Wildfires in the northern forests of Canada and Alaska have far more complex consequences for the climate than simply producing additional greenhouse gas emissions. Research by Earth scientist Max van Gerrevink shows that the climate impact varies greatly by region and can continue for decades. While fires in Alaska contribute to warming on average, wildfires in many parts of Canada currently have a cooling effect. Due to climate change, however, that cooling effect is decreasing.
Different effects in Alaska and Canada
The vast forests of Canada and Alaska are increasingly affected by large and severe wildfires. These fires change the landscape, emit greenhouse gases and influence vegetation, snow cover and permafrost, among other things. As a result, the effects of a fire can remain visible for decades.
In his research, Van Gerrevink brings these different effects together and shows that there is no simple answer to the question of whether northern wildfires warm or cool the climate.
In Alaska, wildfires have a warming effect on average. One important reason is the relatively large release of carbon from vegetation and from carbon-rich frozen soils. When these soils are affected by fire, permafrost can also thaw. This can release additional carbon into the atmosphere.
In many parts of Canada, the current picture is different. There, a fire can temporarily have a cooling effect. After a fire, the ground often remains covered with snow for longer in spring. The bright snow cover reflects much more sunlight back into space than an intact forest. As a result, the landscape absorbs less heat, creating a cooling effect.
Climate change is changing the balance
However, this cooling effect is not permanent. As the climate warms, winters are becoming milder and snow cover is decreasing. Snow also remains on the ground for a shorter period than before. As a result, the difference between a burned area and an intact forest is becoming smaller.
The research shows that the climate balance in northern regions is gradually shifting. “Wildfires that currently still have a cooling effect in some parts of Canada will provide less and less cooling in a warmer climate, and will therefore more often contribute to additional warming,” says Van Gerrevink.
The results make clear that the effects of wildfires should not only be assessed during and shortly after a fire. Processes that unfold in the years afterwards, such as vegetation recovery, changes in snow cover and the thawing of permafrost, also determine the eventual climate impact.
Relevance for nature management and climate policy
The findings from Van Gerrevink’s research are relevant for regions where wildfires are becoming more frequent and more severe. For nature managers and policymakers, it may be important to look not only at the size of a fire, but also at where it takes place and what happens afterwards.
Areas with carbon-rich soils and permafrost may be particularly important, because a fire there can potentially have long-term consequences for the carbon balance. Satellite images can be used after a fire to quickly determine the severity of the damage. That information can then be used in decisions about restoration, forest management and climate adaptation.
The relevance of the research is underlined by the exceptionally large number of wildfires in Canada in recent years. The year 2023 stands out in particular, when more than 15 million hectares went up in flames, more than 3.5 times the size of the Netherlands.
No simple story of ‘fire causes warming’
Above all, the research shows that the climate impact of northern wildfires can differ by region and over time. A fire can both release additional greenhouse gases and cause changes in the landscape that temporarily lead to cooling.
By considering these processes together, a more complete picture emerges of the role of wildfires in the climate. As the northern climate continues to warm, it will become increasingly important to take account of changing snow cover and the vulnerability of carbon-rich soils.
The climate balance of northern wildfires is therefore not a simple story of warming or cooling alone. It is an interplay of processes that differs by region and can continue to have an effect for decades after a fire.