He's hoping the Legislature will send an even stronger message later this year by passing new environmental rules aimed at helping California slash greenhouse-gas emissions over the next few decades.
Approval of the legislation, intended to enact goals outlined by the governor this year, would bolster Brown's calls for global action on climate change with a display of regulatory muscle in his own state.
Oil companies have ramped up opposition, and utilities are angling for changes in the bill that would make it easier for them to fulfill requirements to produce renewable energy. But so far, no one has been able to stop the legislation, which has passed the state Senate and is advancing in the Assembly.
Senate leader Kevin de León (D-Los Angeles), one of the bill's authors and its most high-profile champion in the Legislature, has been meeting individually with Assembly members to further secure their support.
"I'm not taking anything for granted," he said.
The proposal would increase the generation of electricity from renewable sources, boost energy efficiency in older buildings and reduce by half the amount of gasoline used on state roads.
The pope's invitation to Brown for the Vatican conference is a sign that "the world is watching what happens in Sacramento very closely," De León said, and he plans to ensure that the legislation reaches the governor's desk.
"It's one of the most important things that we're going to do this year," Atkins said. "We see this as one of the big challenges on how California moves forward."
Brown is one of dozens of officials from around the world who were invited to the Vatican conference, which will focus on climate change and modern slavery. The governor is scheduled to address the gathering Tuesday and Wednesday.
It's the latest of several international trips the governor has taken to urge others to do more to curb global warming. He's also been rallying states and provinces to sign an agreement to match California's target for reducing emissions by 2050.
The governor has also set an interim goal of requiring the state to cut emissions to 40% below 1990 levels by 2030. It's an ambitious target that members of his administration insist is achievable.
"This isn't something that was just plucked out of thin air," said Mary Nichols, chair of the California Air Resources Board and one of the state's top officials on climate change programs. "This was based on a careful assessment."
De León's legislation is part of the effort to reach that target.
The measure has already been amended to spur the installation of more charging stations for electric vehicles, and De León said he's been talking to utility companies about their concerns.
"The bill is still fluid and dynamic," he said.
The legislation would require utilities to obtain half of their electricity from renewable sources such as solar and wind by 2030, up from a mandate of one-third by 2020. Utilities have expressed conditional support for the bill, but they want rooftop solar panels to be factored into the equation.
"If rooftop solar is a renewable resource, we need to be able to count that toward this goal," said
Another provision of the legislation, slashing the use of gasoline, has been hotly contested by oil companies and questioned by lawmakers from both parties.
Eloy Garcia, a lobbyist for the Western States Petroleum Assn., recently told an Assembly committee that the proposal is unfair and impossible to fulfill.
"It is entirely arbitrary, entirely aggressive, infeasible and we're not even sure what the main purpose is other than to punish petroleum resources," he said.
An analysis from E3, an environmental consulting firm based in San Francisco, said the state could need up to 8 million zero-emission vehicles on the road by 2030 to help slash carbon pollution as much as Brown wants. Right now there are only 142,000 such vehicles on the road, according to the Air Resources Board.
"The market will have to expand, and prices will have to come down," said Jim Williams, E3's chief scientist. "You're going to want an attractive deal for the consumer."
Another sticking point has been leaving the job of implementing the gasoline rules in the hands of the Air Resources Board, a regulatory agency whose leaders are appointed by the governor.
De León said such objections to the legislation, SB 350, should not stand in the way of its passage. He emphasized that lawmakers would "expect transparency and accountability" from the board.
He said it's possible to hit the gasoline target with a mix of policies such as better urban planning to reduce driving distances, increasing the availability of alternative fuels and putting more efficient vehicles on the road.
Some lawmakers remain unsatisfied.
Assemblyman Brian Dahle (R-Bieber) said during a hearing that the legislation needs to be more detailed, especially if the state is trying to portray itself as a world leader in addressing climate change.
"If we get this wrong, we're going to look like fools in California," he said.