WASHINGTON (AP) -- President Barack Obama's push for cleaner-running automobiles is being viewed as the clearest signal yet that he intends to regulate greenhouse gases.
In an ambitious assault on global warming, Obama on Monday directed the Environmental Protection Agency to reconsider previous denials of applications by states wanting to set their own limits on the amount of greenhouse gases allowed in truck and car exhaust.
For a decade, environmentalists and states have urged the federal government to limit tailpipe emissions -- mostly carbon dioxide -- that are blamed for global warming.
For almost as long, the Bush administration refused to use existing law to control greenhouse gases, despite increasing scientific evidence that the Earth is warming and court rulings that said the government has the authority to act.
Should the EPA grant California, 16 states and the District of Columbia permission to set a standard for reducing greenhouse gases from automobiles, experts say federal regulations will soon follow, then limits will be ordered for emissions from refineries and industrial plants.
"There is little question that this is heading in the direction of federal regulation of carbon dioxide," said Michael Gerrard, director of the Center for Climate Change Law at Columbia University in New York City.
Greenhouse gases from automobiles currently are not regulated by the federal government, and the Bush administration opposed state efforts to set restrictions, despite requests dating back to 1999.
The Bush administration instead focused on improvements to fuel economy as a way to reduce greenhouse gas emissions, since cars and trucks burning less fuel would generate less pollution.
On Monday, in a separate action, Obama directed the Transportation Department to set new fuel economy standards for 2011 model-year automobiles.
Both actions will reduce greenhouse gases but could put the states and the federal government on slightly different courses.
The federal Clean Air Act has always allowed states to set stricter standards than the federal government for refineries, factories and other stationary sources of pollution. However, it bars states from setting more stringent pollution standards for motor vehicles because of the problems it might cause automakers.
California's standard, which requires a waiver from the EPA under the Clean Air Act, would require SUVs, minivans and cars starting in model year 2009 to reduce their emissions of greenhouse gases by 30 percent by 2016. To achieve the reductions, the fleetwide average for the state would have to be 35.7 miles per gallon by 2016, and 42.5 miles per gallon in 2020.
The 2007 energy bill signed into law by President George W. Bush set a 35 miles per gallon fuel economy target by 2020.
Industry representatives said if EPA grants the waiver it would trigger the agency to regulate greenhouse gases under the Clean Air Act. The Bush administration refused to use the law, saying it was the wrong tool to address global warming and would cripple the economy.
"Such a move would put the EPA one step closer to making carbon dioxide 'subject to regulation' under the Act," said William Kovacs, vice president of environment, technology and regulatory affairs at the U.S. Chamber of Commerce. "This would almost certainly extend well beyond cars and trucks."
Sixteen states and the District of Columbia already have adopted or are considering adopting California's standards. The states are Arizona, Connecticut, Florida, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, Utah and Colorado.
Even if most of these states adopt the California standard, it will reduce U.S. greenhouse gas emissions by about 3 percent and worldwide greenhouse gas emissions by only 0.6 percent, according to a 2007 report by the Congressional Research Service.
Environmentalists already are pressing the EPA to regulate greenhouse gases on other fronts, including emissions from ships and off-road vehicles, such as ATVs and snowmobiles.