Extreme California Wildfires Emit More Greenhouse Gases — But Scientists Don’t Know Exactly How Much

California’s wildfires are releasing millions of metric tons of carbon into the air — exacerbated by and contributing to climate change. How bad is it?

Scientists don’t know.

Cal Fire says more than 750,000 acres have burned so far in 2018, combusting grass, trees, homes, and all pushing out greenhouse gases.

The fires have consumed three times as much land as the 2013 Rim Fire, which the U.S. Forest Service estimates released 10-to-15 million metric tons of carbon — roughly the equivalent of the emissions resulting from a million Californians over a year.

But that does not mean this year’s fires have produced three times as much carbon.

Scientists say the Rim Fire’s severity burned old, tall trees to the ground, even the stumps. The heat and terrain will differ from this year’s fires, however.

Berkeley researcher Bill Stewart says emissions depend on those factors. “The fire might just go right by [young trees] and they’ll just be singed,” Stewart said. “If it’s burning really hot, everything could burn, so you could get 10 to 15 times as much smoke from the same acre.”

Accurately measuring the fires in real time would require mapping both a blaze’s severity and heat. Stewart also questions the equations that state agencies have used to gauge fire emissions. He says it needs more research.

“You can come up with an answer,” he said, “but the chance the method is correct decreases substantially if you don’t have a lot of people trying to think it through.”

The California Air Resources Board, which oversees the state’s climate-change goals, does not count fire emissions against those goals, although it is currently working on calculating the level of emissions each year. The agency considers the fires part of nature, even as their frequency and severity increase due to man-made climate change.

“The release of biomass carbon into the atmosphere is part of the Earth’s recent carbon cycle (as opposed to burning fossil fuels which releases carbon that has been stored underground for millions of years),” the agency said in an emailed statement.