BERKELEY — In the early 1970s, California faced a one-two punch of doubled oil prices and soaring electricity demand, with new coal and nuclear power plants projected every eight miles along the coast from San Diego to San Francisco.

The plants never got built because a motley band of physicists and state lawmakers cut energy demand down in ways as ambitious as reinventing the fluorescent light bulb and as simple as slapping energy-usage labels on refrigerators.

They also retooled the electricity market so power companies spent money helping people use less energy. Utilities were investing in selling less electricity, but they did not have to build 16 power plants and were guaranteed payback on what they did build or buy.

The state's economy kept growing even though Californians on average consume

40 percent less energy than other U.S. citizens.

Scientists said Friday that exporting California's energy-saving recipe to the rest of the nation, and to China and India, is the first, least-cost and sacrifice-free answer to the global one-two punch of rising fossil energy prices and greenhouse warming.

"This was and remains the lowest-hanging fruit," Nobel Prize-winning physicist and Lawrence Berkeley Laboratory director Steve Chu said Friday. "But it cannot solve it all."

Ultimately, scientists say, the solution lies in revolutionizing the global energy supply to replace the 80 percent filled by oil, natural gas and coal with carbon-free energy sources.

But the speed and size of that transformation depends on energy demand. Energy scientists say cutting demand with more efficient vehicles and buildings is where the earliest gains have to come.

If nations wanted to hold the global rise in temperatures to less than 4 degrees Fahrenheit while keeping their economies growing, a half-percent increase in energy efficiency by 2050 is the difference between replacing the equivalent of all fossil energy supplied today with carbon-free energy and having to come up with twice that amount without the extra efficiency, according to an analysis by John Holdren, a Harvard University energy expert and president of the nation's largest scientific society. "The potential of what we could get is a whole lot bigger on the demand side than what we could get on the supply side," Holdren said Friday at a Berkeley symposium honoring Abe Rosenfeld, a Berkeley physicist considered one of the founders of energy-efficiency concepts.

Climate scientists say rising concentrations of greenhouse gases from human fossil fuel burning have pushed average global temperatures up by more than 1 degree, mostly since the 1970s. Because greenhouse gases persist in the atmosphere for decades, scientists say, another 1 degree of warming is inevitable because of current emissions.

Many scientists believe a doubling of pre-industrial levels of greenhouse gases in the atmosphere is unavoidable, with at least another degree or two of warming that many scientists believe could melt the Greenland ice sheets and raise global sea levels as much as 20 feet.

Dozens of coal-fired plants are planned in the United States, but hundreds are planned in India and China, which is projected to surpass the United States as the largest emitter of greenhouse gases in 2020.

China is building dozens of new power plants — 50 billion to 70 billion watts of mostly coal-fired power — every year, said Mark Levine, leader of the China Energy Group at the Lawrence Berkeley Lab.

"This is, I think, the largest construction project in the world, the construction of Chinese power plants," he said.

Rosenfeld and Susan Kennedy, then head of energy-efficiency programs at the California Public Utilities Commission and now Gov. Schwarzenegger's chief of staff, pitched top Chinese economic officials on avoiding the cost of new power plants by employing California energy-efficiency standards for appliances and buildings.

Inside of five years, Levine expects the Chinese to slow energy consumption by one-fifth through new efficiency programs modeled largely after California's.

The rest of the United States already is inching in a California direction on energy efficiency. Last year's federal energy act borrowed 16 of the state's 2004 appliance and building standards and made them law for the rest of the nation, ending five years in which the federal government failed to upgrade any of its standards.

Energy scientists said there is a lot more to be done nationally and in California. More than 70 percent of greenhouse emissions from electricity generation are tied to powering buildings, especially in wealthy, developed countries, said Robert Socolow, a Princeton University energy analyst.

"It suggests we're moving more and more to a world where it's the electricity in buildings that's the problem, stupid," he said. "We've got to learn, and California can teach us. It suggests we have to reinvent the building."

Rosenfeld, now serving on the California Energy Commission, has plenty of ideas.

His latest passion — cool roofs — just became the rule in California. If a building has a flat roof and no architectural reasons against it, the roof has to be white to reflect incoming solar energy and save up to 20 percent on air-conditioning costs. For people who do not like light-colored roofs, Berkeley scientists invented dark roofing tiles that reflect 30 percent to 40 percent of the infrared light that warms homes and drives up summer electricity bills.

So far, scientists calculate that applying the same idea to cars would save 2 percent to 3 percent on fuel economy.

"People keep asking me, 'Have we used up all the low-hanging fruit?'" Rosenfeld said. "We seem to be a long way from physical limits on refrigerators, air conditioners, cars, what have you. We've got a long way to go."