Former Vice President Al Gore, a 2007 Nobel Peace Prize winner for his work informing the world about the dangers posed by climate change, challenged the 2,200 graduates at Carnegie Mellon University's commencement yesterday to become new "heroes" for the environment.

University officials estimated a record 10,000 people jammed the Gesling Stadium grandstand, lined the track and filled vantage points on the top floor of the parking garage facing the stage to give a standing ovation to the author of the best sellers "Earth in the Balance" and "An Inconvenient Truth."

As the sun emerged from behind gray clouds shortly before noon, Mr. Gore began his keynote address at the 111th Carnegie Mellon commencement with his standard self-deprecating humor: "I'm Al Gore. I used to be the next president of the United States. [deadpan pause] I don't think that's particularly funny."

Then he got serious about his favorite topic and what he foresees as the leadership role the new graduates and their generation must play.

"Because of the current global strategy of taking as much of the carbon out of the ground as quickly as possible, burning it inefficiently and leaving it as a poisonous, dangerous residue in our atmosphere, we now face unprecedented challenges in science, engineering and public policy," said Mr. Gore, who received an honorary doctorate of humane letters from the university.

He said technologies to replace fossil fuel energy with alternative sources are already available, but the political will is lacking.

He urged the graduates to help the United States reclaim its place as a world leader and thereby become the "third hero generation," besides the founding fathers who championed independence and freedom and the Greatest Generation that beat fascism in World War II.

"Solar energy, wind energy and distributed power and geothermal energy and a series of other innovations have reached the stage where we can replace every electron and every BTU from fossil fuel sources without missing a beat," Mr. Gore said. "But we need one ingredient that you represent. We need your political will, your dedication, and we need your hearts."

Also receiving honorary degrees were Norman R. Augustine, former president and chief executive officer of Martin-Marietta and Lockheed Martin and chairman of the National Academies Committee that produced "Rising Above the Gathering Storm," a report about the need for an educated work force; Jeffrey P. Bezos, founder and chief executive officer of Amazon.com; Elizabeth Catlett, artist and sculptor; Suh Nam Pyo, president of the Korea Advanced Institute of Science and Technology and an inventor; and Patrick Colonel Suppes, the Lucie Stern professor of philosophy, emeritus, at Stanford University.

The crowd rained a second standing ovation warmly on Randy Pausch, the Carnegie Mellon computer science professor whose inspirational book, "The Last Lecture," has attracted worldwide attention. Dr. Pausch, who is dying of pancreatic cancer, said a friend recently told him he was "beating the [Grim] Reaper" because it's now been nine months since his doctor told him he would die in six.

"But we don't beat the Reaper by living longer. We beat the Reaper by living well," said Dr. Pausch, who urged the graduates to find and pursue their passion. He put an exclamation point at the end of his remarks by kissing his wife, Jai, and carrying her off stage.

Carnegie Mellon polls its students and faculty for commencement speaker and honorary degree suggestions; Mr. Gore was a faculty nomination. University President Jared L. Cohon made the final decision to invite Mr. Gore. Pittsburgh native Ray Lane, a member of Carnegie Mellon's board of trustees and a general partner in the venture-capital firm of Kleiner Perkins Caufield & Byers, extended the invitation.

Carnegie Mellon does not pay its commencement speakers, and yesterday's address was the only commencement speech on Mr. Gore's schedule this year.

Mr. Gore previously spoke on the university's campus in April 1992, at the opening of the John Heinz III School of Public Policy and Management, and in October 2000, as the Democratic nominee during his campaign for the presidency.

Carnegie Mellon engineering professor Edward S. Rubin, who was a member of the U.N. Intergovernmental Panel on Climate Change, which shared the 2007 Nobel Peace Prize with Mr. Gore, introduced him.

"We've been working on climate issues at CMU for many decades," Dr. Rubin said, "and having Gore come, given recent history and his award, reflects nicely on that work."