Positive Feedbacks

Soot From Forest Fires: Yet One More Amplifying Feedback to Human-Caused Climate Change

Robertscribbler,

8 June, 2014

A new study produced by Los Alamos National Laboratory has found that soot from forest fires is a more powerful amplifying feedback to human caused climate change than previously thought. The study, based on empirical measurements following the 2011 Los Conchas Fire in the lab’s vicinity, found that tiny tar balls produced during burning served to reduce land and air albedo (reflectivity) and resulted in increased levels of solar absorption.

“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, “Both components can potentially increase climate warming by increased light absorption.”

An increasing rate of wildfires is a primary result of human-caused warming. This feedback releases carbon stocks stored in trees and flora back into the atmosphere through burning, adding to the already elevated levels of carbon there. For years, the production of this feedback has been taken into account in climate models that estimate future warming. However, the effect of aerosols like the black tar balls in forest fire soot identified by the Los Alamos study have not been taken into account.

Previous climate models counted aerosols as warming-neutral due to the assumption that black carbon emissions that absorbed sunlight and heated the land and atmosphere were balanced by organic carbon aerosol emissions that reflected sunlight and cooled the land and atmosphere. Unfortunately, the Los Alamos study found that black carbon tar balls outnumbered organic carbon aerosols by a factor of 10 to 1:

“Most climate assessment models treat fire emissions as a mixture of pure soot and organic carbon aerosols that offset the respective warming and cooling effects of one another on climate,” Dubey explained. “However Las Conchas results show that tar balls exceed soot by a factor of 10 and the soot gets coated by organics in fire emissions, each resulting in more of a warming effect than is currently assumed.

“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 2 or more. This has a huge impact on how they should be treated in computer models.”

The Los Conchas fire emissions study provides new information that may help improve the accuracy of climate models going forward. Sadly, it’s bad news to find yet more evidence of sensitivity via amplifying feedbacks in the Earth climate system. Black carbon is also a subject of concern because it coats ice sheets, thereby reducing their overall resilience and reflectivity. In a recent expedition to Greenland, Dr. Jason Box and associates are attempting to measure the effects black carbon soot, some of it from forest fires, have on the great ice sheets there.

“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.

Links:

A Vicious Cycle

The Dark Snow Project

Wildfires May Have Bigger Role in Global Warming