Wildfires the cause of likely 'irreversible' permafrost thaw in Western Canada

People and infrastructure in Canada's North will have to adapt to shifting ecosystems, says researcher.

Wildfires have caused nearly a quarter of all permafrost thaw-2,000 square kilometres-in Western Canada's boreal peatlands over the past 30 years, according to a new University of Alberta study.

"Wildfire is a very important force on the landscape, and what we see here is that it continues to have impacts long after the burning is done," said Carolyn Gibson, who conducted the research as part of her master's degree studies in the Faculty of Agricultural, Life & Environmental Sciences.

The research, published in Nature Communications, showed that wildfires burning across northern peatlands in Alberta and the Northwest Territories triple the rate of abrupt permafrost thaw for up to 30 years after the fire.

Permafrost, a thick underground layer of soil that remains frozen throughout the year, is crucial for carbon retention, water quality and stability of roads, buildings and other infrastructure.

Its thawing poses hazards to both infrastructure and humans by damaging important cultural sites and making travel across the land much more challenging, Gibson noted.

"Indigenous communities in the North have important places out on the land, and there's a common concern among them about the damage permafrost thaw could cause. It can include damage to burial sites, places of important stories, traditional hunting and fishing grounds, and historical travel routes.

"When the permafrost thaws, the ground goes from being solid to something that is very wet and soupy. It's exceptionally difficult to move through these thawed areas, and travel across them may be virtually impossible," she explained.

The effects of wildfire on permafrost in the region included warmer soils, deeper seasonal thaw and an underlying layer of soil that remained unfrozen throughout the entire year.

The situation isn't expected to get better, Gibson said, noting research has already shown that the number of wildfires and the area burned in North America are expected to increase by 25 per cent by 2030 and by 75 to 100 per cent by the end of the century.

"Historically, permafrost in this area underwent a natural cycle of thawing and reforming, but given current climate conditions and projections for the future, this fire-induced thaw appears to be irreversible," she said, citing a report by the United Nations' Intergovernmental Panel on Climate Change predicting that, if we stick to our current path, we could see 3.7 to 4.8 C of warming-or even more-by the end of the century.

"With that temperature rise, it's going to be too warm in these areas for permafrost to regenerate," she said.

The study's findings also suggest climate scientists may be underestimating the magnitude of permafrost loss across the North.

"Given that we don't currently factor fire-induced permafrost thaw into our estimates, we are probably underestimating future greenhouse gas emissions from northern peatlands," Gibson said.

As a result, she said, northern populations will have to start considering the consequences.

"When permafrost thaws, ecosystems shift," she explained.

For community planners and forestry and wildlife managers, she said what becomes important is adaptation.

"We can't prevent the thawing but we can create smart infrastructure that may be more resilient to changing ice conditions in the soil.

"For Indigenous communities, it's about working to understand where and when permafrost is likely to thaw, as this can affect food security as access to traditional hunting grounds becomes impacted," she said.