Suncor Energy (U.S.A.) Inc. v. County Commissioners of Boulder County

On November 25, 2025, Suncor Energy (U.S.A.) Inc., Suncor Energy Sales Inc., and Exxon Mobil Corporation filed their reply brief in support of their request for U.S. Supreme Court review of the Colorado Supreme Court’s May 2025 opinion holding that federal law did not preempt state law claims brought by the City of Boulder and the County Commissioners of Boulder County seeking to hold the companies liable for climate change-related injuries. The companies argued that the question presented—whether federal law precludes the plaintiffs’ state-law claims—“cries out for the Court’s resolution.” The companies contended that the court had constitutional and statutory jurisdiction, that the Colorado Supreme Court’s decision was incorrect and deepened a conflict on the question presented, and that “further percolation” of similar cases in state courts “would provide no benefit.” The case was distributed for the Court’s December 12 conference.

The United States filed an amicus brief in support of Suncor Energy (U.S.A.) Inc., Suncor Energy Sales Inc., and Exxon Mobil Corporation’s petition for writ of certiorari asking the U.S. Supreme Court to review the Colorado Supreme Court’s May 2025 opinion holding that federal law did not preempt claims brought by the City of Boulder and the County Commissioners of Boulder County (together, Boulder) under state law to hold the companies liable for climate change-related injuries. The U.S. contended that review by the Court was warranted because both the Constitution and the Clean Air Act barred Boulder’s state law claims and because the Colorado Supreme Court’s decision conflicted with the Second Circuit’s decision in <a href="https://www.climatecasechart.com/document/city-of-new-york-v-chevron-corp_0ef5">City of New York v. Chevron Corp.</a> on a “frequently recurring issue of exceptional importance,” given the number of other pending cases brought by state and local governments against fossil fuel industry defendants.

Suncor Energy (U.S.A.) Inc., Suncor Energy Sales Inc., and Exxon Mobil Corporation filed a petition for writ of certiorari asking the U.S. Supreme Court to review the Colorado Supreme Court’s May 2025 opinion holding that federal law did not preempt state law claims brought by the City of Boulder and the County Commissioners of Boulder County seeking to hold the companies liable for climate change-related injuries. The petition presented the question of “[w]hether 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.” The companies argued that the Colorado Supreme Court decision had deepened a “clear conflict” on the question, citing the Second Circuit Court of Appeals 2021 decision in City of New York v. Chevron Corp. and decisions by the Seventh and Fourth Circuits in cases concerning interstate pollution. The companies also argued that the Colorado Supreme Court’s decision was contrary to the views of the United States, as expressed in an amicus brief filed in the Maryland Supreme Court in July 2025 in Baltimore’s, Annapolis’s, and Anne Arundel County’s appeals of the dismissals of their climate lawsuits. In addition, the companies argued that Supreme Court review was warranted because of the “enormous legal and practical importance” of the case; they contended that the Colorado Supreme Court’s decision “perpetuates an unsustainable and chaotic patchwork of regulation of interstate and international emissions” and thereby “threatens one of this Nation’s most critical industries.”