LOS ANGELES -- Gov. Jerry Brown dramatically increased California's climate-change goals, committing the state to use renewable energy for half its electricity and make existing buildings twice as energy-efficient in just 15 years.

Brown tried for an even stronger measure that also would have enforced a 50 percent drop in petroleum use by 2030, but was defeated by oil interests. He called that a short-term setback, and 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 Wednesday at the hilltop Griffith Observatory, overlooking the haze of downtown Los Angeles.

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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.

"It's monumental," said Alex Jackson, an attorney with the Natural Resources Defense Council. "For an economy the size of California to commit to getting half of its power needs from renewable energy resources, I think, is a game-changer."

Few question whether the new goal of 50 percent is achievable by 2030, but critics worry that the complex regulations needed to speed the transition from fossil fuels will add unknown costs for consumers and businesses.

Republican state Sen. Jim Nielsen of Gerber predicts more expensive "energy, food and all things that require abundant affordable energy to produce and transport, particularly hurting those California families least able to afford it."

Just how California will meet the new goal isn't clear. Brown left the details to the state's Air Resources Board, Energy Commission and Public Utilities Commission. These boards are led mostly by gubernatorial appointees and have broad influence over economic life.

California's utilities favored the measure. They mostly use natural gas, nuclear energy and some coal, but solar, wind, geothermal and biomass are growing sources of electricity, and regulators are expected to allow them to pass some costs of the transition on to consumers.

The new law also encourages utilities to expand by building many more charging stations for electric vehicles, and provides for fines or penalties if utilities don't meet the goals.

Supporters say Californians can keep saving money through rebates and subsidies as they purchase electric vehicles, replace inefficient light bulbs and appliances, and install solar panels or double-paned windows.

Brown, a Democrat, began this year with a vow to push the most aggressive greenhouse-gas emissions benchmark in North America through the Legislature. He took his campaign around the world, even meeting with the pope in July.

But he lost a key political battle among moderate Democrats in Sacramento amid intense lobbying by the oil industry, which financed a multimillion-dollar advertising campaign that raised fears of job losses if cuts in petroleum use were imposed.

Catherine Reheis-Boyd, president of the Western States Petroleum Association, thanked lawmakers who voted against the proposed cap for keeping California competitive.

Some lawmakers were willing to accept forced cuts in petroleum use if the Legislature could have more power over the Air Resources Board, which has been implementing the greenhouse gas emissions law.

But Brown refused to give up what he sees as his executive authority.

Both houses are controlled by Democrats, but on Wednesday, Brown squarely accused Republicans of failing to do enough to reverse global warming. He recalled that Ronald Reagan was California's governor when the state created the Air Resources Board in response to the Los Angeles smog, and that President Richard Nixon signed the Clean Air Act.

"That was a time when Republicans really got it. We hope they are going to come back to the good old days of Reagan and Nixon, when people cared about clean air and clean water," he said.

California's new goal builds on landmark legislation signed by Republican Gov. Arnold Schwarzenegger in 2006, which laid the groundwork for the first U.S. program to cap and trade emissions, aiming to reduce pollutants to 1990 levels by 2020.

That program, second only to the European Union's in size, enables polluters to buy and sell credits on a market, generating billions in revenues since the state held its first carbon auction in 2012.

Businesses will pay an estimated $2.2 billion in the current budget year to help fund mass transportation including a planned high-speed rail system and pay for appliance rebate programs, building upgrades and forestry and wetland conservation.

Opponents say all this raises costs for consumers, but supporters say initial fears of economic harm have not come true. California's economy is relatively healthy, with an unemployment rate of 6.1 percent in August. That's above the 5.1 percent national average, but the lowest it's been since January 2008.