Forest fires release fine particles, biomass burning aerosols (BBA). These aerosols affect the climate. Usually, they have a cooling effect. It was therefore thought that aerosols from fires in boreal forests also had a cooling effect. But a combination of observations and models shows otherwise, according to a new publication in Nature Climate Change by earth scientists Qirui Zhong (Peking University and guest researcher VU), Nick Schutgens and Sander Veraverbeke (VU), and Guido van der Werf (WuR).
Sunlight
Previous research, based only on model calculations, suggested that aerosols emitted from boreal fires have a strong effect on cloud cover. As a result, more sunlight would be reflected. But the observations and model calculations by Zhong, Schutgens, Veraverbeke and Van der Werf show that the soot in aerosols actually absorbs sunlight. They also show that over the past two decades, emissions from boreal fires increased as temperatures in the regions rose.
Self-reinforcing system
The study shows the importance of properly testing models against observations. Schutgens: "We have discovered a self-reinforcing effect in the climate system. Global warming creates more boreal fires. These may lead to more aerosol emissions, which in turn would lead to further global warming."
A worrying result, which the researchers say urgently needs more research. The scientists also say that management of forest fires in the boreal region could be a worthwhile investment, to slow down the self-reinforcing effect.
Image: Stefan Doerr
