Feb. 2 (Bloomberg) -- The human role in climate change is no longer debatable, U.S. Energy Secretary Samuel Bodman said today, while he defended the president's policy of addressing the issue without mandatory greenhouse gas limits.

Bodman and other Bush administration officials were responding to a report from a United Nations panel that concluded it is more than 90 percent certain the Earth is warming because of carbon dioxide that is released by burning fossil fuels. The report, released today in Paris, predicted rising sea levels, increased storms and more droughts and floods.

``Human activity is contributing to changes in the Earth's climate,'' Bodman said at a press conference in Washington. ``That issue is no longer up for debate.''

President George W. Bush has rejected proposals for mandatory limits on emissions of greenhouse gases. Bush in 2001 went back on a campaign pledge to limit carbon dioxide emissions and withdrew the U.S. from the Kyoto Protocol, the international agreement that forms the basis for caps in Europe and elsewhere.

Democrats who took control of both houses of Congress last month, and some Republicans, are pushing for mandatory emissions rules in conjunction with a trading system that would allow flexibility in how industries comply.

Mandatory Caps

``Today I am again urging the president to show leadership and work with Congress to implement a mandatory, market-based cap and trade program to address this challenge,'' Senator Jeff Bingaman, chairman of the Senate Energy and Natural Resources Committee, said in a statement today. ``The consequences so clearly spelled out in this report, and many others, compel us to act now.''

Bingaman, a Democrat from New Mexico, and Senator Arlen Specter, a Republican from Pennsylvania, are co-sponsoring legislation to set mandatory limits on carbon.

Bodman said the administration still opposes such a move. ``The imposition of a carbon cap in this country may lead to the transfer of jobs and industries abroad,'' he said.

He declined to say whether the president would veto a carbon cap approved by Congress. ``That's a judgment the president needs to make.''

While Bush has acknowledged the need to address climate change and mentioned it in his annual State of the Union address on Jan. 23, the administration has drawn criticism for past action on the issue.

Cooney

This week Democrats in Congress accused the White House of withholding evidence they say will show how administration officials downplayed the dangers of global warming in research reports. The allegations focus on Philip Cooney, a former lobbyist for the American Petroleum Institute who became chief of staff of the White House Council on Environmental Quality.

Cooney is accused of editing reports to play up the uncertainty over the scientific basis for global warming. He resigned in July and joined Exxon Mobil Corp.

Today's report, from the UN Intergovernmental Panel on Climate Change, finds more scientific certainty compared with a 2001 document from the panel, which said the probability of a link was in a range of 66 percent to 90 percent.

``The message is that it does make a difference what we do,'' Gerald Meehl, who contributed to the report, said in a conference call with reporters. ``The longer you wait, the worse the problem gets, and the longer you wait, the more you have to do to do something about it,'' said Meehl, a scientist at the National Center for Atmospheric Research in Boulder, Colorado.

Temperatures are likely to rise by 1.1 degrees to 6.4 degrees Celsius by the end of this century relative to the last, the report said. The probable range for warming in this century is 2 degrees to 4.5 degrees if the concentration of carbon dioxide in the atmosphere doubles from pre-industrial levels.

Uncertainty

``The uncertainties have been narrowed,'' said Stephen Johnson, the administrator of the U.S. Environmental Protection Agency, who appeared with Bodman in Washington today.

The U.S. produced 22 percent of the world's man-made carbon dioxide emissions in 2004, according to figures from the Energy Information Administration, part of the U.S. Energy Department. The International Energy Agency last year predicted China would overtake the U.S. as the biggest carbon emitter in 2009.

The world's 12 largest emitters of greenhouse gases should be called to a summit at the White House, Senator Barbara Boxer said today at the United Nations in New York. She also said she would bring the scientists from the UN panel to Washington to brief lawmakers in the next few weeks.

`Hand in Hand'

Bodman said the administration's energy policies, featured by Bush in his State of the Union speech last month, already ``go hand in hand with our efforts to address climate change.''

There is a short-term need for more research on hydrogen, solar power and ethanol production technologies, Bodman said. Longer term solutions will involve the creation of a new generation of nuclear power plants and coal-fired generators that don't release carbon into the atmosphere.

The administration's refusal to back mandatory caps has put it at odds with General Electric Co. and DuPont Co., which were among 10 companies that urged the government to set a cap that would cut emissions by as much as 30 percent within 15 years.

``We believe that voluntary measures, while constructive, are not sufficient to address an issue of this magnitude by themselves,'' Linda Fisher, vice president and chief sustainability officer for DuPont Co., the third-largest U.S. chemical producer, said in a statement.

To contact the reporters on this story: Jim Efstathiou Jr. in Washington at jefstathiou@bloomberg.net; Tina Seeley in Washington at tseeley@bloomberg.net.

Last Updated: February 2, 2007 16:18 EST