Reversing a decision made under the previous administration, the U.S. Environmental Protection Agency said Tuesday it would grant the controversial request by California to enforce its own vehicle emission rules.

The state first sought the waiver about three and a half years ago but was rejected in December 2007 (see EPA Rejects California Vehicle-Emission Standards). The federal government didn't have regulations over greenhouse gas emissions produced by cars, so California wanted its own program to regulate those emissions.

The previous EPA Administrator, Stephen Johnson, said back then that setting national emissions rules would be more effective than allowing states to create their own. The federal government was starting to do that, he said, so there was no need to grant California the waiver.

The state's rules, approved in 2004, would regulate emissions from air conditioning, combustion engines, the use of flex fuels, etc., said Stanley Young, a spokesman with the California Air Resources Board. The greenhouse gas emissions regulation covers more areas than the existing one governing only tailpipe emissions, which have been regulated under the federal Clean Air Act for decades. 

The EPA now says that California presented ample evidence to show that it should receive a waiver under the federal Clean Air Act to regulate its own greenhouse gas emissions from cars and trucks, or else the emissions could create serious health hazards to the state's residents, according to an EPA official during a press briefing Tuesday. President Obama asked the current EPA Administrator Lisa Jackson to review the previous decision earlier this year.

It's unclear what would be the impact of Jackson's decision. For one thing, the federal government just announced last month that it, too, plans to implement emissions standards for cars and trucks starting in 2012 (see Obama Proposes Higher Fuel Standard, Appeases California and Auto Industry). It would be part of a larger effort to raise the national fuel economy standards for 2012 tp 2016 car model years.

So starting in 2012, automakers could only have to abide by the federal standards, said an EPA official.

The EPA decision would take action effective immediately. California could start regulating greenhouse gas emissions from tailpipes starting with the 2009 car models, said an EPA official.

California Gov. Arnold Schwarzenegger said he's pleased. 

"After being asleep at the wheel for over two decades, the federal government has finally stepped up and granted California its nation-leading tailpipe emissions waiver," Schwarzenegger said in a statement. "This decision is a huge step for our emerging green economy that will create thousands of new jobs and bring Californians the cars they want while reducing greenhouse gas emissions."

Enforcing California's own rules would lead to an emission reduction of 14 percent from the 2008 levels for the average fleet during 2011, Young said. The board expects the cut to reach 30 percent in 2016 (this would happen for both California and federal standards). 

The EPA decision also would affect the 13 other states and the District of Columbia that have adopted California's rules. Those states and D.C. can also now go ahead to implement the rules.

The EPA said it doesn't know how much emissions would be reduced as a result of those other states following California's lead.