Former Vice President Al Gore said Wednesday that the “planet has a fever,” and he prescribed stronger medicine for global warming than anything Congress is considering or likely to enact this year.

In testimony before House and Senate committees, the former Democratic presidential nominee called for an immediate freeze on U.S. carbon dioxide emissions and 90 percent reduction by 2050. He also advocated taxing carbon emissions.

“Each of the recommendations that I made to you are ones that I think are practical as well as aiming high,” Gore told the Senate Environment and Public Works Committee. “I think the cost of not solving this crisis would be devastating to our economy as well. I really think that it is pragmatic as well as idealistic.”

But Gore’s proposals go beyond even the most ambitious climate-control legislation introduced in the Democrat-controlled Congress. Republican support will be needed to pass a bill in the Senate, and House legislation likely will be shaped by chairmen representing coal-producing and automaking districts.

“Sometimes positions like that help to make the mainstream proposals more acceptable,” said David Rohde, a political science professor at Duke University and an expert on Congress. “Sometimes they are counterproductive and reduce the chances of getting anything done.”

He added that Gore and his Academy Award-winning documentary, “An Inconvenient Truth,” have already swayed public opinion.

Gore’s testimony before the Senate panel and the House Energy and Commerce and Science and Technology committees was part of the Democratic leadership’s effort to push climate change to the top of the agenda.

Gore was welcomed back to Capitol Hill, where he represented Tennessee in the House and Senate for 16 years, with glowing praise from fellow Democrats and generally polite skepticism by Republicans. The testiest exchange came during Senate testimony, when James M. Inhofe, R-Okla. — the leading congressional skeptic of human-influenced global warming — challenged Gore to reduce his own home-energy consumption. Gore said he lives a “carbon-neutral life” by buying power generated from non-polluting sources and credits to offset his energy use.

When Gore tried to elaborate, Inhofe cut him off. “You went on for a long time,” he said. “You’ve got to let me have my 15 minutes, Sen. Gore.”

Chairwoman Barbara Boxer, D-Calif., said she would extend Inhofe’s time to let Gore respond. “How can you ask the question and not give the man a minute to answer?” she asked.

Other Republicans questioned the effect Gore’s proposals would have on the U.S. economy. Joe L. Barton of Texas, ranking Republican on the House Energy panel, said a system that caps greenhouse gas emissions by power plants and allows polluters to buy and sell emissions credits would drive up electricity costs and hurt consumers.

“These proposals, especially considering that neither of them includes large emitters of greenhouse gases such as China and India, fail the common-sense test that any legislation should meet,” Barton said. “They provide little benefit at a huge cost.”

Gore argued that many steps he advocates would boost the economy. For example, he said, installing better insulation in buildings would create jobs and cut energy costs.

Sen. Joseph I. Lieberman, I-Conn., credited his former running mate with changing the dynamics of the debate.

“I think we’ve reached the political tipping point,” Lieberman said, citing growing support by some business and faith-based groups for legislation that would limit the emission of pollutants that trap heat in the environment.

Gore warned lawmakers that there are political risks to doing nothing about climate change. He produced boxes at the House hearing filled with more than half a million letters urging Congress to act. He also told lawmakers that he will initiate a “mass persuasion campaign” on July 7 with advertising “in all your districts.”

Still, major obstacles to passing climate change legislation remain. In the House, Energy and Commerce Chairman John D. Dingell, D-Mich., is likely to resist anything that might hurt his state’s automakers. And Energy and Air Quality Subcommittee Chairman Rick Boucher, D-Va., who represents a coal-producing district, is likely to condition any caps on coal-burning power plant emissions on the availability of technology to capture and store carbon dioxide. Gore proposed an immediate ban on constructing any new coal-burning power plants that cannot be fitted to capture and store carbon emissions.

Meanwhile, any Senate bill needs 60 votes to pass and will require support from such moderate Republicans as John W. Warner of Virginia, a swing vote on the Environment committee.

“I think we have to wait a little while,” he said. “We haven’t gotten to the center of gravity yet on this very important argument.”

Jeff Tollefson contributed to this story.