More than a hundred times this year, the grey, billowing smoke hovering above one of Canada’s many forest fires has suddenly been sucked into a chimney of hot air, then exploded several kilometres into the sky.
At the smoky column’s peak, a white, cauliflower-like cloud forms, blocking out the sun. If any plane or helicopter were to be caught beneath, it would be lost in a haze of smoke and darkness.
This is known as a pyrocumulonimbus event – or, as NASA has called it, “the fire-breathing dragon of clouds.” Scientists have only recently begun to understand and track the phenomenon, which in addition to dense clouds is capable of producing rain, hail, lightning and tornadoes – and spreading fire in the process.
The intense cloud formations are produced by extreme heat on the ground, and they have been especially common during this wildfire season. Some 130,000 square kilometres of land has burned in Canada this year, an area more than 10 times larger than the annual average, according to the Canadian National Fire Database.
Mike Flannigan, a professor at Thompson Rivers University who studies wildfires, witnessed what the clouds can do during a visit to the Elephant Hill fire near Ashcroft, B.C., in July, 2017. It was, he now recalls, utterly terrifying.
“Even from a distance you hear a roar like a freight train. The winds that were sucking into it were just amazing, the flames were amazing,” he said. “It was just incredibly powerful.”
A 2022 study published in the journal Nature found that between 2013 and 2021 there were an average of 60 pyrocumulonimbus clouds recorded around the world by satellites each year. There have already been 148 of the storms worldwide this year, according to newer data collected by the same researchers, 129 of them in Canada. The provinces that experienced the largest shares of those were British Columbia, at 47, and Alberta, at 22. In the previous 10 years, Canada had an average of 21 annually.
“As the planet warms, I expect more and more of these to occur,” Mr. Flannigan said.
Pyrocumulonimbus clouds form when the heat of an intense wildfire sends smoke high into the air, sometimes as high as the lower stratosphere. When this happens, the pillar of hot, smoky air cools, and a cloud coalesces at its peak.
The winds produced by these cloud formations are extreme and unpredictable. They can spread flames far faster than normal, and launch embers kilometres away, sparking fresh fires. And they produce lighting, which can also pose a fire risk. During the Sparks Lake wildfire, near Kamloops in June, 2021, a pyrocumulonimbus cloud produced 7,000 lightning strikes and started 30 to 40 new fires within a matter of hours, Mr. Flannigan said.
Tornadoes are also a possibility, though they are rare. During brush fires near Canberra, Australia, in 2003, a twister of flames sped through the area at 30 kilometres an hour and contributed to the destruction of more than 500 properties.
The intensity of the flames, the sudden shifting of winds and the smoky near darkness such a cloud causes can make firefighting treacherous, both by ground and by air.
“There’s not much we can do about these fires except get out of the way,” Mr. Flannigan said.
Normand Lacour, a base manager for Quebec’s wildland firefighting service, the Société de protection des forêts contre le feu, said that is exactly what the organization trains its squad leaders to do – watch for these cloud formations and stay out of their way. Mr. Lacour said he has witnessed the phenomenon twice himself, and was humbled both times.
“You feel small. When I saw it, I felt all the power, all the energy in there. You have to respect it.”
Mike Fromm, a meteorologist with the United States Naval Research Laboratory and one of the lead authors of the 2022 study, is among a small group of scientists who have access to a private database tracking these clouds.
Although B.C. and Alberta have led the country in pyrocumulonimbus formation this year, he said, there have been significant numbers recorded in other provinces and territories. Twenty were in the Northwest Territories, 18 were in Quebec, eight were in the Yukon, six were in Saskatchewan and another six were in Ontario. One storm occurred along the border of B.C. and the Northwest Territories, and another formed between B.C. and Alberta.
Because the phenomenon requires a particularly strong source of heat to occur, Mr. Fromm said, the numbers are an indication of just how intense Canada’s wildfire season has been this year.
He described 2023′s spike in pyrocumulonimbus events as “off the charts.” But he said there is not enough historical data to establish an upward trend.
“We have to understand these storms at a local level much better in order for communities to be prepared for and to be safe from them,” he said.
Mr. Flannigan said it is clear to him that the impacts of climate change are making themselves felt more quickly than expected. “The new reality is that we will have more fires, more pyrocumulonimbus, more smoke, more impacts,” he said.