Diminishing periods of snow cover in northern forests, shortened by climate change, are poised to disrupt a delicate balance in some of the planet’s most climate-sensitive regions – according to new research from McMaster University, VU Amsterdam, and the Woodwell Climate Research Center.
Historically, carbon emissions from northern forest fires were counteracted by the reflective cooling power of snow cover in charred areas, but that is now under threat.
When northern forests burn, the charred landscape sits exposed through long winters. Snow settles over the open ground, creating a surface far brighter than the darker tree canopy of intact forests. This increases the surface brightness, known as surface albedo, which reflects more solar energy. In some regions, this can offset a substantial portion of the warming driven by carbon dioxide (CO2) emitted from wildfires.
For decades, this has been one of the natural processes helping to cool the climate after northern wildfires. However, declining snow cover across northern latitudes is steadily eroding this albedo cooling effect, exposing a feedback loop with serious consequences for the global climate.
“What was once a partial brake on warming is turning into a vicious cycle that accelerates warming and fuels even more intense fires,” says study co-author Alemu Gonsamo, associate professor of Earth, Environment and Society at McMaster.
Gonsamo, along with McMaster researcher Zilong Zhong and an international team of scientists, have shown that wildfires in northern forests are increasingly likely to amplify climate warming rather than counteract it. Their findings were published this week in Proceedings of the National Academy of Sciences.
“Climate change is leading to warmer springs and earlier snowmelt across Canada’s boreal ecosystems, which shortens the period when the exposed bright snow can reflect sunlight on post-fire landscapes,” says Gonsamo.
A comprehensive look at how northern wildfires shape the climate
Canada recently experienced its most extensive wildfire season on record in 2023, followed by the second-largest fire season in 2025 since national burned-area monitoring began in the 1970s. These record-breaking fire years highlight the rapidly escalating scale of wildfires across the northern latitudes.
During the 2023 season, the fires emitted an extraordinary amount of carbon exceeding the annual fossil fuel emissions of nearly every country on Earth.
“Yet the climate impacts of these wildfires extend far beyond the carbon they emit,” says lead author Max van Gerrevink, a PhD candidate in Earth and Climate science at VU Amsterdam.
Many factors influence the impact of wildfires on climate, including vegetation changes, shifting the brightness of the surface, and long-term soil impacts. The research shows that, historically, extended spring snow cover in burn scars has helped cool the climate, a natural effect that the new study finds is now beginning to weaken as spring snow cover diminishes because of climate change.
The consequences of retreating snow cover become especially clear at the scale of individual fires.
“Historically, nearly half of all Canadian wildfires reached a natural climatic break-even point, where snow-driven surface cooling fully offset the warming caused by fire-related emissions. Today, that proportion has fallen dramatically, to only about one in four or five fires,” says Sander Veraverbeke, the study’s senior author and associate professor of Earth and Climate at VU Amsterdam.
The study further shows that fires with higher carbon emissions per unit area are increasingly unlikely to achieve a full climatic offset. Compared to the 1960s, the albedo-driven cooling effect across northern forests has declined by nearly 30 per cent. The mechanism is failing where it matters most – the fires releasing the most carbon are precisely those for which the snow cooling buffer has become least effective, a compounding disadvantage that grows more severe with every degree of warming.
“The highest priority for addressing climate change remains aggressive global greenhouse gas reductions. At the same time, our findings highlight the urgent need to invest in smarter boreal fire management and forest stewardship practices that properly account for both carbon emissions and albedo effects, buying critical time for broader climate solutions while the snow-albedo cooling benefit is still available,” says Gonsamo.
The study authors highlight the need for targeted interventions focused on specific fires and landscapes where suppression pays the greatest climate dividend. Interventions remain both achievable and may in some cases be cost-effective.
