Investigation, Climate Change Lawsuits, and the Supreme Court

Climate change lawsuits against oil companies now number in the dozens across the United States, brought by states, cities, counties, and tribes alleging that fossil fuel producers knew for decades their products would warm the planet and deceived the public anyway. Their entire future turns on one case: on February 23, 2026, the U.S. Supreme Court agreed to decide in Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County whether federal law preempts these state-court claims. A ruling for the oil companies could shut down roughly three dozen similar suits nationwide.¹

The Supreme Court Case That Decides Everything

The Boulder case, No. 25-170, began as a 2018 suit by Boulder, Colorado, officials against Suncor Energy and ExxonMobil, alleging the companies harmed residents’ health, safety, and welfare through the production, promotion, and sale of fossil fuels. In May 2025, the Colorado Supreme Court held the suit could go forward in state court under state-law theories. Suncor and ExxonMobil appealed, arguing that claims tied to interstate and international emissions belong under federal authority.²

The Supreme Court also directed both sides to brief whether it has jurisdiction at this stage. That means the Court could dismiss the case without reaching preemption.¹³⁴ Amicus briefs have poured in from the U.S. government, 26 Republican-led states, the Chamber of Commerce, the American Petroleum Institute, and multiple conservative legal organizations.

What the Lawsuits Actually Claim

Earlier climate suits relied on public nuisance theories and largely failed in federal court. Newer cases shifted the theory toward deception, alleging fossil fuel companies misled the public about the dangers of their products while their own scientists confirmed the link between emissions and warming.⁵ Today’s suits span public and private nuisance, trespass, products liability and failure to warn, consumer fraud, unjust enrichment, civil conspiracy, and in some cases federal RICO violations.⁶

Framing the cases around deception rather than emissions is deliberate. It keeps them in state court under state consumer protection and fraud statutes. The industry has consistently pushed the other direction, trying to move the cases into federal court where preemption arguments carry more weight and where several earlier climate claims were dismissed.⁷

What Congressional Investigators Found

A joint April 2024 staff report from the Senate Budget Committee and the House Oversight Committee, titled Denial, Disinformation, and Doublespeak, concluded the industry had known since at least the 1960s that burning fossil fuels causes climate change.⁸ The report found companies promoted natural gas as a clean “bridge fuel” while internally acknowledging its lifecycle emissions could be as harmful as coal, publicly backed the Paris Agreement while privately calling net-zero targets incompatible with their business plans, and lobbied against carbon pricing and methane rules they claimed to support, often through trade associations.⁹ Exxon, Chevron, Shell, BP, the API, and the Chamber of Commerce withheld or heavily redacted more than 4,000 subpoenaed documents.

Where the Major Cases Stand Now

Honolulu v. Sunoco

The Honolulu case, filed in 2020, is the most advanced state climate accountability suit. In January 2025 the U.S. Supreme Court denied the oil companies’ petition for certiorari, letting the Hawaii Supreme Court’s 2023 ruling stand.¹⁰ In January 2026 a Hawaii trial court denied the defendants’ summary judgment motions on personal jurisdiction, statute of limitations, and geographic scope, clearing the case toward trial.¹¹ The State of Hawaii’s separate suit against BP and others is stayed pending the Boulder decision.¹²

California

In September 2023, California Attorney General Rob Bonta sued ExxonMobil, Shell, Chevron, ConocoPhillips, BP, and the American Petroleum Institute in San Francisco Superior Court, alleging public nuisance, products liability, and violations of state advertising and business laws.¹³ In 2025 a judge coordinated the state’s case with multiple local government suits.⁷ In May 2026, a California appellate court reversed a lower ruling that had dismissed Citgo Petroleum from the coordinated litigation.¹⁴

Massachusetts

Massachusetts Attorney General Maura Healey opened an investigation into ExxonMobil in April 2016 and formally sued in October 2019 under the state consumer protection act, alleging misleading advertising and investor disclosures about climate risks.¹⁵ The case is pending in Massachusetts Superior Court, with discovery disputes into 2026 over internal Exxon documents and the company’s engagements with McKinsey & Company.¹⁶

Washington: Insurance Premiums and a Wrongful Death Claim

Two 2025 filings in Washington test new theories. In November 2025, two homeowners filed Kennedy v. Exxon Mobil Corp. in the Western District of Washington, a proposed class action alleging that decades of climate deception drove up homeowner insurance premiums. It brings federal RICO claims for a nationwide class and Washington consumer protection and fraud claims for a state subclass.¹⁷

In May 2025, Misti Leon filed what experts describe as the first wrongful death lawsuit against fossil fuel companies over climate change. Her mother, Juliana Leon, died of hyperthermia on June 28, 2021, during the Pacific Northwest heat dome, with an internal body temperature of 110 degrees Fahrenheit.¹⁸ The suit, filed in King County Superior Court against BP, Chevron, ConocoPhillips, ExxonMobil, Phillips 66, Shell, and Olympic Pipeline, alleges product liability and public nuisance. Defendants removed it to federal court, but in October 2025 a federal judge sent it back to state court. As of May 2026 motions to dismiss are pending, and in April 2026 the state court denied the defendants’ bid to stay the case.¹⁹

Louisiana: A $745 Million Verdict, Then a Federal Detour

In April 2025, a Louisiana jury awarded $745 million against Chevron for land loss, contamination, and abandoned equipment from historic oil field operations, in a case brought by Plaquemines Parish under the state’s coastal management law. On April 17, 2026, the Supreme Court unanimously ruled in Chevron USA Inc. v. Plaquemines Parish that the case could be removed to federal court under the federal officer removal statute, because Chevron’s wartime crude oil production was closely tied to a federal contract to refine aviation fuel for the military. The Court vacated the state court judgment and sent the case back for further proceedings in federal court without addressing the merits of the verdict.²⁰

The Federal Effort to Shut These Suits Down

In April 2025, President Trump signed an executive order titled “Protecting American Energy from State Overreach,” directing the Attorney General to identify and challenge state and local climate laws, regulations, and lawsuits considered unconstitutional or preempted by federal law. The order described state climate suits as potentially imposing “crippling damages” on the energy sector and singled out New York’s and Vermont’s climate superfund laws as “extortion.”²¹

The Justice Department has since filed a series of suits against states:

Michigan and Hawaii were sued in 2025 to preemptively block their climate liability cases. Federal courts dismissed both for lack of standing, finding the government’s claimed injuries too speculative. The Hawaii case was dismissed with prejudice in April 2026; the Michigan case was dismissed in January 2026.²²
New York and Vermont were sued in May 2025 over their climate superfund laws. The DOJ filed summary judgment motions in August and September 2025, and both cases remain pending.²³²⁴
Minnesota was sued in May 2026 in an attempt to stop its 2020 climate fraud case against ExxonMobil, Koch Industries, and the API.²⁵

Federal courts have so far been unreceptive. Legal scholars describe the administration’s arguments as thin, noting the state cases center on consumer fraud and deception rather than the regulation of emissions.²⁶

The EPA Endangerment Repeal May Backfire on the Industry

On February 13, 2026, the EPA finalized the repeal of the 2009 endangerment finding, which had established that greenhouse gas emissions threaten public health and welfare under the Clean Air Act. The agency also eliminated carbon emissions standards for motor vehicles.²⁷ On February 18, 2026, the Sierra Club and 16 other groups sued in the D.C. Circuit, arguing the repeal contradicts Massachusetts v. EPA, the 2007 ruling that greenhouse gases qualify as air pollutants under the Clean Air Act.²⁸

The repeal cuts against the industry’s own strategy. Since 2011, when the Supreme Court held in American Electric Power v. Connecticut that the Clean Air Act displaced federal common-law nuisance claims against emitters, companies have leaned on the existence of federal regulatory authority to argue that state climate suits are preempted. By disclaiming that authority, the EPA may have weakened the preemption defense and given states more room to litigate and regulate.²⁸

Legislative Shields at the Federal and State Level

On April 17, 2026, Senator Ted Cruz and Representative Harriet Hageman introduced the “Stop Climate Shakedowns Act of 2026” in both chambers. The bill would grant oil and gas companies broad immunity from climate-related emissions suits, dismiss pending climate accountability cases, void existing state climate superfund laws, and block future actions by state, local, or federal entities.²⁹ Observers see the bill as unlikely to reach 60 Senate votes, though it could be attached to must-pass legislation or moved through budget reconciliation.³⁰

Utah and Iowa moved faster. Utah’s HB 222, signed by Governor Spencer Cox in late March 2026, bars civil and criminal liability for climate-related emissions except where a defendant violated a specific enforceable emission limit or permit.³¹ Iowa’s HF 2527, signed by Governor Kim Reynolds on April 30, 2026, prohibits liability for climate damages caused by emissions from agricultural, petroleum, or renewable fuel sources.³² Both laws draw on model language circulated by a group called Consumers Defense under the name “Energy Freedom Act.”³³

What These Suits Are Not

Two prominent efforts against fossil fuel-driven climate harm sit outside the current wave of state accountability suits. The youth case Juliana v. United States, filed in 2015 in Oregon, ended in the federal court system on March 24, 2025, when the Supreme Court denied certiorari after the Ninth Circuit twice directed dismissal for lack of Article III standing. The dismissal was without prejudice, and in September 2025 fifteen original plaintiffs filed a petition with the Inter-American Commission on Human Rights, which can issue only recommendations, not enforceable orders.³⁴³⁵ And the International Court of Justice’s July 2025 advisory opinion, which found states have binding duties to act on emissions and recognized a human right to a clean environment, is not directly enforceable in U.S. courts, though it may influence domestic litigation.³⁶³⁷

The Scale and What to Watch

As of June 2025, more than 3,000 climate-related cases had been filed across 55 national jurisdictions and 24 international or regional bodies, according to the United Nations Environment Programme. The United States accounts for roughly 65 percent. The total has doubled since 2020.³⁸ About 27 percent of the 226 new cases filed in 2024 sought to resist or delay climate policy, and 88 percent of those resistance cases were filed in U.S. courts.³⁹

The Boulder decision, expected by mid-2027, will set the ceiling. If the Supreme Court finds federal law preempts these state-court claims, it closes the door on a strategy that dozens of governments have pursued for close to a decade. If it rules the other way or dismisses on jurisdictional grounds, Honolulu’s case heads for trial, California and Massachusetts continue their fights, and the newer theories from Washington move forward.

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