Wildfire-driven Stratospheric Perturbations:Modelling Insights from the Australian Wildfires

The rising frequency and intensity of wildfire-driven pyro-cumulonimbus (pyroCb) events constitute an important atmospheric perturbation, injecting massive amounts of smoke into the stratosphere. The Australian Black Summer wildfires of 2019–2020 released about a million tonnes of smoke and gases, causing the most significant stratospheric temperature perturbation since 1991 Pinatubo eruption. This study simulates the evolution of smoke plumes from the Australian wildfires using the UKESM1.1 model. The aerosol and greenhouse gas follow the CMIP6 SSP245 scenario, with 0.62 Tg of total smoke injected into the upper troposphere/lower stratosphere based on estimates from Global Fire Emissions Database (GFED). The simulated aerosol layer expands both vertically and horizontally, with significant lofting in the first month following injection, reaching altitudes of ~30 kms, consistent with CALIPSO observations. The modelled zonal-mean aerosol extinction agrees well with OMPS retrievals, with peak values of around 0.006 km⁻¹. However, the modelled stratospheric AOD is higher (up to ~2 times) than the observations showing the aerosols in the model are more optically efficient. Additional sensitivity tests are ongoing to examine whether a higher initial injection altitude in these simulations might be causing the aerosols to remain in the stratosphere longer and decay more slowly. These findings highlight the need for improved observational constraints and modelling strategies to better quantify the global impacts of wildfire-induced stratospheric smoke.