A new study from UC Berkeley indicates that climate models may significantly underestimate carbon emissions from wildfires in boreal forests due to overlooked peat soil burning. Researchers analyzed 2018 wildfires in Sweden and found that smoldering underground fires release ancient carbon stored for centuries. This discrepancy highlights potential gaps in global emission estimates, especially in vast regions like Siberia and Canada.
Wildfires in the boreal forests spanning Alaska, Canada, Scandinavia, and Russia pose a greater threat to the climate than previously estimated, according to research led by Johan Eckdahl, a postdoctoral scholar in UC Berkeley's Energy and Resources Group. Published in Science Advances, the study examined 324 wildfires that occurred across Sweden in 2018, using national forest records and field measurements to map emissions accurately.
The key finding is that these fires often extend into peat soils—layers of partially decomposed plant material accumulated over hundreds or thousands of years under cold, wet conditions. While surface flames are visible from satellites, the slower, smoldering peat fires are frequently missed by models that rely on such observations, which are calibrated more for lower-latitude fires.
"Many of the fires that matter most for the climate don't look dramatic from space," Eckdahl said. "Peatlands and organic soils can smolder for weeks to years, releasing enormous amounts of ancient carbon."
Comparisons with six global wildfire models revealed stark differences. In Gävleborg county, where intense, visible fires burned dry forests, models overestimated emissions. But in neighboring Dalarna county, with lower-intensity burns into thick organic soils, underestimations reached up to 14 times the actual amounts. Field data from 50 sites—19 with high-intensity fires and 31 with lower—measured soil carbon loss by comparing burned and unburned samples.
"Sweden is a very large country, but it's quite small compared to Siberia and Canada," Eckdahl noted. "We may be severely underestimating the impact of the recent extreme fire seasons in these regions."
The team, including co-authors Lars Nieradzik of Lund University and Louise Rütting of Brandenburg University of Technology, emphasizes that local factors like climate, vegetation, and soil influence emissions. Eckdahl is extending this work to U.S. western forests through the Western Fire & Forest Collaborative, focusing on soil microbes' role in recovery.
"Forests in the Lower 48 and those far up north may look very different, but they share the common currency of carbon," he added. This research aims to refine models for better climate adaptation strategies.
