A 2021 study showed that in recent decades, zombie fires have been more common in the boreal forests of Alaska, the United States and Canada during winter, when previous summers were particularly hot. In early 2024, for example, there were ten to twelve times more zombie fires than normal in western Canada. Last summer the country experienced the worst fire season in its history. More than 18 million hectares of forests and grasslands were burned and around 200,000 people were displaced by the fires.
On the other hand, zombie fires also drive climate change because like all combustion processes they release greenhouse gases such as carbon dioxide (CO2) into the atmosphere.
What do winter fires mean for spring and summer?
If smoldering fires are not extinguished by melting snow, the risk of forest fires increases significantly in the following warmer seasons. Due to the lack of oxygen, zombie fires spread only slowly in the dense underground. But when dry leaves and other debris accumulate on the forest floor in spring, a single gust of wind is sometimes enough to reignite the flames.
This means that where there are zombie fires, the bushfire season could start much earlier in early spring rather than late summer. The forecast applies particularly to a dry spring: If there is little snow in the winter, which would moisten the ground during the spring melt, or if there is little rain in the spring, the risk of fire is even greater.