...[A] majority of Supreme Court justices appeared hostile today as to whether states can regulate greenhouse gases as a public nuisance under federal common law...[The] plaintiffs, six states, New York City and several land trusts,...want utilities that operate fossil fuel-fired electric power plants to reduce emissions by invoking federal "public nuisance" common law...The plaintiffs...argue that the power companies are contributing to a public nuisance by releasing greenhouse gases into the air...American Electric Power Co. Inc. and several other power companies [Duke, Xcel, Southern Co.] maintain that the Clean Air Act supplants the federal common law when it comes to greenhouse gas emissions...[The] justices were keen to reach the merits over whether the Clean Air Act and EPA rulemaking had displaced the federal common law...Whatever conclusion the court reaches, it could affect another case on the same issue. Kivalina v. ExxonMobil is in the 9th U.S. Circuit Court of Appeals...