“This is a very bad day all around in western Canada,” he wrote. “Fires went ‘pop’ progressively on the leading edge.” A pyroCb was forming in the southeast corner of British Columbia, near Kamloops, McRae added, noting,“Things could get worse if certain things ‘align.’ ”

Rick McRae, a researcher with Australia’s Capital Territory Emergency Services Agency, was on site helping with fire management. Sensing that this conflagration was going to erupt into something extraordinary, he texted a group of scientists from around the world who since 2013 have been collaboratively studying fire-triggered thunderstorms — technically known as pyrocumulonimbus clouds, or “pyroCbs.”

Early in the evening of August 12, 2017, heat and smoke from an intense wildfire burning in the forests of British Columbia began mushrooming skyward, sucking up ash, blazing wood and vegetation, and water vapour from lakes and streams below.

And align they did.

As fires that would eventually consume 4,700 square miles in British Columbia burned out of control, five fire-driven thunderstorms rose over the conflagration, shooting black smoke and carbon high into the lower stratosphere, spewing noxious gases that were eventually detected almost as far north as the North Pole, and touching off more fires.

At the same time, fires in neighbouring Washington State spawned yet another pyroCb.

“By later that night we were agape about the cluster of pyroCbs and the extremely impressive smoky anvil-shaped clouds,” recalled Mike Fromm, a meteorologist at the U.S. Naval Research Laboratory.

Later, Fromm and David Peterson, a colleague at the Naval Research Laboratory, labeled that day’s cluster of pyrocumulonimbus clouds “the mother of all pyroCbs,” surpassing even the events of Black Saturday in Australia in 2009 when monstrous bushfires killed 173 people, injured 414 others, and burned 1,700 square miles. On that night in February, three clearly distinct pyrocumulonimbus storms erupted across the state of Victoria in southeastern Australia.

Yet another major pyroCb event occurred in May 2016 during a massive wildfire in Alberta that forced the evacuation of 88,000 people in the tar sands community of Fort McMurray. A pyroCb formed over the fire that day, and lightning from the firestorm ignited several new fires in the forest 22 miles northeast of the fire’s front, astonishing wildfire experts.

“I have never heard of lightning causing new fires so far in advance of the main fire,” said Cordy Tymstra, the wildfire science coordinator for the Alberta government.

As a warming world causes larger, more frequent, and more intense wildfires, fire-driven thunderstorm events are on the rise in places — including Texas, Portugal, South Africa, and Argentina — where they have never occurred before.

Mike Flannigan, director of the Canadian Partnership for Wildland Fire Science at the University of Alberta, says that pyroCbs seem to be on the rise because warmer temperatures are likely producing more intense fires with more vigorous plumes of smoke, black carbon, and water vapour, all of which increase the likelihood of pyroCbs.

Whatever the reason, these episodes can wreak havoc on fire-suppression strategies. Flannigan says that pyroCbs fires are extremely hot and chaotic, especially when the plume collapses.

Winds can reach the speed of a tornado. Embers shoot in all directions — in some cases up to three miles. That means sending firefighters in to fight them on the ground is impossible, according to Flannigan.

“PyroCbs like the one that was associated with the Carr fire in California in 2018 can be catastrophic because they can generate tornado-strength vortexes,” says Flannigan.

Pyro clouds continue to puzzle scientists

The physics behind pyroCbs are complex and continue to puzzle meteorologists and atmospheric scientists. What we know is that when super-heated updrafts from an intense fire suck smoke, ash, burning materials, and water vapour high into the sky, these elements cool and form “fire clouds” that look and act like those associated with classic thunderstorms.

The heat and the particulates in the smoke almost always trigger a dynamic reaction that arrests the ability of the cloud to produce precipitation. What’s then left is a lightning storm that moves across the surrounding landscape, triggering more fires, as happened near Fort McMurray.

Interest in pyroCbs is increasing among wildfire scientists. Last month, an entire session at the American Geophysical Union (AGU) meeting in Washington, D.C. was devoted to the subject of pyroCbs and how they can potentially impact weather and climate in the same way volcanic eruptions have in the past. Fromm of the U.S. Naval Research Laboratory has been instrumental in proving that pyroCbs — a long-known, but relatively rare meteorological phenomenon — have as much energy and impact as moderate-sized volcanic eruptions. Fromm and others have shown that smoke and aerosols from wildfires can rise high into the stratosphere, where they can linger for months, scattering the rays of the sun. The impact is similar, though on a much smaller scale, to volcanic eruptions like Mt. Pinatubo in the Philippines, which occurred in 1991. That eruption spewed massive quantities of sulphate aerosol emissions that blocked some of the sun’s rays and cooled the climate globally by about 1 degree Fahrenheit for 15 months.