The U.S. Senate voted against mandatory carbon reductions before the Kyoto negotiations were completed. The treaty was never presented to the Senate for ratification by the Clinton Administration.

"Al Gore has fought the environment battle even as vice president," Mjoes said. "Many did not listen ... but he carried on."

Gore supporters have been raising hundreds of thousands of dollars for petition drives and advertising in an effort to lure him into the Democratic presidential primaries. One group, Draftgore.com, ran a full-page open letter to Gore in Wednesday's New York Times, imploring him to get into the race.

Gore, 59, has been coy, saying repeatedly he's not running for the Democratic presidential nomination in 2008, without ever closing that door completely.

He was the Democratic nominee in 2000 and won the general election popular vote. However, Gore lost the electoral vote to George W. Bush after a legal challenge to the Florida result that was decided by the Supreme Court.

Gore called the award meaningful because of his co-winner, calling the IPCC the "world's pre-eminent scientific body devoted to improving our understanding of the climate crisis."

Gore said he planned to donate his share of the prize money to the Alliance for Climate Protection, a bipartisan nonprofit organization that is devoted to changing public opinion in the U.S. and around the world about the urgency of solving the climate crisis.

The last American to win the prize, or share it, was former U.S. President Jimmy Carter, who won it 2002.

The committee cited the IPCC for its two decades of scientific reports that have "created an ever-broader informed consensus about the connection between human activities and global warming. Thousands of scientists and officials from over 100 countries have collaborated to achieve greater certainty as to the scale of the warming."

It went on to say that because of the panel's efforts, global warming has been increasingly recognized. In the 1980s it "seemed to be merely an interesting hypothesis, the 1990s produced firmer evidence in its support. In the last few years, the connections have become even clearer and the consequences still more apparent."

"It was a surprise," said Carola Traverso Saibante, spokeswoman for the IPCC. "We would have been happy even if (Gore) had received it alone because it is a recognition of the importance of this issue."

But some questioned the prize decision.