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A recent study spearheaded by the University of Washington anticipates that over the next 35 years, escalating boreal fires will actually reduce global warming by 12% on a global scale and 38% in the Arctic region. The aerosols present in smoke reflect more sunlight and brighten clouds, resulting in decreased summer temperatures during the fire season, which leads to less sea ice loss and cooler winter temperatures. Here, New York’s Triborough Bridge is shrouded in smoke stemming from the 2023 Canadian boreal fires.James Andrews/iStock
Even if you reside far from the boreal woodlands in Canada and Siberia, you have probably observed a rise in smoke from their forest fires. During significant wildfires in 2023, the smoke tinted the New York skyline orange and extended as far south as New Orleans. These wildfires have intensified over the past decade due to climate change impacts — hotter summers, diminished snow cover in spring, and the reduction of sea ice. Experts predict that this trend is likely to persist.
However, recent climate change projection models have not incorporated this increase. For instance, the widely referenced sixth Coupled Model Intercomparison Project, or CMIP6, released in the late 2010s, held these fires constant at a relatively low intensity.
A recent study from the University of Washington forecasts that in the upcoming 35 years, rising boreal fires will actually decelerate warming by 12% globally and 38% in the Arctic. This research is the first to highlight the disparity between the recorded surge in boreal fires and the stable fire levels employed in climate models. Because the aerosols in smoke enhance cloud brightness and reflect sunlight, summer temperatures during fire seasons decline in northern areas, resulting in reduced sea ice loss and cooler winter temperatures. This impact occurs despite the warming consequences of the fires themselves from factors such as soot that accumulates on ice.
Researchers released their results on June 3 in the Proceedings of the National Academy of Sciences.
“This study helps us start to better predict the consequences of climate change. The significant rise in these fires in recent years is, in itself, a symptom of that,” stated lead author Edward Blanchard-Wrigglesworth, a UW research associate professor of atmospheric and climate science. “It’s critical to recognize that these escalating fires still pose numerous negative repercussions for human health and forest biodiversity. And if the fires keep rising, they could eventually deplete the forests, reversing the trend. So, I wouldn’t categorize this as positive news. However, it aids our understanding of nature and these patterns.”
Every six or seven years, climate modeling institutions globally collaborate to refresh their projections, utilizing data from the 19th century up to projected figures through 2100. These data encompass aspects like wildfires and anthropogenic carbon emissions. For CMIP6, projected before boreal fires were identified as a clear anomaly, the wildfires were maintained at a constant level from 2015 to 2100.
“If you examine the time series of the fires, it begins to rise around 2015, but it sharply peaks in 2019 and 2021, just as this modeling was nearing completion,” Blanchard-Wrigglesworth noted. “Those years marked significant Siberian fires. And then 2023 experienced an even more severe Canadian fire season.”
Since climate scientists do not foresee the causes of this increase in fires diminishing anytime soon, the team re-ran one of the CMIP6 models with a new boreal fire projection grounded in the current observed trends, resulting in a four-fold surge from 2015 to 2060. This revised modeling accounted for the effects of smoke aerosols. It also took into consideration aspects like the soot from the fires, which settles on Arctic ice, darkening it and causing it to absorb more sunlight (similarly to how sun heats asphalt). Nonetheless, the enhanced reflection of sunlight due to aerosols outweighed this warming effect.
This chart contrasts black carbon emissions from boreal wildfires. The red line illustrates actual observed emissions. The solid blue line represents estimates from the CMIP6 model, while the dotted blue line shows estimates modified based on the recent rise in fires.Blanchard-Wrigglesworth et al./PNAS
Although the fires occur solely in the summer months, researchers found a more pronounced cooling effect during the winter, as the fires obstruct some of the summer sunlight, leading to thicker Arctic ice that endures into the subsequent winter.
The research indicated effects extending far beyond boreal forests. The smoke cools temperatures throughout all seasons from the Arctic down to Northern California at 40 degrees north latitude. The fires also drive tropical precipitation further south because tropical rainfall is partly dependent on the temperature disparity between the two hemispheres.
The authors suggest that future studies should adjust additional climate models to reflect the increasing boreal fires and explore potential changes in the land following these fires.
“I hope our research raises awareness of this issue for further examination and the possible effects of any future human management of these remote fires,” said Blanchard-Wrigglesworth. “If the rise in boreal fires persists unabated in the next decade or two, society might decide to implement some management strategies for boreal fires. However, before we invest substantial resources into that, we must strive to comprehend the potential repercussions.”
Patricia DeRepentigny, from Université Catholique de Louvain, and Dargan Frierson, a UW associate professor of atmospheric and climate science, are co-authors of this paper. This investigation was supported by the National Science Foundation and the European Union.
For further details, reach out to Blanchard-Wrigglesworth at [email protected].