In the early days of the Creek Fire, photographs went viral of what looked like a mushroom cloud billowing into the atmosphere over the blaze. It’s no wonder that type of cloud, known as pyrocumulonimbus, was dubbed by a NASA writer as “the fire-breathing dragon of clouds”: Each one is a towering thunderstorm, complete with thunder, lightning and rain, generated by a wildfire.
“They act as a chimney, funneling smoke from near the surface to high altitudes,” says meteorologist David Peterson of the Naval Research Laboratory in Monterey. “So all that smoke goes straight into those clouds. And it makes one of the dirtiest clouds on earth, if you will, and there are many similarities to a volcanic eruption.”
Today I was flying from San Jose to Las Vegas on SWA & I looked out my window & I saw this cloud. I l found out that it is a cumulonimbus flammagenitus cloud aka pyrocumulonimbus cloud, a type of cloud that forms above a source of heat, such as a wildfire #CreekFire pic.twitter.com/HCqyWiHpNx
— Thalia Dockery (@SweetBrown_Shug) September 6, 2020
Unlike volcanic eruptions, however, not a lot is known about how these extreme storms form or how they influence weather and the climate. That’s because the study of pyrocumulonimbus formations, pyroCbs for short, is relatively young—their name began appearing in scientific literature only in the early 2000s.
Thanks to weather radar and satellite imaging, however, scientists are now able to capture more details about pyroCbs than ever, and the Creek Fire’s imposing cloud should help further the field. “The Creek Fire pyroCb event will likely be studied by the community since it was one of the largest observed in the U.S. and generated a significant amount of attention,” Peterson says.
It turns out that pyroCbs are relatively common. Although most don’t reach the estimated 50,000 feet altitude that the Creek Fire’s did, Peterson still ranks this one as “near the upper end of the moderate scale.” The two largest pyroCbs ever observed were spurred by massive wildfires in 2017 in the Pacific Northwest of the U.S. and Canada, and in southeastern Australia during the country’s devastating 2019-2020 fire season.
“All wildfires that are linked to these really intense pyroCb events are usually very big,” Peterson says. “They burn in fuels that are very dense and allow for an updraft, a smoke column, to persist for a very long period of time.”
Indeed, researchers have found that dust ejected from these largest storms lingered in the stratosphere for months, encircling an entire hemisphere. In fact, as the field has matured, studies have posited that some of the dust thought to have been expelled into the stratosphere by volcanoes could have instead been produced by pyroCbs.
One big unanswered question about pyroCbs, however, is what that dust can mean for the long-term climate, particularly as the particles interact with the sun’s rays on their way to the Earth’s surface. “With a volcanic plume, we know that that will create a cooling effect by reflecting solar radiation back to space,” Peterson says. “Smoke is different in that it has absorptive properties, so the solar radiation actually gets absorbed by the smoke plume.”
So as climate change lengthens wildfire season in the West and increases the likelihood of powerful, destructive blazes, are we likely to see more pyroCbs as well? Researchers just don’t know yet, says Peterson, partly because these extreme storms feed off of not just intense flames, but also specific moisture and pressure conditions in the atmosphere. “There’s multiple moving pieces,” Peterson says. “Understanding the role of pyroCb in the climate system remains one of our biggest research goals in the community.”