Energy Secretary Samuel Bodman warned against "unintended consequences" — including job losses — that he said might result if the government requires economy-wide caps on carbon dioxide from the burning of fossil fuels.

He and other administration officials at a news conference praised the report Friday by a United Nations-sponsored panel of top climate scientist who said there is little doubt the earth is warming as a result of man-made emissions.

But Bodman said technology advancements that will cut the amount of carbon emissions, promote energy conservation, and hasten development of non-fossil fuels can address the problem.

"We have aggressive but practical solutions," added Stephen Johnson, administrator of the Environmental Protection Agency.

More than a half-dozen bills have been introduced, mostly by Democrats, calling for some form of mandatory carbon controls in the United States, which emits a quarter of the earth's carbon dioxide releases into the atmosphere.

Democrats newly in control of Congress and other critics of President Bush's environmental policies pounced on the long-awaited United Nations report like fresh meat.

"Although President Bush just noticed that the earth is heating up, the American public, every reputable scientist and other world leaders have long recognized that global warming is real and it's serious. The time to act is now," said Sen. John Kerry, D-Mass., who with GOP Sen. Olympia Snowe of Maine crafted one of a half-dozen competing bills to address global warming.

Rep. Edward Markey, D-Mass., a senior member of House panels on energy and natural resources, said that "for those who are still trying to determine responsibility for global warming, this new U.N. report on climate change is a scientific smoking gun."

The White House issued a statement less than four hours after the report's release defending Bush's six-year record on global climate change, beginning with his acknowledgment in 2001 that the increase in greenhouse gases is due largely to human activity.

It said Bush and his budget proposals have devoted $29 billion to climate-related science, technology, international assistance and incentive programs — "more money than any other country."

Bush has called for slowing the growth rate of U.S. greenhouse gas emissions, which averages 1 percent a year, but has rejected government-ordered reductions. Last week he also called for a 20 percent reduction in U.S. gasoline consumption over the next 10 years.

Markey said it will be Congress who will have "to meet this challenge by moving aggressively to transition away from forms of energy which have the capacity to destroy the planet as we know it."

Larry Schweiger, president of the National Wildlife Federation, called it already "past time to act and solve global warming with the urgency and determination with which Americans have successfully confronted other threats to our security and to wildlife."

"This report really provides strong weight behind those saying we need much stronger action" from the United States and other nations, said Robert Watson, the World Bank's chief spokesman on global warming and former chairman of the U.N. scientific panel responsible for evaluating the threat of climate change.

Some evangelical Christians who helped Bush win re-election in 2004 demanded he provide more world leadership on the issue in light of the new U.N. report.

"I am absolutely certain that as Christians we need to act today to curb global warming pollution," said Jim Ball, national coordinator of the Evangelical Climate Initiative and president of the Evangelical Environmental Network.