Modelling the Stratospheric Impacts of the Australian Wildfires

Oral Presentation 

The increasing frequency and intensity of wildfire-driven pyro-cumulonimbus (pyroCb) events are emerging as a major atmospheric impact, injecting massive amounts of smoke into the stratosphere. The Australian Black Summer wildfires of 2019–2020 released nearly a million tonnes of smoke, causing the most significant stratospheric temperature perturbation since 1991 Pinatubo eruption. This study simulates the smoke plume from the Australian wildfires using the UKESM1.1 model. The aerosol and greenhouse gas settings follow the CMIP6 SSP245 scenario, with 0.81 Tg of smoke injected into the upper troposphere/lower stratosphere based on composite stratospheric aerosol dataset (COMP; constructed using CALIPSO and OMPS retrievals). The model-simulated aerosol layer expands both vertically and horizontally, with significant lofting in the first month, reaching ~35 km, consistent with CALIPSO observations. The modelled dispersion closely matches zonal-mean extinction data (~0.006 km⁻¹) from COMP. However, the modelled stratospheric AOD is higher (by at least 2 times) than the observations showing the aerosols in the model are more optically efficient, or that the source term is too large, as compared to the observations. Ongoing simulations using UKESM1.1 nudged to ECMWF reanalyses aim to improve model accuracy in assessing wildfire-induced climate impacts. Wildfires are expected to intensify in a warming climate, causing extreme pyroCb events to become a key driver of stratospheric change, including ozone loss, highlighting the need for improved monitoring and modelling of their global effects.