Explainer: France has seen its first 'fire-cloud'. What is it?

France is confronting a severe wildfire season, marked by the evacuation of hundreds of thousands and significant economic impacts during its peak tourist period. Beyond the sheer scale of the blazes, the fires are exhibiting unprecedented behavior, including the formation of the nation's first recorded pyrocumulonimbus cloud, commonly referred to as a 'fire-cloud'.

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You can think of it as like a chimney, which is a fire at the bottom and the smoke going straight up a chimney into the stratosphere.

A pyrocumulonimbus is a towering cloud that develops above intense wildfires when extreme heat propels smoke, ash, and water vapor high into the atmosphere. "You can think of it as like a chimney, which is a fire at the bottom and the smoke going straight up a chimney into the stratosphere," explained David Bowman, a professor of pyrogeography and fire science at the University of Tasmania.

These fire-clouds can dangerously escalate wildfire conditions. They generate powerful winds that can dramatically alter a fire's path and produce lightning, which in turn can spark new ignitions. When the cloud loses energy, it can lead to a "plume collapse," described by Bowman as a "showering of debris, burning debris."

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When the plume collapses, it's a showering of debris, burning debris.

The formation of a fire-cloud near Bordeaux marks a critical and concerning milestone for France and potentially Western Europe. Wildfire coordinator for the French national meteorological service, Jean-Christophe Vincendon, noted that while meteorologists can identify favorable conditions, predicting the exact timing and location of these clouds remains difficult. Marc Vermeulen, head of the Gironde fire and rescue service, added that the unpredictable nature of these fire outbreaks necessitates wider evacuation zones, presenting a substantial challenge for emergency responders. Bowman warned that such phenomena, typically seen in larger wilderness areas like Canada or Australia, could become more common in Europe, calling it a "very gravely serious milestone."

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This is a very gravely serious milestone. It is fascinating, but it is also absolutely disastrous and terrible, and we just don't want more of these things.