A recent study has revealed that the majority of smoke produced by wildfires in Canada originates from soil carbon rather than from burning trees, challenging common assumptions about wildfire emissions and their underlying causes. The findings have important implications for understanding the sources and future impacts of smoke from large-scale fires, such as those currently affecting Northwestern Ontario.

The research, published Monday in the journal Geophysical Research Letters, is based on data gathered during Canada’s record fire season in 2023. Scientists analyzed emissions from wildfires across the boreal forests and found that approximately 75% of the smoke released derives from the combustion of carbon stored in the soil, not from trees and surface vegetation as widely believed.

This insight runs counter to recent claims made by U.S. President Donald Trump, who criticized Canada for alleged forest mismanagement amid smoke dispersal over parts of the northeastern United States. Trump’s rhetoric included threats of new tariffs, arguing that poor Canadian forestry practices were responsible for the cross-border smoke pollution. However, the study’s authors emphasize that soil carbon, a long-standing carbon reservoir, is the dominant contributor to wildfire emissions, thus mitigating the role that forestry management plays in the problem.

“Public perception of fire is very different from reality,” said Alemu Gonsamo, a remote sensing specialist at McMaster University in Hamilton and co-lead author of the study. The research team applied remote sensing technology and field surveys to quantify soil and vegetation contributions to smoke production, helping to clarify the mechanisms behind these continent-scale pollution events.

The findings carry significant consequences for environmental policy and firefighting strategies. Since boreal wildfires are likely to persist amid climate change, smoke emissions will continue to affect air quality over large regions, including urban centers in North America. The study suggests that mitigating smoke impacts will require approaches beyond simply improving forest management practices, given the substantial role of soil carbon combustion.

As wildfires increasingly become a feature of the boreal landscape, understanding the sources and dynamics of their emissions is crucial for preparing public health and environmental responses. This study provides an important foundation for such efforts by refocusing attention on the often-overlooked contribution of soil carbon to wildfire smoke.