Regional to global impacts of boreal biomass burning emissions changes

High latitude wildfire regimes are changing, and boreal regions have seen unprecedented fire activity in recent years. Given the high climate sensitivity of the Arctic and boreal regions, it is important to explore the impacts of these changes. There are also region-specific impacts of biomass burning particular to high latitude regions, such as black carbon (BC) deposition on snow. While many sources of atmospheric pollution are being mitigated, fires are emerging as a growing contributor to poor air quality, both locally to the fire emissions source and across wider regions.

Here we investigate the climate and atmospheric effects of increased biomass burning emissions, including the sensitivity to emission region, focusing on aerosols. We perform idealized emission perturbation experiments in two Earth System Models (CESM2 and NorESM2), where we perturb first all boreal biomass burning emissions and then emissions in smaller regions of interest (boreal North America, East Siberia and West Siberia). These experiments use 2005-2014 as a baseline period, and use the sum of this period as the perturbation, giving an approximately x10 perturbation in the regions of interest, in both fixed SST (30 years) and coupled (200 years) simulations. The strength and location of the aerosol changes studied here (when comparing aerosol optical depth) are comparable to the recent trends in aerosols between 2015-2024 and 2005-2014.

We investigate subsequent effects on modelled atmospheric composition with a focus on the high latitudes, including air quality implications, and climate response, including effective radiative forcing (ERF) and fully-coupled climate response estimates. The preliminary analysis highlights the role of boreal forests in enhancing aerosol optical depth, over the source regions but also extending into the central Arctic, as well as local air pollution levels. Global and Arctic mean ERFs of 0.5 Wm-2 are estimated, with some distinct differences depending on the region of emission, at least for the Arctic average forcing.