Over the past few weeks, major fires have started and spread across northern Alberta, resulting in huge plumes of smoke (see image below from a week ago). Here in Washington State, we experienced several days of high smoke from these fires last week.
I’ve received several emails asking if such fires in Alberta are unusual for this time of year and if global warming (climate change) could be to blame.
In addition, several media outlets have published headline articles on the topic, suggesting that anthropogenic greenhouse gas emissions are the main cause.
Turns out the reality is much more complicated.
Maybe representative The biggest month for wildfires in Alberta, wildfires in Canada are less likely to increase, and human-caused greenhouse gas emissions are only a tiny part of the story.
Canada Wildfire Statistics
Based on the official Canadian government wildfire database, this is a map of wildfires in Canada from 1980-2020. Alberta wildfires typically occur in the northern half of the province, including large areas of boreal forest and grasslands.
What is the long-term trend of wildfires in Canada? Increase due to global warming?
Perhaps surprising to some, the answer is no (see below).
For the whole of Canada, the number of fires is LOWER and there is no clear trend in the burned area.
What about Alberta, where there are a lot of wildfires right now?
The lack of a long-term trend in wildfires is significant: one WILL expect an upward trend if global warming/climate change is a significant contributing factor.
Some have argued that having major fires in Alberta in May points to global warming. They think it’s heating up so fast that the forest fires start early!
But those making such claims need to consider the data. Historically, May has been the most frequent wildfire month in Alberta. (image from an article on trends in the Alberta wildfires below).
Furthermore, many large wildfires in Alberta occurred in May, such as the massive Fort McMurray fire in early May 2016 and the Great Slave Lake fire in 2011.
But why is May such a big month for northern Alberta wildfires?
It has to do with surface fuel. After a long, cool/wet winter, there is a lot of dead fuel (eg hay, annuals) from the previous year lying on the ground after the snow melts. Such light fuel dries very quickly in the first warm weather and is ready to burn by early May.
But the optimal burn season is limited in time. Just a few weeks later, surface vegetation is greening (grass begins to grow, annuals sprout) and such greening REDUCES the flammability of the surface fuel. Which side do you expect to burn in the photo below?
There was a favorable short period in May for the large fires in Alberta before greening. But to take advantage of it, you need favorable drying conditions, which involve a strong, high pressure band over the area. And strong winds and lightning are also favorable.
The setup for the fire earlier this month was almost perfect. In early May, an intense high pressure peak developed over southern Canada (see chart of the difference from normal altitude at 500 hPa below for the 1st to 15th day). May). Red and orange indicate A LOT of normal pressure in the lower atmosphere (about 18,000 ft).
Such high pressure leads to intense drying and warming that dries the surface vegetation before greening occurs. There is no evidence that such a pattern is the result of climate change.
There were periods of dry, strong winds in early May due to large pressure differentials on the edge of the high at lower elevations (see example below on May 6). The strong wind is a primitive accelerator of fire.
You can understand the situation by looking at the weather observed at Edmonton Airport from late April to early May (below). Rain and around 60F in late April, then warm up quickly and windy on April 30 with a spike to 85F on May 1, followed by 86 and 88 on May 3-4.
Perfect weather to dry fuel on the surface, causing lightning at high pressure to move to the east. Human ignition is also distinct abilities.
In summary, there is little evidence that the Alberta wildfires are a climate phenomenon.
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