On the eve of an international climate summit, the EPA on Monday formally declared greenhouse gases to be dangerous pollutants, strengthening President Barack Obama's hand and laying the groundwork for a new 35.5 mpg standard for light vehicles.

The finding is likely to have a greater impact on electric utilities, oil companies and manufacturers than on the auto industry.

The EPA's scientific finding reported that these gases “are the primary driver of climate change,” which can intensify heat waves and increase ozone pollution linked to asthma and other respiratory illnesses.

“The president's appearance in Copenhagen will carry even more weight because it shows that America is taking this issue very seriously and is moving forward,” said Barbara Boxer, the California Democrat who chairs the Senate Environment Committee.

Officials gather this week for the international climate summit in Copenhagen, Denmark, where Obama is to make a Dec. 18 appearance. A big part of his task is to persuade developing countries such as China and India to reduce growth in emissions.

Boxer said the EPA finding also shows that Senate support is needed for the climate change legislation she has introduced. A similar bill passed the House.

The National Association of Manufacturers said Monday that the EPA finding would “hurt manufacturers' competitiveness.”

“The EPA is paving the way to begin regulating carbon emissions across the board, including large stationary sources such as manufacturing plants, hospitals and libraries,” the group said.

In contrast, an auto industry lobbying group offered a more measured response.

“For seven long years, there was a debate over whether states or the federal government should regulate autos,” said Dave McCurdy, head of the Alliance of Automobile Manufacturers.

“President Obama's announcement in May ended that old debate by starting a federal rule-making.”

The Obama administration proposed rules that would require cars and light trucks to attain 35.5 mpg by 2016. The rules, due to be adopted in April, would put the EPA, U.S. Department of Transportation and California and other states on the same page.

Still, Rep. John Dingell, D-Mich., on Monday criticized the EPA's finding, saying regulation of greenhouse gases “should be left to Congress.”

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(Pictured: The declaration that greenhouse gases are dangerous pollutants lays the groundwork for a 35.5-mpg fuel-economy standard.)