Austyn Gaffney
Updated Sat, July 27, 2024
A helicopter buckets water onto smouldering fires outside Jasper, Alberta, Canada, on Friday July 26, 2024. AMBER BRACKEN/Pool via REUTERS
Officials said Thursday that they feared as much as half the town of Jasper, Alberta, had been destroyed by wildfires so intense they generated their own weather.
“It’s a sad day here because Jasper is such a gorgeous place,” Mike Flannigan, a professor of wildland fire at Thompson Rivers University in British Columbia, said Thursday.
The town is the gateway to Jasper National Park, a crown jewel of the Canadian parks system. At least 25,000 residents and tourists were evacuated from their homes before firefighters and emergency personnel also had to flee toxic smoke. The mayor called the destruction “almost beyond comprehension.”
That fire was worsened by a pyrocumulonimbus, or a fire-generated thunderstorm, according to Flannigan.
“They’re by far the most intense fires in the world,” he said.
A pyrocumulonimbus is a huge, smoke-filled thunderstorm generated when the intense heat from wildfires combines with atmospheric conditions ripe for storm formation.
Although these heat-generated storms don’t produce much rain, they can create other types of weather such as hail, strong winds, lightning and tornadoes. Tornadolike winds were reported near the Park fire, which is burning in California.
These storms can also create smoke plumes that can surpass the cruising altitude of a commercial aircraft. They act like a giant chimney: Smoke is pulled up from the wildfire and as the air escapes, more air moves quickly in at the ground level, feeding the fire more oxygen before funneling up and away.
This feedback loop can push out so many smoke particles that the result can be similar to a volcanic eruption.
In the 2019-20 Black Summer fire season in Australia, for example, 38 such storms, also known as pyroCbs, were observed. They injected enough smoke into the atmosphere that scientists likened it to a nuclear winter.
Wildfires that are exacerbated by these types of storms can become nearly impossible to put out. They’re also more hazardous for firefighters, creating more extreme wind conditions and darkening skies.
“They tried to put helicopters on it,” Flannigan said of the wildfires that fueled at least two of these storms this week near Jasper. “They couldn’t stop it, which is unfortunate because it led to a good chunk of the town burning down.”
Why are fire-generated storms happening more often?
Unlike the study of other extreme weather events such as heat waves and hurricanes, the study of these storms is relatively new in scientific circles.
Because data only dates to 2013, it’s difficult to determine a trend, said David Peterson, a meteorologist at the U.S. Naval Research Laboratory in Monterey, California.
“There’s been an increasing number of large and intense wildfires in North America in recent years that likely would suggest there would be more pyroCbs,” Peterson said. “But we still don’t know enough.”
But over the past decade, the number of these storms has grown.
In 2017, four pyroCbs in British Columbia created a volcanic-scale smoke plume that traveled around the globe, lasting more than six months. Then, the Black Summer in Australia sent a smoke plume up that lasted more than year. In 2021, 100 pyroCbs were recorded worldwide, but 2023 shattered that record with 169.
Western Canada seems to be a hot spot. The country’s 2023 fire season spawned 142 of these storms, almost tripling its previous record of 50 in 2021.
Although research has yet to link these types of storms to climate change, studies show that as climate change increases how often extreme wildfires happen, they could also become more frequent.
“In a general sense, if you have more fires, you’ll have more pyroCbs because there are more opportunities to have them sink up, but it depends on atmospheric conditions, too,” Peterson said. “An intense wildfire definitely increases the odds.”
More than 50 pyroCbs have been observed in western North America so far this year, which already puts 2024 in the top three years in the 12-year-old record.
When will we know more?
In October, Peterson and his partners will begin a five-year, NASA-funded study to better understand the effect these wildfires could have on our climate.
“The big open question right now is what is the role of pyroCbs in a warming climate system?” Peterson said. “What are the effects of pushing smoke up extremely high into the stratosphere, especially when smoke that high persists for a year?”
The study will use two NASA aircraft: one that can fly up to 70,000 feet above the storm, requiring the pilot to wear a spacesuit, and a second that can fly through the storm’s upper clouds. The aircraft will collect data in the summers of 2026 and 2027.
In the meantime, the U.S. Naval Research Laboratory is also working with the National Oceanic and Atmospheric Administration and other agencies to develop a more sophisticated warning system. The science is complex because it merges wildfire science with thunderstorm meteorology.
“We need to develop a warning capability for fires that are more likely to generate pyroCbs because it means something different if you’re fighting it, evacuating people, and predicting where the smoke is going,” Peterson said. “Right now, we’re in catch-up mode.”
c.2024 The New York Times Company
Pyrocumulonimbus Clouds
Pyrocumulonimbus clouds are thunder clouds created by intense heat from the Earth’s surface. They are formed similarly to cumulonimbus clouds, but the intense heat that results in the vigorous updraft comes from fire, either large wildfires or volcanic eruptions. So it is, for this reason, the prefix ‘pyro’ is used – meaning fire in Greek.
Pyrocumulonimbus clouds were reported during the Australian bushfires in late 2019/early 2020, and a number have more recently been observed in Siberia with the Arctic heatwave. These intense wildfires reach temperatures above 800°C and can essentially create their own weather systems.
The hot smoke released from these fires acts as a plume of heat into the atmosphere. Hot and very buoyant, the air in the plume rapidly rises. As it rises, it cools and expands. Once cooled sufficiently, water vapour condenses on the ash to form a grey or brown cloud above the plume. At this stage, the cloud is called a pyrocumulus. Still, if enough water vapour is available and the updraft intensifies, it can develop into a pyrocumulonimbus cloud. Then, similar to other thunderstorms, there may be a downburst of intense localised rain. This rain can create a downdraft of cooler air, which can then carry embers from the fire, igniting spot fires away from the source. In some cases, dry lightning from these storms can strike without rain, further spreading the wildfire. They have also been known to dangerously generate fire tornadoes.
Pyrocumulonimbus clouds are thought to be responsible for several aerosol pollutants (such as smoke and ash) trapped in the stratosphere and upper atmosphere. However, a paper by the American Meteorological Society, ‘The Untold Story of Pyrocumulonimbus’, re-evaluated the data from previous stratosphere studies to conclude that volcanic eruptions had been wrongly attributed to these pollutants. Dr Glenn K. Yue, one of the paper’s authors, stated in an article by NASA that one of the reasons for this misinterpretation was that it was initially thought the only force strong enough to penetrate the tropopause in a short period was a volcanic eruption.
As our climate changes, these unusual but significant storms could occur more frequently due to hotter and drier conditions increasing the risk of wildfires.
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