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 AMICUS CURIAE PUBLIC CITIZEN

IN SUPPORT OF RESPONDENTS

SCOTT L. NELSON

Counsel of Record

ALLISON M. ZIEVE

PUBLIC CITIZEN

LITIGATION GROUP

1600 20th Street NW

Washington, DC 20009

(202) 588-1000

snelson@citizen.org

Attorneys for Amicus Curiae

August 2026

i

TABLE OF CONTENTS

Page

TABLE OF AUTHORITIES ...................................... iii

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

SUMMARY OF ARGUMENT .................................... 2

ARGUMENT ............................................................... 4

I.

Under the Supremacy Clause, federal

statutes preempt state laws only when

their text and structure reveal that they

conflict with state law. ......................................... 4

II. The Clean Air Act’s terms limit its preemptive

effects and broadly affirm state authority to

address air pollution. ........................................... 6

III. The Clean Air Act does not impliedly preempt

state common-law principles that would impose

liability on companies that cause harmful air

pollution. .............................................................. 9

A. The Act’s non-preemption clause strictly limits

implied preemption. ......................................... 9

B. Boulder’s theories of liability do not conflict

with the Clean Air Act’s terms or its “purposes

and objectives.” ............................................... 13

1. “Purposes and objectives” preempt

state law, if at all, only in limited

circumstances............................................ 15

2. Boulder’s theories of liability are fully

consistent with the purposes and objectives

evident in the Clean Air Act’s terms. ....... 18

ii

3. This Court’s decision in Ouellette does

not support the oil companies’ impliedpreemption arguments. ............................ 22

IV. The Clean Air Act’s terms limit its preemptive

effects and broadly affirm state authority to

address air pollution. ......................................... 25

CONCLUSION.......................................................... 26

iii

TABLE OF AUTHORITIES

Cases

Pages

Am. Elec. Power Co., Inc. v. Connecticut,

564 U.S. 410 (2011) ....................................... 25, 26

Am. Ins. Ass’n v. Garamendi,

539 U.S. 396 (2003) ............................................. 11

Barnett Bank of Marion County, N.A. v. Nelson,

517 U.S. 25 (1996) ............................................... 14

Calif. Fed. Sav. & Loan Ass’n v. Guerra,

479 U.S. 272 (1987) ....................................... 10, 11

Cipollone v. Liggett Group, Inc.,

505 U.S. 504 (1992) ............................................. 10

CSX Transp., Inc. v. Easterwood,

507 U.S. 658 (1993) ......................................... 6, 16

CTS Corp. v. Waldburger,

573 U.S. 1 (2014) ................................................. 17

Dan’s City Used Cars, Inc. v. Pelkey,

569 U.S. 251 (2013) ............................................. 10

Dep’t of Treas. v. Fabe,

508 U.S. 491 (1993) ............................................. 11

Engine Mfrs. Ass’n v. S. Coast Air

Quality Mgmt. Dist.,

541 U.S. 246 (2004) ............................................. 15

Freeman v. Quicken Loans, Inc.,

566 U.S. 624 (2012) ............................................. 16

FS Credit Opportunities Corp. v. Saba Capital

Master Fund, Ltd.,

146 S. Ct. 1546 (2026) ......................................... 15

iv

Geier v. Am. Honda Motor Co.,

529 U.S. 861 (2000) ............................................. 12

Hencely v. Fluor Corp.,

146 S. Ct. 1086 (2026) ....................................... 1, 5

Hillman v. Maretta,

569 U.S. 483 (2013) ....................................... 17, 18

Hines v. Davidovitz,

312 U.S. 52 (1941) ............................................... 14

Howell v. Howell,

581 U.S. 214 (2017) ....................................... 16–18

Illinois v. Milwaukee,

406 U.S. 91 (1972) ............................................... 25

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987) ....................................... 22–24

Kansas v. Garcia,

589 U.S. 191 (2020) ................................... 5, 14–16

Malone v. White Motor Corp.,

435 U.S. 497 (1978) ............................................. 11

Martin v. United States,

605 U.S. 395 (2025) ......................................... 5, 13

Michigan v. Bay Mills Indian Cmty.,

572 U.S. 782 (2014) ............................................. 17

Monsanto Co. v. Durnell,

146 S. Ct. 2001 (2026) ......................................... 13

Murphy v. NCAA,

584 U.S. 453 (2018) ............................................... 6

Puerto Rico Dep’t of Consumer Affairs v.

Isla Petroleum Corp.,

485 U.S. 495 (1988) ......................................... 5, 26

v

R.J. Reynolds Tobacco Co. v. Durham County,

479 U.S. 130 (1986) ............................................... 8

Retail Clerks Int’l Ass’n v. Schermerhorn,

375 U.S. 96 (1963) ............................................... 11

Rodriguez v. United States,

480 U.S. 522 (1987) ....................................... 15, 16

Sprietsma v. Mercury Marine,

537 U.S. 51 (2002) ...................................................

Tex. & Pac. Ry. Co. v. Abilene Cotton Oil Co.,

204 U.S. 426 (1907) ............................................. 12

Va. Uranium, Inc. v. Warren,

587 U.S. 761 (2019) ................... 6, 9, 10, 12, 16, 17

Whitman v. Am. Trucking Ass’ns,

531 U.S. 457 (2001) ............................................. 19

Williamson v. Mazda Motor of Am., Inc.,

562 U.S. 323 (2011) ............................................. 12

Wyeth v. Levine,

555 U.S. 555 (2009) ............................................... 9

Constitutional Provisions and Statutes

Supremacy Clause, U.S. Const.,

art. VI, cl. 2. ..................................... 2–5, 13, 15, 25

Civil Rights Act of 1964, Title VII,

42 U.S.C. §§ 200e–2000e17 ................................. 11

Clean Air Act, 42 U.S.C. §§ 7401–7671 ..... 2– 4, 6–15,

........................................................................ 18–26

42 U.S.C. § 7401 .................................................. 18

42 U.S.C. § 7401(a)(3)............................................ 7

vi

42 U.S.C. § 7401(b)(3)............................................ 7

42 U.S.C. § 7401(c) .............................................. 22

42 U.S.C. § 7410(a)(2)(A) ..................................... 20

42 U.S.C. § 7411 .................................................... 8

42 U.S.C. § 7412 .................................................... 8

42 U.S.C. § 7416 ................ 8, 10, 12, 13, 15, 19, 23

42 U.S.C. § 7437(b) .............................................. 21

42 U.S.C. § 7470 .................................................. 18

42 U.S.C. § 7470(1) .............................................. 19

42 U.S.C. § 7507 .................................................... 7

42 U.S.C. § 7543 .................................................... 7

42 U.S.C. § 7543(b) ................................................ 7

42 U.S.C. § 7543(e)(2) ............................................ 7

42 U.S.C. § 7545(c)(4)(B) ....................................... 7

42 U.S.C. § 7545(c)(4)(C) ....................................... 7

Clean Water Act, 33 U.S.C. §§ 1251–1389......... 22, 23

33 U.S.C. § 1370 .................................................. 22

Employee Retirement Income Security Act (ERISA),

29 U.S.C. §§ 1001–1461....................................... 11

McCarran-Ferguson Act, 15 U.S.C. §§ 1011–15 ...... 11

National Labor Relations Act (NLRA),

29 U.S.C. §§ 151–169........................................... 12

vii

Other

Cong. Research Serv., Clean Air Act: A Summary of

the Act and its Major Requirements (2022),

https://www.congress.gov/crsproduct/RL30853?hl=RL30853&s=1&r=2 ............ 6

A. Scalia & B. Garner, Reading Law (2012) ...... 11, 16

INTEREST OF AMICUS CURIAE1

Amicus curiae Public Citizen is a nonprofit consumer advocacy organization that appears on behalf

of its nationwide membership before Congress, administrative agencies, and courts on a wide range of issues. Public Citizen has a longstanding interest in

preserving state-law damages remedies against unwarranted claims of preemption by federal law under

the Constitution’s Supremacy Clause. In that regard,

Public Citizen opposes overbroad application of principles of implied conflict preemption that impair the

operation of state law, including state damages remedies, based on courts’ subjective perceptions of the unstated purposes and objectives of federal law. Accordingly, Public Citizen has frequently filed briefs in this

Court and others addressing issues relating to

preemption. See, e.g., Hencely v. Fluor Corp., 146 S.

Ct. 1086 (2026).

Public Citizen also is actively involved in issues

arising from excessive emissions of greenhouse gases

that have contributed to and continue to accelerate

global climate change. Through its Climate and Energy Program, Public Citizen advocates policies that

will move our economy away from reliance on the fossil fuels that generate greenhouse-gas emissions, will

build a resilient and equitable economy, and will hold

industries that contribute to harmful emissions accountable.

These interests come together in this case, in

which oil companies seek to avoid liability for climate––––––––––––––––––––––––

1 This brief was not authored in whole or part by counsel for

a party. No one other than amicus curiae made a monetary contribution to preparation or submission of the brief.

2

related injuries attributable to their commercial conduct by arguing that federal law preempts state common-law actions seeking damages for those injuries.

Public Citizen submits this brief to address the oil

companies’ claim that the Clean Air Act—a law designed to preserve state authority to address air pollution harms—impliedly preempts states from exercising that authority to provide remedies for those injured by climate change resulting from the companies’

wrongful promotion and marketing of fossil fuels.

SUMMARY OF ARGUMENT

In this case, respondents the County and City of

Boulder, Colorado, brought suit in Colorado state

courts seeking to impose damages on the oil companies Suncor and ExxonMobil for allegedly wrongful

commercial conduct that caused injuries in Colorado.

Asserting a number of state common-law rights of action, Boulder alleges that the oil companies produced

fossil fuels and promoted use of those fuels while concealing their knowledge that the resulting atmospheric emissions of greenhouse gases would lead to

global climate change and result in injuries, including

those for which Boulder seeks to recover damages.

Boulder does not claim that the emissions themselves

exceeded standards applicable to their sources or were

otherwise unlawful, but that the oil companies wrongfully caused emissions that they knew would, in the

aggregate, cause injury even if each particular source

of emissions operated lawfully.

The oil companies contend that Boulder’s claims

are preempted by federal law under the Constitution’s

Supremacy Clause because most of the climate-altering emissions that allegedly injured Boulder came

from sources outside Colorado. According to the

3

companies, imposition of liability under state common

law for any damages resulting from the interstate effects of air pollution is contrary to federal law.

The oil companies’ broad claims of preemption are

wrong. Federal law does not broadly displace state

common or statutory law in all matters relating to interstate air pollution. Rather, the terms of the Clean

Air Act—the principal body of federal law addressing

interstate air pollution and the only federal statute

the oil companies invoke for their preemption defense—are fully consistent with Boulder’s state-law

damages claims.

The Clean Air Act’s express terms acknowledge the

primary role of state law in addressing air pollution,

provide for preemption of state law only as to narrowly

defined subjects not implicated by Boulder’s claims,

and otherwise express Congress’s determination not

to preempt state laws concerning air pollution. The

Clean Air Act’s terms thus foreclose any argument

that it expressly preempts Boulder’s claims or that it

occupies the field of controlling and remedying harms

from air pollution.

Because, under the Supremacy Clause, all forms of

preemption must rest on conflict between a federal

law and a contrary state law, the Clean Air Act’s express limits on its own preemptive effect also weigh

heavily against any claim of implied preemption. In

any event, the rest of the Act’s terms provide no support for implied preemption. The oil companies do not

even argue that the Clean Air Act’s commands conflict

directly with the state common-law principles Boulder

invokes, such that it is impossible to comply with or

apply both.

4

Instead, they contend that state common law is

contrary to the “purposes and objectives” of the Clean

Air Act. As this Court has recently emphasized, the

doctrine of implied purposes-and-objectives preemption provides no basis for the Court to attribute purposes to Congress that are not firmly grounded in statutory text. And the Clean Air Act’s text provides no

basis for concluding that its purposes include limiting

state efforts to combat air pollution that do not frustrate the efficacy of the emissions limits and other

anti-pollution requirements that the Act imposes. Instead, the purpose evident in the statute’s text is to

reduce air pollution by imposing minimum emissions

standards for certain sources of some air pollutants.

The liabilities that Boulder seeks to impose go beyond

those that federal law would impose, but they do not

impair the functioning of federal emissions standards,

and (outside the limited scope of its express preemption provisions) the Act’s terms embody no general

purpose of putting a ceiling on states’ ability to remedy air pollution. The state-law tort principles Boulder invokes are therefore not impliedly preempted.

ARGUMENT

I.

Under the Supremacy Clause, federal

statutes preempt state laws only when

their text and structure reveal that they

conflict with state law.

The Supremacy Clause does not provide for

preemption of state laws that are not contrary to federal law. Instead, it states that the Constitution, and

the laws and treaties of the United States made pursuant to it, “shall be the supreme Law of the Land;

and the Judges in every State shall be bound thereby,

any Thing in the Constitution or Laws of any State to

5

the Contrary notwithstanding.” U.S. Const., art. VI,

cl. 2. As this Court has repeatedly explained, the

Clause “supplies a rule of decision when federal and

state laws conflict”—the rule being that “the state law

must yield” to conflicting federal law. Martin v. United

States, 605 U.S. 395, 409 (2025).

When state law is not “contrary” to supreme federal law, the Supremacy Clause’s rule of decision does

not come into play. The Clause does not require state

laws to yield merely because they are viewed as contrary to “some brooding federal interest or … judicial

policy preference”; it declares only the requirements of

the Constitution and the laws and treaties made under it to be supreme. Va. Uranium, Inc. v. Warren, 587

U.S. 761, 767 (2019) (opinion of Gorsuch, J.). “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). “In all cases, the federal restrictions or rights that are said to conflict with state

law must stem from either the Constitution itself or a

valid statute enacted by Congress.” Kansas v. Garcia,

589 U.S. 191, 202 (2020); accord, Hencely, 146 S. Ct.

at 1093.

These principles apply to each of the forms of

preemption this Court has recognized: express

preemption, where the text of a federal statute explicitly identifies the kinds of state laws that are contrary

to its terms; field preemption, where federal law occupies some area so comprehensively and exclusively

that any application of state law is contrary to federal

law; and implied conflict preemption, where state law

is contrary to federal law in the sense that it is impossible to apply or comply with both federal and state

law or, more controversially, where applying state law

6

would defeat the purposes and objectives of federal

law. See Murphy v. NCAA, 584 U.S. 453, 477–79

(2018); Va. Uranium, 587 U.S. at 767 (Gorsuch, J.).

Whatever the form of preemption invoked, the answer

to the question whether state law is contrary to federal law “must … be ‘sought in the text and structure

of the statute at issue.’” Id. at 778 (quoting CSX

Transp., Inc. v. Easterwood, 507 U. S. 658, 664 (1993).

II. The Clean Air Act’s terms limit its

preemptive effects and broadly affirm

state authority to address air pollution.

The Clean Air Act’s text and structure flatly contradict any claim that the Act preempts the imposition

of damages under state law for climate-change-related

injuries caused by emissions of greenhouse gases attributable to the oil companies’ promotion of fossil-fuel

consumption. The Act’s terms require that sources of

certain air pollutants must comply with technologybased limits, which for some sources and pollutants

must be set forth in permits, and it requires states

that are not in compliance with federally prescribed

ambient air quality standards to establish plans to

come into compliance with those standards through

the use of more stringent limits on sources and other

means chosen by the states.2 But with a few specified

exceptions not applicable here, the Act’s text and

structure reveal that state laws are not contrary to the

Act when they address air pollution differently than

the Act and do more to remedy harms resulting from

air pollution than the Act requires.

––––––––––––––––––––––––

2 The Clean Air Act’s provisions are summarized in Congres-

sional Research Service, Clean Air Act: A Summary of the Act and

its Major Requirements (2022), https://www.congress.gov/crsproduct/RL30853?hl=RL30853&s=1&r=2.

7

To begin, the Act expressly recognizes the primacy

of state law with respect to the prevention and control

of air pollution. It provides “that air pollution prevention (that is, the reduction or elimination, through any

measures, of the amount of pollutants produced or created at the source) and air pollution control at its

source is the primary responsibility of States and local

governments.” 42 U.S.C. § 7401(a)(3). And it expressly

states that its purposes include providing “assistance

to State and local governments in connection with the

development and execution of their air pollution prevention and control programs.” Id. § 7401(b)(3) (emphasis added).

More pointedly, the Act precisely identifies the

handful of areas where it preempts state laws by prohibiting states from going further than federal law in

addressing air pollution: It expressly preempts states

from adopting standards for emissions from new motor vehicles or from aircraft, 42 U.S.C. §§ 7543, 7573,

and from adopting certain requirements regarding

components or additives for motor vehicle fuels, id.

§ 7545(c)(4).3 It hammers home the limits on its

preemption of state law by providing that, except as

provided in these sections,

nothing in this [Act] shall preclude or deny the

right of any State or political subdivision thereof

to adopt or enforce (1) any standard or limitation

––––––––––––––––––––––––

3 Even as to these expressly preempted subjects, the Act pro-

vides for California and states adopting its standards to receive

a waiver of preemption of standards for motor-vehicle emissions

and fuel components and additives, and also for waiver of

preemption of fuel standards when such standards are included

in an approved state plan for achieving compliance with ambient

air quality standards. 42 U.S.C. §§ 7543(b) & (e)(2); 7507;

7545(c)(4)(B) & (C).

8

respecting emissions of air pollutants or (2) any

requirement respecting control or abatement of

air pollution; except that if an emission standard

or limitation is in effect under an applicable implementation plan or under section 7411 or section 7412 of this title, such State or political subdivision may not adopt or enforce any emission

standard or limitation which is less stringent

than the standard or limitation under such plan

or section.

Id. § 7416.

The oil companies do not contend that the statelaw tort principles underlying Boulder’s claim fall

within the Act’s express preemption of standards limiting emissions from motor vehicles and aircraft,

standards concerning the formulation of motor vehicle

fuels, or standards or limitations less stringent than

those imposed under the Act. Moreover, the Act expressly rules out any suggestion that it occupies the

field of air-pollution regulation “so comprehensively

that it has left no room for supplementary state legislation.” R.J. Reynolds Tobacco Co. v. Durham County,

479 U.S. 130, 140 (1986). The Act’s explicit acknowledgment of the primary role of state law within that

field, and its affirmation of state authority to enforce

laws that are more stringent than federal standards

except in the few areas where state law is expressly

preempted, directly contradict any such suggestion.

The statute’s unambiguous language thus forecloses

both express and field preemption.

9

III. The Clean Air Act does not impliedly

preempt state common-law principles that

would impose liability on companies that

cause harmful air pollution.

A. The Act’s non-preemption clause strictly

limits implied preemption.

The Act’s language and structure are equally fatal

to the oil companies’ argument that it impliedly

preempts state common-law damages actions against

them for causing pollution. A court cannot determine

whether state law conflicts with the requirements imposed by or the purposes and objectives implicit in federal law without considering the statutory language

that determines what federal law requires and what

purposes and objectives it reflects. See Va. Uranium,

587 U.S. at 767, 778 (Gorsuch, J.). And “[i]n this, as in

any field of statutory interpretation, it is our duty to

respect not only what Congress wrote but, as importantly, what it didn’t write.” Id. at 765. Here, both

considerations strongly cut against implied preemption.

In the Clean Air Act, Congress specified that a

handful of particular types of state laws (including antipollution laws less stringent than federal laws) were

preempted. But, as in Virginia Uranium, Congress

“conspicuously chose to leave untouched” other exercises of state authority over pollution. 587 U.S. at 765

(Gorsuch, J.). Congress’s narrowly defined expresspreemption provisions cut against finding that the

statute has a much broader preemptive sweep. See,

e.g., Wyeth v. Levine, 555 U.S. 555, 575 (2009).

Moreover, Congress did more than narrowly define

the Clean Air Act’s preemptive sweep. Congress went

on to provide that, except for state laws that would

10

permit more air pollution than federal laws, the Clean

Air Act does not preempt state-law standards, limitations, and requirements regarding air pollution (including emissions of pollutants and the control or

abatement of air pollution). 42 U.S.C. § 7416. And

Congress did so in very broad terms, insisting that except for the enumerated express-preemption provisions, “nothing” in the Act shall preclude “any State”

from adopting or enforcing “any” air pollution standard, limitation, or requirement (unless the state

standard is less stringent than a federal one on the

same subject). Id. (emphasis added). In short, Congress wrote a sweeping “non-preemption clause,” Va.

Uranium, 587 U.S. at 769 (Gorsuch, J.), that serves as

the flipside of the statute’s narrow express preemption

provisions.

When Congress explicitly and comprehensively delineates what a statute does and does not preempt, the

statutory language “necessarily contains the best evidence of Congress’ pre-emptive intent,” Dan’s City

Used Cars, Inc. v. Pelkey, 569 U.S. 251, 260 (2013) (citation omitted), and there is no basis for resorting to

“infer[red] congressional intent to pre-empt,” Cipollone v. Liggett Group, Inc., 505 U.S. 504, 517 (1992)

(quoting Calif. Fed. Sav. & Loan Ass’n v. Guerra, 479

U.S. 272, 282 (1987) (plurality)). Application of a state

law that federal law expressly states is not preempted

is not “contrary” to federal law within the meaning of

the Supremacy Clause, and thus such a state law

“cannot be preempted.” Guerra, 479 U.S. at 296

(Scalia, J., concurring in the judgment).

Put another way, applying state law in such circumstances does not present the conflict between

state and federal law that is the premise of implied

conflict preemption. A non-preemption provision

11

avoids situations in which compliance with both state

and federal law is impossible by providing that application or enforcement of state law complies with federal law. Likewise, when a federal law expressly

states that nothing in it preempts a state law, the application of that state law cannot conflict with the purposes or objectives of the federal law. Congress has expressly stated, and enacted into law, its purpose of not

preempting the state law, and courts should not ascribe purposes and objectives to Congress that the

plain language of a statute disclaims. Doing so would

disregard the principle that a statute’s supposed “purpose … cannot be used to contradict [its] text” and that

“the limitations of a text—what a text chooses not to

do—are as much a part of its ‘purpose’ as its affirmative dispositions.” A. Scalia & B. Garner, Reading Law

57 (2012).

For these reasons, the Court has repeatedly held

that broad non-preemption or anti-preemption provisions such as the one in the Clean Air Act preclude

implied preemption of state laws that fall within their

scope. See, e.g., Guerra, 479 U.S. at 282 (plurality) &

295–96 (Scalia, J., concurring in the judgment) (relying on anti-preemption provisions to hold that a California statute requiring pregnancy leave not required

under federal law was not impliedly preempted by Title VII); Am. Ins. Ass’n v. Garamendi, 539 U.S. 396,

428 (2003) (holding that McCarran-Ferguson Act’s

anti-preemption provision forecloses “implied preemption” of state laws regulating the business of insurance); Dep’t of Treas. v. Fabe, 508 U.S. 491, 502

(1993) (same); Malone v. White Motor Corp., 435 U.S.

497, 505 (1978) (holding that anti-preemption provisions in effect before passage of ERISA precluded implied preemption of state pension laws under the

12

NLRA); Retail Clerks Int’l Ass’n v. Schermerhorn, 375

U.S. 96, 103 (1963) (holding that an NLRA provision

stating that nothing in the Act shall be construed to

authorize agency shop agreements that are contrary

to state law precluded implied preemption of state

laws forbidding agency shops).

By contrast, the Court has held that “savings

clauses” that preserve state laws to a more limited extent do not foreclose implied preemption of state laws

outside their scope, see Geier v. Am. Honda Motor Co.,

529 U.S. 861, 867–70 (2000), and it has resisted construing ambiguous savings clauses in a way that

would effectively cause a federal statute to “destroy itself,” Tex. & Pac. Ry. v. Abilene Cotton Oil Co., 204

U.S. 426, 446 (1907). Nonetheless, where a statute includes a savings clause, courts must consider any implied preemption claim with due recognition that a

savings clause contemplates “a continued meaningful

role for state … law.” Williamson v. Mazda Motor of

Am., 562 U.S. 323, 335 (2011); see also id. at 338 (Sotomayor, J., concurring) (same); cf. id. at 339 (Thomas,

J., concurring in the judgment) (stating that savings

clause should be construed to preclude implied

preemption altogether).

Applying these established principles, the Clean

Air Act’s non-preemption provision forecloses implied

preemption of the common-law duties that Boulder invokes. The language of 42 U.S.C. § 7416 is comparable

to that of other provisions to which this Court has

given broad anti-preemptive effect in that it provides

that “nothing” in the Act shall preclude adoption or

enforcement of the state laws it describes. Given that

implied preemption must necessarily be tied to something in a federal law, see Va. Uranium, 587 U.S. at

767 (Gorsuch, J.), Congress’s insistence that nothing

13

in a law has preemptive effect necessarily forbids implied preemption. The scope of non-preemption under

§ 7416, moreover, is easily broad enough to encompass

the state common-law principles Boulder invokes: The

statute protects the right of “any State” to enforce “any

requirement respecting control … of air pollution.”

Boulder’s claims do not seek remedies that impose direct controls on emissions of air pollutants, but they

posit common-law duties not to produce and market

pollution-causing fuels in excessive quantities while

concealing that their use will lead to harmful air pollution. Those duties are, in normal parlance, requirements, see Monsanto Co. v. Durnell, 146 S. Ct. 2001,

2010 (2026), and they relate to control of air pollution.

The Act’s explicit protection of such state laws against

preemption is irreconcilable with the claim that the

Act implicitly preempts them.

B. Boulder’s theories of liability do not

conflict with the Clean Air Act’s terms or

its “purposes and objectives.”

Even if the non-preemption provision were not

enough to foreclose implied preemption of state law by

the Clean Air Act, the oil companies’ claims of implied

preemption would fail. Implied preemption is most

readily found when, despite the absence or inapplicability of an express preemption provision, there is a

clear contradiction between state and federal law,

such that it is impossible for a person to comply with

both or for a judge to apply both. “So, for example,

when a regulated party cannot comply with both federal and state directives, the Supremacy Clause tells

us the state law must yield.” Martin, 605 U.S. at 409.

Likewise, if federal law confers on someone a right to

do something or an immunity from liability for some

14

action, such that it would be impossible both to enforce

that federal right and to apply a state law that would

deny it, the Supremacy Clause directs that state law

yield to federal law. See Kansas v. Garcia, 589 U.S.

191, 211 (2020); see also, e.g., Barnett Bank of Marion

County, N.A. v. Nelson, 517 U.S. 25, 31–33 (1996)

(holding that federal law authorizing national banks

to sell insurance preempts state law forbidding them

to do so).

The state tort law Boulder invokes does not conflict

with the Clean Air Act in either sense. Anyone regulated under the Clean Air Act can comply with all the

Act’s limits on emissions while also fulfilling state

tort-law duties not to wrongfully promote use of pollution-causing fossil fuels. And nothing in the Clean Air

Act confers on the oil companies (or anyone else) a

right or immunity that would be infringed by the imposition of damages liability for the commercial conduct that Boulder alleges caused climate-altering

greenhouse gas emissions.

The oil companies do not contest either of these

points: They identify no respect in which the requirements that the Clean Air Act imposes on sources of air

emissions are in direct conflict with the duties that

Boulder would impose on producers and sellers of

fuels whose use has caused excessive greenhouse gas

emissions. Instead, the oil companies contend that

Boulder’s tort claims are preempted because they conflict with what the oil companies claim are the “purposes and objectives” of the Act’s requirements. The

companies’ invocation of this Court’s past holdings

that implied preemption may occur where state law

“stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress,” Hines v. Davidovitz, 312 U.S. 52, 67 (1941),

15

fails not only because it cannot be squared with

§ 7416, but also because the Clean Air Act does not

embody purposes and objectives that conflict with

Boulder’s theories of liability under state law.

1. “Purposes and objectives” preempt

state law, if at all, only in limited

circumstances.

“Purposes-and-objectives preemption” is unusual

among the Court’s doctrines in that it seems to give

legal effect to a court’s assessment, not of what a federal statute provides, but of the purposes that Congress intended the statute to serve. Treating a statute’s purpose, as opposed to its enacted text, as part of

“the Laws of the United States” that displace state law

under the Supremacy Clause is in tension with the

Court’s usual recognition that “the ordinary meaning

of [statutory] language accurately expresses the legislative purpose,” Engine Mfrs. Ass’n v. S. Coast Air

Quality Mgmt. Dist., 541 U.S. 246, 252 (2004), and its

rejection of the view “that whatever furthers [a] statute’s primary objective must be the law,” Rodriguez v.

United States, 480 U.S. 522, 526 (1987). Put another

way, “[r]ather than augmenting statutes” to make

“the congressional purpose” more “effective,” courts

must “interpret them.” FS Credit Opportunities Corp.

v. Saba Capital Master Fund, Ltd., 146 S. Ct. 1546,

1553 (2026). For this reason, some members of the

Court have disavowed “purposes and objectives”

preemption and urged that the Court “explicitly abandon” it. Garcia, 589 U.S. at 213 (Thomas J., joined by

Gorsuch, J., concurring).

Nonetheless, the Court has in a few instances continued to recognize frustration of federal law’s “purposes and objectives” as a basis for implied

16

preemption of state law. See, e.g., Howell v. Howell,

581 U.S. 214, 222 (2017). At the same time, however,

the Court has made clear that preemption is never a

“freewheeling judicial inquiry into whether a state

statute is in tension with federal objectives,” and that,

“[i]n all cases, the federal restrictions or rights that

are said to conflict with state law must stem from either the Constitution itself or a valid statute enacted

by Congress.” Garcia, 589 U.S. at 202. It follows that,

in the first instance, “ ‘[e]vidence of pre-emptive purpose,’ whether express or implied, must … be ‘sought

in the text and structure of the statute at issue.’ ” Va.

Uranium, 587 U.S. at 778 (Gorsuch, J.) (quoting CSX

Transp., Inc. v. Easterwood, 507 U.S. 658, 664 (1993)).

Thus, a litigant claiming preemption based on conflict

between state law and the requirements, purposes, or

objectives of federal law “must point specifically to ‘a

constitutional text or a federal statute’ that does the

displacing or conflicts with state law.” Id. at 767 (citation omitted). The inquiry turns on “what can be found

in the law itself,” id. at 779, not on “abstract and unenacted legislative desires,” id. at 778. As in other

matters of statutory construction, an understanding

of a federal statute’s purpose must generally be sought

in its text, structure, and context. See Scalia & Garner

56.

Courts considering claims that state law frustrates

a federal statute’s purposes and objectives, moreover,

must remain mindful of the general principles that “no

legislation pursues its purposes at all costs,” Rodriguez, 480 U.S. at 525–26, and that a statute’s purpose

is “not only to achieve certain ends, but also to achieve

them by particular means,” Freeman v. Quicken

Loans, Inc., 566 U.S. 624, 637 (2012). Thus, courts

should be hesitant, at least, to infer an unstated

17

purpose to preempt state laws addressing matters

that a federal statute conspicuously does not touch.

Va. Uranium, 587 U.S. at 765 (Gorsuch, J.). With respect to “purposes and objectives” preemption, as in

other matters of statutory construction, when Congress has enacted “a statute going so far and no further,” courts have no “roving license” to conclude that

“Congress ‘must have intended’ something broader.”

Michigan v. Bay Mills Indian Cmty., 572 U.S. 782, 794

(2014). Similarly, courts should not articulate the purposes of a federal statute at such a high “level of generality” that the statute’s preemptive reach extends

further than the text enacted by Congress warrants.

CTS Corp. v. Waldburger, 573 U.S. 1, 18 (2014). Extending a statute to preempt state laws that affect

matters the statute’s text does not address is rarely if

ever necessary to avoid “an unacceptable obstacle to

the attainment of [the statute’s] purposes.” Id.

For these reasons, where the Court has found state

laws preempted based on a “purposes and objectives”

analysis, it has generally done so in circumstances

where state law would effectively nullify or circumvent explicit requirements or commands of a federal

statute—not simply because the Court concluded that

the legislative purpose would be better or more fully

served by extending the law’s preemptive reach more

broadly. See, e.g., Howell v. Howell, 581 U.S. at 222

(holding that federal law preempted state court orders

that effectively “displace[d] the federal rule” against

treating waived military retirement pay as divisible

community property); Hillman v. Maretta, 569 U.S.

483, 494 (2013) (holding preempted a state law that

“displace[d]” a federal statute’s designation of the

18

beneficiary of a federal employee’s life insurance benefits).4

2. Boulder’s theories of liability are fully

consistent with the purposes and

objectives evident in the Clean Air

Act’s terms.

The terms of the Clean Air Act fall far short of

demonstrating that Congress’s objectives would be

thwarted unless the Act were construed to incorporate

an unstated purpose of preempting state laws that

would impose liability on companies whose deceptive

marketing causes or has caused harmful emissions of

air pollutants. Nothing in the Act’s enacted purposes

and objectives demonstrates that Congress designed

the Act to thwart, as opposed to assist, states in their

efforts to control air pollution and remedy harms it

has caused. See 42 U.S.C. §§ 7401, 7470. The Act’s operative terms, moreover, embody Congress’s evident

purpose to reduce air pollution through specifically

stated means. Those means include the imposition of

technology-based limits on some sources of pollutants,

and the promulgation of air quality standards for certain pollutants, the failure to meet which may require

the imposition of additional controls on emissions

from sources as well as other measures to reduce pollution. The purposes those provisions embody, however, are not frustrated by state efforts to take other

––––––––––––––––––––––––

Although the Court articulated its holding in those two

cases in terms of “purposes and objectives” preemption, Justice

Thomas concurred based on his view that the contradiction between the requirements of federal and state law created a direct

conflict. See Howell, 581 U.S. at 223 (Thomas, J., concurring in

part and in the judgment); Hillman, 569 U.S. at 499–501

(Thomas, J., concurring in the judgment).

4

19

measures to prevent or remedy pollution. To the contrary, the Act expressly recognizes that, with only a

few exceptions, states have the “right” to enforce more

stringent standards, limitations, and requirements

relating to air pollution. 42 U.S.C. § 7416.

To be sure, the Clean Air Act requires that the

emissions standards it imposes on pollution sources of

various types be limited by consideration of such factors as availability of control technology, its practicability, and in some instances, its cost. See Whitman v.

Am. Trucking Ass’ns, 531 U.S. 457, 466–68 (2001) (describing examples of such provisions). But by simultaneously providing that states may impose more stringent standards, see 42 U.S.C. § 7416, the Act forecloses any suggestion that Congress’s purpose in imposing limitations on federal emissions standards

would be thwarted by more demanding state standards.

Even if the Act could reasonably be read to embody

a purpose of foreclosing states from striking a different balance when imposing limits on emissions from

sources of pollutants regulated under the Act, the liability that Boulder seeks to impose here would not require any source to meet any particular emission

standard, let alone any standard more stringent than

standards applicable under the Act. Nor does Boulder

seek to premise liability on the idea that emissions

from particular sources that comply with Clean Air

Act limitations are themselves unlawful. Rather,

Boulder invokes state law to impose liability on the oil

companies for marketing practices that have resulted

in aggregate emissions of greenhouse gases that—

even assuming compliance by each individual source

of emissions with all applicable Clean Air Act requirements—have caused injurious climate change. Such

20

liability does not in any way impair the Act’s efficacy

in achieving its objective of using source limitations to

combat air pollution.

Further, nothing in the Act evinces an additional

purpose of protecting the ability of oil companies or

other commercial actors to promote the use of fuels

and technologies that cause greenhouse gas emissions

or other harmful forms of air pollution. Indeed, the Act

recognizes that emissions limitations applicable to

specific sources will not by themselves prevent harmful air pollution when many separate sources emit pollutants at levels the Act permits, and it encourages

states to address that problem rather than discouraging them from doing so. For example, the Act contemplates that state implementation plans aimed at compliance with ambient air quality standards will include not only emission controls, but also other

measures, including “economic incentives” to control

overall emissions. 42 U.S.C. § 7410(a)(2)(A). Even in

the limited number of instances where the Act does

preempt states from regulating emissions from

sources (such as motor vehicles) more stringently than

do applicable federal standards, it does not suggest

that encouraging use of lower-emission vehicles would

be contrary to its objectives. Cf. South Coast, 541 U.S.

at 258 (distinguishing such programs from preempted

emission standards). Moreover, the Act makes clear

that even when a state meets all applicable federal

ambient air quality standards, it has a legitimate interest in preventing adverse effects that air pollution

may cause “notwithstanding attainment and maintenance of all national ambient air quality standards.”

42 U.S.C. § 7470(1). And the Act specifically recognizes the legitimacy of state efforts to “achieve or facilitate the reduction of greenhouse gas air pollution”

21

by providing federal grants to assist them in those efforts. 42 U.S.C. § 7437(b).

More broadly, neither the Act’s specific terms nor

its overall structure suggests that it imposes a ceiling

beyond which states cannot seek to protect their air.

Nothing in the Act, for example, purports to give federal regulators the authority to balance the overall

costs and benefits of clean air and prevent states from

seeking air that is cleaner than federal emissions

standards have achieved. And nothing in the Act authorizes the federal government to exempt certain

kinds of pollutants (such as greenhouse gases) from

applicable state statutory or common law. The Clean

Air Act’s provisions nowhere show a purpose of authorizing federal regulators to prescribe an optimal

level of air pollution control that would be thwarted by

additional state requirements and remedies.

Thus, state laws are not contrary to the Act’s objectives when, for example, they: impose more stringent limits on emissions from sources covered by the

Act; target pollutants not addressed by federal standards issued under the Act; adopt air quality standards

or other measures aimed at making air cleaner than

federal standards achieve; foster conservation

measures to reduce reliance on fuels and technologies

that, in the aggregate, cause harmful pollution even

when each individual emission from a source meets

federal standards; or, most relevant here, impose liability on entities that injure state residents by engaging in deceptive marketing that causes harmful air

pollution. Such measures align perfectly with the

Clean Air Act’s real purposes and objectives, which

are to regulate emissions in the specific ways the Act

requires while leaving the states ample scope to go

further in pursuing “reasonable … actions, consistent

22

with the provisions of [the Act], for pollution prevention.” 42 U.S.C. § 7401(c).

3. This Court’s decision in Ouellette does

not support the oil companies’

implied-preemption arguments.

Despite the Act’s evident purpose of not broadly

preempting state antipollution measures, the oil companies argue that this Court’s decision in International Paper Co. v. Ouellette, 479 U.S. 481 (1987), supports the view the Clean Air Act impliedly preempts a

state from providing any remedies under its own laws

for pollution emanating from other states. That argument is both fundamentally mistaken and, even if correct, would not require dismissal of Boulder’s claims.

Ouellette held that the permitting scheme established by the Clean Water Act for “point sources” of

water pollutants impliedly prohibits a state from imposing liability under its own laws for regulated discharges of water pollutants in other states, see id. at

493–97, but permits liability to be imposed under the

common law of the state where a source is located even

if the discharge is permitted under the Clean Water

Act, id. at 497–500. That holding rested heavily on the

Court’s reading of a “savings clause” in the Clean Water Act providing in part that nothing in that Act

“shall … be construed as impairing or in any manner

affecting any right or jurisdiction of the States with

respect to the waters (including boundary waters) of

such States.” 33 U.SC. § 1370 (emphasis added). The

Court held that “[t]his language arguably limits the

effect of the clause to discharges flowing directly into

a State’s own waters, i.e., discharges from within the

State,” and thus “does not preclude preemption of the

law of an affected State.” Ouellette, 479 U.S. at 493.

23

By contrast, the Clean Air Act’s broad disclaimer

of preemption of any requirement of any state concerning control of air pollution, 42 U.S.C. § 7416, does not

include the territorial limit on state jurisdiction that

Ouellette found in the Clean Water Act. In the absence

of the language that led the Court in Ouellette to conclude that “the Act itself does not speak directly to the

issue” of preemption of the claims before it, the Court

has no occasion to resort to guidance from “the goals

and policies of the Act in determining whether it in

fact pre-empts an action based on the law of an affected State.” 479 U.S. at 493.

In any event, the considerations that led the Court

to find implied preemption under the Clean Water Act

in Ouellette are not relevant to Boulder’s claims. Ouellette’s application of purposes-and-objectives preemption rested on its conclusion “that if affected States

were allowed to impose separate discharge standards

on a single point source, the inevitable result would be

a serious interference with the achievement of the ‘full

purposes and objectives of Congress.’” Id. (citation

omitted). Consistent with this view, Ouellette held

only that the Clean Water Act “precludes a court from

applying the law of an affected State against an outof-state source.” Id. at 494 (emphasis added).

As explained above, however, Boulder does not

seek to abate or impose liability for emissions from

particular sources, and its theory of liability does not

rest on the explicit or implicit imposition of “separate

discharge standards,” id. at 493, that are different

from those imposed under the Clean Air Act or the law

of the state where emissions occur. Boulder’s theory is

not that the emissions themselves were unlawful, but

that the oil companies acted unlawfully in promoting

and marketing their products, knowing that their use

24

would cause harm even if users complied with all applicable emissions standards. The Clean Air Act does

not regulate such activities or address state regulation

of them. Accordingly, unlike in Ouellette, nothing in

the common-law principles underlying Boulder’s

claim “interferes with the methods by which the federal statute was designed to reach [its] goal[s]” or “upset[s] the balance of public and private interests … addressed by the Act.” Id. at 494.

Finally, as Boulder points out, even assuming that

Ouellette’s reasoning could be applied to the claims

here, Boulder’s action does not necessarily depend on

application of Colorado law. The oil companies could

prevail on their argument that Boulder’s action must

be dismissed only if the statute completely foreclosed

application of state common law to remedy harms resulting from interstate pollution and thus did not permit any state’s law to be applied to impose liability on

the companies. But Ouellette makes clear that the conflict-preemption reasoning on which the Court relied,

if applicable here, would leave Colorado courts free to

provide remedies based on “the law of the source

State.” Id. at 497; see id. at 599–500.5 In short, Ouellette cannot be squared with the oil companies’ assertion that the Clean Air Act preempts any application

of state common law to their conduct.

––––––––––––––––––––––––

5 The Court need not determine whether, if Ouellette’s rea-

soning were applicable here, the law of the “source state” would

be considered to be that of the states from which the oil companies directed their wrongful promotion and marketing efforts or

that of the states where those efforts caused emissions to occur.

Either way, Boulder’s claims must be permitted to proceed, with

choice-of-law determinations to be made at an appropriate time.

25

IV. The oil companies’ remaining arguments

for displacement of state common law are

unconvincing.

The oil companies’ relegation of their claim of implied preemption under the Clean Air Act to last place

among their preemption arguments reflects the absence of support for preemption in the statute’s text.

But the companies’ other preemption arguments are

equally venturesome and unsupported.

The oil companies rely heavily on this Court’s former doctrine that certain claims seeking to abate

emissions of interstate air and water pollution must

be brought under federal common law. See Illinois v.

Milwaukee, 406 U.S. 91, 93 (1972). This Court has

since held, however, that the Clean Air Act has completely displaced that body of federal common law. See

Am. Elec. Power Co., Inc. v. Connecticut, 564 U.S. 410,

423–29 (2011) (AEP). A body of judge-made federal

law that has been superseded by an act of Congress

and has no further force and effect cannot possibly be

a “Law[] of the United States … made in pursuance”

to the Constitution that, under the Supremacy Clause,

is “binding” on judges in the face of contrary state law.

The oil companies therefore must fall back on the

assertion that the Court’s former creation of federal

common law necessarily reflected the Court’s view

that the Constitution itself foreclosed the application

of state common law to matters related to interstate

air pollution, and that the Constitution likewise

preempts Boulder’s state common-law claims. The oil

companies, however, cite no holding by the Court that

the Constitution preempts all forms of state-law liability for harms attributable to interstate air pollution, let alone anything that identifies the

26

“constitutional text,” Puerto Rico Dep’t of Consumer

Affairs, 485 U.S. at 503, that can serve as the source

of that preemption.

Even if the Court’s pre-Clean Air Act federal common law implicitly reflected some constitutional prohibition on the invocation of state common law, there

is no basis for reading that prohibition any more

broadly than the applications of state common law

that the Court held were displaced by federal common

law: namely, attempts to use the common law of “one

State to abate pollution emanating from another

State” by imposing limits on discharges or emissions

from specific sources. AEP, 564 U.S. at 421. Again,

however, Boulder’s claims are not attempts to abate

emissions permitted under the law of the source state,

nor do they rest on the theory that the sources of those

emissions acted unlawfully. The Court’s old federal

common-law decisions did not address claims like

Boulder’s, much less determine that the Constitution

prohibits them.

AEP recognized that the answer to the question

whether federal law preempts a common-law claim involving damages resulting from greenhouse-gas pollution must, in light of the abrogation of federal common

law, be sought in the Clean Air Act, not in the Court’s

abrogated common-law decisions. 564 U.S. at 429. The

absence of any basis in the Act for implied preemption

of Boulder’s claims is therefore fatal to the oil companies’ preemption arguments.

CONCLUSION

If the Court concludes that it has jurisdiction, it

should affirm the decision of the Supreme Court of

Colorado.

27

Respectfully submitted,

SCOTT L. NELSON

Counsel of Record

ALLISON M. ZIEVE

PUBLIC CITIZEN LITIGATION

GROUP

1600 20th Street NW

Washington, DC 20009

(202) 588-1000

snelson@citizen.org

Attorneys for Amicus Curiae

August 2026