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

_________

S UNCOR E NERGY (U.S.A.) I NC., ET AL .,

Petitioners,

v.

COUNTY C OMMISSIONERS

OF B OULDER C OUNTY , ET AL .,

Respondents.

_________

On Writ Of Certiorari

To The Supreme Court Of Colorado

_________

BRIEF AMICUS CURIAE OF PACIFIC

LEGAL FOUNDATION IN SUPPORT

OF PETITIONERS AND REVERSAL

_________

FRANK D. G ARRISON

Counsel of Record

TYLER FRY

Pacific Legal Foundation

3100 Clarendon Blvd.,

Suite 1000

Arlington, VA 22201

202.888.6881

fgarrison@pacificlegal.org

Counsel for Amicus Curiae Pacific Legal Foundation

TABLE OF CONTENTS

Identity and interest of amicus curiae ....................... 1

Introduction and summary of argument ................... 1

Argument .................................................................... 4

I. The Due Process Clause incorporates

common-law causation requirements.............. 4

II. Respondents’ claims fail each requirement

due process imposes ....................................... 11

A. Respondents’ multi-step causal chain

cannot satisfy the foreseeability

requirement .............................................. 12

B. Respondents’ causal chain also fails the

directness and immediacy requirement... 13

C. Aggregate and statistical causation

theories violate the individualized

proof requirements that due process

demands .................................................... 15

D. Respondents’ disproportionate, retroactive,

and punitive damages claims for lawful,

federally authorized conduct independently

violate due process .................................... 17

III. Respondents’ theory would devastate

domestic energy production and undermine

individual economic liberty ............................ 23

Conclusion ................................................................. 26

ii

TABLE OF AUTHORITIES

Cases:

Am. Elec. Power Co. v. Connecticut,

564 U.S. 410 (2011) ................................. 16, 23, 25

Associated Gen. Contractors of Cal., Inc.

v. Cal. State Council of Carpenters,

459 U.S. 519 (1983) ...................................... 7-8, 10

BMW of North America, Inc. v. Gore,

517 U.S. 559 (1996) .............................. 4, 11, 17-19

Bolling v. Sharpe,

347 U.S. 497 (1954) ............................................... 4

Burrage v. United States,

571 U.S. 204 (2014) ......................................... 6, 15

Den ex dem. Murray v. Hoboken Land &

Improvement Co.,

59 U.S. (18 How.) 272 (1855) ............................ 3, 5

Eastern Enterprises v. Apfel,

524 U.S. 498 (1998) .................................... 4, 20-22

Exxon Co., U.S.A. v. Sofec, Inc.,

517 U.S. 830 (1996) ............................................. 10

General Motors Corp. v. Romein,

503 U.S. 181 (1992) ............................................. 20

Gross v. FBL Financial Services, Inc.,

557 U.S. 167 (2009) ............................................. 15

Hamilton v. Beretta U.S.A. Corp.,

96 N.Y.2d 222 (2001) ........................................... 22

Hemi Group, LLC v. City of New York,

559 U.S. 1 (2010) ................................................... 9

Holmes v. Sec. Inv. Prot. Corp.,

503 U.S. 258 (1992) .................................. 3, 6-9, 13

Jefferson v. Lead Indus. Ass’n, Inc.,

106 F.3d 1245 (5th Cir. 1997) ........................ 22-23

iii

Juliana v. United States,

947 F.3d 1159 (9th Cir. 2020) ................. 17, 23, 25

Lexmark International, Inc. v. Static

Control Components, Inc.,

572 U.S. 118 (2014) ............................................... 8

Palsgraf v. Long Island R.R. Co.,

248 N.Y. 339 (1928) ............................................... 8

Rapanos v. United States,

547 U.S. 715 (2006) ............................................... 1

Sackett v. EPA,

598 U.S. 651 (2023) ............................................... 1

Santiago v. Sherwin Williams Co.,

3 F.3d 546 (1st Cir. 1993) .................................... 22

Schaffer ex rel. Schaffer v. Weast,

546 U.S. 49 (2005) ............................................... 15

Sindell v. Abbott Laboratories,

26 Cal. 3d 588 (1980) ........................................... 22

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

538 U.S. 408 (2003) .................................. 11, 18-20

Washington Env’t Council v. Bellon,

732 F.3d 1131 (9th Cir. 2013) .................. 12, 14-16

Weyerhaeuser Co. v. U.S. Fish & Wildlife Serv.,

586 U.S. 9 (2018) ................................................... 1

Other Authorities:

Adler, Jonathan H., Standing in the Hot Seat:

Climate Change Litigation, 8 Engage: J.

Federalist Soc’y Prac. Groups No. 1 (2007) ........ 21

Adler, Jonathan H., Warming Up to Climate

Change Litigation, 3 Va. L. Rev. 63 (2007) ... 16-17

Bacon, Francis, The Elements of the Common

Lawes of England (1630) ................................... 5, 9

iv

1 Blackstone, William, Commentaries on the

Laws of England (1765) ........................................ 5

Chapman, Nathan S. & McConnell, Michael W.,

Due Process as Separation of Powers,

121 Yale L.J. 1672 (2012) ...................................... 5

Inst. for Energy Research, Supreme Court Will

Hear a Climate Case Against Oil Companies

(Feb. 25, 2026) ..................................................... 25

Reid, John Phillip, Constitutional History of the

American Revolution (1995) .................................. 5

Robertson, Cassandra Burke & Rhodes, Charles W.

“Rocky”, Causation’s Due Process Dimensions,

13 Tex. A&M L. Rev. 295 (2025) ........................ 2-3

Viscusi, W. Kip, The Dimensions of the

Product Liability Crisis,

20 J. Legal Stud. 147 (1991) ............................... 24

Wharton, Francis, A Treatise on the Law of

Negligence (2d ed. 1878) ........................................ 6

White, Michelle J., Asbestos and the Future of

Mass Torts, 18 J. Econ. Persp. 183 (2004) .......... 24

IDENTITY AND INTEREST

OF AMICUS CURIAE1

Founded in 1973, Pacific Legal Foundation (PLF)

is a nonprofit, tax-exempt corporation organized under the laws of the state of California for the purpose

of engaging in litigation matters affecting the public

interest. PLF provides a voice for Americans who believe in limited government, private property rights,

and individual freedom.

In furtherance of this mission, PLF attorneys have

participated as lead counsel in several cases involving

environmental regulation, administrative law, and

property rights, including: Sackett v. EPA, 598 U.S.

651 (2023); Weyerhaeuser Co. v. U.S. Fish & Wildlife

Service, 586 U.S. 9 (2018); and Rapanos v. United

States, 547 U.S. 715 (2006). PLF’s Environment and

Natural Resources Practice Group works to remove

government barriers that prevent individuals from

unlocking America’s vast natural resources potential,

advancing America’s energy development free of unreasonable government restrictions, and using natural resources productively.

INTRODUCTION

AND SUMMARY OF ARGUMENT

Respondents City of Boulder and Boulder County

ask this Court to allow a lawsuit to proceed against

two private energy companies in state court for the

full costs of climate change in Colorado—wildfires,

floods, drought, and whatever else may follow—with

Amicus curiae states that no counsel for any party authored

this brief in whole or in part and that no entity or person other

than PLF and its counsel made any monetary contribution

toward the preparation or submission of this brief.

1

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no ceiling on damages and no meaningful limit on retroactive liability. Indeed, Respondents’ theory is

breathtakingly expansive: that because Petitioners

produced and sold fossil fuels, they should be liable in

state court for natural disasters that cannot be directly traced to them. That theory is not simply wrong

as a matter of tort law but threatens to serve as a blueprint for dismantling America’s domestic energy sector through litigation. If accepted, every oil and gas

producer, refiner, and distributor in the country faces

the same exposure—enormous retroactive liability for

unproven damages—in every jurisdiction where a

weather event has caused municipal costs. The upshot is that the energy investment, production, and

innovation on which Americans depend for economic

opportunity, affordable power, and individual liberty

would be suppressed through the accumulated weight

of adverse state court judgments.

While this brief supports Petitioners in reversal, it

addresses an independent constitutional defect that is

inherent in Respondents’ theory.2 The Constitution’s

prohibition on the deprivation of life, liberty, or property without due process of law was designed to prevent exactly this kind of arbitrary, unbounded liability. See Cassandra Burke Robertson & Charles W.

“Rocky” Rhodes, Causation’s Due Process Dimensions,

13 Tex. A&M L. Rev. 295, 300-01 (2025) (explaining

Amicus agrees with Petitioners that, if the federal

government has constitutional authority to regulate greenhousegas emissions and their effects on the global climate, the

structure of the Constitution forecloses Respondents’ state-law

claims for the reasons Petitioners give. See Brief for the

Petitioners 21-43. The due process barrier addressed here

operates independently of that antecedent question.

2

3

that due process limits prevent tort law “from becoming a subterfuge for redistributing wealth . . . in the

absence of any connection between [a defendant’s]

conduct and [a plaintiff’s] harm,” consistent with the

Clause’s traditional role “in ensuring and protecting

fundamental fairness, fair notice, and inalienable

rights”).

And as this Court has explained, what constitutes

“due process” in part depends on “settled usages and

modes of proceeding existing in the common and statute law of England.” See Den ex dem. Murray v. Hoboken Land & Improvement Co., 59 U.S. (18 How.)

272, 277 (1855). Since before the Founding, the AngloAmerican legal tradition has consistently held that

tort liability requires a direct, foreseeable, and proportionate connection between a specific defendant’s conduct and a specific plaintiff’s harm. See Holmes v. Sec.

Inv. Prot. Corp., 503 U.S. 258, 268-69 (1992) (legal

causation requires “some direct relation between the

injury asserted and the injurious conduct alleged,”

and harm “flowing merely from the misfortunes visited upon a third person” is too remote to support liability).

Respondents’ lengthy causal chain—running from

individual production decisions, through global atmospheric systems, through independent weather

events, to specific municipal costs—cannot satisfy

that standard. As Petitioners explain, Respondents’

claims necessarily implicate the emissions of “countless other sources worldwide” and rest on greenhouse

gases that “mixed with other molecules of greenhouse

gases in the atmosphere from other human and natural causes.” Brief for the Petitioners 2, 35-37. No

4

court can, for example, determine what, if any, fraction of Colorado floods is attributable to an energy

company’s production decisions spanning decades.

Foundationally, Respondents’ claims fail on due

process grounds independent of questions this Court

granted certiorari to address. The core defect is causation: Respondents’ multi-step theory cannot satisfy

the foreseeability and directness requirements that

due process demands. And that flaw does not stay

contained. Once a plaintiff is permitted to recover

without proving that a specific defendant’s conduct

caused a specific harm, the remaining constitutional

limits on tort liability unravel with it. Punitive and

retroactive damages lose the proportionality and fairnotice moorings this Court enforced in BMW of North

America, Inc. v. Gore, 517 U.S. 559 (1996), and Eastern Enterprises v. Apfel, 524 U.S. 498 (1998). One constitutional defect breeds others—each compounding

the arbitrary deprivation of property the Due Process

Clause was designed to forbid.

ARGUMENT

I.

The Due Process Clause Incorporates

Common-Law Causation Requirements

The Due Process Clause of the Fifth Amendment

was understood by the founding generation to incorporate the substantive protections embedded in the

English common-law tradition—protections that the

Fourteenth Amendment equally guarantees against

deprivations by state actors and in state-court proceedings. See Bolling v. Sharpe, 347 U.S. 497, 499500 (1954) (holding that the Fifth Amendment’s Due

Process Clause imposes the same prohibition on the

federal government that the Fourteenth Amendment

5

imposes on the states—and that the two clauses must

be read to guarantee equivalent protections). These

protections include settled principles of the common

law that ensured that liability was imposed only

through fair, reliable, and nonarbitrary means. Murray, 59 U.S. at 277.

Heavily influenced by the writings of Sir William

Blackstone and Sir Francis Bacon, the common law

instructed that legal liability required a necessary

connection between an act and its consequence. See 1

William Blackstone, Commentaries on the Laws of

England, 84 (1765) (“So great . . . is the regard of the

law for private property, that it will not authorize the

least violation of it; no, not even for the general good

of the whole community.”).3 These principles required

that legal consequences flow directly and foreseeably

from individual conduct, establishing the causation

requirements that became engrained in American due

process jurisprudence. See Francis Bacon, The Elements of the Common Lawes of England (1630) (“it

were infinite for the law to judge the causes of causes,

and their impulsions one of another; therefore it content itself with the immediate cause”).

While this Court has not squarely held as much, its

due process jurisprudence reflects that causation is

not merely a policy choice, but a constitutional constraint rooted in the common-law tradition that due

process preserves. Because due process incorporates

See also John Phillip Reid, Constitutional History of the

American Revolution 89-92 (1995) (discussing founding-era

understanding of “law of the land”). See also Nathan S.

Chapman & Michael W. McConnell, Due Process as Separation

of Powers, 121 Yale L.J. 1672, 1683-1715 (2012) (tracing due

process to English constitutional tradition).

3

6

those settled common law usages, the causation requirements embedded in that tradition carry constitutional force—they are not merely policy considerations

courts may set aside when convenient. Burrage v.

United States, 571 U.S. 204, 210-11, 214 (2014) (recognizing but-for causation as a “background principle[]” of the legal tradition that courts presume Congress legislates against, confirming that individualized causation is fundamental to our legal system);

Holmes, 503 U.S. at 268 (reflecting the same tradition

in holding that legal liability demands “some direct relation between the injury asserted and the injurious

conduct alleged”). The Court also has rejected “contributing cause” theories that would impose liability

based merely on incremental contributions to a harm,

holding instead that legal causation demands a direct

causal link. Burrage, 571 U.S. at 218-19.

These principles show that causation requirements

have typically limited legal liability to foreseeable,

proximate consequences of individual conduct. 4 The

decisions discussed above—Burrage, Holmes, and

their predecessors—primarily arise in statutory interpretation contexts, where this Court has presumed

that Congress legislates against common-law background principles including individualized causation.

They are not due process holdings on their face. But

the constitutional argument does not depend on characterizing them as such. Those decisions establish

that causation requirements are fundamental to the

Anglo-American legal tradition and that courts presume against their displacement. These cases show

See Francis Wharton, A Treatise on the Law of Negligence 11

(2d ed. 1878) (negligent injuries are those where the actor “may

foresee a probable danger”).

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what the founding era understanding assumed: that

due process forbids imposing liability based on speculative, attenuated, or aggregate theories of causation

untethered from an individual defendant’s conduct.

See Holmes, 503 U.S. at 268 (“[T]he notion of proximate cause reflects ‘ideas of what justice demands

. . . .’ Accordingly, among the many shapes this concept took at common law was a demand for some direct relation between the injury asserted and the injurious conduct alleged.” (citations omitted)).

As discussed below, due process imposes distinct

but related causation requirements that Respondents’

claims cannot satisfy. First, harm must be foreseeable: a defendant can be held liable only for consequences within the reasonable range of apprehension

at the time of the allegedly wrongful conduct. Second,

the causal connection must be direct: the defendant’s

conduct must be the immediate, rather than the attenuated or remote, cause of the plaintiff’s injury.

Third, causation must be individualized: due process

bars liability based on aggregate or statistical theories

that substitute aggregated industry activity for proof

that a specific defendant’s specific conduct caused a

specific plaintiff’s specific harm. Fourth, legal consequences must be proportionate to individual conduct.

The foreseeability requirement is essential in protecting individual liberty and enabling economic activity: it ensures that defendants can anticipate potential liability and adjust their conduct accordingly, and

it prevents unlimited expansion of liability theories

that would make productive activity economically unfeasible. As this Court has recognized, without foreseeability limits, “the judicial remedy cannot encompass every conceivable harm that can be traced to alleged wrongdoing.” Associated Gen. Contractors of

8

Cal., Inc. v. Cal. State Council of Carpenters, 459 U.S.

519, 536 (1983).

The foreseeability requirement has deep roots in

common-law tradition. Chief Judge Cardozo’s opinion

in Palsgraf v. Long Island R.R. Co., 248 N.Y. 339, 344

(1928), famously illustrates that liability extends only

to those “within the range of apprehension.” The opinion articulates the principle that defendants cannot be

held liable for consequences they could not reasonably

foresee: “The risk reasonably to be perceived defines

the duty to be obeyed.” Ibid. Likewise, this Court has

consistently applied these foreseeability principles to

constitutional and statutory liability. In Holmes, 503

U.S. at 268, the Court required “some direct relation

between the injury asserted and the injurious conduct

alleged.” Most importantly, the Court emphasized

that “a plaintiff who complained of harm flowing

merely from the misfortunes visited upon a third person by the defendant’s acts was generally said to stand

at too remote a distance to recover.” Id. at 268-69.

This “third person” language is critical: when harm

flows through the independent decisions and actions

of intervening parties rather than directly from the

defendant to the plaintiff, foreseeability disappears.

Lexmark International, Inc. v. Static Control Components, Inc., 572 U.S. 118, 132-33 (2014), further confirms that proximate cause “generally bars suits for

alleged harm that is ‘too remote’ from the defendant’s

unlawful conduct” and that remoteness exists when

“the harm is purely derivative of ‘misfortunes visited

upon a third person by the defendant’s acts.’” (quoting

Holmes, 503 U.S. at 268). Even where the ultimate

harm is foreseeable in some general sense, the insertion of intervening parties breaks the chain of proximate causation. Id. at 133-34 (quoting Holmes, 503

9

U.S. at 268-69). The presence of an intermediate

step—harm to a third party that then causes plaintiff’s injury, renders the causation too attenuated. In

other words, the Court rejected causation theories

where harm flows through a butterfly chain.

This principle applies with particular force where

multiple intervening steps involve independent actors

making autonomous decisions. In Hemi Group, LLC

v. City of New York, 559 U.S. 1, 10-11 (2010), the Court

rejected a RICO claim where the causal chain required: (1) defendant’s failure to report cigarette

sales; (2) the state’s inability to collect information;

(3) the state’s failure to provide information to the

city; (4) customers’ decisions not to pay city taxes; and

(5) the city’s resulting revenue loss. The Court held

this chain too attenuated because the “theory of liability rests on the independent actions of third parties

and even fourth parties.” Id. at 15. The key principle

from Hemi is that when the causal chain requires independent decisions by actors not controlled by the defendant, foreseeability evaporates—even if the general outcome might have been predictable. These requirements—that harm be foreseeable, that causation

be direct, and that liability does not flow through the

autonomous choices of third parties—apply with full

constitutional force to Respondents’ claims, as Part II

demonstrates.

Independent of foreseeability, traditional commonlaw principles require direct and immediate causal

connection between defendant’s conduct and plaintiff’s harm, along with proportionate responses to individual conduct. As Lord Francis Bacon observed,

“judgeth of acts by that, without looking to any further

degree.” Bacon, The Elements of the Common Lawes

of England, supra. This directness requirement also

10

prevents liability based on attenuated chains involving multiple actors and complex multilayered interactions precisely like those implicated by Respondents’

claims.

This Court has applied directness requirements to

protect constitutional due process in complex causation scenarios. In Associated General Contractors, 459

U.S. at 532-33, the Court emphasized that well accepted common-law doctrines such as “foreseeability

and proximate cause, directness of injury, [and] certainty of damages,” were “well-accepted common-law

rules.” (footnotes omitted). Further, the intervening

causes doctrine, fundamental to due process causation

requirements, prohibits liability when “‘an intervening force supersedes prior negligence’ and thus breaks

the chain of proximate causation required to impose

liability on the original actor.” Exxon Co., U.S.A. v.

Sofec, Inc., 517 U.S. 830, 835 (1996). This directness

requirement is essential for maintaining the constitutional boundaries on legal liability that protect individual economic freedom. The intervening causes that

saturate Respondents’ causal chain—the emissions of

other nations, natural atmospheric variability, and independent land-use decisions—are precisely the kind

of independent forces that sever directness and bar liability under these principles.

The third requirement is individualization. The

Due Process Clause protects individual rights against

collective liability theories that abandon traditional

requirements for individualized proof of causation.

This individualization requirement is the constitutional guarantee that private parties will not be held

responsible for harms they did not individually and

demonstrably cause. Respondents’ reliance on aggre-

11

gate and statistical causation violates these constitutional protections because it would subject private

parties to liability based on collective activities rather

than specific individual conduct. Respondents themselves have admitted that their claims are “based in

part on ‘fossil fuel use by non-parties and the resulting

emissions.’” Brief for the Petitioners at 35 (quoting

Respondents’ own submissions below). The constitutional causation problem is thus self-evident from the

face of the claims.

Finally, the legal consequences must be proportionate, and not punitive. Legal consequences must bear

a reasonable relationship to a defendant’s identified

individual conduct and the harm it actually caused.

This Court has recognized this as a constitutional

command: the Due Process Clause “prohibits the imposition of grossly excessive or arbitrary punishments

on a tortfeasor.” State Farm Mut. Auto. Ins. Co. v.

Campbell, 538 U.S. 408, 416 (2003); see also Gore, 517

U.S. at 574-75. Proportionality also requires fair notice—defendants must be able to anticipate from existing legal frameworks what conduct may expose

them to liability and the severity of that liability.

Gore, 517 U.S. at 574. These requirements apply to

any legal consequence, compensatory or punitive, that

deprives a private party of property without the individualized causal foundation due process demands.

II.

Respondents’ Claims Fail Each Requirement Due Process Imposes

The constitutional requirements established in

Part I—foreseeability, directness, individualized causation, and proportionality—are not satisfied by Re-

12

spondents’ claims. Each of the liability theories Respondents advance thus independently violates due

process.

A. Respondents’ Multi-Step Causal Chain

Cannot Satisfy the Foreseeability Requirement

Respondents’ theory requires a court to find:

(1) that the Companies’ specific production and marketing decisions (2) contributed some incremental

fraction to global greenhouse gas concentrations

(3) that in turn shifted global climate systems (4) that

in turn worsened specific weather events in Colorado

(5) that in turn caused quantifiable municipal infrastructure costs. Connecting each of these steps is the

emissions of hundreds of nations, natural climate variability, decades of compounding atmospheric physics,

and countless independent third-party decisions. See

Washington Env’t Council v. Bellon, 732 F.3d 1131,

1143-44 (9th Cir. 2013) (finding the causal chain between specific emissions sources and climate-related

injuries “too tenuous” where impacts are “scientifically indiscernible”). This multi-step chain involving

“third persons” (such as energy producers and global

emitters) whose independent decisions break any connection is precisely the type of “remote” causation

Holmes held insufficient. Because Respondent cannot

tie a foreseeable chain of actions to harm, instead relying on speculative chains involving countless intervening actors, its claims fail the standard Holmes reflects—and that the Due Process Clause, through its

incorporation of common-law causation tradition,

makes constitutionally required.

Indeed, climate change represents precisely the

type of unforeseeable consequence that traditional

13

causation doctrine, as illustrated in Palsgraf, was designed to exclude from legal liability. The distinction

between general scientific knowledge and specific legal foreseeability is crucial for protecting individual

liberty through predictable legal standards. While the

companies may understand that fossil fuel use contributes to global emissions, this general knowledge

does not create the specific, individualized foreseeability that due process requires for legal liability. See

Holmes, 503 U.S. at 268 (foreseeability requires “some

direct relation between the injury asserted and the injurious conduct alleged”).

No private energy company could reasonably have

foreseen, at the time of any specific production decision, that it would bear legal responsibility for a particular municipal flood-damage cost decades later.

Abandoning foreseeability requirements for climate

cases would destroy the constitutional protections

that enable energy innovation and development. Energy producers and individual Americans making energy-related decisions would face unlimited liability

for global phenomena beyond their control or reasonable anticipation. This outcome would violate the due

process principles designed to protect individual liberty through predictable legal frameworks.

B. Respondents’ Causal Chain Also Fails

the Directness and Immediacy Requirement

Independent of foreseeability, Respondents’ multistep causal chain cannot satisfy the directness requirement that Part I establishes as a separate and

independently sufficient constitutional bar.

The Companies’ production activities do not directly cause floods or wildfires in Boulder. At most,

14

they—along with a multitude of other actors—may

contribute to a global concentration of greenhouse

gases which interact with atmospheric systems over

decades to alter regional climate patterns, which may

affect weather events, which may cause municipal

costs. See, e.g., Washington Env’t Council, 732 F.3d at

1143-44 (holding the causal chain between local agencies’ failure to regulate five oil refineries and plaintiffs’ climate-change related injuries was “too tenuous” because the refineries had a “scientifically indiscernible” impact on climate change).

Respondents’ causation theory is exactly the type

of tenuous chain theory that fails the directness requirement of due process. The actions of these companies as they relate to energy production do not directly cause climate change but, at most, contribute to

global emissions that interact with complex climate

systems involving countless variables. Indeed, climate change does not directly cause Respondents’ alleged damages, and at most contributes to environmental conditions that may affect the environment

through multiple intervening factors. The attenuation of causation becomes even more pronounced

when examining the nature of the claimed injury itself. A temperature increase of one to two degrees

Fahrenheit does not, on its own, constitute cognizable

legal harm to any specific party. Rather, Respondents’ theory requires multiple attenuated causal steps

beyond temperature change. Other nations’ energy

policies, natural climate variability, technological developments, market forces, and individual consumer

choices all independently influence the global phenomena Respondents attribute to these two defendants—and each independently severs the causal

chain.

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C. Aggregate and Statistical Causation

Theories Violate the Individualized

Proof Requirements That Due Process

Demands

Respondents’ aggregate causation theory abandons

precisely the individualized proof requirement that

Part I establishes as a constitutional floor. Rather

than showing that Petitioners’ specific conduct caused

a specific, quantifiable harm, Respondents rely on collective industry emissions as a proxy for individual

causation—a substitution the Due Process Clause

does not permit.

This Court’s decisions in Burrage v. United States,

571 U.S. 204 (2014), and Gross v. FBL Financial Services, Inc., 557 U.S. 167 (2009), suggest these constitutional parameters. In Burrage, the Court rejected a

“contributing cause” theory that would impose liability where the defendant’s contribution was one factor

among several in producing the ultimate harm, holding instead that legal causation requires a direct butfor link: the harm “would not have occurred” absent

the defendant’s conduct. 571 U.S. at 218-19. The

Court’s decision reflects our constitutional tradition,

not merely statutory interpretation. Id. at 210-11

(but-for causation is a “background principle” of the

legal tradition incorporated into modern law). In

Gross, the Court confirmed that “the ordinary default

rule [is] that plaintiffs bear the risk of failing to prove

their claims,” 557 U.S. at 177 (quoting Schaffer ex rel.

Schaffer v. Weast, 546 U.S. 49, 56 (2005)), and that

departures from this default require clear affirmative

justification. See also Schaffer, 546 U.S. at 56-57. In

an ocean of actors, no one can demonstrate that any

specific party more likely than not caused any specific

16

injury to any particular plaintiff. See Washington

Env’t Council, 732 F.3d at 1144 (“Because a multitude

of independent third parties are responsible for the

changes contributing to [p]laintiffs’ injuries,” the

Court concluded, “the causal chain is too tenuous to

support standing.”).

When fossil fuel producers contribute an infinitesimal fraction to global emissions yet face liability for

worldwide climate impacts through an overexpanded

causation analysis, the legal response is grossly disproportionate to individual conduct and independently violates due process. The constitutional

problem is compounded in the damages context specifically. Unlike prospective relief, compensatory and

punitive damages are a permanent action requiring a

court to determine what fraction of a company’s historical production caused what fraction of a municipality’s weather-derived repair costs. No methodology

exists for that determination, and the absence of any

coherent damages methodology is itself a signal that

this causal theory cannot support liability. See Am.

Elec. Power Co. v. Connecticut, 564 U.S. 410, 428

(2011) (“The expert agency is surely better equipped

to do the job than individual district judges issuing ad

hoc, case-by-case” emissions rulings.).

Even more, no statistical analysis can demonstrate

that Petitioners’ production decisions in any particular year, rather than, for example, China’s energy

plants, other producers, or any of countless contributing factors, more likely than not caused any particular flood event in Boulder County. The global climate system involves millions of variables and individual decisions across decades or centuries. See Jonathan H. Adler, Warming Up to Climate Change Liti-

17

gation, 3 Va. L. Rev. 63, 67-69 (2007) (discussing challenges of establishing causation in climate litigation

where harms result from cumulative effects of countless individual decisions and emission sources, and

the global nature of emissions). Subjecting any individual defendant to liability based on statistical contribution to this global phenomenon abandons the individualized proof that Burrage and Gross reflect as a

background constitutional principle—one embedded

in due process tradition and one that Respondents

cannot satisfy. See also Juliana v. United States, 947

F.3d 1159, 1169-70 (9th Cir. 2020) (acknowledging

“many of the emissions causing climate change happened decades ago or come from foreign and non-governmental sources”).

D. Respondents’ Disproportionate, Retroactive, and Punitive Damages Claims

for Lawful, Federally Authorized Conduct Independently Violate Due Process

Respondents’ theories independently violate the

proportionality and fair-notice requirements framework this Court established in Gore and State Farm.

In Gore, 517 U.S. at 575, the Court held that due

process prohibits awards that are “grossly excessive”

relative to the defendant’s conduct. The Court’s analysis emphasizes that constitutional due process requires reasonable proportionality between legal consequences and individual conduct. Gore identified

three guideposts for evaluating the constitutionality

of punitive damage awards: (1) the degree of reprehensibility of the defendant’s conduct; (2) the ratio of

the punitive award to the actual or potential harm suffered by the plaintiff; and (3) the difference between

the punitive award and the civil penalties authorized

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or imposed in comparable cases. 517 U.S. at 574-75.

State Farm reinforced these guideposts and made

clear that they are constitutional requirements, not

mere factors in a balancing test: “The Due Process

Clause of the Fourteenth Amendment prohibits the

imposition of grossly excessive or arbitrary punishments on a tortfeasor.” 538 U.S. at 416.

Gore identified several factors relevant to reprehensibility, including whether the conduct “evinced an

indifference to or a reckless disregard of the health or

safety of others,” whether the “conduct involved repeated actions,” and whether “the harm was the result

of intentional malice, trickery, or deceit, or mere accident.” 517 U.S. at 576-77. Petitioners produced and

sold fossil fuels—a product that was legal, federally

regulated, urged by government policy, and upon

which is essential to the American economy and

American consumers. The federal government did not

merely permit fossil fuel production—it authorized

drilling on federal lands and waters, provided tax incentives for exploration and production, contracted for

fuel for the Department of Defense, and generally

made domestic energy production a cornerstone of national security policy. Conduct the government has

authorized, subsidized, and promoted across administrations cannot be characterized as reprehensible to

justify massive punitive sanctions. Gore, 517 U.S. at

579 (conduct involving “no deliberate false statements, acts of affirmative misconduct, or concealment

of evidence of improper motive” is at the low end of the

reprehensibility scale). The Court emphasized in

State Farm that punitive damages may not be used to

punish defendants for lawful out-of-state conduct or

for conduct that did not harm the plaintiff, 538 U.S. at

422-23—yet Respondents’ punitive theory is precisely

19

a vehicle for punishing the Companies for production

activity spanning the globe and across decades, nearly

all of which bore no demonstrable relationship to any

specific harm in Colorado.

Because Respondents cannot establish what fraction of its flood and wildfire costs are attributable to

Petitioners’ specific actions rather than natural climate variability or the actions of other parties, the

compensatory award itself has no basis. The Court in

Gore cautioned that “[e]lementary notions of fairness

enshrined in our constitutional jurisprudence dictate

. . . the severity the penalty that a State may impose,”

517 U.S. at 579, and in State Farm held that “ratios

greater than those [the Court] ha[s] previously upheld

may comport with due process where ‘a particularly

egregious act has resulted in only a small amount of

economic damages.’” 538 U.S. at 425 (quoting Gore,

517 U.S. at 582).

Respondents’ compensatory damages claim suffers

the same constitutional deficiency as its punitive

claim, and for the same reason. A compensatory

award is constitutionally grounded in the proposition

that a defendant caused an identified harm at an identified magnitude. Here, because Respondents cannot

establish what fraction of municipal costs are attributable to any individual defendant’s specific conduct rather than the emissions of millions of other

global actors, any award framed as “compensatory”

necessarily functions as a punitive sanction. It punishes the defendant not for causing Respondents’

harm solely by participating in the fossil fuel industry.

An award untethered from individual causation is not

compensatory in any constitutional sense; it is a penalty imposed on a defendant for its share of an industry. Gore and State Farm’s proportionality framework

20

applies with equal force to such awards. See State

Farm, 538 U.S. at 423 (“a defendant should be punished for the conduct that harmed the plaintiff, not for

being an unsavory individual or business”).

Respondents’ damages claims also reach back to

production and marketing decisions made across several decades—many of which occurred long before any

court recognized any type of climate change tort claim;

long before current climate attribution science existed

as a legal tool; and long before any regulatory or legal

framework put private energy companies on notice

that their federally permitted activities might expose

them to state tort damages. This retroactive imposition of liability constitutes an independent due process violation regardless of whether the underlying

causation theory is permitted to proceed.

In Eastern Enterprises v. Apfel, 524 U.S. 498

(1998), a majority of the Court expressed serious constitutional concern about retroactive liability of this

magnitude. The plurality struck down the Coal Industry Retiree Health Benefit Act as a regulatory taking in part because it imposed “severe retroactive liability on a limited class of parties that could not have

anticipated the liability” and that this retroactivity

raised concerns because it “deprive[d] citizens of legitimate expectations and upset settled transactions.”

Id. at 533 (quoting General Motors Corp. v. Romein,

503 U.S. 181, 191 (1992)). Justice Kennedy, concurring in judgment, also recognized that imposing liability for conduct that occurred before any legal duty existed raises serious constitutional concerns, even if

their analytical frameworks differed. Id. at 547-49

(Kennedy, J., concurring in the judgment and dissenting in part) (concluding that the Coal Act must be in-

21

validated as violative of due process based on our nation’s history of “distrust” with retroactive statutes

and that stating that due process protections “must be

understood to incorporate our settled tradition

against retroactive laws of great severity”). The core

constitutional principle is clear: individuals and private parties are entitled to rely on existing law in ordering their affairs, and imposing substantial liability

based on legal theories that did not exist when the

conduct occurred violates the fair notice guarantee

embedded in due process.

The retroactivity problem is particularly acute

here. Climate change tort theories—the proposition

that private energy companies are liable in state court

for the diffuse global harms of climate change—did

not exist as a recognized legal claim when Petitioners

made the production decisions Respondents challenge. The first serious legal scholarship proposing

such liability emerged in the late 1990s and early

2000s. See Jonathan H. Adler, Standing in the Hot

Seat: Climate Change Litigation, 8 Engage: J. Federalist Soc’y Prac. Groups No. 1 (2007) (surveying the

emergence of climate tort theory as a novel legal proposition). The Colorado trial court did not deny the

Companies’ motion to dismiss until 2024 and no court

had ever imposed damages liability on a private energy company for climate change at the time of the

challenged conduct. The Companies therefore conducted their operations under federal regulatory

frameworks that sanctioned fossil fuel production,

with no indication that such production would expose

them to state-law tort damages of the magnitude Respondents seek.

The retroactivity problem is compounded by the aggregate causation structure. Because Respondents

22

cannot identify what fraction of their claimed damages results from any one defendant’s historical emissions in any particular year, any damages award necessarily rests on an arbitrary analysis on a global

scale and across decades of lawful commerce. The

combination of retroactive liability and arbitrary apportionment falls squarely within the due process prohibition recognized in Eastern Enterprises. 524 U.S.

at 528-29 (striking down liability that was “severe,”

“retroactive,” imposed on “a limited class of parties,”

and based on conduct occurring under a different legal

regime). The Companies’ situation is even more constitutionally troubling than the coal company’s in

Eastern Enterprises: not only is the liability retroactive, but it is based on causal theories that did not exist, imposed for conduct that was affirmatively authorized and subsidized, measured by an aggregate

global phenomenon rather than any identified specific

harm, and potentially unlimited in scope.5

5 Market share liability—the doctrine introduced in Sindell v.

Abbott Laboratories, 26 Cal. 3d 588 (1980)—cannot bridge

Respondents’ causation gap. Sindell arose from a specific,

narrow evidentiary problem: plaintiffs injured by DES, a

chemically identical drug manufactured by hundreds of

companies, could not identify which manufacturer’s specific

product their mother had ingested decades earlier. The causal

mechanism was scientifically established; only the tortfeasor’s

identity was unknown. Courts have consistently refused to

extend the doctrine beyond that context. See Hamilton v. Beretta

U.S.A. Corp., 96 N.Y.2d 222, 240-41 (2001) (rejecting market

share for handguns—products not fungible and marketing

practices not uniform); Santiago v. Sherwin Williams Co., 3 F.3d

546, 552 (1st Cir. 1993) (rejecting for lead paint); Jefferson v.

Lead Indus. Ass’n, Inc., 106 F.3d 1245, 1253 (5th Cir. 1997)

(market share theory “would create too much risk that a

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III.

Respondents’ Theory Would Devastate

Domestic Energy Production And Undermine Individual Economic Liberty.

If Respondents’ causation theory is accepted—if a

private energy company’s fractional contribution to

global greenhouse gas emissions is sufficient to establish state-court liability for climate-related municipal

costs—then every oil and gas producer, mining operation, natural gas distributor, and petroleum refiner

faces unlimited retroactive liability in every jurisdiction where a weather event has caused municipal

costs. This Court has already recognized that courts

are ill-suited to serve as ad hoc greenhouse gas regulators. See American Electric Power, 564 U.S. at 428

(“The expert agency is surely better equipped to do the

job than individual district judges issuing ad hoc,

case-by-case” greenhouse gas rulings.); see also Juliana, 947 F.3d at 1175 (“[T]he plaintiffs’ case must be

made to the political branches or to the electorate at

large,” because courts lack the institutional competence to manage climate policy.). Allowing these state

tort claims to proceed on Respondents’ causation and

damages theories produces the same result through a

different door. Here, the consequences of altering national energy policy by accepting Respondents’ claims

illustrate the fundamental problem with climate-causation litigation. Because market share theory, if

adopted, would apportion that unlimited exposure

across every participant in the domestic energy industry, the potential liability is effectively uncapped.

defendant will be held liable for more harm than it caused, or,

worse yet, without causing any harm at all to the plaintiff”).

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If Respondents prevail, the consequences will not

be confined to Colorado. Many climate-change cases

are pending across the nation, each resting on the

same speculative causal chain and each seeking the

same open-ended damages. If cases of this nature

were permitted to continue flooding our judicial system, with each asserting a variation on the same causation theory Respondents’ advance, the economic

consequences would devastate American energy production and the individual liberty it enables. The economic stakes are not abstract. When liability exposure is unlimited, retroactive, and uninsurable, investment in domestic energy production, exploration,

and development stops. The entrepreneurs and independent producers who have driven American energy

abundance cannot survive untethered liability measured by an entire global industry. See Michelle J.

White, Asbestos and the Future of Mass Torts, 18 J.

Econ. Persp. 183, 184-87 (2004) (documenting how expanded and unpredictable liability theories in asbestos litigation created over $200 billion in liabilities

and bankrupted more than 100 companies despite

limited evidence of individual causation in many

cases). Unlimited climate liability would prevent individual entrepreneurs and innovators from developing America’s vast energy resources. See W. Kip Viscusi, The Dimensions of the Product Liability Crisis,

20 J. Legal Stud. 147, 148-58 (1991) (expanded and

unpredictable liability regimes cause market withdrawals and cost increases that harm consumers).

Respondents’ counsel has publicly acknowledged

that “[t]ort liability is an indirect carbon tax” and that

the purpose of this litigation is to accomplish through

state court judgments what environmental advocates

have been unable to accomplish through the political

25

branches. Inst. for Energy Research, Supreme Court

Will Hear a Climate Case Against Oil Companies

(Feb. 25, 2026). See American Electric Power, 564

U.S. at 427 (Congress and the Executive are the

proper forums for “complex balancing” of climate policy considerations, not courts). That is not a tort

claim—it is an admission that this litigation is policy

by other means. The political branches are the constitutionally designated forums for making the fundamental policy choices about energy production, climate risk, and economic development that Respondents’ claims implicate. When state tort liability becomes the mechanism for making those choices,

through the accumulation of case-by-case judicial determinations that private energy companies are

forced to continuously defend, judicial power expands

far beyond its constitutional domain. See Juliana, 947

F.3d at 1171 (courts cannot resolve disputes “entrusted, for better or worse, to the wisdom and discretion of the executive and legislative branches”).

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CONCLUSION

The Due Process Clause requires that liability rest

on a direct, foreseeable, and proportionate causal connection between a specific defendant’s conduct and a

plaintiff’s specific harm. Respondents’ claims satisfy

none of those requirements. The causal chain that

somehow stretches from energy production decisions

to municipal damages is far too attenuated and too

saturated with independent intervening causes to

support liability. If this causation theory is blessed,

the potential punitive damages and retroactive liability that may result would likely devastate America’s

energy development and harm all Americans who rely

on abundant energy to make their lives better.

Respectfully submitted,

F RANK D. G ARRISON

Counsel of Record

T YLER F RY

Pacific Legal Foundation

3100 Clarendon Blvd.,

Suite 1000

Arlington, VA 22201

202.888.6881

fgarrison@pacificlegal.org

Counsel for Amicus Curiae Pacific Legal Foundation

MAY 2026