Global warming blamed for rise in ‘zombie’ forest fires

Researchers find that fires in Canada and the US survive rain and snow to re-emerge

Water droppers battle an out of control forest fire after the city of Prince Albert declared a state of emergency over a fast-moving wildfire, prompting some residents to evacuate, in Prince Albert, Saskatchewan, Canada May 18, 2021.  REUTERS/David Stobbe
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Global warming has led to rise in "zombie" forest fires in the northern hemisphere that return to life despite being covered by snow over the winter.

Researchers found that fires continued to smoulder during the winter months, feeding on peat and fallen spruce needles before building in ferocity after the winter snow has melted, according to a study published in the journal Nature.

The climate is warmer faster in boreal forests of the far northern hemisphere than in most other places, making it more likely that "overwintering" fires survive winter snows.

Using Nasa satellite images, the team from Amsterdam in the Netherlands examined fires in Alaska in the US, and in the Northwest Territories of Canada.

They noticed that the fires often restarted in the spring in areas where forests had burned the previous year.

Most forest fires start because of human activity or lightning strikes. But the team discovered that the flames re-emerged before lightning season and in regions with little human habitation.

They found that the numbers of "zombie fires" were linked to warmer summers and could account for up to a third of the total burn areas.

These included the re-emergence of a fire in Alaska that in 2015 covered an area the size of Paris.

Rebecca Scholten, of Vrije University, Amsterdam, said: “We expect that more overwintering fires will occur with climate warming.”