A University of Wyoming study found that smoke from forest fires has a greater cooling effect than any computer models scientists have built would predict.
The study looked at the impact of mountain fires on global climate, using data from the University of Wyoming and other foreign research groups, compared with results from climate model simulations,” said Shane Murphy, associate professor of atmospheric science at the University of Wyoming. The main conclusion of this study is that the cooling effect of mountain fire smoke is greater than predicted by various existing climate models.”
The study, published Jan. 12 in the journal Nature Communications, describes how the structure, particle size and mixing state of the components within aerosols volatilized by burning vegetation combine to determine the optical properties of smoke in the atmosphere, a major factor in how these aerosols affect the atmospheric energy balance.
“We found that simulated aerosols or smog within most climate models are darker and more absorbent than the observed smog. This factor influences the results predicted by the individual models.” Hunter Brown, an atmosphericist and lead author of this study, said.
“This means that within the simulated system, more sunlight is absorbed by the smog and warms the atmosphere, contrary to what is actually observed. Actual observations and research data show that smoke with poorer absorption reflects more light into space, which has a cooling effect.”
Studies have shown that the color of smoke from mountain fires depends largely on the type of vegetation and the climate of the area where the fires occur. In general, hot, dry woodland fires like those in Africa and Australia produce smoke that is darker and absorbs more light, while smoke from fires in cooler, wetter regions like North America and northern Asia is much lighter and has lower light absorption.
However, when the researchers adjusted the aerosol data in a model to the observed data, the model still predicted higher smoke absorbance than the observed values for the African region. Brown said this may be a result of the model’s overly simplistic simulation of the aerosol evolution process, which does not reflect the actual situation.
Brown said the study comparing the computer model with actual global observations is valuable information for climate model researchers to help reduce uncertainties in climate model assessments of the effects of mountain fire smoke on climate.
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