Pyrocumulonimbus clouds, or pyroCbs, can generate thunder, lightning and tornado-force winds, in addition to belching out burning embers.
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 some 2,400 homes and buildings were destroyed in the inferno. It would become one of the costliest and most destructive wildfires in that nation's history, but scientists had other reasons to pay close attention to it.
As the fire raged and threatened to engulf the entire community, The Beast started to exhibit some odd behavior, growing so intense it spawned "fire clouds" that created their own weather.
This rare weather phenomenon has most recently been observed in southeastern Australia, where unprecedented wildfires have burned over 27 million acres of land and 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 of these storms.
Fire clouds, known as pyrocumulonimbus clouds or pyroCbs, can generate thunder, lightning and tornado-force winds, in addition to belching 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 of land around the world burn every year from 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 do 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 different 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 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 three ingredients are crucial to their formation: 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 gets funneled 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.
Though 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."
According to Fromm, 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 in fire clouds has grown within the scientific world because they pose a significant risk to communities and firefighters. Once these fire-generated storms break out, there's not much 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 that these voracious fire clouds can have on the climate.
A2018 study published in the journal Climate and Atmospheric Science and co-authored by Fromm found that the amount of aerosols lofted into the stratosphere from pyroCbs is equivalent to a moderate-size volcano eruption.
As has been observed after volcanic eruptions, these plumes of ash and other fine particles can actually have a cooling effect because they absorb solar radiation, which decreases the amount of sunlight that reaches the Earth's surface. The Mount St. Helens eruption in 1980, for example, helped cool the planet by approximately 0.1 degree Celsius.
Flannigan said scientists are only starting to comprehend the potential impacts of aerosols from fire clouds, but knowing 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."