Greentech ambassador and former Vice President Al Gore on Thursday urged Americans to produce electricity only from renewable and carbon-free sources within 10 years.

Gore, who shared the 2007 Nobel Peace Prize for his work highlighting humans' impact on climate change, gave his recommendations on how the country could dramatically increase its production of wind,solar geothermal and other types of renewable energy. He spoke in Washington, D.C.

He championed replacing older power grids with a national electric grid that could easily ferry electricity from solar and wind farms across the country. A national grid also would help create the necessary infrastructure for plug-in electric cars, Gore said.

He also restated his belief in imposing a carbon tax on oil consumption, the cost of which would be offset by reducing payroll taxes (see Al Gore Backs Carbon Tax). Gore also urged politicians to cap carbon-dioxide emissions, which contribute to global warming.

"To those who say 10 years is not enough time, I respectfully ask them to consider what the world's scientists are telling us about the risks we face if we don't act in 10 years," he said. "The leading experts predict that we have less than 10 years to make dramatic changes in our global warming pollution lest we lose our ability to ever recover from this environmental crisis.

"When the use of oil and coal goes up, pollution goes up. When the use of solar, wind and geothermal increases, pollution comes down."

The 10-year goal is ambitious, considering renewable energy makes up only a tiny portion of the overall electricity production in the United States.

Most of the electricity generated in the country comes from coal-fired power plants, while renewable energy such as wind and solar makes up about 8.6 percent, the Associated Press reported. According to the U.S. Energy Information Administration, solar power accounted for 1 percent of the energy generation in the country in 2006, while wind power made up 4 percent.

Setting lofty goals for curbing carbon-dioxide emissions and the world's reliance on fossil fuel is in vogue. The International Energy Agency last month concluded that the world needs an extra $45 trillion in clean-energy investments to cut emissions by 50 percent by 2050 (see Can You Spare $45T to Curb Global Warming?).

Texas oilman and wind-energy advocate T. Boone Pickens also recently launched an all-out media to campaign for his plan on reducing the country's need for oil imports. He has set out to promote more wind-energy production and natural-gas-powered cars (see T. Boone Pickens Has a Plan).

At the Intersolar conference in San Francisco this week, Arthur J. Nozik, a senior research fellow at the National Renewable Energy Laboratory, sparked debate when he said the world will need to generate at least 15 terawatts of energy - about half of its expected energy requirement - from carbon-free sources by 2050 in order to keep emissions at a bearable level.

The figures were based on 1998 research from Martin Hoffert, a physics professor at New York University.

Hoffert's forecast of the world's renewable-energy needs would be tough to realize by the solar industry alone, said Eric Wesoff, a Greentech Media analyst who moderated the panel discussion on different types of solar technologies, including the use of quantum dots.

"We can't reach that in any feasible way without growing [solar-energy production by] 100 percent a year, and we would need some revolution in material science," Wesoff said after the panel discussion. "Good luck with that."

Another panelist, Tonio Buonassisi from the Massachusetts Institute of Technology, said the goal is attainable given how fast the solar industry has grown. In 2007, solar-cell production jumped nearly 51 percent from the year before, according to research from the Prometheus Institute, a partner of Greentech Media.

Buonassisi, who leads a photovoltaic research group at MIT, said researchers have far to go before they can squeeze more performance from materials used to convert sunlight into electricity. The most efficient solar cells on the market today can convert 22 percent of the sunlight that strikes them.

"The growth potential for PV is over underestimated. Once grid parity is reached, the price will be flat for several hundred gigawatts while the cost comes down, so the growth potential is enormous," Buonassisi said.

Nozik said the public, including Intersolar attendees, still haven't grasped the correlation between human population growth and energy consumption. The world's population, currently 6 billion, is projected to increase to 10 billion or 11 billion by 2050.

"Many people feel that Earth cannot sustain the projected population estimates. The economic growth can't sustain itself as well," said Nozik, who added after the panel discussion that it's unlikely Hoffert's renewable energy goal could be reached.

"It's too late. We've wasted 30 years," Nozik said. "Our lab was formed by President Carter, and now the funding is less than we had in 1980."