Although it is difficult to determine how the Supreme Court justices might rule in a major environmental case argued on April 19, they asked several questions related to whether the courts or another branch of government should establish the nation's policies on global warming and whether, in a hypothetical common-law public-nuisance case, a federal regulation would supersede a determination by a district judge.

At issue in the case, American Electric Power v. Connecticut, is whether states and individuals can sue utilities under federal common law for contributing to global warming and force them to reduce emissions of CO?. Legal observers say it is one of the most significant environmental cases since the 2007 landmark Massachusetts v. EPA decision, which gave the Environmental Protection Agency broad legal authority to regulate greenhouse gases under the Clean Air Act.

Some construction organizations worry that, if the court were to favor the states and conservation groups in the American Electric Power v. Connecticut suit, that ruling would set a dangerous precedent upon which virtually any party claiming injury from global warming could file a nuisance lawsuit to halt development or construction projects, says Amy Chai, senior counsel to the National Association of Home Builders, which filed an amicus brief in the case.

The case originates from public-nuisance lawsuits filed in 2004 by Connecticut, several other states and conservation organizations against the five biggest emitters of greenhouse gases in the U.S. The states and conservation groups claimed their constituents suffered as a result of GHG emissions from the utilities and asked that the utilities be required to cap CO? emissions. In turn, the utilities argued that the states lacked legal standing.

The court could end up with a 4-4 split decision, as Justice Sonia Sotomayor recused herself from the case. Justice Ruth Bader Ginsburg noted that the EPA already is working on a regulation and that the regulatory process takes a certain amount of time to finalize.

Barbara Underwood, solicitor general for New York, who argued for the states, noted that there are efforts to derail those regulations, saying, “It would be very surprising if this court would conclude that the promise of federal regulation would displace the common law.”

But outside of the courthouse, Peter Keisler, a partner with the Washington, D.C., office of Sidley Austin, who argued for the utilities, said, “This isn't a case about what the policy on natural climate change is going to be. It's about which branch of government should decide what a global-warming policy should be.”