Climate change is driving more intense wildfires in Canada, according to a new modeling study, with fuel aridity and rising temperatures amplifying burn severity, particularly over the last several decades. The findings underscore the growing impact of climate change on wildfire behavior, with the most severe effects concentrated in Canada’s northern forests. Fueled by ongoing climate change, Canada – one of the most forested and fire-prone regions in the Northern Hemisphere – is grappling with increasingly severe and prolonged wildfire seasons. 2023 marked a record-breaking fire season. Over seven times the historic average area burned that year. Burn (or fire) severity is a crucial metric used to measure the ecological impacts of wildfires and can inform ecosystem responses, landscape resilience, and fire management strategies. However, comprehensive national-scale modeling of burn severity and its key drivers remains limited, challenging scientists’ ability to generate long-term, high-temporal-resolution (e.g., daily) estimates. Addressing these gaps is crucial for understanding how climate change shapes wildfire dynamics across Canada’s vast and remote forests. Weiwei Wang and colleagues combined 40 years of spatiotemporal wildfire data to build a multinomial logistic regression (MLR) model to investigate the factors influencing burn severity across 10 Canadian ecozones. Wang et al. found that fuel aridity – the amount and moisture of flammable vegetation – was the most significant driver of forest fire burn severity and that summer months were more prone to severe burning. The most severe fire conditions have occurred over the last 2 decades. The analysis also revealed variation in the effect of individual drivers across different regions in Canada. Northern Canada experienced a marked increase in burn severity driven primarily by changing climate, whereas fuel aridity and vegetation type played a more critical role in southern Canada. “From an ecological perspective, the increase in fire activity in boreal forests, especially in the northern regions of the world, has raised grave concerns about the health and function of biomes that act as important carbon sinks,” writes Jianbang Gan in a related Perspective. “Cooperation between the US, Canada, and Russia, which share 93% of the global boreal forest, is needed to effectively manage fire while preserving this valuable ecosystem of the northern hemisphere.”

For reporters interested in trends, in an October 2024 Science study (www.science.org/doi/10.1126/science.adl5889), Jones et al. show how vegetation dynamics coupled to weather were the primary drivers of forest fire carbon emissions from 2001 to 2023 in the nontropical regions of the world. In another October 2024 Science study (www.science.org/doi/10.1126/science.adk5737), Balch et al. found that the growth rate and intensity of wildfires across the U.S. has substantially increased between 2001 and 2020.