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As the smoke from wildfires in Northwestern Ontario blanketed parts of the northeastern United States earlier this month, former President Donald Trump attributed the air quality crisis to Canada’s forest mismanagement. However, a recent study published in the journal *Geophysical Research Letters* challenges this narrative, highlighting that a staggering three-quarters of emissions from these wildfires originate not from trees above ground, but from carbon stored in the soil.
A Shift in Understanding Wildfire Emissions
The study, led by Alemu Gonsamo, a remote sensing specialist at McMaster University, meticulously analysed the dynamics of wildfire emissions during Canada’s unprecedented fire season of 2023. This year saw a record-breaking area of approximately 150,000 square kilometres—over four per cent of the country’s forests—consume in flames, releasing carbon emissions equivalent to those of a large nation.
Gonsamo and his team aimed to clarify the contributions of above-ground vegetation and soil carbon to total wildfire emissions. Their findings indicate that the carbon locked away beneath the surface plays a far more significant role than previously understood. “Public perception of fire is very different from reality,” Gonsamo stated, reinforcing the need for a nuanced perspective on wildfire management.
The Scale of the Crisis
The events of 2023 have had a profound impact on air quality across North America. Smoke billowed from extensive fires in northern Quebec, enveloping cities such as New York and Washington in a dense haze. This season’s wildfires were not isolated incidents; they were part of a wider pattern of severe fires occurring in Alberta, British Columbia, and the Northwest Territories.
Research indicates that the carbon emissions from the Canadian wildfires in 2023 reached between 469 million and 639 million tonnes. This amount is striking, equating to roughly two-thirds of India’s annual fossil fuel emissions. Such staggering figures underscore the urgency of addressing the underlying causes of these wildfires, particularly in light of ongoing climate change.
The Role of Soil Carbon
Gonsamo’s research underscored the critical role of soil carbon in wildfire emissions, revealing that the layers of decaying vegetation and organic matter in the forest floor represent a vast reservoir of carbon. When forest soils become sufficiently dry, they ignite and release significant amounts of carbon, contributing to the smoke that drifts southward into the United States.
The study found that in areas affected by recent fires, soil typically contained between 20 and 60 kilograms of carbon per square metre in the top metre alone. In drier northern regions, soil carbon levels can exceed 90 kilograms per square metre, further amplifying emissions if ignited.
Climate Change and Future Wildfires
The research team relied on a comprehensive soil carbon inventory developed in 2021 and conducted fieldwork in areas ravaged by fire in 2023, particularly in northern Quebec. Their approach combined field data with machine learning techniques to assess the variability of carbon content across different landscapes. The study concluded that approximately 76 per cent of emissions from the 2023 wildfires originated from below-ground carbon, totalling 554 million tonnes of carbon released.
Dr. Werner Kurz, a retired research scientist who contributed to the study, noted that climate change exacerbates wildfires by lowering water tables and accelerating permafrost melt, thereby increasing the availability of soil carbon for combustion. The interaction of these factors suggests that future wildfire seasons could release even more carbon into the atmosphere.
Mike Flannigan, a fire scientist at the University of Alberta, emphasised the role of flash droughts in intensifying wildfire behaviour. Rapid drying conditions may lead to larger fires that are difficult to control, particularly when winds carry smoke across borders.
Why it Matters
The findings of this study have far-reaching implications for how we understand and respond to wildfires in Canada and beyond. As climate change continues to alter weather patterns, the increased frequency and intensity of wildfires will pose significant challenges for air quality and ecological health across North America. Rather than attributing blame, it is crucial to recognise the complex interplay of factors contributing to wildfire emissions and to implement informed strategies that prioritise both environmental protection and public health.