A federal court of appeals has rejected an attempt by a dozen states and environmental organizations to force the Environmental Protection Agency to regulate greenhouse gas emissions as air pollutants.

In a 2–1 decision, a panel of the U.S. Court of Appeals for the District of Columbia ruled that EPA acted properly when it denied a petition in 2001 that sought to compel the agency to order reductions in carbon dioxide and other greenhouse gas emissions from new motor vehicles.

Judge A. Raymond Randolph said EPA had ample discretion in the matter. The agency, he said, examined the evidence and denied the petition after thoroughly reviewing the Clean Air Act and its legislative history. He did not address EPA’s claim that it lacked legal authority to order reductions in greenhouse gas emissions under the Clean Air Act. Randolph said the only question before the court was “whether EPA properly declined to exercise that authority.”

Judge David Tatel dissented, saying that greenhouse gases “plainly fall within the meaning” of air pollutants to be regulated under the act. If EPA determines that the gases contribute to air pollution that endangers public health, “then EPA has authority—indeed, the obligation—to regulate their emissions from motor vehicles.”

Massachusetts Attorney General Tom Reilly (D) expressed disappointment that the court failed to rule on whether EPA has authority to regulate greenhouse gases. “Despite the overall ruling, Judge Tatel— the only judge to address the merits of the authority issue—firmly rejected EPA’s claim that it lacked authority in his dissenting opinion,” he noted.