Study Shines Light On Mysterious ‘Brown Carbon’ While Over A Dozen Western Fires Fume

CREDIT: AP/ Ted S. Warren

Washington Gov. Jay Inslee views the Chiwaukum Creek Fire near Leavenworth, Wash., from the air, Friday, July 18, 2014.

While the politics and mechanisms of funding wildfire suppression have been the main confusion underlying this year’s season thus far, a new study gives insight into a little-known element of wildfires’ impact: brown carbon.

Congress was unable to settle on important measures for funding wildfires before heading home for the August recess. Because of this U.S. Agriculture Department chief Tom Vilsack said that about $400 million meant for “making the forest better, healthier and more resilient” will have to instead be put toward fighting this year’s fires. Congressional inaction means that by the end of August all of the Forest Service’s appropriated fire-fighting money could be exhausted, according to Vilsack. The cost of wildfire suppression has grown from 13 percent of the Forest Service budget a decade ago to more than 40 percent in 2014.

Before the recess Congress was considering treating wildfires like earthquakes and hurricanes, which would make extra emergency funding available to fight fires so fire-prevention funds wouldn’t run dry.

While some members of Congress will be able to ignore the immediate impacts of their indecision, those in states along the Pacific coast, where fires have been raging recently, will face hard questions and harsh realities. In Washington state, fires have already burned more than 350,000 acres, about five times the annual average. More than 340 homes have been lost in the Carlton complex wildfire, the largest in state recorded history. Washington state Gov. Jay Inslee has requested emergency assistance from the federal government. The state has already spent $91 million fighting fires this summer.

As of this weekend, up to 16 major wildfires were burning in the Northwest. Last night nine new wildfires were set off by lightning in northeastern California.

Funding is not the only thing up in the air when it comes to wildfires. A new study led by Carnegie Mellon University with scientists from the Los Alamos National Laboratory and the University of Montana focuses on brown carbon, a major component of smoke from wildfires. It is well known that black carbon, or soot, has a significant impact on global warming. Wildfires account for one-third of Earth’s black carbon. While black carbon consists solely of carbon molecules, brown carbon contains a number of organic materials that make it hard to identify and model. Brown carbon has a similar atmospheric warming impact as black carbon, but its prevalence and warming efficiency as evident in wildfire smoke is less known.

The study found that the amount of brown carbon coming from a wildfire didn’t depend so much on what was being burned but rather corresponded with the amount of black carbon present in the smoke. This in turn relies on the burning style of the fire, such as the size of the flames or the duration of smoldering.

“Experimentalists have known about the existence of brown carbon for a while, but its “brownness”, which dictates its warming effect has not been well understood,” Rawad Saleh, a postdoctoral researcher at Carnegie Mellon and lead author of the study, told ThinkProgress.

Saleh said that particulate light-absorbers like black and brown carbon warm the planet in a fundamentally different way than greenhouse gases like carbon dioxide and methane. While GHGs absorb outgoing infrared solar radiation, preventing it from going back into space, black and brown carbon absorb incoming solar radiation, causing them to heat up. Black carbon absorbs solar radiation efficiently at all visible wavelengths, however brown carbon absorbs more in the shorter blue wavelengths than the longer red wavelengths, which gives it its brown color.

“The current IPCC report puts global warming by black carbon at approximately one-third that of carbon dioxide, but there is no mention of brown carbon.” said Saleh. “Our back-of-the-envelope calculations show that the warming by brown carbon can be one-fourth to one-half that of black carbon. Of course, detailed climate modeling is required to get more accurate numbers.”

Saleh said he and his fellow researchers are in the process of doing just this in an effort to help climate models predict the warming effect of brown carbon.