The U.S. Supreme Court heard oral arguments in Suncor Energy v. Boulder County over whether federal law bars Colorado's climate claims against oil companies or allows them to proceed in state court. In 2018, Boulder County and the City of Boulder sued ExxonMobil and Suncor Energy in Colorado state court, alleging that the companies' production and promotion of fossil fuels contributed to climate change and caused costly harms, including flooding, wildfires, drought and property damage. The companies argued that federal law overrides the state-law claims and sought to move the case to federal court. After years of litigation, the Colorado Supreme Court ruled in 2025 that the claims could proceed under state law. The U.S. Supreme Court agreed to hear the companies' appeal.