Understanding the critical elements of the pyrocumulonimbus storm sparked by high-intensity wildland fire

High-intensity wildland fires can produce extreme flaming and smoke emissions that develop into a fire-cloud chimney, reaching into the upper troposphere or lower stratosphere. Termed pyrocumulonimbus, these storms are both conventional and counterintuitive. They have been observed to produce lightning, hail, downdraft wind hazards, and tornadoes as expected with severe convective storms, but counterintuitively, they are not associated with significant precipitation. Pyrocumulonimbus storms have been noticed outside wildfire expert circles following Australia’s Black Summer in 2019/20, and have since repeatedly made headlines in the United States. However, much is unknown about their behavior, energetics, history, and impact on the Earth/atmosphere system. We address several questions and science challenges related to these unknowns. Our worldwide record of pyrocumulonimbus events from 2013 to 2021 shows that the phenomenon is neither new nor rare. Despite high occurrences in 2019 and 2021, these data do not support identification of a trend. Future studies require an expansive record of pyrocumulonimbus occurrence globally and regionally, both historically and continuously forward in time.