CHICAGO--Former U.S. Vice President Al Gore last night called on scientists to communicate the urgency of climate change to political leaders and the public, saying that humanity has little time to change course before risking disastrous global consequences.

Speaking to an overflow audience at the AAAS Annual Meeting, the 2007 Nobel Peace Prize winner welcomed the signs that long years of political and policy gridlock in the United States are ending. But, he said, scientists must use their knowledge and their respected status in the community to press for broad, swift changes in energy and environmental policies.

"I believe in my heart that we do have the capacity to make this generation one of those generations that changes the course of humankind. The stakes have never been higher," Gore told the scientists, educators, students, and journalists in the audience. "Become a part of the struggle. We need you."

Watch the video of Al Gore's special invited address to AAAS.

Roughly 3000 people greeted Gore with a standing ovation as he took the stage at Chicago's Fairmont Hotel. Gore has been a leader on climate and energy issues since he was a member of the U.S. House of Representatives in the 1980s. But after losing the 2000 presidential election on a disputed vote-count in Florida--he won the popular vote nationwide--he rededicated himself to climate policy. He lectured worldwide and made "An Inconvenient Truth," a climate change documentary which won an Academy Award and helped earn him the Nobel Peace Prize in 2007.

In introducing Gore, AAAS President James J. McCarthy cited the impact of his work: "No single individual deserves more credit...for our public acceptance of climate science--public acceptance that has emboldened growing numbers of mayors, governors, senators, and presidential candidates to embrace the urgency of addressing anthropogenic climate change."

During the next 50 minutes, the audience gave him rapt attention. Gore said he welcomed the changes in Washington, D.C., and the growing commitment of Americans to address climate and energy challenges. He praised the "very large and robust green stimulus component" in the financial recovery bill approved Friday by the Senate and sent to President Barack Obama.

But as Gore surveyed the escalating damage being caused by climate change, it was clear that even with strong support in Congress and the White House, meeting the challenge will be profoundly difficult.

With charts and images, Gore described the immediate nature of the threat: Record-high global temperatures. The shrinking Arctic ice cap. Diminishing ice in the high Himalayas and droughts in China. Drought in California and an "extraordinary" die-off of trees in the American West. A 500-year flood that has wrecked Cedar Rapids, Iowa. Wildfires in Greece that nearly toppled a government, and wildfires this month in Australia that have left scores of people dead and sparked a new national debate about climate change.

But today, Gore said, the climate problem is interwoven with a national security crisis and the world financial meltdown. The common thread? "Our absurd over-dependence on carbon-based fuels."

When you pull on the thread, he said, "then all three of these crises can begin to unravel, and we hold in our hands the answer which is this generational, one-off investment to switch from an energy infrastructure that's based on expensive, dirty, and vulnerable fuels, based on carbon, and switch instead to an infrastructure based on fuels that are free, from the sun and the wind and geothermal sources, efficiency and science, innovation and ingenuity."

Already, he said, the shift away from carbon-based fuels has begun. One of his slides showed dozens of proposed coal-fired power plants in the United States that have been cancelled in recent years. At the same time, projects and proposals for renewable fuels are on the rise.

"The urgent question," he said, "is how quickly we can make that shift, how quickly we can stop deforestation and introduce much higher levels of efficiency and conservation, [which are] the easiest ways to reduce global warming pollution, and shift to renewable sources of energy."

But in response to the changing political and economic climate, Gore said, the U.S. coal industry has invested a half-billion dollars in advertising and lobbying to reinforce the misleading message that coal is clean and efficient.  

"When they spend $500 million putting their version of this story in the minds of the American people," he told the AAAS audience, "it increases the importance of <i>you</i> being willing to speak out and, as civic scientists, of finding ways to communicate the truth about what this huge increase in global warming pollution is doing."

The room grew hushed as Gore moved toward his close.

"We have a full-blown political struggle to communicate the truth," he said. "...This is a task for all of us. And those of you who have not been engaged in trying to communicate effectively in your communities--to those who respect you and who understand that you have worked hard to obtain the knowledge and wisdom that you have--this is no time to sit back. This is an historic struggle.

"We as a species must make a decision. How absurd that sounds--it sounds absurd because we've never made a decision as a species and it seems implausible to think that we could. But we've now reached a stage where continuing on our present course would threaten the entirety of human civilization.

"Many of the most distinguished members of your professions, in scientific fields, have been saying now, for a few years, that in their estimation, we could have around a decade within which to make major changes in our direction lest we lose the opportunity to retrieve a climate balance that is favorable for human life and human civilization...

"And the only way that's going to happen is if those of you who are in a position to exercise influence and communicate your understanding of what this is all about make a decision to get involved....

"I'm asking you for help. I believe in my heart that we do have the capacity to make this generation one of those generations that changes the course of humankind. The stakes have never been higher. We have the knowledge, we have the emerging technology, we have new leadership, we have cabinet members and science advisers and NOAA heads and policymakers in all of the important positions who are of you, who are your colleagues...

"If I could," Gore concluded, "I would motivate you to leave this city after this meeting and start getting involved in politics. Keep your day job, but start getting involved in this historic debate. We need you."

The audience responded with a standing ovation that lasted over a minute, until Gore had left the room.