LOS ANGELES — Gov. Jerry Brown began his fourth and final term on Monday proposing a broad reduction in California’s energy consumption over the next 15 years — including a call to slash gas consumption by cars and trucks by as much as 50 percent — as part of what he said would be a sweeping campaign to heighten the state’s role in the fight against global warming.

Mr. Brown, a longtime champion of electric cars and limiting greenhouse gas emissions, called in his inauguration speech for 50 percent of California’s electricity to come from renewable energy sources by 2030, up from the current goal of one-third by 2020, and doubling the energy efficiency of existing buildings.

Mr. Brown was in effect proposing that California, which is already viewed as at the forefront in the battle to curb emissions, greatly expand cutbacks put in place in the state’s landmark 2006 greenhouse gas emission bills. And he made clear that he would use his final years in office to try to make this happen.

“Taking significant amounts of carbon out of our economy without harming its vibrancy is exactly the sort of challenge at which California excels,” Mr. Brown, 76, said as he was sworn in. “This is exciting, it is bold and it is absolutely necessary if we are to have any chance of stopping potentially catastrophic changes to our climate system.”

His speech, delivered to a joint session of the Legislature in Sacramento, looked to the past and to the future, and brimmed with references to his family’s long history in California governance.

Mr. Brown’s goals drew opposition from some Republicans, who warned that the kind of things the governor was discussing could worsen the business climate here by imposing new regulations and potentially taxes.

“At what point does being on the leading edge of environmental reform impact our ability to create jobs?” said Bob Huff, a Republican and the Senate minority leader.

But the governor, a Democrat, will be working with a Legislature controlled by Democrats that has historically embraced these kinds of aggressive environmental programs. On this topic, at least, he was speaking to a friendly crowd.

“California has been leading the country in building the low-carbon economy of tomorrow,” said Kevin de León, a Democrat who is president pro tem of the State Senate. “The ambitious goals the governor stated today are admirable, but we need to make the necessary investments in advanced technology to get us there.”

Indeed, Democrats, at least in their initial response to the speech, seemed more intent on trying to push Mr. Brown away from his pledge of austerity and toward restoring cuts that the state had made during a long, difficult fiscal period.

“Not all Californians have come back from the recession,” said Toni G. Atkins, the Democratic speaker of the Assembly. “We have to make sure that we are looking out for them.”

Alex Jackson, the legal director for the California Climate Project with the Natural Resources Defense Council, called Mr. Brown’s goals achievable, noting that the state already seemed well on its way toward surpassing the 2020 deadline for drawing one-third of its electricity from renewable resources. “This is a big deal,” he said. “The beacon of climate and clean energy emanates from the West.”

The governor used broad brushes to describe how the state might accomplish what he acknowledged was an aggressive — and potentially costly — plan. Mr. Brown has repeatedly been an advocate of electric cars, signing legislation to support them and promoting them in a series of speeches devoted to global warming, and on Monday he said he saw that as one of a number of ways to achieve his goals.

“I envision a wide range of initiatives: more distributed power, expanded rooftop solar, micro-grids, an energy imbalance market, battery storage, the full integration of information technology and electrical distribution, and millions of electric and low-carbon vehicles,” Mr. Brown said.

“All of this is a very tall order,” he added. “How we achieve these goals and at what pace will take great thought and imagination mixed with pragmatic caution. It will require enormous innovation, research and investment.”