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 Writ of Certiorari

to the Supreme Court of Colorado

BRIEF OF CITY AND COUNTY

GOVERNMENTS AS AMICI CURIAE

IN SUPPORT OF RESPONDENTS

Victor M. Sher

Counsel of Record

Matthew K. Edling

Michael Burger

Martin Quiñones

Sher Edling LLP

100 Montgomery St., Ste. 1410

San Francisco, CA 94104

(628) 231-2500

vic@sheredling.com

matt@sheredling.com

michael@sheredling.com

marty@sheredling.com

Counsel for Amici Curiae

Mosaic - (301) 927-3800 - Cheverly, MD

49261_Ltrhd.indd

1

6/11/08

12:44:0

i

TABLE OF CONTENTS

Page

INTEREST OF AMICI.........................................

1

INTRODUCTION AND SUMMARY OF

ARGUMENT....................................................

2

ARGUMENT........................................................

7

I. Claims for Climate-Change Related

Injuries That Premise Liability on

Deceptive Marketing Are Separable

and Categorically Different From Claims

Premised on Polluting Conduct.................

7

A. Claims targeting deceptive marketing

do not premise liability on the

defendants’ having emitted pollution

or having merely manufactured and

sold a product that creates pollution....

8

B. Deception-based claims seek relief for

injuries caused by the defendants’

deception, not all harms for which

greenhouse gas emissions are a

but-for cause..........................................

11

II. Even Assuming That Claims Targeting

Polluting Conduct or the Production and

Sale of Polluting Products Are Preempted,

Deception-Based Claims Are Not..............

15

A. The Constitution does not preempt

claims targeting a defendant’s deceptive

business practices simply because the

alleged deception concerns conduct that

crosses state borders.............................

16

1. The Constitution does not prohibit the

operation of state law to redress

misrepresentations about interstate

pollution............................................

16

ii

TABLE OF CONTENTS—Continued

Page



2. The “extraterritoriality principle”

this Court once applied in some

Dormant Commerce Clause cases

has no independent force, and the

concerns petitioners raise are

adequately addressed by existing

constitutional constraints on state

choice-of-law rules............................

19

3. Foreign affairs considerations do

not preempt, and in fact support,

state laws targeting misrepresentations

about a product’s impacts on the

24

environment......................................

B. The Clean Air Act Does Not Speak

to or Regulate Marketing Practices and

Does Not Preempt State Law Claims to

Remedy Consumer Deception...............

28

CONCLUSION.....................................................

33

iii

TABLE OF AUTHORITIES

Page

Cases

Alaska Packers Ass’n v. Indus. Accident Comm’n,

294 U.S. 532 (1935).................................................20

Allstate Ins. Co. v. Hague,

449 U.S. 302 (1981)...........................................20, 24

Am. Beverage Ass’n v. Snyder,

735 F.3d 362 (6th Cir. 2013).............................22, 23

Am. Ins. Ass’n v. Garamendi,

539 U.S. 396 (2003)...........................................24, 25

Arizona v. United States,

567 U.S. 387 (2012).................................................28

Ass’n of Taxicab Operators USA v. City of Dallas,

720 F.3d 534 (5th Cir. 2013)...................................32

Bates v. Dow Agrosciences LLC,

544 U.S. 431 (2005).................................................13

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

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

2024 WL 3204275

(Colo. Dist. Ct. June 21, 2024)................................14

BMW of N. Am., Inc. v. Gore,

517 U.S. 559 (1996).................................................21

BP P.L.C. v. Mayor & City Council of Baltimore,

593 U.S. 230 (2021)...................................................3

Brown v. Estate of Fletcher,

210 U.S. 82 (1908)...................................................21

California v. ARC Am. Corp.,

490 U.S. 93 (1989)...................................................19

Chamber of Com. of the U.S. v. Whiting,

563 U.S. 582 (2011)...........................................31, 32

iv

TABLE OF AUTHORITIES—Continued



Page

City & Cnty. of Honolulu v. Sunoco LP,

537 P.3d 1173 (Haw. 2023).......3, 4, 6–12, 23, 31, 32

City of Milwaukee v. Illinois,

451 U.S. 304 (1981).................................................17

City of New York v. Chevron Corp.,

993 F.3d 81 (2d Cir. 2021)..................................9, 10

Delaware v. Monsanto Co.,

299 A.3d 372 (Del. 2023)...........................................9

District of Columbia v. Exxon Mobil Corp.,

89 F.4th 144 (D.C. Cir. 2023)...................................3

Dobbs v. Jackson Women’s Health Org.,

597 U.S. 215 (2022).............................................4, 15

Edenfield v. Fane,

507 U.S. 761 (1993).................................................19

Energy & Env’t Legal Inst. v. Epel,

793 F.3d 1169 (10th Cir. 2015)...............................22

English v. Gen. Elec. Co.,

496 U.S. 72 (1990).............................................29, 30

Fla. Lime & Avocado Growers, Inc. v. Paul,

373 U.S. 132 (1963)...........................................19, 31

Franchise Tax Bd. v. Hyatt,

538 U.S. 488 (2003)...........................................20, 24

Franchise Tax Bd. v. Hyatt,

587 U.S. 230 (2019)...........................................17, 21

Fuld v. Palestine Liberation Org.,

606 U.S. 1 (2025).....................................................21

Gen. Motors Corp. v. United States,

496 U.S. 530 (1990).................................................29

Georgia v. Tenn. Copper Co.,

206 U.S. 230 (1907).................................................17

v

TABLE OF AUTHORITIES—Continued



Page

Gibbons v. Ogden,

22 U.S. (9 Wheat.) 1 (1824)...............................15, 22

Goodyear Atomic Corp. v. Miller,

486 U.S. 174 (1988).................................................30

Grp. Health Plan, Inc. v. Philip Morris USA, Inc.,

344 F.3d 753 (8th Cir. 2003)...................................12

Hencely v. Fluor Corp.,

146 S. Ct. 1086 (2026)...............................................4

Hinderlider v. La Plata River &

Cherry Creek Ditch Co.,

304 U.S. 92 (1938)...................................................18

Illinois v. City of Milwaukee,

406 U.S. 91 (1972).............................................17, 18

In re Methyl Tertiary Butyl Ether (“MTBE”)

Prods. Liab. Litig.,

725 F.3d 65 (2d Cir. 2013)......................................31

In re Rail Freight Fuel Surcharge Antitrust Litig.,

292 F. Supp. 3d 14 (D.D.C. 2017)...........................12

In re Volkswagen “Clean Diesel” Mktg.,

Sales Pracs., & Prods. Liab. Litig.,

959 F.3d 1201 (9th Cir. 2020).................................32

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987).................................................29

Kansas v. Garcia,

589 U.S. 191 (2020).................................................31

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

565 U.S. 625 (2012).................................................29

LePage’s Inc. v. 3M,

324 F.3d 141 (3d Cir. 2003)....................................12

vi

TABLE OF AUTHORITIES—Continued



Page

Loper Bright Enters. v. Raimondo,

603 U.S. 369 (2024).................................................28

Lorillard Tobacco Co. v. Reilly,

533 U.S. 525 (2001).................................................19

Mayor & City Council of Baltimore v. BP P.L.C.,

31 F.4th 178 (4th Cir. 2022)...................................10

Medellín v. Texas,

552 U.S. 491 (2008).....................................24, 26, 28

Merrick v. Diageo Americas Supply, Inc.,

805 F.3d 685 (6th Cir. 2015)...................................29

Missouri v. Illinois,

180 U.S. 208 (1901).................................................17

Murphy v. Nat’l Collegiate Athletic Ass’n,

584 U.S. 453 (2018).................................................28

Myers v. United States,

272 U.S. 52 (1926)...................................................21

Nat’l Pork Producers Council v. Ross,

598 U.S. 356 (2023).......................................5, 21, 22

New Jersey v. City of New York,

283 U.S. 473 (1931).................................................17

New York v. New Jersey,

256 U.S. 296 (1921).................................................17

North Carolina ex rel. Cooper v.

Tenn. Valley Auth.,

615 F.3d 291 (4th Cir. 2010)...................................29

Ohio v. Wyandotte Chems. Corp.,

401 U.S. 493 (1971).................................................17

Oxygenated Fuels Ass’n Inc. v. Davis,

331 F.3d 665 (9th Cir. 2003).............................29, 31

vii

TABLE OF AUTHORITIES—Continued



Page

People v. ConAgra Grocery Prods. Co.,

17 Cal. App. 5th 51 (2017)..................................9, 12

Phillips Petroleum Co. v. Shutts,

472 U.S. 797 (1985).................................................20

Puerto Rico Dep’t of Consumer Affairs v. ISLA

Petroleum Corp.,

485 U.S. 495 (1988).................................................15

Rhode Island v. Shell Oil Prods. Co.,

35 F.4th 44 (1st Cir. 2022)......................................10

Silkwood v. Kerr-McGee Corp.,

464 U.S. 238 (1984).................................................30

State Farm Mut. Auto. Ins. Co. v. Campbell,

538 U.S. 408 (2003).................................................21

Sun Oil Co. v. Wortman,

486 U.S. 717 (1988).............................................5, 23

Trump v. Cook,

2026 WL 1855613 (U.S. June 29, 2026).................21

Trump v. Slaughter,

2026 WL 1855612 (U.S. June 29, 2026).................21

Va. Uranium, Inc. v. Warren,

587 U.S. 761 (2019).................................................15

Watson v. Emps. Liab. Assurance Corp.,

348 U.S. 66 (1954)...................................................23

Wyeth v. Levine,

555 U.S. 555 (2009).................................................31

Youngstown Sheet & Tube Co. v. Sawyer,

343 U.S. 579 (1952).................................................24

Zschernig v. Miller,

389 U.S. 429 (1968).................................................24

viii

TABLE OF AUTHORITIES—Continued



Regulations

Page

Rescission of the Greenhouse Gas Endangerment

Finding and Motor Vehicle Greenhouse Gas

Emission Standards Under the Clean Air Act

91 Fed. Reg. 7686 (Feb. 18, 2026)..........................28

Other Authorities

United Nations Framework Convention on

Climate Change,

May 9, 1992, 1771 U.N.T.S. 107.............................25

Rep. of the Conf. of the Parties on Its

Twenty-First Session,

¶ 51, U.N. Doc. FCCC/CP/2015/10/Add.1 (2016) ...26

United States–Mexico–Canada Agreement

art. 21.4(2)–(3), Nov. 30, 2018................................27

OECD Guidelines for Protecting Consumers

from Fraudulent and Deceptive Commercial

Practices Across Borders 11 (2003) .......................27

Municipal Code of Chicago §§ 2-25-090,

4-276-470, 4-276-480 ..............................................14

New York City Code §§ 20-700, 20-703......................14

1

INTEREST OF AMICI

Amici are local governments or their legal officers

representing more than six million residents in California, Hawaii, Illinois, and New Jersey. All have

brought suit against various oil-and-gas companies,

and some against the largest industry association. The

local governments’ complaints allege that those defendants developed extensive, highly accurate knowledge

of the threats posed to the climate by the intended use

of their fossil fuel products, but for many years failed

to warn and affirmatively misled consumers and the

public about those severe, widespread harms.

Amici bring varying common law and statutory

causes of action under the laws of their respective

states. First, most amici allege that the companies’

long-running campaigns of misleading marketing,

failures to warn, and related deceptive conduct led

consumers to purchase and use fossil fuel products in

greater amounts and for longer than they would have

absent the deception, causing and exacerbating injuries to amici and their residents. Those amici pursue

claims including public and private nuisance, trespass, and failure to warn, among others. Because amici recognize that some levels of fossil-fuel use would

have been part of the mix of international and domestic energy sources even if the defendants had behaved

truthfully, their claims seek to recover for only those

injuries flowing from the defendants’ wrongful deception—not climate change writ large—through remedies including nuisance abatement within their respective jurisdictions and damages. Second, some

amici have brought claims to enforce consumer protection laws that prohibit unfair or deceptive business

practices, and seek remedies including statutory penalties and disgorgement. Claims in the latter category

are not before the Court in this case and are outside

2

the scope of the Question Presented, as petitioners

and their amici agree.

Respondents in this case, the County Commissioners of Boulder County and the City of Boulder, Colorado (together, “Boulder”), assert “two distinct theories of liability.” Opp. Cert. at 3. Like amici, Boulder

alleges petitioners misled the public about the role

their fossil fuel products play in causing and exacerbating climate change, and seek to recover for ongoing

injuries caused by that deception. See ibid. Boulder

also alleges petitioners are liable for “knowingly

caus[ing] and contribut[ing] to the alteration of the climate” through their production and sale of fossil fuels.

Ibid. Amici have an interest in protecting their deception-focused claims and theories, which are distinct

from Boulder’s upstream production and sales claims.

Amici agree with Boulder that none of their claims

or theories are preempted. Neither the Clean Air Act

(“CAA”), nor the federal common law it displaced, nor

anything in the Constitution prohibits states from

providing remedies for injuries caused by climate

change. However, even if Boulder’s theory premising

liability on petitioners’ knowing contribution to climate harms were foreclosed by some federal rule,

their theory premised on petitioners’ extensive wrongful promotion and marketing practices would not be.

Amici write to explain that petitioners’ preemption

theories are particularly inapposite as applied to deception-based claims.

INTRODUCTION AND

SUMMARY OF ARGUMENT

Like Boulder, amici allege that their fossil-fuel defendants violated well-established state-law duties by

“promoting fossil fuels while allegedly concealing their

environmental impacts.” See BP P.L.C. v. Mayor &

3

City Council of Baltimore, 593 U.S. 230, 234 (2021).

They contend industry leaders like petitioner Exxon

Mobil Corp., through internal research and research

shared within trade groups, became “aware of the

global warming phenomenon caused by their products” as early as the 1960s, and developed a precise

understanding of the severe harms their products

would cause. City & Cnty. of Honolulu v. Sunoco LP,

537 P.3d 1173, 1183 (Haw. 2023). And like Boulder,

amici allege that instead of disclosing their knowledge, the defendant oil-and-gas companies and their

surrogates “for decades intentionally misled the public about the impacts of climate change and the role

that defendants’ fossil fuel products have played in

exacerbating those impacts.” Pet. App. at 3a.

The defendants’ deception efforts intensified in the

1980s, during which they not only failed to warn about

their products’ known dangers, but also “actively

worked to discredit scientific evidence that supported

the existence of global warming.” Honolulu, 537 P.3d

at 1182. More recently, as the public’s understanding

of the causes of climate change has begun to catch up

with the defendants’, those defendants pivoted to a

strategy of misrepresenting their fossil fuel products

as “clean” or “green” and misrepresenting the extent

of their investment in renewable energy. See, e.g., District of Columbia v. Exxon Mobil Corp., 89 F.4th 144,

148 (D.C. Cir. 2023). Fundamentally, amici’s complaints “challenge the promotion and sale of fossil-fuel

products without warning and abetted by a sophisticated disinformation campaign.” Honolulu, 537 P.3d

at 1181 (quotation omitted).

Most amici assert tort claims including public and

private nuisance, trespass, and failure to warn, which

seek remedies for climate-change related injuries in

their respective jurisdictions caused by defendants’ de-

4

ception. As local governments, amici face enormous

present and future costs stemming from climate

change phenomena such as rising sea levels, increasingly frequent and intense storms, flooding, heat

waves, droughts, wildfires, salt-water intrusion of water resources, and increased coastal water acidification. See, e.g., id. at 1182–83. Those claims seek relief

including damages and nuisance abatement for injuries flowing only from the incremental increase in fossil-fuel consumption caused by the challenged deception. Some amici also plead enforcement claims under

local ordinances that prohibit unfair and deceptive

acts and practices (“UDAP claims”); amici’s claims under those ordinances do not seek to recover for environmental injuries caused by the defendants’ deception

and do not require any showing that the deception

caused tangible harm. Those claims instead aim to

remedy and prevent false and misleading marketing

directed at amici’s residents, and seek statutory penalties and injunctive relief against further deception.

Boulder’s case presents deception-based theories

and a theory premised on petitioners’ knowing contribution to climate-related harms. Neither are preempted under any of petitioners’ theories. Petitioners assert that state law is always preempted whenever it

touches any set of facts involving pollution that crosses state boundaries. But because “[n]o constitutional

provision says it is preempted,” Hencely v. Fluor Corp.,

608 U.S. ___, 146 S. Ct. 1086, 1093 (2026), petitioners

“must show that the r[ule] is somehow implicit in the

constitutional text,” Dobbs v. Jackson Women’s Health

Org., 597 U.S. 215, 235 (2022). They cannot. Petitioners similarly argue that the Constitution necessarily

federalizes any set of facts “involving” interstate air

pollution, citing cases that applied the displaced federal common law that once governed certain nuisance

5

cases brought by States to enjoin pollution entering

interstate streams or drifting across state borders.

Petrs. Br. at 24–26. That common law, however, was

abrogated by the Clean Air Act, and cannot be resurrected through the Constitution’s atextual interstices.

And in any event, it never would have applied to deception-based claims.

Petitioners invent a new “extraterritoriality principle” to support their interstate pollution argument,

under which every application of State law must be

deemed “bounded by the States’ respective borders.”

Petrs. Br. at 24 (quotation omitted). That supposed

principle has no basis in the Constitution’s text or this

Court’s precedents. This Court has, to the contrary, repeatedly declined to adopt such a rule because “the legislative jurisdictions of the States overlap” and “it is

frequently the case . . . that a court can lawfully apply

either the law of one State or the contrary law of another.” Sun Oil Co. v. Wortman, 486 U.S. 717, 727

(1988). Because “virtually all state laws create ripple

effects beyond their borders,” the Court recently

“decline[d] . . . incautious invitations” to “recognize an

‘almost per se’ rule against the enforcement of state

laws that have ‘extraterritorial effects.’ ” Nat’l Pork

Producers Council v. Ross, 598 U.S. 356, 390–91 (2023).

Even if petitioners’ constitutional arguments had

merit in some contexts, they would still fail as applied

to claims premised on deception. Advertising and consumer protection are well-recognized subjects within

the States’ police authority, and those types of claims

have never been subject to a uniform federal rule of

decision. By the same token, claims to remedy deceptive marketing do not implicate States’ “competing

claims to regulate shared natural resources,” contra

Petrs. Br. at 3, even where the alleged deception concerns a product’s environmental impacts.

6

Petitioners’ foreign policy arguments fare no better.

The United States’ climate negotiations with other

countries have addressed whether national governments should pay compensation for climate change to

other national governments. The potential liability of

private parties has never been part of the discussion.

Even if petitioners’ concerns were sufficient to preempt other claims or theories, moreover, they would

not preempt claims focused on companies’ misleading

and deceptive statements. The United States has no

foreign policy interest in protecting manufacturers

from the consequences of their deceptive marketing.

Nor does any such interest arise simply because the

allegedly deceptive practices mislead consumers and

the public about climate change.

Petitioners’ preemption arguments under the Clean

Air Act, which are meritless with respect to all of

Boulder’s claims, see Resp. Br. at 43–51, are especially

inapposite as applied to deception-based claims. The

simple reason is that the “CAA does not concern itself

in any way with the acts that trigger liability . . . ,

namely: the use of deception to promote the consumption of fossil fuel products.” Honolulu, 537 P.3d at 1205

(quotation omitted). No recognized preemption principle applies, and petitioners’ amorphous argument

that state law generally conflicts with the Act’s “structure” is not a legitimate basis for implied preemption.

See Petrs. Br. at 44.

7

ARGUMENT

I. Claims for Climate-Change Related Injuries

That Premise Liability on Deceptive

Marketing Are Separable and Categorically

Different From Claims Premised on

Polluting Conduct.

State-law claims alleging that a manufacturer is liable for violating a duty not to mislead consumers

about the environmental impacts of its products differ

materially from claims alleging that the manufacturer

violated either a duty not to pollute or a duty not to

introduce polluting products into the marketplace

knowing they will cause environmental harms. “Numerous courts have rejected similar attempts by oil

and gas companies to reframe complaints alleging

those companies knew about the dangers of their products and failed to warn the public or misled the public

about those dangers” as attempts to regulate or punish

the lawful and truthful sale or consumption of fossil

fuels. Honolulu, 537 P.3d at 1201. If this Court reaches

petitioners’ merits arguments, it should likewise examine the actual elements of Boulder’s claims and affirm. The Court should resist petitioners’ suggestion to

treat all claims that in some way touch fossil fuels or

climate change as analytically indistinguishable.

Claims targeting misleading marketing or consumer

deception have always been cognizable under state

law. Boulder’s deception-based claims here are likewise not preempted by the Clean Air Act or the Constitution because those claims do not, and do not seek to,

regulate interstate air pollution, among other reasons.

8

A. Claims targeting deceptive marketing do

not premise liability on the defendants’

having emitted pollution or having merely

manufactured and sold a product that

creates pollution.

The crux of petitioners’ constitutional theory is

that state law can never “resolve claims seeking relief from the effects of interstate air and water pollution,” because those disputes necessarily implicate

the interests of states as “coequal sovereigns with

competing claims to regulate shared natural

resources” that “lack the power to regulate conduct

beyond their borders.” Petrs. Br. at 3; see id. at 13.

Even if those premises were correct—and they are

not for the reasons discussed in Respondents’ Brief

and below—deception-based theories do not implicate those concerns.

Deception-based claims do not regulate interstate

pollution for the simple reason that they do not “incentivize[]—much less compel[]—Defendants to curb

their fossil fuel production or greenhouse gas emissions.” Honolulu, 537 P.3d at 1201. That is so because in a deception case “liability is causally tethered to [the defendants’] failure to warn and deceptive

promotion,” and “the source of [the p]laintiffs’ alleged

injury” is the defendants’ “allegedly tortious marketing conduct, not pollution traveling from one state to

another.” Ibid. (quotation omitted). Boulder’s deception claims “seek compensation for [petitioners] allegedly tortious conduct” in misleadingly marketing

their products, not the release of greenhouse gases

from their lawfully sold products. See Pet. App. at

21a. The court below therefore correctly “reject[ed

petitioners’] contention that [Boulder’s] action is, in

essence, an attempt to regulate [greenhouse gas]

emissions.” Ibid.

9

The deception theory Boulder asserts is not novel.

Similar theories give rise to claims under “tort causes

of action [that] are well recognized,” particularly nuisance and failure to warn, and those causes of action

are “tethered to existing well-known elements.” Honolulu, 537 P.3d at 1195. See, e.g., People v. ConAgra

Grocery Prods. Co., 17 Cal. App. 5th 51, 83–85, 101–04

(2017) (affirming public nuisance judgment for injuries caused by deceptive marketing of lead paint); Delaware v. Monsanto Co., 299 A.3d 372, 383–87 (Del.

2023) (reversing dismissal of public nuisance claim for

harms caused by deceptive marketing of PCBs). No

claims that Boulder or amici assert would require a

plaintiff to prove, or a court to find, that greenhouse

gas pollution above a certain level is per se unreasonable. A judgment for the plaintiff on such a claim thus

would “not prevent Defendants from producing and

selling as much fossil fuels as they are able, as long as

Defendants make the disclosures allegedly required,

and do not engage in misinformation.” Honolulu, 537

P.3d at 1185 (quotation omitted).

A comparison with City of New York v. Chevron

Corp., 993 F.3d 81 (2d Cir. 2021), illustrates the point.

The Second Circuit held that New York City’s claims

were preempted because they sought to hold fossil fuel

companies directly liable for the climate impacts

caused by “those companies’ admittedly legal commercial conduct in producing and selling fossil fuels around

the world.” Id. at 86. The City expressly admitted that

its “particular theory of the claims asserted . . . d[id]

not hinge on a finding that those activities themselves

were unreasonable or violated any obligation other

than the obligation to pay compensation,” and relied

instead on “a narrower theory that would require Defendants to pay for the severe harms resulting from

their lawful and profitable commercial activities.” Br.

10

for Appellant at 19, City of New York v. BP P.L.C., No.

18-2188, 2018 WL 5905772 (2d Cir. Nov. 8, 2018). New

York City made clear that its theory of liability did not

require any showing that the defendants deceptively

marketed their products in New York or anywhere

else, or even that they violated any duty of care. See

also ibid. (“Nuisance and trespass offer a means to reallocate the costs imposed by lawful economic activity.”). That is why the Second Circuit held that the City’s

theory would “effectively impose strict liability for the

damages caused by fossil fuel emissions,” such that the

defendants could not “avoid all [ongoing future] liability” unless they “cease[d] global production [of fossil

fuels] altogether.” 993 F.3d at 93. A judgment for New

York City on that theory, the Second Circuit reasoned,

would thus “compel [the defendants] to develop new

means of pollution control”; and that result would “regulate cross-border emissions,” albeit “in an indirect and

roundabout manner.” Ibid. (quotations omitted).

Numerous courts, including in the decision below,

have disagreed with City of New York’s preemption

analysis, especially with respect to federal common

law. Pet. App. 19a–20a; see also e.g., Honolulu, 537

P.3d at 1198–1200; Mayor & City Council of Baltimore

v. BP P.L.C., 31 F.4th 178, 202–04 (4th Cir. 2022);

Rhode Island v. Shell Oil Prods. Co., 35 F.4th 44, 55–

56 (1st Cir. 2022). But even assuming the Second Circuit’s holdings were correct, its reasoning does not apply to the materially different allegations and theories

at issue in Boulder’s deception-based claims.

The United States urged that very distinction between City of New York’s theories and deception-based

claims in opposing the petitions for certiorari in Honolulu. See Brief for United States as Amicus Curiae,

Sunoco LP v. City & Cty. of Honolulu, Nos. 23-947 &

23-952 (U.S. Dec. 10, 2024). Deception-focused claims

11

“differ from those addressed in City of New York” and

the cases the Second Circuit relied on, because “none

of those other decisions involved state-law claims . . .

alleging the violation of a duty not to deceive, rather

than a duty not to pollute.” Id. at 19–20. The Second

Circuit’s reasoning focused on the “specialized body of

federal common law [that] imposed on polluters certain duties not to pollute,” before it was displaced by

the Clean Water Act and Clean Air Act. Id. at 16. Neither the former federal common law nor either of the

statutes that displaced it “ ‘concern[s] itself’ with the

kind of deceptive marketing alleged here.” Id. at 18

(quoting Honolulu, 537 P.3d at 1186).

B. Deception-based claims seek relief for

injuries caused by the defendants’

deception, not all harms for which

greenhouse gas emissions are a but-for

cause.

The scope of relief sought makes plain the critical

distinction between deception-based theories of liability and theories that might regulate emissions. Amici

have consistently made clear that they seek relief “only

for the effects of climate change allegedly caused by

Defendants’ breach of” state law duties not to deceive.

Honolulu, 537 P.3d at 1185–86. Amici seek relief for

harms flowing from the defendants’ deception. They do

not seek remedies for all anthropogenic climate change,

or even for all injuries caused by the defendants’ fossil

fuel products.

Amici will prove at trial that the defendants’ deception was a substantial cause of amici’s injuries, over

and above any harms flowing from fossil fuel use that

would have occurred absent the defendants’ wrongful

deception. Amici will demonstrate causation and damages in part through expert testimony showing that

12

the defendants’ failure to warn, misrepresentations,

and misleading promotion and marketing substantially altered consumer behavior and slowed the public’s

transition from fossil fuels to other primary sources of

energy, which in turn exacerbated the plaintiffs’ injuries. Analogous causation and damages evidence is frequently used in antitrust litigation, for example, to

prove conditions that would have prevailed but for the

alleged anticompetitive conduct. See, e.g., In re Rail

Freight Fuel Surcharge Antitrust Litig., 292 F. Supp.

3d 14, 56 (D.D.C. 2017) (damages calculations in antitrust cases “compare plaintiffs’ actual experience”

against what it “would have been, ‘but for’ the antitrust violation”) (citation omitted), aff’d, 934 F.3d 619

(D.C. Cir. 2019); LePage’s Inc. v. 3M, 324 F.3d 141, 165

(3d Cir. 2003) (similar). Similar evidence also has been

used to show harm to consumers from deceptive marketing in cases concerning lead paint and tobacco,

among other products. See, e.g., ConAgra Grocery

Prods., 17 Cal. App. 5th at 104 (deceptive promotion of

lead paint, for use known to be hazardous, contributed

to public nuisance); Grp. Health Plan, Inc. v. Philip

Morris USA, Inc., 344 F.3d 753, 763 (8th Cir. 2003)

(deceptive marketing of light and low-tar cigarettes).

Contrary to petitioners’ assertions, such factual determinations do not constitute “a policy determination

of the appropriate level of greenhouse-gas emissions.”

Petrs. Br. at 36. Resolving them will not entail, let

alone require, normative decisions about consumer

choice, reasonableness of national or sectoral emissions

levels, atmospheric greenhouse gas concentrations, or

climate policy. As noted above, proving this theory

would “not prevent Defendants from producing and

selling as much fossil fuels as they are able” so long as

they “do not engage in misinformation.” Honolulu, 537

P.3d at 1185. And the possibility that some companies

13

might voluntarily reduce production or change other

business practices in response to a judgment is immaterial. Preemption analysis asks whether state and federal law impose irreconcilable duties. It “does not call

for speculation as to whether a jury verdict will prompt

[a] manufacturer to take any particular action.” Bates

v. Dow Agrosciences LLC, 544 U.S. 431, 445 (2005).

Several amici supporting petitioners assert that it

would be impossible for any plaintiff to prove causation between the defendants’ misrepresentations and

the plaintiff’s injuries, or prove injury above a speculative level. See, e.g., Br. Amicus Curiae of Pac. Legal

Found. at 11–22 (May 20, 2026); Br. Amicus Curiae of

Prof. Richard Epstein, et al. at 24–28 (May 21, 2026).

Amici are confident those assertions are wrong, and

look forward to proving their cases. But even if the

evidence were ultimately inadequate—and no case

has advanced far enough to test or even conduct discovery on those points—those unremarkable statelaw questions of proof do not rise to constitutional significance. Nothing in federal law or the U.S.

Constitution bars amici from putting forth their cases

because they involve challenging questions of proof.

Regardless of how the Court decides any of Boulder’s

claims, the UDAP claims asserted by some amici and

other local governments are not implicated by the

questions before the Court, as petitioners and their

amici agree. Br. Amicus Curiae of Prof. Todd. Zywicki,

et. al at 3 (May 21, 2026) (UDAP claims “are not within

the scope of the questions presented to this Court.”).

The cities of Chicago and New York have both brought

UDAP enforcement claims, for example, that do not

“seek[] relief for injuries allegedly caused by the effects

of . . . greenhouse-gas emissions on the global climate.”

Contra Pet.I. The cities request civil penalties and other remedies authorized by their respective ordinances

14

prohibiting deception of the cities’ consumers, such as

injunctions against unfair business practices. See Municipal Code of Chi. §§ 2-25-090, 4-276-470, 4-276-480;

NYC Code §§ 20-700, 20-703.1 At oral argument before

the Colorado Supreme Court, Exxon’s counsel conceded that claims seeking such “traditional relief” under

consumer protection statutes would not be preempted

under petitioners’ theories.2 In any event, no UDAP

claims are before the Court. Boulder initially pleaded

UDAP claims under Colorado law, but those claims

were dismissed without prejudice on particularity

grounds in the trial court, and were not before the Colorado Supreme Court on appeal. See Bd. of Cnty.

Comm’rs of Boulder Cnty. v. Suncor Energy (U.S.A.),

Inc., 2024 WL 3204275, at *32–33, *39 (Colo. Dist. Ct.

June 21, 2024); App.141–42.

The attorneys general of Connecticut, Massachusetts, Minnesota, and Vermont, among others, have also brought UDAP

enforcement actions under their respective States’ laws. See Connecticut v. Exxon Mobil Corp., No. HHDCV206132568S (Conn.

Super. Ct.); Massachusetts v. Exxon Mobil Corp., No.

1984CV03333 (Mass. Super. Ct.); Minnesota v. Am. Petroleum

Inst., No. 62-CV-20-3837 (Minn. Dist. Ct.); Vermont v. Exxon Mobil Corp., No. 21-CV-2778 (Vt. Super. Ct.).

1

2 See Oral Argument at 14:45, Cnty. Comm’rs of Boulder Cnty.

v. Suncor Energy USA, Inc. (Colo. Feb. 11, 2025) No. 2024SA206,

available at app-api.live.coloradojudicial.gov/api/embedded/

share-media?id=99ebdc24-f671-40f5-806b-7a5799625a46 (“Colorado has a consumer protection act. Most states do. That’s fine as

long as the relief that is being sought is the traditional relief.”).

15

II. Even Assuming That Claims Targeting

Polluting Conduct or the Production and

Sale of Polluting Products Are Preempted,

Deception-Based Claims Are Not.

Petitioners acknowledge that their preemption arguments do not rest on any statutory or constitutional

text. See Petrs. Br. at 23–24, 44–46. That should be

the end of the inquiry. “There is no federal pre-emption in vacuo, without a constitutional text or a federal

statute to assert it,” Puerto Rico Dep’t of Consumer

Affairs v. ISLA Petroleum Corp., 485 U.S. 495, 503

(1988), and it is never sufficient in a preemption analysis “for any party or court to rest on a supposition (or

wish) that ‘it must be in there somewhere,’ ” Va. Uranium, Inc. v. Warren, 587 U.S. 761, 767 (2019) (Gorsuch, J., lead opinion). Petitioners’ arguments that

the Constitution and Clean Air Act implicitly preempt

Boulder’s claims are meritless, and would not apply to

deception-based claims in any event.

The Court has repeatedly cautioned against the

fast-and-loose preemption analyses petitioners advocate, which rely on “brooding federal interest[s]” and

“judicial policy preference[s]” that “should never be

enough to win preemption of a state law.” Va. Uranium, 587 U.S. at 767. A litigant hoping to supplant

state law “must point specifically to ‘a constitutional

text or a federal statute’ that does the displacing or

conflicts with state law.” Ibid. (quoting ISLA Petroleum, 485 U.S. at 503). That is especially true where a

party argues the Constitution directly preempts state

law, because all “[c]onstitutional analysis must begin

with ‘the language of the instrument.’ ” Dobbs, 597

U.S. at 235 (quoting Gibbons v. Ogden, 22 U.S. (9

Wheat.) 1, 186–189 (1824)).

16

A. The Constitution does not preempt claims

targeting a defendant’s deceptive business

practices simply because the alleged

deception concerns conduct that crosses

state borders.

1. The Constitution does not prohibit the

operation of state law to redress

misrepresentations about interstate

pollution.

For the reasons stated in Respondents’ Brief, there

has never been a constitutional prohibition against

state law applying to every dispute potentially bearing on “interstate pollution.” See Resp. Br. at 23–38.

In petitioners’ telling, federal law must govern all

such cases—no matter the specific parties, claims, or

facts—because they implicate the states’ “competing

claims to regulate shared natural resources,” see

Petrs. Br. at 3, in the same manner and to the same

extent as one state suing its neighbor to settle a territorial dispute. That would be a startlingly broad

rule, and it lacks any grounding in the Constitution or

this Court’s precedents. But even if there were some

basis for it, petitioners’ rule would not reach Boulder’s

deception-based claims. Claims alleging false advertising or deceptive business practices have never been

subject to a uniform federal rule of decision. And deception-based claims like Boulder’s are outside the

ambit of the defunct federal common law because, unlike in the cases petitioners cite, those claims cannot

alter or define the states’ respective interests in shared

environmental resources.

For much of the twentieth century, this Court recognized federal common law rules of decision “to abate a

public nuisance in interstate or navigable waters” or a

nuisance caused by air pollution traveling from anoth-

17

er state. See Illinois v. City of Milwaukee, 406 U.S. 91,

104 (1972) (“Milwaukee I”). That body of law first arose

in original actions in this Court by a plaintiff State,

and was confined to such actions for 60 years. See Ohio

v. Wyandotte Chems. Corp., 401 U.S. 493, 495–96

(1971) (“[T]his Court has often adjudicated controversies between States and between a State and citizens

of another State seeking to abate a nuisance that exists in one State yet produces noxious consequences in

another.”).3 The Court reasoned that those disputes

could only be resolved under a federal rule of decision

because they “involve[] a direct conflict between sovereigns,” and the States could not constitutionally “supply rules of decision governing disputes implicating

their conflicting rights.” Franchise Tax Bd. v. Hyatt,

587 U.S. 230, 246–47 (2019) (“Hyatt III”) (cleaned up).

In adopting federal rules of decision for those cases,

the Court analogized interstate pollution nuisance cases to “interstate disputes over borders,” “water rights”

in interstate streams and lakes, and “the interpretation

of interstate compacts,” id. at 246 (collecting cases).

Those types of cases were “recognized as presenting fed3 See e.g., City of Milwaukee v. Illinois, 451 U.S. 304, 311

(1981) (nuisance suit by Illinois “to eliminate all overflows and to

achieve specified effluent limitations on treated sewage” into

Lake Michigan by cities in Wisconsin); New Jersey v. City of New

York, 283 U.S. 473, 476–77 (1931) (nuisance suit by New Jersey

to “restrain[] the city from dumping garbage . . . off the coast of

New Jersey”); New York v. New Jersey, 256 U.S. 296, 298 (1921)

(nuisance suit by New York to “enjoin[]” New Jersey from “discharging . . . sewage” into New York Harbor); Georgia v. Tenn.

Copper Co., 206 U.S. 230, 236 (1907) (nuisance suit by Georgia to

enjoin copper companies from “discharging noxious gas” that

drifted across border from Tennessee); Missouri v. Illinois, 180

U.S. 208, 242–43 (1901) (nuisance suit by Missouri to enjoin Illinois from “drawing . . . the sewage of the city of Chicago into the

Mississippi river” through artificial channels).

18

eral questions,” Hinderlider v. La Plata River & Cherry

Creek Ditch Co., 304 U.S. 92, 110 (1938), because they

resolved the directly conflicting rights of states against

one another. The federal common law of interstate nuisance reached its zenith with Milwaukee I, which held

that such claims were cognizable not only in this Court

but in the district courts, “[t]he rule of decision being

federal.” Milwaukee I, 406 U.S. at 108 n.10.

Petitioners insist that notwithstanding the abrogation of all potentially relevant federal common law by

the Clean Water and Clean Air Acts, the Constitution

independently prohibits state law from “redress[ing]

inherently transboundary issues such as global climate

change,” regardless of the legal or factual context.

Petrs. Br. at 3. They say every case involving interstate

pollution represents a zero-sum dispute directly between States that would be decided through war or diplomacy if the States were fully independent sovereigns. See id. at 22. But all the federal common law

pollution nuisance cases that petitioners cite alleged

that the defendant unlawfully polluted a shared air or

water resource and sought to enjoin or restrict further

pollution. See Pets. Br. at 24–26; see also n. 3 supra.

None involved claims like Boulder’s that hinged on a

duty to disclose or not to deceive consumers, or involved

any analogous claim for fraud, failure to warn, or deceptive business practices. Theories of liability and requested relief in deception-based cases do not require

anyone, anywhere, to alter their practices emitting pollution or lawfully selling products that pollute—the defendants need only market their products truthfully to

avoid future liability. Adjudicating whether private entities have breached that age-old common law duty

does not require a court to authorize or prohibit any

entity’s right to pollute a shared natural resource, much

less to allocate such rights among States.

19

Deception-based claims implicate none of the federal

concerns petitioners assert, and in fact seek to vindicate traditional state prerogatives. This Court has long

recognized that States hold a core “substantial” “interest in ensuring the accuracy of commercial information in the marketplace.” Edenfield v. Fane, 507 U.S.

761, 769 (1993). Petitioners’ deception-based liability

turns on alleged misconduct this Court has likewise

long recognized as traditionally regulated by the

States, including misleading advertising, e.g., Lorillard Tobacco Co. v. Reilly, 533 U.S. 525, 541–42 (2001),

unfair business practices, California v. ARC Am. Corp.,

490 U.S. 93, 101 (1989), and consumer fraud, Fla. Lime

& Avocado Growers, Inc. v. Paul, 373 U.S. 132, 144–46

(1963). States have never been precluded from redressing deceptive marketing that affects their residents

simply because the defendant’s business is national in

scope. Cf. Brief of Alabama, et. al., as Amici Curiae at

22 (May 21, 2026) (arguing that “[r]esolving an interstate controversy under a single State’s law is a violation of state sovereignty”). Petitioners and their amici

complain that vindicating those core state interests

might be contrary to other States’ policy preferences,

but those concerns are already protected by existing

constitutional doctrines as discussed below.

2. The “extraterritoriality principle” this

Court once applied in some Dormant

Commerce Clause cases has no

independent force, and the concerns

petitioners raise are adequately

addressed by existing constitutional

constraints on state choice-of-law rules.

The strict constitutional prohibition against “extraterritorial” application of state law that petitioners

advance does not exist. Petitioners ask in essence that

20

the Court constitutionalize choice-of-law determinations normally governed by state law and reduce them

to a single rule: no extraterritorial application. But

the Court decades ago “abandoned” efforts to “embark

on the constitutional course of balancing coordinate

States’ competing sovereign interests to resolve conflicts of laws,” finding that method left the Court

“[w]ithout a rudder to steer us.” Franchise Tax Bd. v.

Hyatt, 538 U.S. 488, 496, 499 (2003) (“Hyatt I”). Nothing about this case suggests the Court should return

to that rudderless course. Existing guardrails established pursuant to the Commerce, Due Process, and

Full Faith and Credit Clauses, among others, already

constrain conflicts of law in multi-state cases, with

thorough grounding in text and history.

No supposed “extraterritoriality principle” flows

from the Due Process or Full Faith and Credit Clauses.

The modern rule under both provisions is that “a

State’s substantive law [may] be selected in a constitutionally permissible manner” where there exists “a significant contact or significant aggregation of contacts,

creating State interests, such that choice of its law is

neither arbitrary nor fundamentally unfair.” Id. at 494

(quotation omitted); Phillips Petroleum Co. v. Shutts,

472 U.S. 797, 821–22 (1985). See also Allstate Ins. Co.

v. Hague, 449 U.S. 302, 310–13 (1981); Alaska Packers

Ass’n v. Indus. Accident Comm’n, 294 U.S. 532, 541–42

(1935). And no such rule flows from the Commerce

Clause: This Court recently rejected the proposition

“that any question about the ability of a State to project its power extraterritorially must yield to an ‘almost

per se’ rule under the dormant Commerce Clause” that

“would cast a shadow over laws long understood to

represent valid exercises of the States’ constitutionally

reserved powers” and “provide neither courts nor litigants with meaningful guidance in how to resolve dis-

21

putes over them.” Pork Producers, 598 U.S. at 375–76.

The handful of cases petitioners cite are inapposite.

See Petrs. Br. at 24. Some of them address Full Faith

and Credit questions under the Court’s now-obsolete

framework. See Brown v. Estate of Fletcher, 210 U.S.

82, 95 (1908). Others address due process limitations

on personal jurisdiction, Fuld v. Palestine Liberation

Org., 606 U.S. 1 (2025), or punitive damages, State

Farm Mut. Auto. Ins. Co. v. Campbell, 538 U.S. 408

(2003); BMW of N. Am., Inc. v. Gore, 517 U.S. 559

(1996). None stands for petitioners’ sweeping prohibition against any application of one State’s law outside

the physical borders of the State.

The rigid extraterritoriality rule this Court has declined to find in the Constitution’s words does not lurk

implicitly between them, either. There are, of course,

“constitutional doctrines that are not spelled out in the

Constitution but are nevertheless implicit in its structure and supported by historical practice.” Hyatt III,

587 U.S. at 247. But when this Court has identified

implicit constitutional rules, it has done so only after

an exhaustive analysis of historical practice. In Hyatt

III, for example, the Court held that the States enjoy

sovereign immunity in each other’s courts only after

investigating a wide array of sources, including the

Declaration of Independence, Blackstone’s Commentaries, the Federalist, nineteenth-century treatises,

eighteenth-century state and federal jurisprudence,

and the Constitutional Convention Debates. See id. at

236–48; see also, e.g., Trump v. Cook, 609 U.S. ___,

2026 WL 1855613, at *4–6 (U.S. June 29, 2026); Trump

v. Slaughter, U.S. ___, 2026 WL 1855612, at *7–11

(U.S. June 29, 2026); Myers v. United States, 272 U.S.

52, 109–77 (1926) (affirming President’s power to remove officers after discussing colonial practice, debates

of the First Congress, nineteenth-century treatises,

22

and executive practices “acquiesced in by the whole

government for three-quarters of a century”).

Historical practice contradicts petitioners’ proposed

rule that state law may never reach conduct outside

the state’s physical borders. “Since the founding, States

have enacted an ‘immense mass’ of ‘[i]nspection laws,

quarantine laws, [and] health laws of every description’ that have a ‘considerable’ influence on commerce

outside their borders.” Pork Producers, 598 U.S. at 375

(alteration in original) (quoting Gibbons, 22 U.S. (9

Wheat.) at 203). For a time, the Court located an extraterritoriality rule in the Commerce Clause, on the

premise that “[a] State’s power to ‘protect the lives,

health, and property’ of its residents was ‘essentially

exclusive,’ ” and “the Federal Government’s power ‘to

regulate commerce among the several states’ was ‘also

exclusive.’ ” Am. Beverage Ass’n v. Snyder, 735 F.3d

362, 377 (6th Cir. 2013) (Sutton, J., concurring). “But

that line has come and gone,” and state and federal

governments have long shared regulatory authority

over commerce once within each other’s exclusive domains. See id. at 378. The extraterritoriality rule soon

became “the most dormant doctrine in dormant commerce clause jurisprudence,” Energy & Env’t Legal

Inst. v. Epel, 793 F.3d 1169, 1170 (10th Cir. 2015)

(Gorsuch, J.), with good reason: “In our interconnected

national marketplace, many (maybe most) state laws

have the ‘practical effect of controlling’ extraterritorial

behavior.” Pork Producers, 598 U.S. at 374.

Having interred the extraterritoriality principle derived from the Commerce Clause, the Court should

not “revive and rebuild” that principle from ill-defined

constitutional interstices “into a weapon far more

powerful” than exists in the text itself. Epel, 793 F.3d

at 1175. “Although extraterritoriality underlies th[e]

constitutional imperatives” imposed by the Due Pro-

23

cess and Commerce Clauses, among others, “it carries

no freestanding weight outside of them.” Snyder, 735

F.3d at 380 (Sutton, J., concurring). That Boulder’s

claims may be cognizable under some States’ laws and

not others’ does not alter the calculus or present a

problem of constitutional dimensions. Choice-of-law

rules exist to address precisely that situation, because

“the legislative jurisdictions of the States overlap” and

“it is frequently the case” as a feature of the federal

system “that a court can lawfully apply either the law

of one State or the contrary law of another.” Sun Oil

Co. v. Wortman, 486 U.S. 717, 727 (1988). One State’s

decision to “use its police powers to protect its citizens

from alleged deceptive marketing,” Honolulu, 537

P.3d at 1207, does not infringe the sovereignty of

States that take an opposing position.

The United States as amicus makes the novel assertion that state law may only apply to conduct occurring outside the state where “the [in-state] effects of

the out-of-state conduct [are] direct, traceable, and

particularized,” creating a “legal fiction of constructive presence” by the defendant within the state. U.S.

Br. at 22, 25. That is not the law, and the United

States has not identified any case support for that

proposition since at least 1916. See id. at 21–23. That

is unsurprising, since this Court has long since held

that “[a]s a consequence of the modern practice of conducting widespread business activities throughout

the entire United States, . . . more states than one

may seize hold of local activities which are part of

multistate transactions and may regulate to protect

interests of its own people, even though other phases

of the same transactions might justify regulatory legislation in other states.” Watson v. Emps. Liab. Assurance Corp., 348 U.S. 66, 72 (1954). The constitutional

question is whether there exists a “significant contact

24

or significant aggregation of contacts, creating state

interests,” not constructive presence in that state,

“such that choice of its law is neither arbitrary nor

fundamentally unfair.” Hyatt I, 538 U.S. at 494 (quotation omitted). The Court has long since abandoned

“a choice-of-law analysis which, for all intents and

purposes, g[ives] an isolated event . . . controlling constitutional significance” where “there might have been

contacts with another State . . . which would make application of its law neither unfair nor unexpected.”

Hague, 449 U.S. at 308 n.11. The United States’ assertion that state law can only reach a defendant’s out-ofstate conduct if the defendant “can be treated as constructively, if not actually, present in the State where

the effects occur,” U.S. Br. at 21, ignores more than a

century of contrary jurisprudence.

3. Foreign affairs considerations do not

preempt, and in fact support, state laws

targeting misrepresentations about a

product’s impacts on the environment.

Foreign affairs decisions can preempt state law

through field preemption where a State intrudes into

the field of foreign relations by “establish[ing] its own

foreign policy,” Zschernig v. Miller, 389 U.S. 429, 441

(1968), or through conflict preemption where there is a

“sufficiently clear conflict” between state law and an

“express federal policy,” Am. Ins. Ass’n v. Garamendi,

539 U.S. 396, 419–20 & n.11, 425 (2003). To constitute

a “rule of domestic law” with preemptive force, a foreign policy position, “as with the exercise of any governmental power, ‘must stem either from an act of

Congress or from the Constitution itself.’ ” Medellín v.

Texas, 552 U.S. 491, 523–24 (2008) (quoting

Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579,

585 (1952)). By the same token, the Court evaluates

25

potential conflicts between state law and foreign policy

against “the backdrop of traditional state legislative

subject matter.” Garamendi, 539 U.S. at 425. Otherwise-valid state laws do not impermissibly invade federal prerogatives unless they “produce something more

than [an] incidental effect in conflict with express foreign policy of the National Government.” Id. at 420.

For the reasons explained in Respondents’ Brief and

detailed by other amici, no foreign policy considerations

preempt claims like Boulder’s, nor sweepingly preempt

all state law that touches on greenhouse gases or other

pollution originating outside the United States. See

Resp. Br. at 41–42. Boulder’s claims do not establish

any foreign policy and do not conflict with any express

foreign policy the United States has adopted.

The United States avers that it “has long opposed

the establishment of liability and compensation

schemes at the international level for alleged climate

change,” and that Boulder’s claims “create[] new frictions in all international negotiations that implicate

climate policies.” U.S. Br. at 3, 9, 27; Decl. of Christopher Landau ¶18, Dkt. No. 12, United States v. Minnesota, No. 26-cv-2456 (D. Minn. May 11, 2026). Those

assertions rest on incorrect premises, and are insufficient to preempt Boulder’s claims regardless. The only

potentially relevant, Senate-ratified treaty that could

constitute domestic law with preemptive force is the

1992 United Nations Framework Convention on Climate Change (“Framework Convention”), May 9,

1992, 1771 U.N.T.S. 107, but that agreement does not

set emissions targets for member nations and does not

address national or individual liability for harms

caused by climate change. The 2015 Paris Agreement,

from which the Trump Administration has withdrawn, contains a section concerning loss and damages that also explicitly “does not involve or provide a

26

basis for any liability or compensation” on the part of

any member nation or its citizens. Rep. of the Conf. of

the Parties on Its Twenty-First Session, ¶ 51, U.N.

Doc. FCCC/CP/2015/10/Add.1 (2016). Neither of those

international agreements contain any express policy

in conflict with Boulder’s claims, and the United

States has not attempted to show otherwise.

Insofar as the United States has opposed international liability for climate change, it has done so with

respect to one national government’s liability to another national government. See Decl. of Todd Stern ¶24,

Dkt. No. 43, United States v. Minnesota, No. 26-cv-2456

(D. Minn. June 18, 2026) (statement by former United

States Special Envoy for Climate Change that “[t]he

United States’ negotiating efforts have never concerned

the liability of non-governmental actors” under state

law, “or any other compensation that may occur under

domestic law”). No treaty or executive agreement to

which the United States is a party suggests that private actors may not be held liable under one nation’s

laws for injuries related to climate change. To the extent Boulder’s claims do not align with the President’s

goals in inchoate negotiations with other countries generally, that does not constitute express foreign policy

under this Court’s precedents. See Medellín, 552 U.S.

at 524 (state convictions found by International Court

of Justice to be in violation of international law not preempted by presidential memorandum because while

President’s “interests in ensuring the reciprocal observance of the Vienna Convention, protecting relations

with foreign governments, and demonstrating commitment to the role of international law” are “plainly compelling,” they “do not allow us to set aside first principles”). This Administration’s general foreign policy

objectives do not carry the force of law and cannot preempt Boulder’s claims.

27

Petitioners’ arguments are particularly weak with

respect to Boulder’s deception-based claims. Neither

the Framework Convention nor the Paris Agreement

speaks to the issue, and the United States has never

suggested it has a foreign policy interest in allowing

oil-and-gas companies—or companies in any industry—to misrepresent their products’ dangers without

consequence. To the contrary, express United States

foreign policy supports strong measures to protect consumers and prevent deceptive business practices. The

free trade agreement between the United States, Mexico, and Canada requires, for example, that “[e]ach

Party shall adopt or maintain national consumer protection laws or other laws or regulations that proscribe

fraudulent and deceptive commercial activities,” and

declares that “coordination between the Parties to address these activities effectively is important and in

the public interest” because “fraudulent and deceptive

commercial activities increasingly transcend national

borders.” United States–Mexico–Canada Agreement

art. 21.4(2)–(3), Nov. 30, 2018 (entered into force July

1, 2020). As a founding member of the 38-nation Organisation for Economic Co-operation and Development, moreover, the United States is expected to maintain domestic laws that offer “[e]ffective mechanisms

to stop businesses and individuals engaged in fraudulent and deceptive commercial practices,” as well as

“[e]ffective mechanisms that provide redress.”4

Against the longstanding backdrop of state authority over consumer protection, deceptive business practices, and advertising, state laws addressing mislead4 See OECD Guidelines for Protecting Consumers from Fraudulent and Deceptive Commercial Practices Across Borders 11

(2003), https://www.oecd.org/en/publications/oecd-guidelines-forprotecting-consumers-from-fraudulent-and-deceptivecommercial-practices-across-borders_9789264103573-en-fr.html.

28

ing marketing of fossil fuels in no way conflict with

the United States’ foreign policy interests. See, e.g.,

Medellín, 552 U.S. at 532 (rejecting preemption based

on presidential action that would “reach[] deep into

the heart of the State’s police powers”).

B. The Clean Air Act Does Not Speak to or

Regulate Marketing Practices and Does

Not Preempt State Law Claims to Remedy

Consumer Deception.

Petitioners argue that the Clean Air Act’s “pervasive statutory scheme clearly intended to ‘dominate

the field’ of interstate pollution regulation” such that

any “[a]pplication of state tort law in that area” would

“be inconsistent with the Act” and thus preempted.

Petrs. Br. at 44.5 Not so. Field preemption “occurs

when federal law occupies a field of regulation so comprehensively that it has left no room for supplementary state legislation.” Murphy v. Nat’l Collegiate Athletic Ass’n, 584 U.S. 453, 479 (2018) (cleaned up). In

those circumstances, “[s]tates are precluded from regulating conduct in a field that Congress, acting within

its proper authority, has determined must be regulated by its exclusive governance.” Arizona v. United

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

5 The United States has taken the position that it lacks authority under the Clean Air Act to regulate greenhouse gas emissions

from mobile sources but retains authority to regulate those emissions from stationary sources. See U.S. Br. at 34 n.4; 91 Fed. Reg.

7686 (Feb. 18, 2026). Those assertions are, at minimum, in serious

tension with each other, and with the petitioners’ and the United

States’ field and conflict preemption arguments here. Especially

given that tension, the executive’s views on the Act’s preemptive

effect on Boulder’s claims should be accorded little weight. See

Loper Bright Enters. v. Raimondo, 603 U.S. 369, 412 (2024).

29

The Clean Air Act does not occupy the field of interstate air pollution, as this Court and the courts of appeals have long recognized. The Act’s saving clauses

“negate[] the inference that Congress ‘left no room’ for

state causes of action,” Int’l Paper Co. v. Ouellette, 479

U.S. 481, 492 (1987) (construing Clean Water Act’s

materially identical saving clauses), and “[t]he Clean

Air Act generally seeks to preserve state authority,”

Oxygenated Fuels Ass’n Inc. v. Davis, 331 F.3d 665,

670–71 (9th Cir. 2003). See also North Carolina ex rel.

Cooper v. Tenn. Valley Auth., 615 F.3d 291, 302 (4th

Cir. 2010); Merrick v. Diageo Americas Supply, Inc.,

805 F.3d 685, 694 (6th Cir. 2015). Stated more directly, the Act makes “the States and the Federal Government partners in the struggle against air pollution.”

Gen. Motors Corp. v. United States, 496 U.S. 530, 532

(1990). As for deceptive marketing, the Act does not

speak to those concerns at all, much less “occupy [that]

field exclusively.” Kurns v. R.R. Friction Prods. Corp.,

565 U.S. 625, 630 (2012) (quotation omitted).

Even if the CAA preempted the field of “interstate

pollution regulation” as petitioners suggest, Petrs. Br.

at 44, deception-based claims would fall well outside

that field. Petitioners assert that Boulder’s claims

regulate interstate pollution because “[i]nterstate

emissions” form “a critical step in the causal chain between petitioners’ alleged conduct and respondents’

alleged injuries.” Id. at 36. But the field preemption

inquiry asks whether state and federal law “are directed to the same subject,” Kurns, 565 U.S. at 634

(quotation omitted), and deception-based claims are

not directed to any subject covered by the CAA. “[N]ot

every state law that in some remote way may affect”

an occupied field is preempted. English v. Gen. Elec.

Co., 496 U.S. 72, 85 (1990).

30

This Court has repeatedly rejected similar attempts

to expand preempted fields beyond Congress’s clear

intent. In Silkwood v. Kerr-McGee Corp., for example,

the Court held that “a state-authorized award of punitive damages arising out of the escape of plutonium

from a federally-licensed nuclear facility” was not preempted, despite “the federal government’s express desire to maintain exclusive regulatory authority over

the safety aspects of nuclear power.” 464 U.S. 238,

241, 248, 258 (1984). Federal law gave the Nuclear

Regulatory Commission “exclusive authority to regulate safety matters” at nuclear facilities, but that field

did not encompass all “damages for radiation injuries.” Id. at 256. To the contrary, even though a punitive damages award involved finding that the defendant was “grossly and wantonly reckless” in exposing

the plaintiff to radiation hazards, see id. at 245–46

(quotation omitted), the Court rejected the argument

that because such an award “punishes and deters conduct related to radiation hazards, it falls within the

prohibited field,” id. at 249.

The Court reached conclusions similar to Silkwood

in cases concerning workers’ compensation awards for

injuries at a federally owned nuclear facility, see Goodyear Atomic Corp. v. Miller, 486 U.S. 174, 179–86

(1988), and claims of retaliation by nuclear facility

employees for reporting inadequate radiation safety,

see English, 496 U.S. at 80–86. In each of those cases,

it made no difference for field preemption purposes

that nuclear safety practices were “a critical step in

the causal chain’ leading to the plaintiffs’ injuries.”

See Petrs. Br. at 44. So too here: Even if the CAA preempted the field of interstate air pollution, the field

does not encompass misleading statements to consumers about that pollution.

31

There is no conflict preemption either. Conflict preemption occurs where “compliance with both federal

and state regulations is a physical impossibility,” Fla.

Lime & Avocado Growers, 373 U.S. at 142–43, or

where state law stands as an “obstacle to the accomplishment and execution of the full purposes and objectives of Congress,” Wyeth v. Levine, 555 U.S. 555,

563–64 (2009) (quotation omitted). The latter category, often referred to as obstacle preemption, cannot

arise from the mere “possibility that federal enforcement priorities might be upset” or by an “overlap” in

subject matter with state law. Kansas v. Garcia, 589

U.S. 191, 212 (2020). Rather, “a high threshold must

be met if a state law is to be preempted for conflicting

with the purposes of a federal Act.” Chamber of Com.

of the U.S. v. Whiting, 563 U.S. 582, 607 (2011) (quotation omitted). Neither impossibility nor obstacle preemption applies to Boulder’s deception-based claims.

It is obviously possible for companies to comply with

their state-law duties not to deceive consumers and

with whatever emissions-related duties the Clean Air

Act imposes on them. “Defendants could simply avoid

federal and state liability by adhering to the CAA and

separately issuing warnings and refraining from deceptive conduct as required by [state] law; it is not a

‘physical impossibility’ to do both concurrently.” Honolulu, 537 P.3d at 1207 (citation omitted). Obstacle

preemption is no better fit. Courts have consistently

held that state law claims with a much closer nexus to

air pollution regulation do not interfere with or inhibit the Clean Air Act’s purposes and objectives.6 Claims

6 See, e.g., Oxygenated Fuels, 331 F.3d at 672–73 (state ban on

gasoline additive “enacted for the purpose of protecting groundwater” did not interfere with Clean Air Act’s “central goal of . . .

reduc[ing] air pollution” or “inhibit federal efforts to fight air pollution”); In re Methyl Tertiary Butyl Ether (“MTBE”) Prods. Liab.

32

targeting deceptive marketing of fossil fuels do not

hamper the Clean Air Act’s purposes and objectives

for the simple reason that the Act “expresses no policy

preference and does not even mention marketing regulations.” Honolulu, 537 P.3d at 1205.

Petitioners’ Clean Air Act preemption arguments

are not supported by any recognized preemption analysis. They essentially ask the Court to find that Boulder’s claims are against the CAA’s gestalt, without

any further specificity or textual underpinning. But

an assertion of statutory preemption “does not justify

a ‘freewheeling judicial inquiry into whether a state

statute [or claim] is in tension with federal objectives,’ ” because “it is Congress rather than the courts

that pre-empts state law.” Whiting, 563 U.S. at 607

(cleaned up). The Court should reject petitioners’ position, especially with respect to deception-based claims.

Litig., 725 F.3d 65, 95–96, 104 (2d Cir. 2013) (state common law

claims concerning same gasoline additive not preempted because

defendants “could have complied with [the CAA]” and state law

duties); In re Volkswagen “Clean Diesel” Mktg., Sales Pracs., &

Prods. Liab. Litig., 959 F.3d 1201, 1216, 1219–20 (9th Cir. 2020)

(Clean Air Act “precludes state or local governments from imposing any restriction that has the purpose of enforcing emission

characteristics for pre-sale, motor vehicles,” but does not preempt laws “prohibiting tampering with air pollution control systems in motor vehicles” after sale of new vehicle); Ass’n of Taxicab Operators USA v. City of Dallas, 720 F.3d 534, 535, 540–42

(5th Cir. 2013) (municipal ordinance granting “head-of-the-line

privileges” to taxicabs running on compressed natural gas “ahead

of gasoline-powered taxis in the queue for soliciting passengers”

at regional airport not preempted).

33

CONCLUSION

The Colorado court correctly held that Boulder’s

claims are not preempted by the Constitution or the

Clean Air Act. Claims alleging that oil-and-gas companies have misled consumers about the climate

harms their products pose are even further afield and

fall within traditional areas of state regulation. The

Court should hold that claims targeting deceptive

marketing or promotion of products are not preempted, and affirm.

Respectfully submitted,

Victor M. Sher

Matthew K. Edling

Michael Burger

Martin Quiñones

Sher Edling LLP

100 Montgomery St., Ste. 1410

San Francisco, CA 94104

Counsel for Amici Curiae

August 3, 2026

34

AUTHORIZED LAW OFFICERS

OF AMICI CURIAE

CITIES AND COUNTIES

Mary B. Richardson-Lowry

Corporation Counsel

City of Chicago

John D. Nibbelin

County Attorney

County of San Mateo

Victoria J. Takayesu

Corporation Counsel

County of Maui

Brandon W. Halter

County Attorney

County of Marin

Arlene Q. Perez

Corporation Counsel

City of Hoboken

David Chiu

City Attorney

City and County

of San Francisco

Ryan Richardson

Oakland City Attorney

Dana Viola

Corporation Counsel

City and County

of Honolulu

Jason M. Heath

County Attorney

County of Santa Cruz

Shannon Moore

Interim City Attorney

City of Richmond