Burning soil and peat drove most emissions in Canada’s record 2023 wildfire season

AGU press contact: Sean Cummings, [email protected] (UTC-7 hours)

Researcher contact: Alemu Gonsamo Gosa, McMaster University, [email protected] (UTC -4 hours)

McMaster University press contact:
Andrea Lawson, [email protected] (UTC -4 hours)

HAMILTON - Most of the carbon released during Canada's record-breaking 2023 wildfire season came from burning soil and peat, rather than trees, according to new research from McMaster University.

The study, published 27 July in the journal Geophysical Research Letters, found that underground carbon stores accounted for 76 per cent of wildfire emissions, helping drive a fire season that released nearly a quarter of the world's wildfire emissions that year.

Researchers estimate the 2023 wildfires burned 15.1 million hectares - seven times Canada's 20-year average - and released 610 million tons (554 million tonnes) of carbon.

"Canada stewards 20 per cent of the world's soil organic carbon in its peatlands and soils. Future wildfire risk is not just about losing forests, it's about releasing these vast stores of carbon that have accumulated underground over millennia into the atmosphere," explains Alemu Gonsamo, associate professor in the School of Earth, Environment & Society, who has long studied Canada's land ecosystems.

Peatlands are waterlogged ecosystems that have traditionally helped stop fires from spreading. But hotter and drier conditions in recent years have lowered water levels, turning normally fire-resistant peatlands into massive smoldering fuel sources.

"When fires start under these conditions, they can burn deep into peat and soil, releasing carbon that took thousands of years to accumulate in a single fire season," says Gonsamo.

Canada is home to about 420,000 square miles (1.1 million square kilometres) of peatlands. The Hudson Bay Lowlands alone, which are the second largest peatland complex in the world, store an estimated 33 billion tons (30 billion tonnes) of carbon.

The findings highlight the vulnerability of Canada's soil carbon stores to intensifying wildfires.

"For years we've focused mostly on the trees that burn. This study shows we must also pay attention to what's happening beneath the surface," says Gonsamo. "While forest management remains important, its impact is limited because many of these fires occur in remote, unmanaged areas. Prolonged hot and dry conditions are allowing smoldering ground fires to persist and releasing significant amounts of stored carbon."

One-third of all wildfire carbon emissions in 2023 were linked to peatlands alone.

"What we're seeing is a shift from these landscapes storing carbon to releasing large amounts of it during extreme wildfire seasons," says Gonsamo. Once that carbon is released, it contributes to further warming and increases the risk of future fires.

The climate impact of the 2023 Canadian wildfires was enormous. In carbon dioxide terms, the emissions were roughly three times greater than Canada's annual human-caused greenhouse-gas emissions reported for 2022.

"There is no alternative to reducing global greenhouse gas emissions to slow climate change and curb the growing intensity of wildfire emissions in Canada and elsewhere," says Gonsamo.

"Addressing the root cause of increasingly severe fire seasons requires coordinated global action on climate change. This cannot be done by Canada alone."

Notes for journalists:

This is published in Geophysical Research Letters, an AGU journal. View and download a PDF of the study here. Neither this press release nor the study is under embargo.

Paper title:

"Three-fourths of Carbon Emissions from 2023 Record-Breaking Wildfires in Canada Traced to Soil and Peat Combustion"

Authors:

• Zilong Zhong, School of Earth, Environment & Society, McMaster University, Hamilton, Ontario, Canada.
• Chinyere Ottah, School of Earth, Environment & Society, McMaster University, Hamilton, Ontario, Canada.
• Brendan M Rogers, Woodwell Climate Research Center, Falmouth, Massachusetts, USA.
• Sander Veraverbeke, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands. School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom.
• Stefano Potter, Woodwell Climate Research Center, Falmouth, Massachusetts, USA.
• Werner A Kurz, Forest Service, Natural Resources Canada, Victoria, British Columbia, Canada.
• Lucas Ribeiro Diaz, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
• Spencer Christensen, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
• Alemu Gonsamo Gosa, School of Earth, Environment & Society, McMaster University, Hamilton, Ontario, Canada.

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This press release was originally published by McMaster University: news.mcmaster.ca/burning-soil-and-peat-drove-most-emissions-in-canadas-record-2023-wildfire-season/