California is continuing to lower its greenhouse gas emissions, but the transportation sector remains a stubborn obstacle in the state’s aggressive fight against climate change, new data show.

The California Air Resources Board said Monday that the state’s emissions fell 1% in 2017, the most recent year available, to 424 million metric tons. The state is now well past its 2020 goal of reducing greenhouse gas levels to 1990 levels — 431 million metric tons.

Clean-energy improvements in the heavily regulated electric sector have driven a lot of the emissions decline. In 2017, electricity emissions fell 9% — more than any other sector.

For the first time since the state began tracking greenhouse gas emissions, clean energy sources powered most of the state’s electric grid, according to Gov. Gavin Newsom’s office.

Now California faces much more ambitious goals of cutting greenhouse gas emissions about another 40% by 2030, and 80% by 2050. The latest numbers indicate that polluting cars and trucks are a big hurdle toward hitting that target: Vehicle tailpipes were the source of 37% of the emissions in 2017. Their total output rose 0.7% but “showed signs of leveling off,” according to Newsom’s office.

“California is proving that smart climate policies are good for our economy and good for the planet,” Newsom said in a statement. “As the Trump Administration attempts to obliterate national climate protections, California will continue advancing the cause of American climate leadership.”

Notably, the annual inventory released by the state tallies emissions of carbon dioxide and other pollutants but does not include wildfires, which can undo a lot of the state’s climate gains.

“It is very problematic, and a significant public health and safety concern,” said Katelyn Roedner Sutter, manager of U.S. climate for the Environmental Defense Fund. “It’s part and parcel of the larger question about what do we do to prevent wildfires, but we certainly cannot ignore those emissions.”

The emissions drop in 2017 came even as California’s economy grew at 3.6%, which was higher than the national average, Newsom’s office noted. Roedner Sutter called it a strong sign that reducing emissions does not have to restrict economic growth.

“You can decouple them,” she said. “You can grow your economy and reduce emissions at the same time.”

Still, experts say transportation will be a tough area to make dramatic improvements.

“We’ve kind of wrung out the easy stuff from the electric sector, and I think we’re going to now be turning toward the more challenging sectors,” said James Bushnell, a UC Davis economics professor who has advised the air resources board on climate policy. “We haven’t really figured out the effective means to do the reduction in those sectors, as we’ve done with electricity.”

One way California has tried to lower emissions is through fuel-efficiency standards that the Trump administration is trying to unwind. Four major automakers recently signed onto a deal with the state in which they agreed to clean up their fleets anyway.

Assemblyman Phil Ting, D-San Francisco, said he was not surprised to see transportation-related emissions go up, in part because cost-of-living challenges in high-priced areas have forced many people to live farther from their workplaces, giving them a longer commute even though they might be driving a more fuel-efficient car.

Ting noted that, in regards to the state’s tally, most of the 2017 greenhouse gas emissions from tailpipes came from passenger cars.

“Most people, when they think of emissions, they’re thinking it must be the semi trucks and the FedEx and the UPS trucks, when in reality, the data says it’s you and me driving our cars to work, driving to the grocery store, going on our nice, long trips,” he said. “We need to clearly get people out of their passenger vehicles or we need to change what’s emitted by passenger vehicles.”

The Legislature is currently considering a bill carried by Ting, AB1046, that he hopes will encourage more people to buy electric cars by “re-envisioning” the state’s rebate program for them. Ting said he wants to make it more financially attractive for people to buy electric cars sooner rather than later.

State officials said the emissions from California’s industrial sectors, which accounted for 21% of all the greenhouse gases they tracked in 2017, fell slightly or stayed the same. Fossil-fuel-dependent refineries and hydrogen production were responsible for a third of that, while the rest came from sources such as extraction of oil and gas, cement plants, glass manufacturers and food processors.

The state said it continues to see small annual increases of methane emissions and is looking beyond dairy farms to tackle the problem. A regulation adopted by the air resources board is designed to lower methane emissions from oil and gas production and other facilities and target methane emissions from landfills.

Bushnell said California should also focus on creating and implementing policies that will be attractive to other states.

“California is such a small chunk of the global emissions that all that really matters is whether what we’re doing here gets picked up and tried elsewhere,” he said.

J.D. Morris is a San Francisco Chronicle staff writer. Email: jd.morris@sfchronicle.com Twitter: @thejdmorris

Correction: An earlier version of this story contained a misplaced quote. Kaitlyn Roedner Sutter’s comments on a “very problematic” emissions source pertained to wildfires.