The scale of the Canadian wildfires, which ravaged millions of hectares, surprised by their ability to affect populations living thousands of kilometers away. An international study has just measured this reach, highlighting the direct impact of fine particles contained in the smoke on public health, from North America to Europe.
An unprecedented season
Fires multiplied in Canada between May and September 2023, in a climate made more favorable by global warming. Nearly 18 million hectares (44.5 million acres) were reduced to ashes, an area larger than England.
These massive fires released enormous plumes of smoke, darkening the sky and triggering repeated health alerts. Authorities observed an immediate deterioration in air quality across the North American continent.
But the uniqueness of the event also lies in the scale of atmospheric dispersion. Masses of particles spread as far as Europe, confirming that the effects of such fires extend far beyond national borders.
Revealed health impacts
Researchers estimated that 354 million people breathed air with fine particle concentrations exceeding the threshold recommended by the World Health Organization. These PM2.5 particles can penetrate deep into the lungs and enter the bloodstream.
The study distinguishes between deaths related to acute exposure, during a few days of high concentration, and those caused by more diffuse chronic exposure. The former are associated with immediate heart attacks or respiratory distress. They number 5,400 in the United States and Canada.
The latter are more numerous, as they involve cardiovascular or pulmonary pathologies aggravated by months of polluted air. The toll is estimated at nearly 70,000 premature deaths across North America and Europe.
Unprecedented modeling
To obtain these results, scientists combined satellite observations, chemical transport models, and machine learning techniques. They then cross-referenced this data with epidemiological models establishing links between pollution and mortality.
The exercise involved uncertainties, particularly due to the lack of comparable precedents. Researchers therefore had to rely on expanded databases regarding exposure to fine particles.
Despite these limitations, the study published in
Nature provides the first quantification of the intercontinental health impact of wildfires. It highlights a previously underestimated dimension of these disasters.
Article author: Cédric DEPOND