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How climate change may be fueling Canada’s fire season

A photo provided by the Canadian Armed Forces shows a view of the wildfires in Fort McMurray, Alberta, on May 4. (Canadian Armed Forces via European Pressphoto Agency)

A devastating wildfire continues to rage around Fort McMurray in Alberta, Canada, having grown to more than ten times its original size and forced tens of thousands of people to flee their homes. Now, as firefighters struggle to contain the flames, some experts are saying that the blaze was likely helped along by factors related to climate change — which may also be contributing to a bigger trend in lengthier, more intense Northern fire seasons.

Around the same time the Fort McMurray fire sprang up (it arose Sunday from unknown causes), researchers from the Rutgers University Global Snow Lab released some alarming findings. According to satellite data, last month saw the lowest area of snow cover in the northern hemisphere of any April in the past 50 years, at just over 27.9 million square kilometers of coverage. The previous record-holder was April of 1968, with 28 million square kilometers.

While all the factors that played into the low snow extent remain to be explored, the findings generally suggest that this year’s mild winter caused snow to melt faster and earlier than in previous years, said David Robinson, the New Jersey state climatologist, who helps run the Rutgers Global Snow Lab. And some scientists, including Robinson, have suggested that the low snow extent could make for a dryer, more severe fire season in the north.

The intensity of a wildfire season depends on several key factors, according to Mike Flannigan, director of the Western Partnership for Wildland Fire Science at the University of Alberta. The three basic ingredients for a fire are fuel, in the form of trees or brush; an ignition source, usually lightning or humans; and hot, windy weather.

“What’s really important is fuel moisture — so how dry the fuels are determines whether the fire will start, whether it’s from human causes or lightning,” Flannigan said. “If the fuels are wet, the fire won’t start.”

Typically, a heavy snow cover in the winter means that melting in the spring will add moisture to both the soil and the organic fuels that feed fires when the weather warms. Thus, the two snow-related factors that may affect a fire season are how early the snow melts and how much water it releases when it does so.

Robinson has suggested that earlier melting, like what we’ve seen in the northern hemisphere this spring, can give forests and grasslands a chance to dry out earlier and provide the potential for a longer fire season. It’s a point other experts have raised as well.

“The earlier the snow melts, the longer the fire season — so the more days during which fires can ignite and burn,” said David Martell, a forestry professor and fire expert at the University of Toronto, by email, although he noted that he’s unaware of any studies that have explicitly investigated this connection.

However, Flannigan feels that the timing of snowmelt may not be as important as the total amount of moisture it releases. In any case, he noted that this past winter was unusually dry for Canada, setting the stage for a rough start to fire season — and Robinson also noted that April’s record-low snow cover could have been partly caused by the fact that “there was less of it to melt.”

Regardless, earlier melting and shallower snowpack to begin with were likely brought on by a combination of several factors, including the lingering effects of last year’s unusually severe El Niño event and the influence of climate change.

“El Niño in this part of the world [means] mild winters, dry winters, typically followed by mild springs and dry springs — and that’s exactly what’s happened,” Flannigan said. Alberta, in particular, did experience a dry winter with unusually low levels of precipitation and was in the throes of an especially warm April when the Fort McMurray fire struck.

From a broader perspective, though, Robinson pointed out that the low snow extent observed in April is part of a longer trend that’s likely related to the ongoing march of climate change. Three out of the five lowest April snow extents have occurred in the past 10 years — and overall, low snow cover in the spring has occurred more and more frequently in the past several decades.

The pattern is most pronounced in May and June, Robinson said, noting that April’s low record almost certainly indicates that we’ll be seeing unusually low snow cover during the next few months, as well. And he added that “snow extent of the last decade is declining at a rate in the spring that’s more pronounced than the rate that [Arctic] sea ice is declining in the summer.”  

It’s possible that declines in snow cover may even be contributing to climate change through a kind of feedback effect, he pointed out. Snow helps to reflect sunlight away from the Earth and back out into space — so less snow cover means more solar radiation is being absorbed, which leads to greater warming of the Earth’s surface. This, in turn, causes more snow to melt.

Still, snow is just one of many weather- and climate-related factors that may play a role in a fire season’s severity. The outbreak in Alberta may have been influenced by low snowpack or early melt, contributing to overall dry conditions — but as Martell pointed out, low humidity and high winds were also important factors. And the way the rest of the season plays out will depend on similar conditions, including temperature, humidity, rainfall and wind speeds.

These are all factors that scientists believe have been influenced by climate change over the past few decades and will likely continue to change in the future. Fire seasons in both Canada and Alaska have lengthened in recent years as blazes break out earlier and earlier — and as temperatures continue to rise in the coming decades, these seasons may become even longer and potentially more intense.  

As far as the rest of this year’s Northern fire season goes, concerns are already running high — in addition to Alberta’s severe start to the season, Alaska, which experienced one of its worst fire seasons ever last year, just saw its warmest April on record. (And, in fact, the state’s fire season has already gotten an early start, with first wildfire of the year breaking out at the end of February). But, according to Martell, moderate weather and more rainfall later in the spring and summer could still cause conditions to calm down this year. For now, it’s a wait-and-see game.

Overall, though, while it’s notoriously difficult to pin any single incident on climate change, the events in Alberta can safely be taken as the latest symptom in a much broader pattern — one that, thanks to the ongoing effects of climate change, may continue to build in the coming years.