On June 21, 2007, the U.S. Environmental Protection Agency announced that by the end of 2007 it would rule on the State of California’s pending request for a waiver of federal preemption of state regulations limiting vehicle emissions of carbon dioxide and other greenhouse gases. Because vehicle emissions are regulated under the Clean Air Act, California’s more stringent emissions regulations would run afoul of federal law unless the EPA granted such a waiver.

The California Air Resources Board filed its request for a waiver on December 21, 2005. EPA deferred ruling on the request pending the Supreme Court’s resolution of Massachusetts v. EPA, which considered whether carbon dioxide and other greenhouse gases were subject to regulation as air pollutants under the Clean Air Act. The Court issued its decision on April 2, 2007, and on April 26, California gave EPA official notice of its intent to sue the agency to compel it to act on California’s waiver request. On June 13, the office of Governor Arnold Schwarzenegger informed EPA that the state was poised to file suit as soon as the statutory six-month notice period ended.

Eleven other states – Vermont, New York, New Jersey, Massachusetts, Connecticut, Maine, Rhode Island, Pennsylvania, Maryland, Washington and Oregon – have adopted California’s vehicle emissions standards. EPA’s grant of California’s waiver request would allow those standards to go into effect in these states.