The varying intensity of Northern Hemisphere wildfires from year to year has a significant influence on the extent of Arctic ice, according to a study published in the journal Science Advances. The significant emanations certain years would favor the formation of clouds in the Far North, which would slow the melting of the pack ice up to a certain point.
The researchers, based at the University of Colorado at Boulder and the National Center for Atmospheric Research, revisited the most recent climate models. They found that the greenhouse effect caused by the accumulation of GHGs in the atmosphere – even if it is the main factor of global warming – could not fully explain the annual variations in ice extent over the Arctic Ocean.
They noted that from the mid-1990s to the mid-2000s, the decadal loss of sea ice was the greatest on record, at a rate of decline of 13.3%. This corresponded to a period during which there were fewer forest fires in the northern hemisphere.
However, from the mid-2000s until the end of the 2010s, the sea ice retreated a little less rapidly, ie by 4% at a ten-year rate. This period saw greater than average fire intensity.
In a press release, the researchers explain that forest fires release small carbon particles, aerosols and various gaseous compounds which are transported by atmospheric currents and which can reach the Arctic. These particles would then contribute to the formation of airborne droplets and clouds in high latitudes.
When there are a lot of aerosols released in a year with intense fires, it can lead to more and thicker clouds. However, in years when forest fires are rarer, the clouds are thinner, which allows more solar radiation to pass through the atmosphere and melt the ice during the summer, explains the team led by Patricia DeRepentigny, postdoctoral researcher atu National Center for Atmospheric Research.
Scientists have noted a link between marked concentration of aerosols in the atmosphere, the formation of thicker clouds and colder temperatures on the ground. But this relationship is not linear and many factors come into play, the researchers point out.
It should also be noted that the global climate is subject to cyclical variations that extend over several years, such as the phenomenon El Nino or La Nina or the Arctic Oscillation.
In addition, work had already shown that the retreat of the ice floe in the Arctic is accelerating global warming and contributing to the multiplication of forest fires in the northern hemisphere, the researchers point out.
“The Arctic is often seen as that region that we don’t have to worry too much about because it’s so far from home. But the fact that there’s this feedback between what’s happening here with the forest fires and the variation in the sea ice, and the fact that the shrinking sea ice may cause more forest fires, that brings us closer little more of the Arctic”, observes the researcher.
The researchers point out that their work is based on the use of models. Whether the relationship they shed light on will hold up with new observations over the years remains to be seen. That will allow them to improve their simulation.
“The objective we are aiming for is to make these climate simulations more reliable and to give us projections which can then inform political decision-makers and societal choices” with regard to climate change, says Patricia DeRepentigny.
Moreover, a study has already highlighted a phenomenon whereby soot (black carbon) released from forest fires that can be transported to the Arctic can contribute to the melting of sea ice when it settles on the ice. This creates a darker surface which collects the sun’s rays and accelerates the melting. However, the extent of this mechanism and its impact on the climate remain to be clarified.
As an illustration, the animation below shows the movement of smoke from forest fires in eastern Siberia towards the Arctic, in the summer of 2021.
This week’s climate graphic is on Siberian wildfires and how the smoke from these blazes straddled the Arctic Circle in August and led to the highest carbon emissions on record
—Steven Bernard (@sdbernard) September 17, 2021