The Environmental Protection Agency on Friday justified blocking California and other states from cracking down on auto emissions by saying the problems of global warming aren't unique to one state.

In a 48-page document describing the reasoning behind its much-criticized decision, the EPA argues that California doesn't have the "compelling and extraordinary conditions" required for a waiver under the Clean Air Act, because the rest of the nation also suffers the effects of global warming.

EPA Administrator Stephen L. Johnson, who has faced lawsuits and angry denunciations since making the decision in December, told The Associated Press in a phone interview that legislative history shows California must have a unique problem in order to justify a federal waiver to implement a vehicle emissions law stricter than the federal government's.

"I'm not saying that California isn't experiencing problems as a result of global climate change," Johnson said. "There are in fact other parts of the country that are actually worse."

Environmentalists and California officials disagree with Johnson's interpretation, contending that California has been granted Clean Air Act waivers in the past to deal with problems that are also happening elsewhere, such as diesel pollution.

Critics also contend that California does, in fact, have uniquely worse problems from global warming compared with other states, including wildfire risks, air pollution and water supply shortages.

"Clearly Johnson hasn't spent much time in California. Doesn't he know the simple scientific fact that hotter air causes more smog?" said Frank O'Donnell, executive director of Clean Air Watch, a Washington advocacy group.

"This reads like something written up in the board room of General Motors," O'Donnell said.

The Clean Air Act gives California special authority to regulate vehicle pollution because the state began such regulations before the federal government. But a federal waiver is required, and if California gets one, then other states can adopt California's standards, too.

California's tailpipe emissions law would have forced automakers to cut greenhouse gas emissions by 30 percent in new cars and light trucks by 2016.

Twelve other states — Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont and Washington — had adopted California's tailpipe standards and the governors of Arizona, Colorado, Florida and Utah had said they also plan to adopt them. The rules were under consideration elsewhere, too.

In denying the waiver request, Johnson argued that a nationwide approach would be better and said it would be provided by a new law raising fuel economy standards that was signed by President Bush in December. Automakers applauded Johnson's decision.

California officials argued that California's law would be stronger and act faster.