A federal appeals court has upheld the Environmental Protection Agency’s (EPA) finding that greenhouse gases contribute to global warming and are a threat to public health. The opponents argued that EPA rules setting emissions standards for cars and light trucks, and requiring construction and operating permits for the nation’s largest emitters of greenhouse gases, such as coal-fired power plants, were based on a faulty interpretation of the Clean Air Act, and therefore capricious and heavy handed.

But in its opinion, the U.S. Court of Appeals for the District of Columbia Circuit rejected the challenge to the agency’s authority, saying the EPA’s "interpretation of the...Clean Air Act provisions is unambiguously correct."

EPA Administrator Lisa P. Jackson called the ruling "a strong validation of, in the court’s own words, the ‘unambiguously correct’ approach we have taken in responding to the 2007 Supreme Court decision." In that decision, the high court ruled that the EPA was obligated under the Clean Air Act to clarify whether greenhouse gases were an air pollutant, and regulate them if they were. The agency subsequently determined that the gases constituted a pollutant and a danger to public health, and issued an emissions rule for cars and some trucks.

The ruling gave the EPA "a green light to keep moving forward" with a second round of vehicle emissions standards according to a spokesperson for the National Resources Defense Council.