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Gov. Jerry Brown rolled out one of the world's boldest targets for fighting climate change this week, announcing a statewide goal of "carbon neutrality." Achieving that goal would require California — the world's fifth-largest economy — to reduce its global warming pollution dramatically over the next 25 years, bringing carbon emissions as close to zero as possible, and making up the difference by sucking carbon out of the atmosphere.

It's a herculean task, and government mandates alone probably can't make it happen, energy experts say. Carbon neutrality will require Californians to drive less overall and use cars that aren't powered by oil, a fundamental lifestyle shift in a state known for its freeways, gas stations and suburban sprawl. The push for carbon neutrality might also force local officials to focus on getting more housing built in existing neighborhoods, creating denser communities that encourage walking, biking and public transit.

Nobody knows what the changes will look like in practice. Brown signed an executive order setting a target of carbon neutrality by 2045, but the document doesn't specify what steps California should take get there. It also doesn't have the force of law.

In other words: If you drive a gas guzzler, no one's about to tell you to stop.

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But Brown's executive order is still a key milestone on a long road toward cleaner cars, energy experts say. They point out that California's existing targets for reducing planet-warming emissions also started as executive orders before being passed into law.

"The executive order changes everything," said Bruce Nilles, a senior fellow at the Rocky Mountain Institute, a think tank based in Boulder, Colorado that publishes research on energy and climate change. "Twenty-five years from now, all of our transportation modes need to be clean. It gives us a very clear target."

California has already made huge strides replacing the fossil fuels that power its millions of homes and business with climate-friendly energy sources like wind and solar. Brown signed a bill this week committing the state to 100 percent clean electricity by 2045.

But electricity accounts for just 16 percent of California's carbon emissions, according to the state's official tally. The biggest source of climate pollution, by far, is transportation, which is responsible for 41 percent of the state's carbon emissions. California's cars and trucks burn enormous amounts of gasoline, a refined form of oil — one of three fossil fuels, along with coal and natural gas, that scientists have found to be mostly responsible for global warming.

And unlike emissions from electricity, which have been falling, transportation emissions are on the rise. After dropping during the economic slowdown of the Great Recession, carbon pollution from transportation rose by 4 percent from 2014 through 2016. Seventy percent of those emissions came from passenger cars in 2016, with more than 20 percent coming from trucks. The rest mostly came from airplanes, ships and trains.

Meanwhile, California is far from meeting its existing targets. Six years ago, Brown set a goal of putting 1.5 million zero-emission vehicles on the road by 2025. Earlier this year, he increased that goal to 5 million by 2030. But just 450,000 electric cars have been sold in California since 2011, including 92,000 this year, industry data indicate. Brown also set a target of 250,000 charging stations by 2025. Today there are just 17,000.

Changing how Californians get from place to place will be a bigger challenge than reshaping the electricity sector, said Max Baumhefner, an attorney focused on clean vehicles at the Natural Resources Defense Council, a nonprofit environmental group.

"There are only so many electric utilities out there, and we can pass laws and regulations that require them to buy clean power and invest in energy efficiency," Baumhefner said. "It's more challenging when you're dealing with tens of millions of individual consumers considering what kind of car they want to buy."

While the Golden State is far from reaching its goals, Baumhefner is optimistic. He said the cost of a lithium-ion battery has dropped 80 percent in recent years and continues to drop, which should help electric vehicles achieve "cost parity" with oil-powered cars by the mid-2020s. He also pointed to plans by California's three big investor-owned utilities — Southern California Edison, Pacific Gas & Electric and San Diego Gas & Electric — to spend more than $750 million on charging stations and rebates to support electric vehicles. Those investments are expected to make it easier and cheaper for drivers to go electric, while also boosting utility profits by expanding the market for electricity.

California has already taken steps to encourage drivers to buy cleaner cars, said Chris Busch, research director for Energy Innovation, a San Francisco-based think tank. For instance, the state offers rebates of $2,500 for fully electric cars, $1,500 for plug-in hybrids and $5,000 for hydrogen-powered vehicles. Low-income Californians can receive an additional $2,000 in rebates. The state also has a mandate that will require car companies to ensure about 8 percent of new car sales are zero-emission vehicles by 2025. The goal of the mandate is to push carmakers to design and market clean cars that consumers want to buy.

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Modeling by Energy Innovation shows that over 40 percent of new passenger car sales need to be zero-emission vehicles by 2030 to meet the governor's goal of 5 million clean cars on the road by that year, Busch said. He's confident the state is on the right path.

"The state has all the right policies in place, and you would expect over time those are going to need to get ramped up," Busch said.

The highest-profile electric automaker is Tesla, whose Model 3 sedan starts at $35,000 and has a range of 220 miles. But other companies have started selling electric vehicles at relatively low prices. The 2018 Nissan Leaf, for instance, starts at $29,990 and has a range of 151 miles. The latest Ford Focus Electric starts at $29,120 and has a range of 115 miles. The 2019 Chevrolet Bolt starts at $36,620 and has a range of 238 miles.

"People don't know that you can buy an affordable long-range (electric vehicle) now, and that there's dozens of EV models out there that could meet their needs," said the NRDC's Baumhefner. "A lot of people might have heard of Tesla, but they don't know about the Nissan or the Chevy, and they don't buy cars that they don’t know exist."

Part of the problem is a lack of publicity, Baumhefner said. Even the rollout of Tesla's Model 3, he said, got less press coverage than "a single Kim Kardashian tweet."

"I guess we need to get Kim tweeting about EVs," he said.

There's more California can do to electrify transportation, said Nilles from the Rocky Mountain Institute. He pointed out that the California Public Utilities Commission regulates ride-sharing companies like Uber and Lyft, as do many city governments.

"What is stopping cities and/or the state from setting a (clean energy standard) for shared services? 'OK, Uber and Lyft, in 5 years, half of your cars have to be electric. And in 10 years, all of your cars have to be electric,'" Nilles said.

California's biggest challenge might be cutting down on driving.

The California Air Resources Board's 2017 "scoping plan," a comprehensive outline of how the state might meet its climate change targets, says Californians will need to drive fewer miles for the state to reduce emissions sufficiently over the next decade. State law calls for California to reduce its carbon emissions 40 percent below 1990 levels by 2030. Achieving those reductions would require Californians to drive 7 percent fewer miles in 2030 than currently projected — an average decrease of 1.5 miles per person, per day.

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Regional planning agencies are already required under state law to develop strategies for reducing planet-warming emissions from transportation. Those plans, known as Sustainable Communities Strategies, focus on getting housing built near public transit in urbanized areas, investing in public transit and pathways for bikers and pedestrians, and minimizing sprawl, according to the California Air Resources Board. The Southern California Association of Governments' regional plan, which covers the Coachella Valley, is designed to reduce carbon emissions 19 percent below 2005 levels by 2035.

One of the projects included in the regional plan is daily rail service between Los Angeles and the Coachella Valley — a long-awaited option that is likely still years away.

But the regional plans, even if fully implemented, won't reduce driving enough for the state to meet its climate goals, according to the Air Resources Board's climate report. The report says state officials and local governments need to get more housing built near transit stations, design streets that prioritize walking and biking, and promote the use of bike-sharing and car-sharing services. The report also says high-speed rail is key, since train travel can reduce the need for carbon-intensive airplane trips within the state.

Nilles said there are "enormous upsides" to getting people out of their cars, even on top of the climate benefits. Those upsides include less lung-damaging air pollution, less time sitting in traffic and improved health. Nilles pointed to shared bikes and electric scooters as emerging options that are helping people get comfortable with driving less.

For Gov. Brown, setting a target of carbon neutrality is about more than California. Climate change is a global problem that requires global solutions, and the governor has long sought to influence the rest of the world by implementing ambitious policies in California and showing that they work. That's why he signed the carbon neutrality order this week, in advance of the Global Climate Action Summit in San Francisco.

Reshaping how Californians get around might be the state's biggest climate challenge yet. But Busch, from Energy Innovation, thinks the Golden State will get it done. He noted that California had recently reached its first climate change target — bringing carbon emissions back down to 1990 levels by 2020 — four years ahead of schedule.

"California has set bold targets before that seemed like challenges and aggressive, but we've hit them," Busch said. "We're making this statement on a track record of success."

Sammy Roth writes about energy and the environment for The Desert Sun. He can be reached at sammy.roth@desertsun.com, (760) 778-4622 and @Sammy_Roth.