The Arctic winter typically snuffs out the seasonal wildfires that erupt in this region. But every once in a while, a wildfire comes along that refuses to die. These “zombie fires,” also called “holdover fires,” are blazes that burn in one season, die down and smolder through the winter by slowly combusting within peat and other soils, only to reignite the next spring.
For the past several years, these zombie fires have been recorded in northern Siberia, with 2020 being a particulaerly bad fire season. And such fires were also anecdotally reported during the summer of 2019, Merritt Turetsky, a University of Colorado professor who studies peat and wildfires, tells Axios.
A recent study published in the journal Nature on Wednesday, explains that to survive the winter, fires have to burn especially hot and deep, and it makes no difference how much rain or snow falls on the ground.
“The sheer fact that this is happening is already pretty crazy and shows how fast this region is changing because of climate change,” said Sander Veraverbeke, a landscape ecologist at Vrije Universiteit Amsterdam and co-author of the study.
“We know that fires can start in the fire season by lightning and humans. Now we can have another cause of burned area. If it happens near a fire scar from the year before, early in the season, and there’s no lightning and it’s not human, then it’s an overwinter fire,” he added, according to Reuters.
Boreal forests are the Earth’s largest land biome
The boreal forest (or “taiga”) is the world’s largest land biome, spanning eight countries – including Canada, China, Finland, Japan, Norway, Russia, Sweden and the United States – in the far Northern Hemisphere. In total, all the boreal forests represent about 30 percent of the global forest area.
Boreal forests are special, in many ways. The fauna growing in the forests have adapted over thousands of years to living in a region where winter can last for months on end, while the growing season is at most, about 130 days.
Like all forests they absorb carbon dioxide –a main contributor to global warming and climate change, removing it from the atmosphere and helping to keep the entire planet healthy. However, the quality of soil in the boreal forest is inferior to that of the soil found in deciduous forests, partly because of the colder climate.
The fallen leaves and moss do not always decompose into the soil, and the needles from the evergreen trees tend to be acidic. Permafrost is thawing and even the peat below the surface is burning, and insect outbreaks have gobbled up increasing numbers of trees. Climate zones are moving north ten times faster than forests can migrate.
Russia’s Siberian boreal forests are not the only region seeing zombie fires. Sections of boreal forests in Canada’s Northwest Territories and in Alaska are also seeing an increase in their “overwintering” fires.
Zombie fires in the Boreal forest will become more common
The study found that three main factors are leading to an increase in zombie fires, and that are tied to global warming: summer temperature extremes, large annual fire extents, and fires that burn deeper into the soil.
Already this spring, fires are erupting in Canada and Siberia, with scientists tracking them, often via Twitter, using satellite imagery.
The paper underscores the need for governments to start collecting official statistics on holdover fires and early season peat fires, said climate researcher Jessica McCarty of Miami University in Ohio, in an email to Axios.
“More importantly, this paper gives our first estimates of how much holdover fires may be contributing to annual burned area totals and from there we can better understand emissions,” she said.
“What has been in the past a relatively rare phenomenon might become something more frequent and catastrophic,” said Nancy Fresco, a landscape ecologist and climate researcher at the University of Alaska Fairbanks
