Los Angeles - California Governor Jerry Brown signed an ambitious climate change bill on Wednesday, aiming to increase the state's use of renewable electricity to 50% and make existing buildings twice as energy-efficient by 2030."The goal is clear, and California is in the forefront," Brown said at a signing ceremony at the hilltop Griffith Observatory, where a hazy downtown Los Angeles provided the backdrop.Brown tried for an even stronger measure that would have also directed state regulators to cut petroleum use by half in the next 15 years, but oil interests defeated that part of the package. He characterised the loss as a short-term setback. Still, the final bill lacked the punch Brown might have hoped to deliver when he attends the United Nations climate change conference in Paris in November.The Legislature approved the watered-down SB350 in the final hours of the legislative session on September 11.The measure does not specify how California will achieve these far-reaching goals, deferring the details to the state's Air Resources Board, Energy Commission and Public Utilities Commission. The boards' members are mostly appointed by the governor and have broad influence over the state's economic life.Democratic leaders blamed a multimillion-dollar advertising campaign by oil companies, which raised fears of job losses, for defeating the petroleum reduction requirement.At the bill signing, Brown recalled environmental legislation supported by President Nixon and lamented that current Republicans often oppose action on climate issues.Brown, a Democrat, began the year setting the most aggressive greenhouse-gas emissions benchmark in North America. He took his campaign to the Vatican, where he met with the pope in July, and met with other world leaders on the issue.Senate President Pro Tem Kevin de Leon, a Los Angeles Democrat, embraced the governor's goals when he introduced SB350. The measure sailed through the Senate but met resistance from moderate Democrats when the Assembly returned from summer recess.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 in charge of implementing an already ambitious greenhouse gas emissions law Republican Governor Arnold Schwarzenegger signed in 2006.But Brown refused to give up what he sees as his executive authority.