Wednesday, July 10, 2013

Wildfires even more damaging

Wildfires cause even more damage than many climate models assume. Much has been written about the threat that wildfires pose to people's safety and health, to crop yields, and the quality of soils and forests.

In addition, wildfires pose a huge threat in terms of climate change, not only due to the impact of emissions on the atmosphere, but there's also the impact of particles (soot, dust and volatile organic compounds) settling down on snow and ice, speeding up their demise through albedo changes. This contributes to the rapid decline of the sea ice and snow cover in the Arctic, a decline that has been hugely underestimated in many climate models.

Furthermore, global warming and accelerated warming in the Arctic cause extreme weather conditions in many places, an impact that is again underestimated in many climate models.

A team of scientists from Los Alamos and Michigan Technological University, led by Swarup China, points out that continued global warming will make conditions for wildfires worse, as was already noted in earlier studies, such as this 2006 study. They also point at the conclusion of a recent study that more biomass burning will lead to more ozone, less OH, and a nonlinear increase of methane's lifetime.

Mixing and classification of soot particles. Field-emission
scanning electron microscope images of four different
categories of soot particles: (a) embedded, (b) partly coated,
(c) bare and (d) with inclusions. Approximately 50% of the
ambient soot particles are embedded, 34% are partly coated
and 12% have inclusions. Only 4% of the particles are bare
soot (not coated or very thinly coated). Scale bars, 500 nm.
Right, spherical tar balls dominate in the emissions.
The scientists recently completed an analysis of particles from the Las Conchas fire that started June 26, 2011, and was the largest fire in New Mexico's history at the time, burning 245 square miles. One of the scientists, Manvendra Dubey, said

 “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. 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.”

Finally, many climate models ignore the threat of large, abrupt methane releases in the Arctic. As discussed in many earlier posts at Arctic-news blog, accelerated warming in the Arctic threatens to spiral out of control as methane levels rise over the Arctic, causing destabilization of methane hydrates and further methane releases, escalating into runaway global warming. 

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