SACRAMENTO, Calif. >> California has set a goal of phasing out electricity produced by fossil fuels by 2045 under legislation signed today by Gov. Jerry Brown.

Brown, who has positioned California as a global leader in the effort to reduce greenhouse gas emissions, approved the measure as he prepares to host a summit in San Francisco of climate change leaders from around the world starting Wednesday.

The measure represents the latest in a string of ambitious environmental initiatives as California seeks to fill a void left by President Donald Trump’s decision to withdraw from the Paris climate accord and his efforts to boost the coal industry.

The state is pushing to rapidly expand adoption of electric vehicles and has created a “cap and trade” program to put a price on carbon emissions, creating incentives to reduce them. It’s working toward a goal, pushed by Brown and adopted by lawmakers, to reduce greenhouse gas emissions by 40 percent over the next 12 years.

But the efforts have drawn criticism from business groups worried about rising electric bills. Some environmentalists who say Brown is too cozy with oil and gas interests and plan to disrupt the San Francisco summit.

The renewable energy measure would require California’s utilities to generate 60 percent of their energy from wind, solar and other specific renewable sources by 2030. That’s 10 percent higher than the current mandate.

The goal would then be to use only carbon-free sources to generate electricity by 2045. It’s merely a goal, with no mandate or penalty for falling short.

“It’s not going to be easy and will not be immediate, but it must be done,” Brown said. “California is committed to doing whatever is necessary to meet the existential threat of climate change.”

California’s renewable energy goal is not as ambitious as Hawaii, which has adopted a 100 percent renewable energy mandate.

Phasing out fossil fuels would be a massive change in the energy grid. Utilities rely on natural gas plants to meet demand when renewables fall short, particularly in the early evening when the sun sets and people turn on their air conditioners as they get home from work.

Utilities are already dealing with an abundance of solar energy during peak times, which must be offloaded to other states when there’s not enough demand locally for the power.

Renewable energy experts have looked to batteries that can store solar energy generated in the afternoon as one solution, but the technology is not ready for wide-scale deployment. Another potential solution is pumped storage, in which water is pumped uphill in the afternoon using solar energy and then released through hydroelectric generators after the sun sets.

Brown has often faced criticism that he’s too lenient with the oil industry, including from environmental groups pushing him to create a moratorium on new oil and gas wells in the state.

California has nearly 54,000 active wells, some of them close to urbanized areas in Southern California and the Central Valley, according to state data.

California ranked sixth among states in crude oil production in May, the latest data available from the U.S. Energy Information Administration. The state ranks 15th in natural gas production. California’s production of crude oil has fallen steadily since the mid-1980s.

Business groups also opposed the measure amid concerns that it would raise the price of energy and, together with California’s other environmental and labor protections, make it hard to compete with firms in other states.

“If we’re going to have these first in the nation laws, we want to see first in the nation benefits,” said Rob Lapsley, president of the California Business Roundtable.

The measure was written by state Sen. Kevin de Leon, a Los Angeles Democrat who is running for U.S. Senate against fellow Democratic U.S. Sen. Dianne Feinstein.

“Today we’re setting a marker that will be remembered by future generations,” de Leon said.

California has met its goal to reduce total greenhouse gas emissions to 1990 levels, an accomplishment that relied heavily on building cleaner power plans.

But electricity accounts for only 16 percent of California’s emissions. Further reducing carbon discharges will require a significant reduction in vehicle emissions, which have inched up recently.

After signing the bill today, Brown also signed an executive order directing the state to achieve “carbon neutrality” by no later than 2045. After that, he says the state should emit net negative greenhouse gas emissions.

The order directs several state agencies to set targets for artificially removing carbon dioxide from the air through a process known as “sequestration.”