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Wildfires in the North American boreal forest burn vast tracts of land every year, continuously changing the terrain while affecting plant physiology, permafrost thaw and carbon fluxes. Climate warming has been shown to lead to larger areas being burned annually, as seen in the record fire season of 2023 that burned a land mass about seven times greater than an average fire year.

Now new research, published in AGU Advances, finds that beyond decimating old-growth forests and releasing large amounts of CO2 into the atmosphere, wildfires warm the surface of the land substantially for about five decades in the summer and slightly cool land temperatures in the winter.

Researchers at Dalhousie University analyzed satellite images and field observations of the land-atmosphere energy exchange at more than 100 sites in Alaska and Canada over several years. They found that after a wildfire, the forest has fewer leaves, absorbs less sunlight due to the exposed snowpack, and heat is less efficiently transferred from the forest to the atmosphere, which causes warming and cooling depending on the season and the time since the wildfire disturbance.

After a wildfire, forests initially lose less water to the atmosphere, then experience increased water loss for about 30 years before returning to lower, pre-fire levels again. These changes in forest water loss further complicate impacts on the surface climate due to the surface cooling effect of evaporating water.

This research shows that wildfires over the past five decades are estimated to have warmed the boreal forest during the day by about 0.3 °C in the summer while cooling it by 0.02 °C in the winter, resulting in an annual warming of 0.12 °C. With increased wildfire activity, annual daytime surface temperatures in the Canadian boreal forest are estimated to further warm, reaching 0.16 °C by 2050.

Manuel Helbig, an assistant professor of Atmospheric Science at Dalhousie and the study's lead author, is available to discuss how this research illustrates the potential for accelerated surface warming with increased wildfire activity, something that needs to be accounted for when formulating ambitious climate policies and related climate mitigation targets.

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Media contact:

Alison Auld
Senior Research Reporter
Communications, Marketing and Creative Services
Dalhousie University
Cell: 1-902-220-0491
Email: alison.auld@dal.ca