The wildfires currently tearing through Australia aren’t just unprecedented—they’re catastrophic, as one fire researcher put it. Climate change and fierce heat waves have dried the landscape into swaths of tinder, and all it takes is a single spark to unleash wildfires so powerful, they create their own weather.
Researchers have been catching Australia’s fires in the act of producing pyrocumulonimbus clouds, or pyroCbs. These ominous phenomena take two ingredients: a mass of hot air that produces an updraft, in this case columns of smoke-filled air. And two, they need an unstable atmospheric environment that allows the updraft to continue rising higher than it otherwise would, says Scott Bachmeier, a research meteorologist at the University of Wisconsin, Madison. As the mass climbs higher, the smoky air cools and forms into a pyrocumulonimbus cloud, a soup of water and smoke particles towering miles into the sky. (Though to be clear, the cloud itself isn’t on fire.)
If you take a look at the GIF above, you can see two pyroCbs sprouting, captured by satellite in the infrared spectrum. In the top panel we see the fires, and the bottom panel shows cloud-top temperatures. Red pixels indicate the heat of the wildfire, whereas violet indicates a cloud-top temperature of -70 degrees C. The colder it is, the higher the altitude. The low temperatures reveal that a pyroCb is soaring into the sky.
And another one forming here.
For hundreds of millions of years, thunderclouds and their lightning have been natural partners to fire. Any wildfire is likely to spread when strong surface winds carry embers perhaps miles ahead. “But what’s carried aloft by the pyroCb updraft are copious amounts of smoke particles, which then get carried up to or even ejected above the pyroCb cloud top,” says Bachmeier. If wildfires are sprouting pyroCbs that strike the landscape with lightning without also dumping water, the conflagration will spread all the more readily.