The U.S. lags behind other countries in the race for clean technology even though it has the greatest "innovation machine" in the world, U.S. Secretary of Energy Steven Chu told a Stanford University audience Monday.

But the clean-tech race is not just between nations -- it's a global race against time, Chu warned.

And Stanford students and faculty should seize leadership in the worldwide effort to minimize climate change and its catastrophic impacts, Chu said.

In a speech that ranged from climate science to politics to humor, Chu, a Nobel Prize-winning physicist and former Stanford professor, said there is no longer any doubt that climate change is occurring.

"The overwhelming scientific consensus is that humans are altering the destiny of the planet," he told more than 1,700 Stanford students and faculty in Memorial Auditorium.

"If we plow on as usual it could be catastrophic; it could be very bad, or very, very bad. But it's not going to be, 'Nothing's going to happen.'

"What we've already done (to the planet) won't be fully felt for over 100 years" because it takes time for the trapped heat to mix with cold deep-ocean temperatures to reach a new equilibrium, Chu said.

He warned that the most scientifically credible estimates put global warming between 3 degrees centigrade and 6 degrees-plus centigrade if people continue with business as usual.

The coldest part of the last Ice Age was only 6 degrees centigrade colder than the earth is today -- when Ohio and Pennsylvania were covered year-round in ice, he said.

"We don't know in detail what 6 degrees warmer will look like, but it will be an equally profound change," Chu said.

Chu called for sustained scientific collaboration to address the challenge, citing innovations that historically came out of places such as AT&T Bell Laboratories, Los Alamos, the MIT Radiation Lab and the Metallurgical Lab at the University of Chicago.

"Scientists have come to the service of our country in times of national need," he said.

The Recovery Act is "making an $80 billion down payment on a clean-energy economy, including $8 billion in energy innovation," he said.

Last week Chu announced that $100 million in Recovery Act funding will be available for research in grid-scale energy storage, electrical-power technology and energy efficiency in buildings.

Asked later why he is not mounting a clean-energy effort on the scale of the Manhattan Project that led to the first atomic bomb during World War II, Chu said there is not enough money.

"Tell your people in Congress how important it is," he told the audience. "I agree -- we should do that."

The most important policy needed to stimulate innovation and investment in clean tech is a "long-term signal in the form of a price on carbon that will slowly ratchet up, and a cap on carbon," he said.

Such a signal could provide certainty to utility companies that are debating whether to go in the direction of nuclear, wind, coal or gas, he said. And it would liberate financial markets to loan money to new technologies.

"A slight change in those long-term signals will cause the American innovation machine to respond," he said.

"It will align incentives and say, 'You can make money if you make clean energy.'

"If we do that, we will win.

"Right now we're in a state of paralysis. Many businesses say, 'No, no, we can't do this; this country was founded on cheap energy and that's what I want.'

"But that's just holding off the inevitable. If we hold off the inevitable for another five years or 10 years, we'll lose because other countries are ahead. We will play catch-up and the United States is at risk. Energy touches everything in the United States. It is very important."

Stanford is "poised to be a major player in this green energy revolution," Chu said, citing the university's past leadership in semiconductors, computers and biotechnology.

"It's a new industrial revolution and it's essential for American competitiveness," he said.

The U.S. must use energy more wisely, deploy the low-carbon technology we have, improve energy storage and "discover the breakthroughs we need."

Other countries are now in the lead on auto fuel efficiency, batteries, electricity transmission, power electronics and nuclear power, he said.

China currently spends $9 billion a month to diversify and improve its clean-energy supply, with a goal of generating 10 percent of its electricity from renewable sources by this year and 15 percent by 2020.

"They have huge targets in wind energy and have taken astounding leadership in that big market," Chu said.

"I asked the head of their state grid, 'This costs a lot of money -- how do you do it?'

"He said, 'Of course nobody likes money taken out of their wallet, but we tell them (government leaders) how important it is.'

"Different system," Chu said, to laughter from the audience.

"A country essentially run by engineers is a good thing. Well, it's not all good. I'd rather live here -- but there are some advantages."

Chu urged Stanford students to educate themselves about climate challenges and to "make energy efficiency a social norm" by turning off lights, buying fuel-efficient vehicles, conserving water and using the "sleep mode" setting on computers.

He also urged students to "get as quantitative education as you can so that you can regress data and analyze it."