Alaska Fires Warm the Planet While Canada Fires Cool It - Permafrost Is Why

Walk across burned ground in interior Alaska and you are standing above one of the most carbon-dense soils on Earth. Beneath the char lies permafrost - frozen organic matter accumulated over thousands of years. When fire rips through and the ground thaws, stored carbon enters the atmosphere. The warming that follows invites more fire, which thaws more permafrost.

A study published in Nature Geoscience provides the most comprehensive accounting to date of how northern wildfires affect the global climate system. The findings resist simple summary. Fires in Alaska, on balance, warm the planet. Fires in Canada, on balance, cool it. The difference comes down to one factor: permafrost.

Two Biomes, Two Carbon Stories

The research team, led by Max Van Gerrevink, a doctoral student at Vrije Universiteit Amsterdam, combined historical fire records with satellite imagery, climate data, and machine learning to quantify net long-term climate impacts of fires across Alaska and western Canada between 2001 and 2019. The dataset covers nearly two decades of fire seasons and maps multiple climate-forcing factors simultaneously at continental scale.

The divergence in outcomes traces to geology. Canada's boreal forests and tundra sit over terrain scraped largely clean by glaciers. Permafrost exists there, but it is less extensive and less vulnerable than in Alaska. When fires burn through Canadian forests, they leave bare ground that, come winter, is blanketed by snow. That snow reflects sunlight back into space - a process called albedo - creating a cooling effect that, over the study period, outweighed the warming from carbon released during combustion.

Alaska is different. Much of the state sits atop vast stores of permafrost - organic soils frozen for millennia. When fire removes the vegetation and organic layer above, the frozen ground begins to thaw. That thaw releases carbon dioxide and methane not just during the fire itself, but for years and decades afterward. The long-term carbon pulse from post-fire permafrost degradation tips the net climate balance into warming territory.

"While the majority of northern forest fires in North America are currently exerting a climate-cooling influence, this is likely to change as northern forests continue to warm," Van Gerrevink said. "Continued warming is expected to reduce snow cover and shorten its duration, which may substantially alter the net climate impacts of future fires as it reduces the dominant cooling source from increased reflectivity from snow."

The Carbon Beneath the Surface

Scott Goetz, a Regents' professor at Northern Arizona University, and Michelle Mack, Regents' professor in NAU's Department of Biological Sciences, are co-authors who helped seed the research framework roughly two decades ago. Senior author Brendan Rogers at the Woodwell Climate Research Center - a former postdoc of Goetz - brought those ideas to completion.

Goetz and Mack describe the permafrost carbon problem in stark terms. About 70 percent of the terrestrial Arctic lies in Siberia and Eurasia - and that territory looks more like Alaska than Canada. It holds deep, vulnerable permafrost over enormous areas. If fire activity increases there as climate models project, the carbon consequences could dwarf anything observed in North America to date.

"It's a call that we really have to take this seriously - the more fires there are, the more rapidly permafrost is going to thaw," Mack said. "Maybe we need to think about slowing down these natural fires. It would buy us time while we figure out other solutions to decarbonize the atmosphere."

A Strategy for Fire Managers

Most fires in the study were sparked naturally by lightning in remote areas where suppression is logistically and economically impractical. But the findings point toward a practical triage approach that does not require fighting every fire equally.

"One clear takeaway is that fire managers could attempt to prioritize fighting fires in areas that are permafrost-rich, because that's where the bulk of the carbon is stored and vulnerable post-fire," Goetz said. "When rich organic soils are combusted, there is a big pulse of carbon dioxide. Then, as permafrost thaw follows, it continues to emit more carbon over the years after."

Not all fire suppression delivers equal climate benefit. A fire burning through a Canadian spruce stand with shallow organic soils carries different long-term consequences than a fire burning above deep Alaskan permafrost. Risk mapping that incorporates permafrost carbon stocks could help agencies direct limited resources toward fires with the largest potential climate costs.

A Fragile Equilibrium

The cooling effect of Canadian fires is real - but the researchers are careful not to frame it as reassurance. The cooling depends on snowpack, and snowpack depends on cold winters. Cold winters are becoming less reliable as the climate warms. As snow cover shrinks in extent and duration, the albedo benefit that currently offsets carbon emissions from Canadian fires will weaken. The 2023 Canadian fire season - which burned more than 18 million hectares and produced smoke blanketing cities across North America - showed how quickly those seasons can intensify.

The study's data end in 2019 and do not capture those more recent extremes, which means current estimates of warming from northern fires may be conservative. The research also relies on satellite-derived estimates of permafrost carbon loss rather than direct soil measurements, introducing uncertainty in translating broad patterns to specific fire events. Local soil conditions, fire intensity, and post-fire vegetation recovery all influence how much carbon is ultimately released - factors difficult to fully capture at continental scale.

The broader implication is that managing northern fire requires thinking on two timescales simultaneously: the immediate smoke and heat of the fire itself, and the slow, multi-decade release of permafrost carbon that follows. The second problem does not end when the flames go out.