"A decarbonized future is the reason we're here," Brown said at a signing ceremony in Los Angeles. "What we're doing here is very important, especially for low-income families."

The bill also requires a doubling of energy efficiency in buildings by 2030.

Brown insisted that the world needs to wean itself off fossil fuels as quickly as possible.

"What has been the source of our prosperity now becomes the source of our ultimate destruction, if we don't get off it. And that is so difficult," Brown said at a signing ceremony at the hilltop Griffith Observatory, overlooking the haze of downtown Los Angeles, which try as it might cannot claim to have invented smog. A London resident coined the term in 1905.

California already has some of the world's toughest air quality standards, and set a mandate in 2006 to derive a third of its electricity from renewable sources such as solar, wind and geothermal by 2020. State regulators say they already hit 25 percent last year, as huge solar farms sprouted in the desert and towering windmills went up along mountain passes.

Environmentalists cheered the new law even though language to cut petroleum use by 50 percent over 15 years was stripped from the bill after objections from the oil industry and some lawmakers.

"I'm disappointed that we don't have the petroleum piece," bill author Senator Kevin de Leon said after the signing. "But two measures dealing with the energy efficiency and renewable energy are far-reaching and the most advanced in the world."