globally and historically.”); id. ¶ 399 (“Suncor is one of the

largest sources of GHG emissions both globally and

historically.”). By respondents’ own admissions, both

the emissions and the harms alleged (and the atmospheric phenomena that are indispensable causal links

between the emissions and the harms), as set forth in

the Amended Complaint, span the entire globe.

Respondents’ claims thus implicate uniquely federal interests, in multiple respects. It would be sufficient

that they concern “air and water in their ambient or

interstate aspects,” which “undoubtedly” calls for a

federal rule of decision, AEP, 564 U.S. at 421 (citation

omitted); Milwaukee I, 406 U.S. at 103. But there is

more: they also implicate foreign policy and the United

States’ sovereign interests. The “international nature

of the controversy” is another reason why it is “inap-

10

propriate for state law to control.” Tex. Indus., 451

U.S. at 641.

The Second Circuit correctly held that federal, not

state, law must control cases like this one. In City of

New York v. Chevron Corp., the Second Circuit confronted the question “whether a nuisance suit seeking

to recover damages for the harms caused by global

greenhouse gas emissions may proceed under New

York law.” 993 F.3d at 91. The court’s “answer is simple: ‘no.’” Id. The Second Circuit reasoned that federal

law governs in this area, leaving no role for state law,

because this “is an interstate matter raising significant

federalism concerns,” in no small part since “a substantial damages award like the one requested by the City

would effectively regulate the [defendants’] behavior

far beyond New York’s borders.” Id. at 92. “Such a

sprawling case is simply beyond the limits of state

law.” Id.

3. The necessity of a uniform federal approach in

mitigating climate change is accentuated by the difficult policy choices inherent in balancing the United

States’ environmental and energy needs. There are

important trade-offs to consider, all of which have

enormous consequences. As this Court has explained,

“[t]he appropriate amount of regulation in any particular greenhouse gas-producing sector” requires “informed assessment of competing interests”: “Along

with the environmental benefit potentially achievable,

our Nation’s energy needs and the possibility of economic disruption must weigh in the balance.” AEP,

564 U.S. at 427.

The federal government has been grappling with

this dilemma for decades. Congress undoubtedly takes

11

national energy needs very seriously, including by

providing for oil and gas production. E.g., 43 U.S.C.

§ 1802(1) (“establish[ing] policies and procedures for

managing the oil and natural gas resources of the Outer Continental Shelf … to achieve national economic

and energy policy goals, assure national security, reduce dependence on foreign sources, and maintain a

favorable balance of payments in world trade”). In

1992, the United States joined the United Nations

Framework Convention on Climate Change, May 9,

1992, S. Treaty Doc. No. 102-38, 1771 U.N.T.S. 107. In

that treaty, the signatories agreed that they “shall …

[t]ake climate change considerations into account, to

the extent feasible, in their relevant social, economic

and environmental policies and actions, and employ

appropriate methods … formulated and determined nationally, with a view to minimizing adverse effects on

the economy, on public health and on the quality of the

environment, of projects or measures undertaken by

them to mitigate or adapt to climate change.” Id. art.

4(1)(f) (emphasis added).

Indeed, by enacting the Clean Air Act, Congress has

designated the Environmental Protection Agency

(EPA) “as primary regulator of greenhouse gas emissions.” AEP, 564 U.S. at 428. And since AEP, Congress has repeatedly taken legislative action in this area. In the Inflation Reduction Act of 2022, for example,

the term “greenhouse gas” appears no fewer than 147

times. Pub. L. No. 117-169, 136 Stat. 1818. That term

appears another 39 times in the Infrastructure Investment and Jobs Act, Pub. L. No. 117-58, 135 Stat.

429 (2021). And Congress recently recalibrated its climate policy with the One Big Beautiful Bill Act, Pub.

L. No. 119-21, 139 Stat. 72 (2025), which “makes signif-

12

icant alterations to public incentives for climate and

energy-related investments.” Mia Beams & Akkshath

Subrahmanian, Council on Foreign Relations, Congress’s “One Big Beautiful Bill” Will Shrink Renewable

Energy Investments—Yet Some Technologies Are Preserved (Aug. 4, 2025), https://www.cfr.org/article/

congresss-one-big-beautiful-bill-will-shrink-renewableenergy-investments-yet-some.

To allow each of the fifty States—let alone each of

the thousands of municipalities, suing in hundreds of

state trial courts—to impose their own preferred policy

solutions to this complex global challenge, with each of

these governments naturally focused on local rather

than national benefit, would create a plainly “irrational

system of regulation” that “would lead to chaotic confrontation between sovereign states.” Ouellette, 479

U.S. at 496-97 (citation omitted). As the Second Circuit correctly concluded, allowing state-law suits in

this area to proceed, thereby “subjecting” companies’

“global operations to a welter of different states’ laws,”

“would further risk upsetting the careful balance that

has been struck between the prevention of global

warming, a project that necessarily requires national

standards and global participation, on the one hand,

and energy production, economic growth, foreign policy, and national security, on the other.” City of New

York, 993 F.3d at 93.

In short, this is a case in which “there is an overriding federal interest in the need for a uniform rule of

decision or where the controversy touches basic interests of federalism.” Milwaukee I, 406 U.S. at 105 n.6.

Federal law must therefore control.

13

4. The structural limitations that the Constitution

imposes on the application of state law to quintessentially national issues are reinforced by the Due Process

Clause. That Clause likewise limits the authority of

States to regulate matters that are insufficiently connected to the State. See Gerling Glob. Reins. Corp. v.

Gallagher, 267 F.3d 1228, 1237-38 (11th Cir. 2001);

Fuld v. Palestine Liberation Org., 606 U.S. 1, 14 (2025);

Home Ins. Co. v. Dick, 281 U.S. 397, 407-08 (1930); Bonaparte v. Tax Court, 104 U.S. 592, 594 (1881) (State

may not legislate “except with reference to its own jurisdiction”). This Court has referred to these “territorial limits on state authority” as “the Constitution’s

horizontal separation of powers.” Nat’l Pork Producers

Council v. Ross, 598 U.S. 356, 376 & n.1 (2023).

Respondents seek to regulate transactions far beyond their municipal borders (and even Colorado’s),

demanding that business practices and communications that occur elsewhere conform to their preferred

standards—or be penalized. In doing so, they seek to

control lawful activities in other States and effectively

override the energy policies of sister States, as well as

of the federal government. Respondents’ theory is in

serious tension with the due process limits on any one

State’s authority to prescribe legal rules beyond its

own borders.

B. Respondents’ packaging of their claims

makes no difference to the conclusion

that the claims are preempted by federal

law.

Regardless of whether respondents seek to enjoin

greenhouse gas emissions directly, they certainly do

seek to regulate such emissions. As the Tenth Circuit

14

recognized in an earlier phase of this litigation, this

suit is, at least in part, a suit “for damages allegedly

caused by climate change.” Bd. of Cnty. Comm’rs of

Boulder Cnty. v. Suncor Energy (U.S.A.) Inc., 25 F.4th

1238, 1248 (2022). The Amended Complaint demands

that petitioners “pay[] their share of the costs Plaintiffs

have incurred and will incur because of Defendants’

contribution to alteration of the climate.” Am. Compl.

¶ 6. It is a truism that “‘regulation can be effectively

exerted through an award of damages,’ and ‘[t]he obligation to pay compensation can be, indeed is designed

to be, a potent method of governing conduct and controlling policy.’” Kurns v. R.R. Friction Prods. Corp.,

565 U.S. 625, 637 (2012) (quoting San Diego Bldg.

Trades Council v. Garmon, 359 U.S. 236, 247 (1959))

(brackets in original); see also City of New York, 993

F.3d at 92 (same conclusion in similar climate suit);

Minnesota v. Am. Petroleum Inst., 63 F.4th 703, 719

(8th Cir. 2023) (Stras, J., concurring) (recognizing that

similar climate suit sought to “change the companies’

behavior on a global scale”).

It makes no difference that respondents have

framed this dispute as arising, in part, from misleading

marketing relating to climate change, just as it would

make no difference if a dispute between two States regarding interstate air or water pollution also happened

to involve allegations of misleading statements, breach

of contract, or any other alleged violation of federal or

state law. It is “the interstate or international nature

of the controversy [that] makes it inappropriate for

state law to control,” Tex. Indus., 451 U.S. at 641 (emphasis added), not the precise causes of action pleaded.

Here, the gravamen of the dispute is the oil companies’

alleged responsibility for climate change impacts at-

15

tributed to greenhouse gas emissions. That dispute

must be governed by federal law, for the reasons given

above. See pp. 6-13, supra.

As the Second Circuit held in rejecting a similar argument in a parallel climate suit by New York City,

“[a]rtful pleading cannot transform the City’s complaint into anything other than a suit over global

greenhouse gas emissions.” City of New York, 993 F.3d

at 91. Such a suit must be governed by federal law.

C. The displacement of federal common law

by federal statute does not authorize

state law to regulate a uniquely federal

area.

1. The Colorado Supreme Court’s principal reason

for concluding that respondents’ state law claims are

not preempted is that federal common law related to

greenhouse gas emissions has been “displaced by the

federal legislation authorizing EPA to regulate carbondioxide emissions,” AEP, 564 U.S. at 423, and therefore

“that common law no longer exists.” Pet. App. 17a.

The majority below echoed the Hawaii Supreme

Court’s reasoning that “displaced federal common law

plays no part in this court’s preemption analysis.” Pet.

App. 20a (quoting City & Cnty. of Honolulu v. Sunoco

LP, 537 P.3d 1173, 1199 (Haw. 2023)).

As the decision below acknowledged, that reasoning

directly conflicts with the Second Circuit’s holding in

City of New York. See Pet. App. 19a-20a. There, the

Second Circuit explained “state law does not suddenly

become presumptively competent to address issues

that demand a unified federal standard simply because

Congress saw fit to displace a federal court-made

standard with a legislative one.” 993 F.3d at 98. “Such

16

an outcome is too strange to seriously contemplate.”

Id. at 98-99. The Second Circuit embraced the reasoning of the Seventh Circuit in Illinois v. City of Milwaukee (Milwaukee III) that, despite Milwaukee II’s holding that the federal common law recognized in Milwaukee I was displaced, “[t]he very reasons … for resorting to federal common law in Milwaukee I are the

same reasons why the state claiming injury cannot apply its own state law to out-of-state discharges now.”

731 F.2d 403, 410 (7th Cir. 1984).

The Colorado Supreme Court conceded that its reasoning directly conflicts with the holdings of both the

Second and Seventh Circuits. Pet. App. 19a-20a. Yet

it rejected the “preemption analysis” in those decisions

as “‘backwards reasoning.’” Pet. App. 19a (quoting

Honolulu, 537 P.3d at 1199). This Court should grant

certiorari to resolve that acknowledged split.

2. There is nothing “backwards” about the Second

and Seventh Circuit’s preemption analyses. Those circuits correctly apply the basic rule that “if federal

common law exists, it is because state law cannot be

used.” City of Milwaukee v. Illinois, 451 U.S. 304, 313

n.7 (1981) (Milwaukee II); see Tex. Indus., 451 U.S. at

641 & n.13 (federal law governs where the nature of

the claim “makes it inappropriate for state law to control”). That Congress displaced federal common law

simply means that the federal courts are no longer in

the business of formulating federal standards. See

AEP, 564 U.S. at 423-24 (explaining that “it is primarily the office of Congress, not the federal courts, to prescribe national policy in areas of special federal interest”). Displacement in no way eliminates or undermines the overriding federal interest in the dispute,

much less throws open the door for the courts of the

17

fifty different States to engage in their own piecemeal

resolution of these distinctly federal issues under a variety of competing and conflicting state and local laws.

State law was incompetent to address the issue before

congressional action, and it remains so after it. The

court below wrongly treats congressional displacement

of federal common law as though it were Dr. Frankenstein—“infus[ing] a spark of being into the lifeless

thing” that is state law. Mary Shelley, Frankenstein

58 (Penguin Classics rev. ed. 2003).

Precisely because of the need for uniformity—the

reason why federal common law was necessary in the

first place—a displacing federal statutory scheme must

provide the authoritative answer on what remedies are

available, even if the answer is “none.” Thus, “‘resorting to state law’ on a question previously governed by

federal common law is permissible only to the extent

‘authorized’ by federal statute.” City of New York, 993

F.3d at 99 (brackets omitted) (quoting Milwaukee III,

731 F.2d at 411). Under the reasoning of the Colorado

and Hawaii Supreme Courts, however, congressional

attempts to supply a uniform federal standard by statute would bring to life the very same disuniform statelaw rules that were, and remain, incompetent to address this national problem. That would be so even if

that federal legislation were to “adopt[] verbatim a

judge-made common law rule.” Id. at 98-99. Congress

could enact statutes codifying the very same courtsupplied rules governing interstate water rights, interstate air carrier liability, and interstate disputes over

intangible property, see p. 7, supra, and according to

the Colorado and Hawaii Supreme Courts (and respondents), state law claims on those subjects would

suddenly become viable, triggering the very same prob-

18

lems that initially prompted the formulation of a federal rule.

That makes no sense. Federal problems remain

federal problems, regardless of whether the necessary

uniform, federal standard to deal with them is supplied

by federal courts or federal statute. In the (few) areas

where federal common law would apply but for displacement by Congress, “the implicit corollary” is that

“state common law [is] preempted.” Ouellette, 479 U.S.

at 488.

D. The CAA also preempts respondents’

state law claims.

Respondents’ claims also conflict with, and are

preempted by, the CAA itself. The CAA “delegate[s]”

authority to EPA to “deci[de] whether and how to regulate” greenhouse gas emissions, and “entrusts” to EPA

the “complex balancing” of “competing interests.” AEP,

564 U.S. at 426-27. For example, Title II of the CAA

gives EPA authority to determine whether to establish

emissions standards for the transportation sector, including vehicles, aircraft, locomotives, motorcycles, and

nonroad engines and equipment.

42 U.S.C.

§§ 7521(a)(1)-(2), (a)(3)(E), 7571(a)(2)(A), 7547(a)(1),

(a)(5). The CAA also provides EPA with authority to

determine whether emissions of a pollutant from “stationary sources,” such as power plants, refineries, and

oil and gas wells, should be regulated and at what levels.

AEP, 564 U.S. at 426; see 42 U.S.C.

§ 7411(b)(1)(A)-(B), (d). “If EPA does not set emissions

limits for a particular pollutant or source of pollution,

States and private parties may petition [EPA] for a

19

rulemaking on the matter … [but there is] no room for

a parallel track.” AEP, 564 U.S. at 425.6

The citizen-suit savings clause of the CAA, 42

U.S.C. § 7604(e), preserves a “slim reservoir of state

common law” for suits brought under the law of the

State that is the source of the emissions. City of New

York, 993 F.3d at 99-100. But that narrow carveout

underscores that the CAA leaves no other avenue for

state law claims with respect to air pollution for which

the authority to regulate has been delegated to EPA.

In Ouellette, this Court analyzed parallel provisions of

the Clean Water Act and held that the statute “precludes a court from applying the law of an affected

State against an out-of-state source” but permits “a

nuisance claim pursuant to the law of the source

State.” 479 U.S. at 494-497. The same is true of the

CAA. See City of New York, 993 F.3d at 100.

Respondents complain of emissions from all over

the planet, not emissions originating in Colorado—yet

6 EPA has proposed to rescind its GHG emissions standards for

new motor vehicles and engines and has described a number of

alternative rationales and pathways for doing so. These include

the proposed rescission of EPA’s 2009 “endangerment finding,”

which concluded that GHG emissions from new motor vehicles

and engines contribute to air pollution which may endanger public

health or welfare within the meaning of section 202 of the Clean

Air Act. See 90 Fed. Reg. 36,288 (Aug. 1, 2025). Regardless of

whether EPA finalizes the proposed rule, and regardless of which

rationale or rationales EPA relies on if EPA does so, that potential

future action would not affect the points made in this brief. Matters of interstate air quality are not matters on which a single

State can apply its own law; and whatever specific rules the federal government may apply in that area, a federal decision not to

regulate is not an authorization for States to impose their own

regulation.

20

they seek to hold petitioners liable under Colorado law.

Such claims are preempted by the CAA’s comprehensive regulatory scheme.

II. This Court should grant certiorari now.

This case is one of at least 31 lawsuits filed by state,

local, and tribal governments since 2017 that seek

competing remedies for overlapping claims alleging

harm arising from emissions outside the borders of the

plaintiff governments’ respective jurisdictions.7 And

7 Cnty. of San Mateo v. Chevron Corp., No. 17CIV03222 (Cal. Su-

per. Ct. July 17, 2017); City of Oakland v. BP p.l.c., No.

RG17875889 (Cal. Super. Ct. Sept. 19, 2017); City of Santa Cruz v.

Chevron Corp., No. 17CV03243 (Cal. Super. Ct. Dec. 20, 2017);

Cnty. of Santa Cruz v. Chevron Corp., No. 17CV03242 (Cal. Super.

Ct. Dec. 20, 2017); City of New York v. BP p.l.c., No. 18-cv-182

(S.D.N.Y. Jan. 9, 2018); City of Richmond v. Chevron Corp., No.

C18-00055 (Cal. Super. Ct. Jan. 22, 2018); Bd. of Cnty. Comm’rs of

Boulder Cnty. v. Suncor Energy (U.S.A.), Inc., No. 2018CV30349

(Colo. Dist. Ct. Apr. 17, 2018); King Cnty. v. BP p.l.c., No. 18-211859-0 (Wash. Super. Ct. May 9, 2018); Rhode Island v. Shell Oil

Prods. Co., No. PC-2018-4716 (R.I. Super. Ct. July 2, 2018); Mayor

& City Council of Balt. v. BP p.l.c., No. 24-C-18-004219 (Md. Cir.

Ct. July 20, 2018); Massachusetts v. ExxonMobil Corp., No. 1984CV-3333 (Mass. Super. Ct. Oct. 24, 2019); City & Cnty. of Honolulu v. Sunoco LP, No. 1CCV-20-0000380 (Haw. Cir. Ct. Mar. 9,

2020); Minnesota v. Am. Petroleum Inst., No. 62-CV-20-3837

(Minn. Dist. Ct. June 24, 2020); Dist. of Columbia v. Exxon Mobil

Corp., No. 2020 CA 002892 B (D.C. Super. Ct. June 25, 2020); City

of Hoboken v. Exxon Mobil Corp., No. HUD-L-003179-20 (N.J. Super. Ct. Sept. 2, 2020); City of Charleston v. Brabham Oil Co., No.

2020-CP-10-03975 (S.C. Ct. Comm. Pleas Sept. 9, 2020); Connecticut v. Exxon Mobil Corp., No. HHDCV206132568S (Conn. Super.

Ct. Sept. 14, 2020); Cnty. of Maui v. Sunoco LP, No. 2CCV-20000283 (Haw. Cir. Ct. Oct. 12, 2020); City of Annapolis v. BP p.l.c.,

No. C-02-CV-21-000250 (Md. Cir. Ct. Feb. 22, 2021); Anne Arundel

Cnty. v. BP p.l.c., No. C-02-CV-21-000565 (Md. Cir. Ct. Apr. 26,

2021); Vermont v. Exxon Mobil Corp., No. 21-CV-02778 (Vt. Super.

Ct. Sept. 14, 2021); Municipality of Bayamon v. Exxon Mobil

21

two States have now enacted so-called “superfund”

statutes that likewise seek to impose liability on energy producers for global greenhouse gas emissions,

prompting suits by the Chamber, the United States,

and other parties to declare those statutes preempted

and unlawful. See Chamber of Commerce of the U.S.A.

v. Moore, No. 24-cv-1513 (D. Vt.); Chamber of Commerce of the U.S.A. v. James, No. 25-cv-1307

(N.D.N.Y.); United States v. Vermont, No. 25-cv-463 (D.

Vt.); United States v. New York, No. 25-cv-3656

(S.D.N.Y.); West Virginia v. James, No. 25-cv-168

(N.D.N.Y.).

The collision of state law decisions, and the growth

of “conflicting disputes, increasing assertions[,] and

proliferating contentions would seem to be inevitable”

if these 30-plus actions (and counting) proceed with

States and municipalities applying their laws to claims

of cross-border pollution originating all over the world.

Milwaukee I, 406 U.S. at 107 n.9 (citation omitted).

The array of state law actions seeking relief under

“vague and indeterminate” standards (Milwaukee II,

451 U.S. at 317) threatens to seriously (and perhaps

Corp., No. 22-cv-1550 (D.P.R. Nov. 22, 2022); Cnty. of Multnomah

v. Exxon Mobil Corp., No. 23CV25164 (Or. Cir. Ct. June 22, 2023);

People v. Exxon Mobil Corp., No. CGC23609134 (Cal. Super. Ct.

Sept. 15, 2023); Municipality of San Juan v. Exxon Mobil Corp.,

No. 23-cv-01608 (D.P.R. Dec. 13, 2023); Shoalwater Bay Indian

Tribe v. Exxon Mobil Corp., No. 23-2-25215-2 (Wash. Super. Ct.

Dec. 20, 2023); Makah Indian Tribe v. Exxon Mobil Corp., No. 232-25216-1 (Wash. Super. Ct. Dec. 20, 2023); City of Chicago v. BP

p.l.c., No. 2024CH01024 (Ill. Cir. Ct. Feb. 20, 2024); Bucks Cnty. v.

BP p.l.c., No. 2024-01836-0000 (Pa. Comm. Pleas Ct. Mar. 25,

2024); Maine v. BP p.l.c., No. PORSC-CV-24-442 (Me. Super. Ct.

Nov. 26, 2024); Hawaii v. BP p.l.c., No. 1CCV-25-717 (Haw. Cir.

Ct. May 1, 2025).

22

irreversibly) undermine the federal government’s ability to respond to global climate change. And although

the claims thus far have been brought against companies in the energy industry, there seems to be no clear

reason why the plaintiffs could not try to sue any alleged contributor to global climate change on the same

or similar theory, in any state court with personal jurisdiction.

This Court should grant certiorari now to restore

the supremacy of federal law, before state courts begin

accepting the remedial demands of aggressive localgovernment plaintiffs and imposing their own professed solutions. Attempts to regulate the entire global

climate from local courthouses will only hinder a uniform federal response. If the Court does not act now,

the Court may be forced to deal with the issue in a

more urgent fashion, potentially on the emergency

docket. The Court should resolve this important matter now.

23

CONCLUSION

The petition for a writ of certiorari should be granted.

Respectfully submitted.

ANDREW R. VARCOE

STEPHANIE A. MALONEY

U.S. CHAMBER

LITIGATION CENTER

1615 H Street, NW

Washington, DC 20062

JESSE LEMPEL

GOODWIN PROCTER LLP

100 Northern Avenue

Boston, MA 02210

October 9, 2025

WILLIAM M. JAY

Counsel of Record

GOODWIN PROCTER LLP

1900 N Street, NW

Washington, DC 20036

wjay@goodwinlaw.com

(202) 346-4000

Counsel for Amicus Curiae

the Chamber of Commerce

of the United States of

America