As forest fires wipe out Canada’s boreal forest, a study highlights the role these fires could play in slowing global warming.
Two million hectares already consumed. More than 26 000 people displaced. The forest fires currently raging in Canada got off to a very strong start this year. And very early too, leading to fear the worst for this summer. Canada is still reeling from the aftermath of the fires of 2023, which ravaged more than 17 million hectares, suffocating its American neighbor as far away as New Orleans before reaching Europe. We still remember the surreal images of the New York skies turning orange, proof of deteriorating air quality.
While every summer the Arctic burns up under the influence of global warming, a new study shows that fires could actually slow down global warming.
Published last Tuesday in Proceedings of the National Academy of Sciences, a team of researchers from the University of Washington and the University of Louvain in Belgium reveal the details of this paradox, which stems from the underestimated frequency of fires affecting Arctic regions.
The scale of fires in Siberia and Canada has intensified over the past decade. In 2019 and 2021, particularly critical periods saw flames destroy millions of hectares of forest. The fires of 2023 were among the most destructive, notably due to extreme heat and intense winds. These fires are directly fueled by the effects of climate change: higher summer temperatures, reduced spring snow cover, and rapidly declining sea ice. Added to this is drier ground, making it easier for flames to spread. This worrying trend is set to continue over the coming decades, according to climatologists’ projections.
Until recently, international climate models had not taken sufficient account of the increasing intensity and frequency of these fires. The CMIP6 climate model, used to forecast climate change up to 2100, had assumed that these fires would remain relatively constant and of low intensity. However, recent events show a different reality, with fire peaks in 2019, 2021 and 2023. In response to this reality, the University of Washington team recalibrated their projections, incorporating a significant increase in boreal fires up to 2060. The result: an increase in boreal fires would slow global warming by 12% worldwide and by 38% in the Arctic.
Although the burning of forests releases large quantities of carbon dioxide, contributing to global warming, the smoke produced by these fires surprisingly plays a cooling role. Aerosols in the smoke reflect sunlight, brightening clouds. This reflection reduces solar irradiance on the earth’s surface, particularly in northern regions. This phenomenon lowers summer temperatures in the Arctic, slowing the melting of sea ice and contributing to a temporary cooling of the region.
The effect is all the more marked in winter. Fires, by obscuring part of the summer sky, make the Arctic colder, allowing sea ice to remain thicker and last longer during the winter months. This dynamic leads to a negative feedback effect, where the increased presence of sea ice can slow warming in the region.
However, the effect can only be short-term, as this cooling does not compensate for the long-term warming effects of fires on the global climate. Rising carbon dioxide and soot particles, which settle on the ice and darken it, also contribute to ice melt, in contrast to the cooling effect of aerosols.
The effects of these fires are not limited to the boreal regions. The resulting smoke is carried over vast distances by the winds and cools not only the Arctic, but also temperate regions as far north as the latitude of Northern California. It also modifies tropical precipitation patterns, pushing them southwards, as it disturbs temperature differences between the hemispheres.
Not exactly good news
On a global scale, these fires have significant ecological and health consequences. “It’s important to remember that these increasing fires still have a lot of negative impacts for human health and for forest biodiversity,” notes Edward Blanchard-Wrigglesworth, research associate professor of atmospheric and climate science at the University of Washington and lead author of the study, in a press release issued by the University. “And if the fires continue to increase, eventually they could burn through the forests and the trend could reverse. So I wouldn’t say this is good news. But it helps us better understand nature and these trends.” Boreal forests also play an essential role in climate regulation, acting as carbon sinks. Their degradation could exacerbate the climate crisis, with global repercussions.
This understanding is particularly important for fire management. The researchers therefore call for the increase in boreal fires to be taken into account in climate models and their consequences. “If the increase in boreal fires continues unabated over the next decade or two, society may decide we want to manage boreal fires more. But before we put a lot of resources toward that, we need to try to understand the possible consequences.”
A better understanding of the complex interactions between fire, aerosols, warming and cooling is essential for refining future climate forecasts. Revised data on boreal fires could also help to adapt fire management strategies, a worrying symptom of our planet’s evolution.