The U.S. Court of Appeals for the District of Columbia found the EPA's reading of the act to be "unambiguously correct," The Washington Post reported. The court rejected arguments that the EPA improperly delegated its authority to a number of research groups by relying on their findings that greenhouse gases emitted by vehicles and other sources like coal-burning power plants contribute to global warming.
The EPA was challenged by the Coalition for Responsible Regulation, a group that includes the states of Texas, Nebraska, North Dakota, Alabama and Virginia, along with industry groups. Several states backed the EPA.
Ken Cuccinelli, Virginia's Republican attorney general, said he would appeal to the U.S. Supreme Court.
The three-judge panel said the appellants' main argument was "little more than a semantic trick." In their ruling, they said the EPA was engaged in a normal scientific process.
"This is how science works. EPA is not required to re-prove the existence of the atom every time it approaches a scientific question," the opinion said.