After the Environmental Protection Agency (EPA) (defendant) declined several private petitions to issue regulations governing greenhouse-gas emissions from new automobiles, a group of states (including Massachusetts) (plaintiffs) brought suit against the EPA seeking declaratory relief on the issue of whether the EPA had the statutory authority to regulate greenhouse-gas emissions under the Clean Air Act; and if so, whether its stated reasons for refusing to do so were consistent with the Clean Air Act. Massachusetts alleged, among other things, that the EPA’s failure to regulate these emissions would ultimately result in loss of its coastal lands due to increased global warming from the emissions. The EPA claimed that the Clean Air Act (CAA) did not authorize the agency to issue regulations to address global climate change and, moreover, that Congress had not yet finished investigating the scientific merits of climate change. The EPA further argued that it was not wise to regulate such emissions at that time. The Court of Appeals for the District of Columbia Circuit agreed and held in favor of the EPA. Plaintiffs appealed. The U.S. Supreme Court granted certiorari to review.