On June 21, 2011, the U.S. Supreme Court in American Electric Power (AEP) v. Connecticut held that the Clean Air Act (CAA), and the U.S. Environmental Protection Agency (EPA) actions it authorized, displaced any federal common-law right to seek abatement of carbon dioxide (CO2) emissions from fossil fuel-fired power plants. The widely anticipated decision was important, because it clarified the court’s approach to legislative displacement and dismissed federal common-law public nuisance claims.