Massachusetts v. Environmental Protection Agency

After the EPA (defendant) declined private petitions to regulate greenhouse-gas emissions from new cars, a group of states including Massachusetts (plaintiffs) sued, seeking a declaration on whether the Clean Air Act (CAA) gave the EPA authority to regulate such emissions and whether its refusal to do so was lawful. Massachusetts alleged that unregulated emissions would accelerate global warming and cause it to lose coastal land, while the EPA argued the CAA did not authorize climate-related regulation, that Congress had not finished studying the science, and that regulating at this time was simply unwise. The D.C. Circuit sided with the EPA, and the states appealed.