Even fire scientists are stunned by the scale of disruption and damage wrought by an out-of-control wildfire that swept into Fort McMurray, Alta., on Tuesday. But when it comes to the underlying factors that allowed the blaze to become so severe so quickly, experts say larger forces are at play and there is a growing risk of similar events occurring across the northwest.
Weather is a crucial enabler of wildfires. In the past few days, the weather in Fort McMurray – including a lack of precipitation, unseasonably warm temperatures and strong winds – all combined to create the ideal scenario for a small fire to grow and spread.
But these conditions, especially the high temperatures, are part of a year-long pattern than can be attributed to El Nino, a periodic warming of waters in the east-central Pacific Ocean that was at its strongest in recent months since 1997-98.
"Alberta had a bad fire year that year," said Mike Flannigan, a University of Alberta professor who specializes in the interaction of fire with weather and climate. While El Nino is by no means the only factor influencing fire in the region, "it seems to be one of the triggers," he added.
Faron Anslow, a climatologist at the Pacific Climate Impacts Consortium at the University of Victoria, has been closely following the impact of El Nino on neighbouring British Columbia.
"Over the winter, it was quite a bit warmer than normal … and then in the north, especially, it really dried out," he said.
The effect can also be seen in the latest surface temperature data obtained by Terra, a NASA climate satellite that monitors the entire globe every one to two days. Monthly averages for March and April were well above normal by as much as 5 C in some cases. This has contributed to a general drying out of the area and exacerbated what fire scientists refer to as the "spring dip" – the period between the disappearance of snow and the appearance of new forest growth, when moisture levels are lower than at other times of the year.
"In this case, it's an unfortunate coincidence of location and weather overlapping on those lead-up conditions," said Meg Krawchuk, a biologist at Oregon State University who studies the relationship between fire, geography and forest ecosystems.
A still larger question in the background is the influence of climate change. In recent years, researchers have debated the significance of an apparent pause in the upward march of global temperatures starting around 1998. That pause appears to have come to an end with the current El Nino, and Environment Canada has forecast a hotter-than-normal summer with a better than 60-per-cent probability for most of Alberta and British Columbia.
Looking further ahead, the warming trend due to greenhouse gas emissions is expected to have a complex influence on wildfires. The likelihood of fire increases with temperature, but a warming climate also puts more moisture in the air, which can produce more intense precipitation.
Together with colleagues, Dr. Flannigan set out to untangle these interlinked effects in a study that was published last January in the journal Climate Change. The team found that heat wins out over precipitation when it comes to fire risk. The average rainfall in a given location would have to increase by as much as 15 per cent to compensate for the drying caused by a 1 C rise in average temperature due to global warming. That points to a future in which even a modest rise in temperature will translate into a higher risk of extreme fires.
Linking specific wildfires to climate change is another matter, however, because so many other factors are involved, including local forest-management practices.
A panel report issued in March by the U.S. National Academy of Sciences found that it is possible, in some cases, to estimate the influence of climate change on certain types of extreme weather events. But the problem with trying to say whether any one event is or isn't due to climate change is that all weather events are playing out in a context where climate change is under way.
"It's a changed system," said Francis Zwiers, a climate statistician who was on the U.S. panel and directs the University of Victoria consortium.
What is more relevant to those affected by wildfires is that there is every reason to expect an increased risk in the long term and, together with that risk, a need to better protect communities. In that sense, Dr. Flannigan said, the Fort McMurray disaster "may be a glimpse of things to come" that could spur significant action.