Poleward transport of smoke aerosol from extreme boreal wildfires

In recent decades, surface air temperatures in the Arctic increased faster than average global temperatures. At the same time, weather conditions that favor wildfires became more frequent globally and will likely continue to do so in a warming climate. This might lead to an increase in fire activity in most areas of the world, but particularly in regions with moderate moisture supply that are rich in biomass, such as North American temperate forests and boreal forests.

Extreme wildfires potentially emit large quantities of smoke that can be elevated as high as to the stratosphere, thereby possibly leading to a long-lasting atmospheric perturbation. Smoke aerosol is mostly composed of black carbon (BC) and organic carbon (OC). While BC mainly impacts the climate by heating the atmosphere through absorption of solar radiation, OC particles are important as cloud condensation nuclei, affecting cloud and precipitation formation. In light of the rapid Arctic warming, it is crucial to understand the role of smoke aerosol from wildfires in the Arctic climate system.

Using multidecadal simulations with the global aerosol-climate model ECHAM6.3.0-HAM2.3., it is analyzed on which pathways BC and OC emitted during extreme boreal wildfire events are transported towards the Arctic and how their transport patterns differ from those of smoke particles originating from moderate boreal wildfires. The contribution from the wildfire aerosol to the total poleward aerosol flux is calculated, and it is quantified which fraction of boreal wildfire aerosol reaches the Arctic region in the course of extreme fires. Transport heights, the accurate representation of which still poses a challenge to current climate models, are compared to height-resolved measurements of smoke aerosol.