Alemu Gonsamo, an associate professor at McMaster University, led a study revealing that the 2023 Canadian wildfire season burned deep into peat and soil, releasing carbon that had been stored for thousands of years. According to the research published in the journal Geophysical Research Letters, the fires burned an estimated 15.1 million hectares of land, seven times greater than the 20-year average. This massive blaze season accounted for nearly a quarter of all global wildfire emissions in 2023.
Carbon stored beneath the surface
Canada's peatlands and soils are home to roughly 20 percent of the world's soil carbon. The country's peatlands cover about 1.1 million square kilometers, including vast wetland regions like the Hudson Bay Lowlands. This area is the second-largest peatland complex globally and holds an estimated 30 billion tonnes of carbon. In the past, these wetlands acted as natural barriers, preventing fires from spreading due to their high moisture content and dense structure.
However, in recent years, long heatwaves and extended dry spells have altered the region's natural defenses. These changing conditions have led to declining water levels, causing thick layers of moss and soil to dry out. What was once a fire-resistant environment has now become a source of smoldering fuel. The transformation has exposed long-buried carbon to direct combustion, significantly increasing the scale and impact of the wildfires.
Shift in fire behavior
When fires begin under these dry conditions, flames no longer stop at the surface but instead burn deep into the soil and peat layers. This deep burning accounted for one-third of all carbon emissions from Canadian wildfires in 2023. Gonsamo explains that these underground fires pose unique challenges for firefighting crews and forestry teams. Unlike surface fires, these subterranean blazes can persist for weeks or even months, making them extremely difficult to extinguish using traditional methods.
While managing forests remains a key strategy in preventing wildfires, its effectiveness is limited when fires occur in remote and unmanaged areas. Prolonged heat and dry conditions allow these underground fires to continue smoldering, releasing massive amounts of carbon into the atmosphere. As a result, northern landscapes that once served as carbon sinks are now major sources of emissions during extreme wildfire seasons.
Landscape transformation and climate impact
Once-stable northern landscapes, which had sequestered carbon for millennia, are now rapidly losing that stored carbon due to intense underground fires. Once released into the atmosphere, this carbon contributes directly to global warming, which in turn creates even hotter and drier conditions. This warming cycle increases the likelihood of future, potentially even worse fire seasons.
The total impact of the 2023 Canadian wildfire season was staggering. When measured in terms of carbon dioxide emissions, the fires released roughly three times the amount of greenhouse gas emissions that Canada reported from human activities in 2022. These emissions are primarily the result of rising global temperatures and prolonged dry weather, factors that local firefighting efforts alone cannot control.
Gonsamo emphasizes that reducing global greenhouse gas emissions is essential to slowing climate change and curbing the growing intensity of wildfires in Canada and other regions. No single country, including Canada, can tackle this crisis alone.
To fully understand the scale of the problem, the research team, led by McMaster University scientist Zilong Zhong alongside Gonsamo and Chinyere Ottah, used satellite tracking, ground-level measurements, and machine learning models. When converted into carbon dioxide, the total emissions surpassed two billion tonnes of CO₂.
The study also highlights a gap in current climate tracking systems. Many of these fires burn in remote, unmanaged northern regions, meaning their full environmental impact is often overlooked in official reports. As a result, global climate assessments may underestimate the true extent of carbon emissions caused by wildfires, particularly those that burn deep into peat and soil.