In 2016, a wildfire so large and destructive that it was nicknamed "The Beast" tore through Fort McMurray, a town in northeastern Alberta surrounded by boreal forests in the middle of the Canadian province's oil-rich tar sands.
More than 88,000 people were evacuated, and 2,400 homes and buildings were destroyed in the inferno. It would become one of the costliest and most destructive wildfires in the country's history, but scientists had other reasons to pay close attention to it.
As the fire raged and threatened to engulf the community, The Beast started to exhibit some odd behavior, growing so intense that it spawned "fire clouds" that created their own weather.
The rare weather phenomenon has most recently been observed in southeastern Australia, where unprecedented wildfires have burned more than 27 million acres of land and where more than 100 blazes are still active. And scientists say they're seeing fire clouds more often as climate change makes fire seasons longer and wildfires more intense.
Researchers are only beginning to understand the consequences.
A fire cloud, known as a pyrocumulonimbus cloud, or pyroCb, can generate thunder, lightning and tornado-force winds, as well as belch out burning embers — all of which can help spread already fast-moving fires.
Mike Fromm, a meteorologist at the Naval Research Laboratory in Washington, D.C., has been studying fire clouds for the past two decades, but he said his early research was met with disbelief.
"The whole idea of the pyroCb was completely foreign to the scientific community," he said. "Probably within the last 10 years, we've gone from a huge amount of skepticism to acceptance of the idea that the pyroCb not only exists but that it's a fairly regular phenomenon."
In that time, wildfire research has come a long way, but fire clouds have remained mysterious and understudied.
It's estimated that more than 980 million acres around the world burn every year in wildfires, according to Mike Flannigan, director of the Canadian Partnership for Wildland Fire Science at the University of Alberta in Edmonton. But it's not known what percentage of wildfires generate fire clouds.
When they break out, however, the results can be devastating.
"These storms are high-intensity, erratic, dangerous and hard to predict," Flannigan said. "In Fort McMurray, there was a pyroCb that lit new fires 20 to 30 kilometers (12 to 19 miles) downwind."
On Feb. 7, 2009, a day that became known as "Black Saturday," six fire clouds broke out across the Australian state of Victoria in the midst of one of the continent's worst wildfires. And in 2018, California's deadly Carr fire was so intense that it unleashed a rare fire tornado with 143 mph-winds.
"That would have been a really damaging regular tornado, let alone adding fire to the mix," Flannigan said.
'A new reality'
Scientists aren't sure why some wildfires produce fire clouds while others don't, but they know that three ingredients are crucial: heat, dry conditions and wind.
Sometimes when a fire rages with enough intensity, it can create updrafts that pull ash, smoke and water vapor into an enormous column that funnels high into the atmosphere. As the hot air rises, it cools and condenses to form clouds, similar to what happens with regular thunderstorms.
"The fire itself has to be large enough to create this thermal bubble that is sufficient to break into the atmosphere and start this going," Fromm said.
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Although more data across longer periods of time is needed, there are some indications that fire-generated storms could occur more frequently in the future. Studies have shown that global warming is making certain regions hotter and drier, increasing the frequency and severity of wildfires, which, in turn, can increase the likelihood of fire clouds, Flannigan said.
"I don't like to use the term 'new normal,' because it indicates a plateau or a shift to another state," he said. "It's kind of a new reality. We're going to see more and more fires and more and more dangerous conditions. Not every year is going to be a bad fire year, but on average, we're going to see a lot more bad fires."
Fromm said fire clouds are also being detected in parts of the world where they had never been seen before, such as South Africa, Portugal and Argentina.
Interest has grown within the scientific world because fire clouds pose a significant risk to communities and firefighters. Once the fire-generated storms break out, there's little that emergency crews can do to stop them.
"With these high-intensity fires, you can drop water or fire retardant on them, but it's like spitting on a campfire," Flannigan said. "There's not much you can do. You basically have to get out of the way."
But scientists are also interested in studying the impact the voracious fire clouds can have on the climate.
Fromm was a co-author of a 2018 study published in the journal Climate and Atmospheric Science that found that the amount of aerosols lofted into the stratosphere from pyroCbs is equivalent to the release of a moderate volcano eruption.
As has been observed after volcanic eruptions, the plumes of ash and other fine particles can actually have a cooling effect because they absorb solar radiation, which decreases how much sunlight reaches Earth's surface. The Mount St. Helens eruption in Washington state in 1980, for example, helped cool the planet by about 0.1 degree Celsius.
Flannigan said scientists are only starting to comprehend the potential impacts of aerosols from fire clouds. But given that climate change is increasing the likelihood of these storms, the potential fallout could be pervasive.
"Wherever you can have a high-intensity fire, a pyroCb is fair game," he said. "We've got to get our act together as a global community or there are going to be far more serious consequences than what we're seeing this year in Australia."