Wildfires More Likely to Cause Climate Warming than Previously Thought: A Study

Wildfires, with their "witch's brew" of carbon-containing particles, may be responsible for more climate change than previously thought, say scientists from Los Alamos National Laboratory and Michigan Technological University, who determined that the actual particles emitted by fires are very different than those used in current computer models.

Conventional wisdom states that fire-driven particles contain black carbon or soot that absorbs sunlight to warm the climate and organic carbon or smoke that reflects sunlight to cool it. However, in a paper published in the journal Nature Communications, researchers explain that, based on an analysis of the morphology and composition of the aerosols emitted by the Las Conchas fire of 2011, the spherical carbonaceous particles called tar balls were about 10 times more abundant than soot.

"We've found that substances resembling tar balls dominate, and even the soot is coated by organics that focus sunlight," said senior laboratory scientist Manvendra Dubey, explaining that "both components can potentially increase climate warming by increased light absorption."

Furthemore, the bare soot particles, which are composite porous fractal structures made of tiny spherical carbon, are significantly modified by the organics emitted by the fire. In all, 96 percent of the soot from the fire is coated by other organic substances, with 50 percent being totally coated.

In regards to why this is important for climate change, Dubey noted that, while most climate assessment models perceive fire emissions as a mixture of pure soot and organic carbon aerosols that cancel each other out, the tar balls far exceed soot and the soot gets coated by organics in fire emissions, meaning that fires are more likely to result in warming than previously believed.

"Tar balls can absorb sunlight at shorter blue and ultraviolet wavelengths (also called brown carbon due to the color) and can cause substantial warming," he said. "Furthermore, organic coatings on soot act like lenses that focus sunlight, amplifying the absorption and warming by soot by a factor of two or more. This has a huge impact on how they should be treated in computer models."

Based on this study, the researchers argue that a more realistic framework is needed that includes a realistic representation of carbonaceous aerosols in regards to climate warming.

"The fact that we are experiencing more fires and that climate change may increase fire frequency underscores the need to include these specialized particles in the computer models, and our results show how this can be done," Dubey said.