Greenhouse gas emissions from automotive vehicles are best addressed at the national level, the U.S. Environmental Protection Agency (EPA) has determined. Accordingly, EPA has denied California's request for a waiver of federal standards, through which the state hoped to impose stricter regulations on automobile emissions.

A request made by California and 16 other states for a waiver under the Clean Air Act was provisionally denied by the EPA on December 19. The waiver would have allowed the states to impose a 30 percent reduction in tailpipe emissions by 2016, a move that would require automakers to average 43 mpg for passenger cars by then. A formal written decision from the EPA is scheduled to be completed by the end of February.

Governor Arnold Schwarzenegger expressed disappointment at the EPA's decision, and his administration vowed to sue EPA as many times as it takes to overturn the ruling.

"We are deeply disappointed that the [EPA] administrator has chosen to deny our waiver, and we are even more discouraged that he did it on such flimsy grounds," California Air Resources Board chairwoman Mary Nichols said in a press teleconference. "We are not happy and intend to pursue our legal remedies. We will sue and sue and sue and sue until we get our legal rights."

California Senator Barbara Boxer has also sharply criticized the decision. Two congressional committees have asked the EPA to turn over documents and emails surrounding the decision, while California and more than a dozen of the states have filed suit to overturn the decision in the U.S. Court of Appeals in San Francisco.