Canada’s peatlands are tinderboxes that are more likely to ignite in a warming world

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When a devastating forest fire raged near Parry Sound, Ont., in 2018, Sophie Wilkinson, a postdoctoral researcher at McMaster University, was busy gathering data at a study site in northern Alberta. But once she knew her colleagues working near the fire were safe, all she wanted to do was get back there to see the result.

Nestled in a rocky inlet of Georgian Bay, Parry Sound is far from Canada’s Arctic and Subarctic wilderness. But the area has something in common with those more northerly reaches: an abundance of peat – dense layers of partly decayed vegetation that accumulate in moist places, generally over centuries. Long a neglected component of the landscape, peat is now in the scientific spotlight because of all the carbon that’s locked up in its pungent bulk. In a world increasingly ablaze with wildfires, the fate of that carbon is a matter of serious concern.

When peat burns, its carbon is released, and the peat switches from being a storehouse to a source of greenhouse gas emissions. This summer’s extensive fires in peat-rich Siberia loosed about as much carbon dioxide into the atmosphere as the Greater Toronto Area has generated over the past five years.

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MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE:

GEOLOGICAL SURVEY OF CANADA

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MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE:

GEOLOGICAL SURVEY OF CANADA

Total peatland (%)

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MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: GEOLOGICAL SURVEY OF CANADA

Globally, peatlands are estimated to store about 550 gigatonnes of carbon, more than all of the forests in the world combined. About one-quarter of that peat is found in Canada, with particularly dense concentrations in the Hudson Bay Lowlands and the Mackenzie River basin. Studies suggest this asset in Canada’s carbon accounting is at risk due to changing patterns of wildfire.

By chance, the Parry Sound fire, which ultimately consumed 11,362 hectares of woodland, burned across an area of peat deposits that McMaster scientists, led by ecohydrologist Mike Waddington, have been studying for seven years. Dr. Wilkinson is a member of the team, and with so much information at hand about what was there before, she was able to go in after the conflagration to measure precisely what impact the fire had.

“It was utterly desolate,” she said. “There was so little soil left that most of the trees had fallen over after they had burned, as well.”

Though fire is a natural process, what was striking about the Parry Sound event was its intensity and the way it penetrated into areas that would typically be considered too wet to burn easily. Dr. Wilkinson and her colleagues found that peat deposits that were less than 70 centimetres thick were completely incinerated. Areas like this may not return as peatlands, but instead be taken over by deep-rooted deciduous trees that drink up moisture. Trees store carbon too, but peat stores more, so a net loss of peatland after a fire is bad news for the climate.

The study, published Tuesday in the journal Environmental Research Letters, comes with a silver lining. Areas of deeper peat were shown to survive the fire and stay wet enough to rebound. But the work sheds new light on how vulnerable peatlands have become in places that are burning differently than they did in the past as the climate warms.

That trend is now indisputable, said Matthew Jones, an Earth systems scientist at the University of East Anglia in the U.K. In a brief released this week, Dr. Jones and four co-authors examined 116 separate studies and found that all of them either directly strengthen or are consistent with evidence that climate change is increasing the frequency and severity of wildfires in multiple regions of the globe. Not surprisingly, among the areas most affected by the trend are those that have been prominent in the news due to record-setting fires in the past year, including California and eastern Australia.

“By and large, the picture is that of a warming, drying world – which is not helpful when it comes to fires,” Dr Jones said. He added that forward-looking studies using climate models "are all pointing to this situation getting worse the more the temperature rises.”

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For now, the change in Canada is less extreme than in the western U.S., but it’s heading in the same direction. While the area burned has doubled in Canada since the 1970s, in California it has increased by about a factor of five, said Mike Flannigan, a professor at the University of Alberta who studies the link between climate change and fire.

Yet, the Arctic is also warming faster than the rest of the world, and this is where peatland is likely to play a bigger role in releasing carbon, creating a positive feedback cycle that spurs warming even further.

“That can really tip the effect of the wildfire season, even if the amount of area burned doesn’t change,” Dr. Wilkinson said.

Daniel Thompson, a fire scientist with Natural Resources Canada, said that fire in Canada’s northwest is clearly on the rise and is affecting peatlands in a way that’s different from the past.

The numbers bear this out. Of the 10 most severe wildfires in Canadian history, six have occurred within the past decade, all in the northwest. These include the Fort McMurray fire of 2016, which stands as Canada’s costliest natural disaster, and the massive fires near Yellowknife in 2014, which collectively burned an area larger than all of Vancouver Island.

While the numbers are startling, “this is not a new disturbance to the system,” Dr. Thompson said. "It’s more a question of frequency and intensity.”

Many of these Canadian wildfires have been raging in areas that are covered in peat. Sometimes referred to as “zombie fires,” there’s evidence that peat fires in the North can smoulder on through the winter and resurface anew in spring. And unlike the dramatic and very visible damage that fire has wrought further south, the most profound effects may be out of sight and underground. This is because peat often overlaps with another key feature of the Northern landscape: permafrost.

Permafrost is the permanently frozen ground that persists year-round below surface soil. When the Northern landscape burns, the permafrost below loses a measure of insulation that protects it during the summer months. Instead, the blackened, sooty surface left behind in a fire’s wake is ideal for absorbing sunlight and warming up the ground.

The loss of permafrost due to climate change is already a problem for Northern communities because it destabilizes the ground and threatens infrastructure. More broadly, scientists fear that melting permafrost is releasing methane, a potent greenhouse gas, creating another feedback loop that can further accelerate climate change. In this scenario, fire adds another boost.

David Olefeldt, a wetland scientist at the University of Alberta, has been examining the interaction of peat, permafrost and fire. He said the effects are likely not all in one direction, in part because melting permafrost may also act to suppress fire. “More fire and more thaw changes the landscape to become wetter and less treed, and therefore it burns less," he said. He’s currently studying the question, an example of how little scientists can say for certain about the fate of Northern ecosystems and their ultimate impact on the globe even as unprecedented change is under way. A shift in vegetation due to warming is yet another factor that has been difficult for researchers to take into account when modelling future change.

For Merritt Turetsky, director of the Institute of Arctic and Alpine Research at the University of Colorado, Boulder, the field is in urgent need of a co-ordinated and multidisciplinary effort to track the new reality in the North, and how changing fire conditions are playing into the story.

“We used to think of the Arctic as the last [ecosystem] unshaped by fire," she said. “That’s not true any more."

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