The Environmental Protection Agency on Monday formally declared that greenhouse gases, primarily from the burning of fossil fuels, pose a threat to human health and need to be reduced.
The declaration clears the path for the Obama administration to begin regulating emissions from power plants, factories, automobiles and other major sources of carbon dioxide pollution, perhaps starting as early as next year. The announcement, called an "endangerment finding," also makes it clear that President Obama considers climate change legislation to be a top priority, despite opposition from some elements in Congress and on the world stage.
The administration chose the opening day of the U.N. climate summit in Copenhagen to make its declaration as a sign to world leaders that Washington is determined to cut its greenhouse gas emissions. The U.S. stance has been considered critical to the adoption of a political agreement at the 192-nation conference, which concludes Dec. 18. Mr. Obama plans to be in Copenhagen at the end of the event with more than 100 world leaders.
The move also was seen as a prod to Congress to act on climate change legislation. The EPA now claims the authority to act if lawmakers do not.
Environmental groups praised the move as fresh evidence that Mr. Obama is committed to clean energy development, while business, farm and oil organizations decried what they called a misguided step that will raise consumer energy bills during economic turmoil.
Keith McCoy, a vice president at the National Association of Manufacturers, said the EPA finding "will have a cascading effect on the ability of all manufacturers to grow and prosper" and predicted that any new regulations would not be effective.
"It is doubtful that this endangerment finding will achieve its stated goal, but it is certain to come at a huge cost to the economy," he said.
EPA Administrator Lisa P. Jackson portrayed the declaration as a way to launch "reasonable efforts" to fight climate change. At the same, she reiterated that she would prefer that Congress enact legislation to lower greenhouse gas emissions rather than leave the task solely to her agency.
Climate change legislation - including a controversial "cap-and-trade" system to limit greenhouse gas emissions - passed the House in June but is stalled in the Senate at least until spring.
"This year, 2009, the United States government is saying once and for all that we are in the clean energy and climate arena, that with respect to climate pollution, we will act," Mrs. Jackson said at a news conference Monday.
She said the immediate practical impact will be to allow the EPA to require higher automobile and truck mileage standards for new vehicles and to mandate carbon emissions controls at new or expanding power plants and factories.
However, she said, the EPA has no plans to demand reductions by existing power plants and other major sources of pollution.
White House spokesman Robert Gibbs said the administration continues to favor the cap-and-trade bill, which would expressly direct the EPA to regulate carbon dioxide emissions.
"The president continues to strongly believe that the best way forward is through the passage of comprehensive energy legislation," Mr. Gibbs said Monday.
The debate over climate change has been rocked in recent weeks by the release of private e-mails from senior researchers in England and the United States that appear to show that the scientists manipulated data to strengthen their case and conspired to stifle the views of critics in top scientific journals.
Mrs. Jackson rejected demands to delay her finding until after the e-mail controversy is resolved.
"The vast body of scientific evidence not only remains unassailable, it has grown stronger. And it only points to one conclusion - that greenhouse gases from human activity are increasing at unprecedented rates and are affecting our environment and threatening our health," she said.
Jeff Holmstead, EPA air administrator in the George W. Bush administration who now heads the environmental strategies group at the law firm Bracewell and Giuliani, said the endangerment declaration is primarily symbolic for now.
"It does not have any immediate effect and does not impose any regulations or requirements on anyone," he said. "But it is a necessary prerequisite for the regulation of greenhouse gases from cars, trucks, businesses, factories, farms and potentially even apartment buildings, schools and hospitals."
Daniel J. Weiss, director of climate strategy at the liberal Center for American Progress, said the declaration should stand as a reminder to Congress that the administration will curtail greenhouse gas emissions by regulation if the House and Senate do not act.
"Such an approach is no one's first choice but is a backstop to ensure pollution reductions should conservatives succeed in thwarting progress and reform," he said.
But opponents of climate change legislation warned that Mr. Obama is on track to limit business growth and raise energy prices to achieve his environmental goals.
Thomas J. Donohue, president of the U.S. Chamber of Commerce, which has opposed cap-and-trade legislation, said new regulations could affect even small emitters of carbon dioxide, despite an EPA proposal to confine any new greenhouse gas rules to about 14,000 major sources that emit 250,000 or more tons per year of carbon dioxide.
"An endangerment finding from the EPA could result in a top-down, command-and-control regime that will choke off growth by adding new mandates to virtually every major construction and renovation project. The devil will be in the details, and we look forward to working with the government to ensure we don't stifle our economic recovery," Mr. Donohue said.
Charles T. Drevna, president of the National Petrochemical and Refiners Association, a group that fears that greenhouse gas regulations will force oil companies to shut down domestic refineries in favor of imported motor fuels, called the EPA decision "another example of federal policymakers failing to consider the long-term consequences of a regulatory action for consumers and the economy as a whole."