The former vice president, whose global-warming documentary An Inconvenient Truth won two Oscars last month, demanded that lawmakers "show courage" by taking dramatic steps to curb changes in the Earth's climate. Among the steps Gore suggested: a ban on incandescent light bulbs and a freeze on the USA's yearly emissions of gases linked to global warming.

"We do not have time to play around with this," Gore warned several dozen members of the House science and energy committees. "We do not have the luxury of playing political football." He called the situation a "planetary emergency."

Rep. Joe Barton, R-Texas, whose district includes oil and manufacturing interests, challenged Gore on whether carbon dioxide emissions cause global warming. Barton vented some of his displeasure at Gore's remarks by reading a newspaper as Gore talked.

Many scientists agree the Earth is warming because of "greenhouse gases" being added to the atmosphere by human activity. The most common greenhouse gas is emitted when fuels such as gasoline and coal are burned. Some scientists say the Earth has been warming naturally.

Banks of TV cameras whirred and dozens of photographers clicked away as Gore testified. Reporters and onlookers were packed into overflow rooms for his first Capitol Hill appearance since 2001. At that time, the failed Democratic presidential candidate, in his capacity as Bill Clinton's vice president, presided over the Senate as it counted electoral votes from the 2000 election.

Gore made no mention of the 2008 presidential campaign. Some polls show he would be among the top contenders if he were to run for his party's presidential nomination.

Former House speaker Dennis Hastert, R-Ill., referred to Gore as a "movie star" and said he agreed with Gore that the debate over the science of global warming has been settled.

Gore's longtime concerns about global warming "really do make you look like a prophet," said Rep. Ed Markey, D-Mass., head of a new House committee on global warming. "It would be wise for the Congress to listen to your warnings, because history has borne you out."

In the afternoon, it was senators' turn to listen to Gore, who compared global warming to the devastation after World War II. "Now this generation and this Senate faces such a challenge," Gore told the Senate Environment and Public Works Committee. "The stakes are high, but the people are hopeful, and it can be done."

Sen. James Inhofe, R-Okla., sparred a little with Gore, asking him to promise that Gore's large Nashville home will use no more energy than the average American home. Inhofe once declared global warming "the greatest hoax ever perpetuated on the American people."

Gore declined to make that pledge, saying he pays extra for electricity from sources such as wind power, which emits no greenhouse gases.

"In terms of changing the way you live," Inhofe said, "I think it's very difficult for you to ask other people to do it unless you're willing to do it."