What is the impact of increasing boreal forest fires on Arctic climate and sea ice?

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Boreal forests cover large areas of northern Asia and North America, mainly over Siberia, Canada, and Alaska. In recent years, these forests have been affected by an increase in fires, caused in part by warmer summers and less snow in the spring. These fires emit large amounts of smoke which can be blown by winds northward to the Arctic. Once this smoke gets to the Arctic, it can both cool the climate by reflecting sunlight, but also warm it (if the smoke is nearer the surface, or if the small smoke particles reach the ice and snow on the surface, as they can darken it and absorb more sunlight). As we expect temperatures to continue to warm everywhere on the planet, it is likely that large boreal fires will continue and even become more common. We plan to study the impact that the smoke may have on Arctic climate and sea ice using climate models. In the past, these climate models have not taken into consideration an increase in these boreal fires, and our work will help us determine if this is an important process to get right for understanding future changes in Arctic climate and sea ice. As we prepare for the next generation of climate models that help inform the United Nations’ panel on climate change, our results will also help highlight the importance boreal forest fires may have for climate change in the Arctic.Biomass burning from boreal forest fires can impact Arctic climate and sea ice via the atmospheric transport of aerosols, particularly black carbon, from source regions into the Arctic. While in the atmosphere, aerosols can have either a positive (warming) or negative (cooling) radiative forcing, depending on their elevation. Black carbon can also be deposited onto the sea ice or snow at the surface, where it has a positive radiative forcing because it darkens it and absorbs more sunlight. While fully coupled climate models simulate these processes, the amount of biomass burning is prescribed as a set forcing. In the most recent set of climate model runs that help inform the United Nations’ panel on climate change, simulations from 2015 to 2100 used fixed projections of boreal biomass burning emissions that did not anticipate an increase in forest fires. However, in the real world we have observed a dramatic increase in boreal biomass burning over the last 10 years, in part due to warmer summers and reduced spring snow cover (which itself is driven by warmer springs), and the emissions of black carbon are already more than double what the climate models used over 2015-2100. We plan to study the impact that an increase in boreal biomass burning has on Arctic climate and sea ice by running climate model simulations that prescribe an increase in aerosol emissions based on the recent observed growth in these fires. We also plan to study the impact that wind patterns have on the transport of smoke from boreal forest fires, as it is known that certain weather patterns can promote the likelihood of forest fires. This coupled interaction between weather and fires is currently missing in climate models, and our work will help us determine how important winds, in addition to the amount, severity and seasonality of fires are in determining how much black carbon is transported into the Arctic. Our results will serve to inform stakeholders of the importance of boreal forests for Arctic climate in the coming decades. As the community prepares for the next round of climate model simulations, our results will help inform the modeling community on the importance of both increasing boreal forest fires and the interaction of fires and winds on Arctic climate and sea ice.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.