Two groups of plaintiffs filed separate suits in federal district court against four major electric-power companies and the Tennessee Valley Authority (defendants) asserting that the carbon-dioxide output from the companies’ fossil-fuel-fired power plants significantly contributed to global warming and created a substantial and unreasonable interference with public rights in violation of federal common law and state law. The first group consisted of eight states and New York City. The second group was comprised of three nonprofit land trusts (plaintiffs). Both lawsuits requested injunctive relief requiring each defendant to cap its carbon-dioxide emissions and then reduce emissions by a specified amount for each subsequent year. The district court dismissed both suits as presenting non-justiciable political questions. The United States Court of Appeals for the Second Circuit reversed, and the United States Supreme Court granted certiorari.