California’s annual climate check-up is out. The good news is the electricity we use is getting much cleaner. The bad news? Greenhouse emissions from cars and trucks aren’t budging.

Every fall, the California Air Resources Board (CARB) releases data on the state’s biggest emitters of heat-trapping gases, which are regulated under the state's cap and trade program. In 2016, their combined carbon dioxide emissions were 16 million metric tons lower than in 2015 – a “huge and unexpected drop,” according to economist Michael Wara, who directs Stanford’s Climate and Energy Policy program and closely follows state emissions trends. For comparison, emissions in 2015 fell less than 2 million metric tons below 2014 levels.

Most most of the drop was due to the continued shift away from fossil fuels and towards renewable sources for energy, especially solar. In 2016, solar electricity generation in California jumped by nearly a third. Meanwhile, the LA Department of Water and Power stopped buying coal-fired electricity from the largest coal plant in the West, the Navajo Generating Station in Arizona.

Contribution of each sector of the economy to total carbon dioxide emissions in California in 2015. CARB

But emissions from cars and trucks -- the largest contributors to climate pollution in the state -- were slightly higher than they were in 2015. That’s because gas prices were lower in 2016 compared to previous years, so people drove more, said Rajinder Sahota, who oversees cap and trade and other climate programs at CARB.

Policies targeting transportation emissions are also newer than those targeting electricity generation. For example, California’s greenhouse gas emissions standards for cars and pick-up trucks weren’t passed until 2012, where as the state has been requiring utilities to get more of their power from renewables since 2002.

Weekly retail gas prices on the West Coast, 2008-present. EIA

“These policies take a little while to actually get established,” Sahota said. “It’s about turning over fleets of vehicles, which doesn’t happen overnight.”

In addition, Sahota said the state can't tell people what kind of car to drive or how much to drive – which is essentially what CARB is doing to utilities by telling them them need to get 50 percent of their electricity from renewable sources by 2030.

“We have said to the utilities, ‘If you want to do business, you have to drive this kind of power plant,’” Wara said. “Imagine the politics of saying to everyone in California, ‘Guess what? You have to get rid of your SUV and get into a more fuel efficient vehicle.’ That’s a non-starter.”

Instead, the state relies on incentives to help people offset the costs of new electric cars, has programs to encourage people to scrap polluting vehicles, and is assisting with the construction of EV charging infrastructure.

A new study by The Nature Conservancy suggests there is yet another way to reduce our carbon emissions: increase the amount of carbon that gets absorbed into wetlands, forests and the soil. The study, published in Proceedings of the National Academy of Sciences, found that aggressively restoring wetlands, reducing timber harvesting, preventing grassland loss and supplementing soils could capture enough carbon to account for up to 17 percent of California’s goal of cutting emissions to 40 percent below what they were in 1990 by 2030.

“There’s very few ways in which we can pump carbon dioxide out of the atmosphere, and managing and conserving land is one of those ways,” said lead author Richard Cameron, the director of science and land programs for The Nature Conservancy.

Wildfires, however, can upend that equation: turning forests from a place where carbon gets stored into a source of the greenhouse gas.

CARB’S latest draft of its “scoping plan,” the document that helps the state meet its emissions reduction goals, includes land restoration, tree planting, and avoiding wildfires as ways to get to that 2030 goal.