Suncor Energy Inc. v. County Commissioners of Boulder County and the Future of Climate Activism

By Sharon Chou ’28

In the next decade, the rise in the global average temperature from pre-industrial levels will likely exceed the United Nations Paris Agreement’s ambitious 1.5°C target, which scientists consider key to avoiding some of climate change’s most catastrophic effects. (1) However, achieving the Paris Agreement’s primary goal of limiting global warming to 2°C is still possible. (2) Every degree of warming prevented could save lives, spare economies, and avoid devastating climatic tipping points. (3) Climate activists are attempting to lower emissions in a variety of ways, including through climate lawsuits. However, a case on the Supreme Court’s docket this year may jeopardize those lawsuits in state courts. If the Supreme Court forecloses state-level climate litigation in Suncor Energy Inc. v. County Commissioners of Boulder County, courts as a whole could be eliminated as an avenue for climate activism. 

Lawsuits against fossil fuel companies have been occurring for decades, but climate litigation in this area continues to evolve. (4) These lawsuits attempt to hold fossil fuel companies financially responsible for the damages of the climate crisis they have contributed to. (5) During the first wave of litigation in the early 2000s, a small number of states, localities, and proposed classes sued fossil fuel companies mainly under claims of public nuisance, (6) a common-law cause of action. In this context, the plaintiffs’ argument is that fossil fuel companies have compromised the general right to atmospheric stability through their emissions. (7) The majority of these lawsuits were brought in federal court, where they almost all immediately failed. Federal judges dismissed these claims, stating that they presented questions more suitable for the executive or legislative branches to decide.  

In the second, larger wave of litigation against fossil fuel companies starting in the 2010s and stretching into the present, plaintiffs have shifted their focus to state courts and moved beyond public nuisance claims. (8) Some suits accuse these companies of fraud or deception, claiming that the industry was aware of the harms caused by its products and deliberately concealed these harms from the public. (9) Many plaintiffs seek financial compensation for the damages of climate change. (10) 

Before courts tackle the substance of these cases, they must first reckon with the issue of the appropriate venue. (11) Legal battles over whether these lawsuits should be heard in state or federal courts have been playing out across the country, with fossil fuel companies vying to move litigation to the federal level. Other than a narrow, procedural ruling in 2021, the Supreme Court has declined multiple requests to review lower court decisions over the past few years. (12) (13) It has chosen to stay out of the debate—until now. 

Suncor Energy Inc. v. County Commissioners of Boulder County

Suncor Energy Inc. v. County Commissioners of Boulder County (pending) is a climate accountability lawsuit filed under state law by the City of Boulder and Boulder County against Suncor Energy and ExxonMobil. The plaintiffs accuse the fossil fuel companies of knowingly contributing to climate change by producing and selling fossil fuels while concealing the dangers associated with their use. The case involves claims of public nuisance, private nuisance, trespass, unjust enrichment, and deceptive trade practices under the Colorado Consumer Protection Act. The City of Boulder and Boulder County seek monetary compensation for past and future damages as well as the cost of climate mitigation. (14) 

Suncor and Exxon argue the state lawsuit should be dismissed because it seeks to regulate greenhouse gas emissions and is therefore preempted by federal environmental laws like the Clean Air Act and the structure of the U.S. Constitution. (15) In their petition to the Supreme Court in August 2025, they claimed that “as the Court has recognized for over a century, the structure of our constitutional system does not permit a State to provide relief under state law for injuries allegedly caused by pollution emanating from outside the State.” (16) The companies argue climate change is a global issue, so either the federal courts or Congress should act instead. (17)

However, Boulder claims the local governments “are not asking [the] Court to stop or regulate the production of fossil fuels” and “emissions in Colorado or elsewhere; they ask only that Defendants help remediate the harm caused by their intentional, reckless and negligent conduct.” A Colorado trial court and the Colorado Supreme Court agreed, thus allowing Boulder’s claims to proceed under state law. (18)

If the Supreme Court reverses the Colorado Supreme Court’s ruling, it could cut off similar lawsuits at the knees. (19) However, climate lawsuits are brought under different laws, with Boulder’s case containing a variety of claims in and of itself, so the impact of the Supreme Court ruling is hard to predict. (20) The justices could foreclose state lawsuits based on the impacts of emissions or based on deception, or both. (21) Oral arguments are expected in the fall, with a decision likely to take place before the end of 2026. (22)

State vs. Federal Courts

The question of whether state law is preempted by federal law in climate litigation, and therefore whether state courts are an appropriate venue for these lawsuits, is significant. The plaintiffs believe local judges and juries to be more sympathetic to their arguments. The fossil fuel companies presumably share that view, persistently attempting to move climate litigation to the federal level instead. (23) In addition, given the much greater number of state judges, (24) the plaintiffs have a higher chance of finding one who allows their case to go to trial if they litigate in state courts across all fifty states rather than in federal court. (25)

Federal climate lawsuits also face unfavorable precedent. In American Electric Power Co. v. Connecticut (2011), the Supreme Court ruled that a federal common law nuisance claim was displaced by the Clean Air Act. The justices argued Congress delegated the regulation of carbon dioxide emissions to the EPA, so federal courts have no authority to do so through federal common law. The Court stated that it would be problematic to rely on “district judges issuing ad hoc, case-by-case injunctions.” The Court added that district courts do not have the scientific, economic, and technical resources of an agency. Despite this strong condemnation of the regulation of emissions through federal courts in the American Electric opinion, the Supreme Court did not outline the general implications for federal common law nor address whether the Clean Air Act preempts state law. (26) The second wave of climate litigation has primarily occurred in state courts to avoid the potential application of this precedent. (27) 

Climate lawsuits face a lower threshold for dismissal in federal courts. In the context of interstate water pollution, the Supreme Court has previously articulated that federal common law is much more easily displaced by federal legislation than state common law is preempted by it. In Milwaukee v. Illinois (1981) (“Milwaukee II”), the Court highlighted the limited nature of federal common law. It stated that state common law is “routine” while federal common law is an “unusual exercise of lawmaking by federal courts.” With a different and much more rigid standard for the preemption of state law due to the state courts’ greater lawmaking power, it is possible for the same piece of legislation to displace federal common law but not preempt state common law. (28) 

Conclusion

Given the unfavorable legal environment at the federal level, activists risk losing climate litigation as a viable strategy altogether if the Supreme Court precludes state climate lawsuits in Suncor Energy Inc. v. County Commissioners of Boulder County. Climate lawsuits against fossil fuel companies are uniquely helpful in adapting to and mitigating climate change, so such a ruling would be a substantial blow to the climate movement. Evidently, holding fossil fuel companies financially liable for climate damages and the cost of adaptation is beneficial for communities forced to adapt to climate change. 

Climate lawsuits also have the potential to help mitigate the climate crisis through settlements that contain policy components and through the impact of litigation on public opinion. Climate activists have taken inspiration from the successful litigation against tobacco companies, as state-level lawsuits against Big Tobacco led to expansive settlements that functionally acted as legislation. More than forty-five tobacco companies, including the four largest in America, settled with forty-six states under the Major Settlement Agreement (MSA). The MSA requires annual payments by tobacco companies to the states, raising the prices of cigarettes and providing money for smoking prevention programs. It also eliminated tobacco company practices that obscured their products’ health risks and restricted the marketing of tobacco products. (29)(30) 

Even if climate lawsuits are not ultimately successful, they provide negative publicity for the fossil fuel industry that could help mobilize change outside the courts. In the discovery phase of a climate lawsuit, courts demand that fossil fuel companies hand over relevant documents and information. (31) During discovery and trial, plaintiffs can construct a narrative about how much the industry knew and what it did with that knowledge. What weakened the tobacco industry and changed the politics of tobacco were lawsuits that revealed to the public the extent of the industry’s deceit. (32) The once-powerful tobacco lobby lost supporters on Capitol Hill as the industry lost credibility and public opinion turned against it. (33) Moreover, the rigorous nature of the litigation process means claims must be backed up with reason, evidence, and expert testimony. (34) In an age of misinformation, climate lawsuits may boost public belief in the science of human-caused climate change. The facts revealed during climate lawsuits and the bad press that follows may be more impactful than the lawsuits’ ultimate outcomes. If public support for addressing climate change increases, Congress or the executive branch may be pushed to act. 

However, the publicity effects of lawsuits only occur when they are not dismissed during preliminary motions. For legal areas where courts rule that federal common law is displaced by federal legislation or state common law is preempted by that legislation, lawsuits would be dismissed before discovery and trial, not triggering the same public scrutiny. 

Without the assistance of litigation, the question is whether other avenues of climate activism will be enough to manage an increasingly dire climate crisis. 

Endnotes

(1) “The World Is Likely to Exceed a Key Global Warming Target Soon. Now What?,” United Nations Environment Programme, November 5, 2025, https://www.unep.org/news-and-stories/story/world-likely-exceed-key-global-warming-target-soon-now-what.

(2) Piers M. Forster et al., “Indicators of Global Climate Change 2024: Annual Update of Key Indicators of the State of the Climate System and Human Influence,” Earth System Science Data 17, no. 6 (June 19, 2025): 2641–80, https://doi.org/10.5194/essd-17-2641-2025.

(3) “World Likely Exceed Target.” 

(4) “Climate Change Will Impact Almost Every Major Area of Commercial Litigation,” Quinn Emanuel Trial Lawyers - Quinn Emanuel Urquhart & Sullivan, LLP, May 3, 2024, https://www.quinnemanuel.com/the-firm/publications/climate-change-will-impact-almost-every-major-area-of-commercial-litigation/#:~:text=Virtually%20all%20were%20brought%20in,their%20cases%20in%20state%20court.

(5) Lee Hedgepeth, “Supreme Court to Decide Key Issue in Fate of State and City Suits Against Oil Companies Over Climate Change,” Inside Climate News, February 23, 2026, https://insideclimatenews.org/news/23022026/supreme-court-looks-at-state-city-oil-climate-lawsuits/#:~:text=Fossil%20fuel%20companies%2C%20in%20turn,the%20next%20step%20toward%20justice.%E2%80%9D.

(6) “Climate Change Impact Litigation.” 

(7) “Yale Experts Explain Climate Lawsuits,” Yale Sustainability, August 16, 2023, https://sustainability.yale.edu/explainers/yale-experts-explain-climate-lawsuits. 

(8) Joana Setzer and Catherine Higham, “Global Trends in Climate Change Litigation: 2025 Snapshot,” Grantham Research Institute on Climate Change and the Environment, June 25, 2025, https://www.lse.ac.uk/granthaminstitute/publication/global-trends-in-climate-change-litigation-2025-snapshot/.

(9) “Climate Change Impact Litigation.” 

(10) Miranda Green, “The Supreme Court Case That Could End Local Climate Suits,” Atmos, March 4, 2026, https://atmos.earth/political-landscapes/the-supreme-court-case-that-could-end-local-climate-suits/.

(11) Daniel Farber, “The Climate Change Lawsuits Against Big Oil, Explained,” The Appeal, January 29, 2021, https://theappeal.org/the-lab/explainers/the-climate-change-lawsuits-against-big-oil-explained/#:~:text=The%20lawsuits%20against%20oil%20companies,interstate%20pollution%20under%20state%20law.

(12) “Boulder and Exxon’s Coming Supreme Court Clash, Explained,” Center for Climate Integrity, March 2, 2026, https://climateintegrity.org/news/view/boulder-and-exxons-coming-supreme-court-clash-explained.

(13) “Climate Change Impact Litigation.” 

(14) “Board of County Commissioners of Boulder County v. Suncor Energy (U.S.A.), Inc.,” The Climate Litigation Database, accessed April 12, 2026, https://www.climatecasechart.com/document/board-of-county-commissioners-of-boulder-county-v-suncor-energy-u-s-a-inc_8a3b.

(15) “Boulder and Exxon’s Clash.” 

(16) Suncor Energy (U.S.A.) Inc. et al. v. County Commissioners of Boulder County et al., petition for writ of certiorari, No. 25-170 (U.S. May 2025).

(17) Green, “End Local Climate Suits.” 

(18) “Boulder and Exxon’s Clash.” 

(19) Green, “End Local Climate Suits.” 

(20) “Boulder and Exxon’s Clash.” 

(21) Green, “End Local Climate Suits.” 

(22) Amy Howe, “Supreme Court Agrees to Hear Case on Colorado Dispute over Climate Change,” SCOTUSblog, February 23, 2026, https://www.scotusblog.com/2026/02/supreme-court-agrees-to-hear-case-on-colorado-dispute-over-climate-change/.

(23) Farber, “Lawsuits Against Big Oil.” 

(24) “FAQs: Judges in the United States,” Institute for the Advancement of the American Legal System, June 12, 2014, https://iaals.du.edu/publications/faqs-judges-united-states. 

(25) “Yale Experts Climate Lawsuits.” 

(26) Megan Brown, “Supreme Court Issues Unanimous Decision in AEP v. Connecticut,” Wiley, June 20, 2011, https://www.wiley.law/article-1956. 

(27) “Climate Change Impact Litigation.” 

(28) Karen C. Sokol, “Seeking (Some) Climate Justice in State Tort Law,” Washington Law Review 95, no. 3 (2020): 1383, https://doi.org/10.2139/ssrn.3727541. 

(29) “The Master Settlement Agreement,” National Association of Attorneys General, accessed April 14, 2026, https://www.naag.org/our-work/naag-center-for-tobacco-and-public-health/the-master-settlement-agreement/. 

(30) “Tobacco Industry Litigation,” Industry Documents Library, accessed April 14, 2026, https://www.industrydocuments.ucsf.edu/resources/litigation-background/.

(31) Farber, “Lawsuits Against Big Oil.” 

(32) “Yale Experts Climate Lawsuits.” 

(33) Kristi Keck, “Big Tobacco: A History of Its Decline,” CNN, June 19, 2009, https://edition.cnn.com/2009/POLITICS/06/19/tobacco.decline/. 

(34) “Yale Experts Climate Lawsuits.”