ExxonMobil and Suncor Climate Lawsuit Heads to the Supreme Court

The ExxonMobil and Suncor climate lawsuit is a case brought in 2018 by Boulder County, the City of Boulder, and San Miguel County against ExxonMobil and Suncor Energy, accusing the companies of concealing what their own scientists knew about climate change while continuing to produce and sell fossil fuels that damaged Colorado communities. After eight years of procedural fights, the U.S. Supreme Court agreed on February 23, 2026, to hear the case, with oral argument expected in fall 2026 and a decision likely by mid-2027.¹

Who Sued and What They Want

The three Colorado local governments filed their complaint on April 17, 2018, in Boulder County District Court, naming Suncor Energy (U.S.A.) Inc., Suncor Energy Sales Inc., and ExxonMobil Corporation as defendants.² The suit brings state common-law claims for public nuisance, private nuisance, trespass, unjust enrichment, and civil conspiracy, along with a claim under the Colorado Consumer Protection Act.³

The plaintiffs say they have already spent millions responding to wildfires, flooding, drought, and damage to public infrastructure tied to a warming climate, and they want the companies to pay those costs rather than leaving them to local taxpayers.⁴ Categories of damages include wildfire response and mitigation, flood control and drainage repair, drought management, building repairs, and broader climate adaptation planning.⁵ The complaint does not name a total dollar figure.

One boundary matters here. The plaintiffs are not asking any court to shut down oil and gas operations, cap emissions, or set energy policy. They are asking for money damages tied to the companies’ past conduct.

The “Knew and Concealed” Allegations

Much of the factual weight of the case rests on ExxonMobil’s own internal research. A 2023 study in the journal Science, led by Harvard researchers, analyzed 32 internal ExxonMobil documents and 72 peer-reviewed publications produced or sponsored by the company’s scientists between 1977 and 2003. It found that Exxon’s internal climate projections were remarkably accurate, predicting warming of roughly 0.20°C per decade, with 63% to 83% of projections matching observed temperatures and an average skill score of 72%.⁶

Exxon’s scientists dismissed the possibility of a coming ice age, predicted human-caused warming would be detectable around the year 2000, and estimated the carbon budget needed to stay below 2°C.⁷ The researchers identified what they called a “systematic discrepancy” between that internal knowledge and the company’s public messaging. Starting in the late 1980s and early 1990s, they said, Exxon publicly cast doubt on climate science, overemphasized uncertainties, and denigrated the very climate models its own scientists were using.⁶

Earlier reporting on internal documents surfaced around 2015 showed Exxon senior scientist James Black telling the company’s management committee in 1977 that there was a “general scientific agreement” that burning fossil fuels was influencing the climate. By 1978, Black warned that doubling atmospheric CO2 could raise global temperatures by two to three degrees Celsius. The company then spent over $1 million on a project to measure ocean CO2 absorption.⁸

ExxonMobil has rejected the characterization that its conduct was deceptive. A company spokesperson said the documents were publicly available and have been misrepresented, and that the company has long been involved in climate research.⁸

Eight Years Fighting Over Which Court Hears the Case

The defendants tried repeatedly to move the case to federal court, arguing that claims touching global climate change belong there. The U.S. District Court for the District of Colorado sent it back to state court in 2019, and the Tenth Circuit affirmed that remand in February 2022, rejecting all six grounds the companies offered for federal jurisdiction.⁹ The U.S. Supreme Court declined to intervene on the jurisdictional question in April 2023.³

Back in Boulder County District Court, the defendants moved to dismiss on multiple grounds. On June 21, 2024, the trial court largely denied those motions, letting the common-law claims proceed. It rejected arguments based on federal preemption, the foreign affairs doctrine, separation of powers, the dormant Commerce Clause, due process, and the First Amendment. The court did dismiss Suncor’s Canadian parent for lack of personal jurisdiction, and dismissed the Colorado Consumer Protection Act claim without prejudice as untimely.³

The Colorado Supreme Court’s Preemption Ruling

The defendants took the preemption question to the Colorado Supreme Court on interlocutory review. On May 12, 2025, a 5-2 majority ruled that federal law does not preempt the plaintiffs’ state common-law claims.⁵

The court’s reasoning ran along several lines. It held that the Clean Air Act had displaced federal common law on climate-related pollution, so federal common law could no longer serve as a basis to preempt state claims. It found no form of Clean Air Act preemption applied: no express preemption provision exists in the statute, Congress did not occupy the entire field (the court pointed to savings clauses preserving state-law remedies), and the plaintiffs’ damages claims did not conflict with federal law because they sought money rather than an injunction against operations.⁵ The court emphasized that the lawsuit targets “upstream producers for harms stemming from the production and sale of fossil fuels” rather than trying to regulate emissions directly.¹⁰

Justices Samour and Boatright dissented.¹¹ The majority sent the case back to the trial court, noting it took “no opinion on the ultimate viability” of the claims on the merits.⁵

What the Supreme Court Will Decide

The fossil fuel companies filed their petition for certiorari on August 8, 2025, presenting the question: “Whether federal law precludes state-law claims seeking relief for injuries allegedly caused by the effects of interstate and international greenhouse-gas emissions on the global climate.”¹ Their brief argues that claims about interstate pollution injuries are “inherently federal,” that Colorado wrongly let state law fill a gap left by the Clean Air Act’s displacement of federal common law, and that the litigation interferes with national energy policy and foreign affairs.¹²

The Supreme Court granted certiorari on February 23, 2026, and added a second question of its own: whether the Court has statutory and Article III jurisdiction at all, since the Colorado ruling was interlocutory rather than a final judgment.¹³

Petitioners filed their merits brief on May 14, 2026. The respondents’ brief is due July 27, 2026. Argument is expected in fall 2026, with a decision likely by mid-2027.¹

A key reason the Court took the case is a split among appellate courts. The Second Circuit, in City of New York v. Chevron Corp. (2021), held that state tort law cannot be used to impose liability for global greenhouse gas emissions, calling climate change a “uniquely international problem of national concern” that is “beyond the limits of state law.”¹⁴ The Colorado Supreme Court and the Hawaii Supreme Court reached the opposite conclusion, treating the cases as state-law claims about deceptive marketing and production rather than attempts to regulate emissions.

Support has poured in on both sides. The U.S. Solicitor General filed an amicus brief backing the companies, arguing the Clean Air Act preempts Boulder’s claims and that Colorado’s territorial sovereignty does not reach globally mixed emissions.¹⁵ Alabama and 25 other states, the American Petroleum Institute, the U.S. Chamber of Commerce, the National Association of Manufacturers, members of Congress including House Majority Leader Steve Scalise and Senator Ted Cruz, and former foreign affairs officials including Michael Pompeo and Nikki Haley also filed briefs supporting the companies.¹⁶

A New Complication: EPA Rescinding the Endangerment Finding

An unusual tension has developed inside the federal position. On February 18, 2026, the EPA finalized the rescission of the 2009 Greenhouse Gas Endangerment Finding, which had been the legal foundation for federal regulation of greenhouse gas emissions from motor vehicles under the Clean Air Act. The agency called the action the “single largest deregulatory action in U.S. history” and said the Clean Air Act does not authorize the EPA to regulate greenhouse gas emissions from new motor vehicles.¹⁷

That position sits awkwardly next to the companies’ preemption defense, which rests on the idea that the Clean Air Act gives the EPA authority over greenhouse gases and that federal regulation is the exclusive framework. If the EPA itself now says it lacks that authority, the preemption argument gets harder. Legal analysts at Skadden noted that preemption arguments “are likely to fail if EPA does not have the authority to regulate GHG emissions under the CAA.”¹⁸ How the Supreme Court will handle that tension is one of the open questions heading into argument.

Why the Ruling Reaches Far Beyond Boulder

More than 30 lawsuits filed by cities, counties, states, and tribal governments target fossil fuel companies over climate damages and alleged deception. Attorneys general in at least 12 jurisdictions, including California, Massachusetts, Minnesota, Connecticut, Delaware, Vermont, Hawaii, and the District of Columbia, have brought their own climate-related actions.¹⁹ Honolulu’s case, filed in 2020, survived a Supreme Court certiorari denial in January 2025 and is moving toward trial after a Hawaii trial court denied multiple summary judgment motions in January 2026.²⁰

The federal government has moved directly against state climate suits. In May 2026, the Department of Justice filed a complaint against Minnesota seeking to block its climate fraud lawsuit, arguing the state was attempting to “set national energy policy” in violation of federal preemption and the Constitution. The DOJ filed similar suits against Hawaii, Michigan, New York, and Vermont in 2025, though the Hawaii and Michigan cases were dismissed for lack of standing.²¹

Because Suncor Energy v. County Commissioners of Boulder County will decide whether federal law preempts state common-law climate claims as a category, the ruling could determine whether any of these cases proceed. A ruling for the companies would effectively shut down most climate accountability litigation nationwide. A ruling for Boulder would clear the way for cases across the country to move toward trials on the merits for the first time.

1
SCOTUSblog. Suncor Energy Inc. v. County Commissioners of Boulder County
2
Center for Climate Integrity. Boulder, CO
3
Climate Case Chart. Board of County Commissioners of Boulder County v. Suncor Energy U.S.A. Inc.
4
Boulder County. Colorado Supreme Court Advances Historic Climate Accountability Case Against ExxonMobil and Suncor
5
Justia. County Commissioners of Boulder County v. Suncor Energy U.S., Inc.
6
Science. Assessing ExxonMobil’s Global Warming Projections
7
Harvard Gazette. Harvard-Led Analysis Finds ExxonMobil Internal Research Accurately Predicted Climate Change
8
Scientific American. Exxon Knew About Climate Change Almost 40 Years Ago
9
U.S. Court of Appeals for the Tenth Circuit. Board of County Commissioners of Boulder County v. Suncor Energy (U.S.A.) Inc.
10
Colorado Bar Association. In Re County Commissioners of Boulder County v. Suncor Energy USA, Inc.
11
Colorado Judicial Branch. In Re County Commissioners of Boulder County v. Suncor Energy USA, Inc.
12
U.S. Supreme Court. Suncor Energy Petition for Certiorari
13
U.S. Supreme Court. Docket for No. 25-170
14
vLex. City of New York v. Chevron Corp.
15
U.S. Supreme Court. United States Amicus Brief in Suncor v. Boulder
16
U.S. Supreme Court. Docket for No. 25-170
17
U.S. Environmental Protection Agency. Final Rule Rescission of Greenhouse Gas Endangerment
18
Skadden. The Future of Climate Change Regulation
19
Center for Climate Integrity. Hawaii Sues Big Oil for Climate Deception
20
Climate Case Chart. City and County of Honolulu v. Sunoco LP
21
U.S. Department of Justice. Justice Department Files Complaint Against Minnesota