Seminar 12 (March 26, 2025) of the CleanCloud series. 

Speaker is Prof. Philip Stier (University of Oxford).

Abstract:
Aerosol-cloud interactions have persistently remained the single greatest uncertainty in anthropogenic perturbations to the climate system. The associated radiative effects have traditionally been assessed by global general circulation models (GCMs), aiming to model the chain of microphysical processes from aerosols acting as cloud condensation via cloud microphysics to the global energy balance. However, this relies on a complete representation of a very complex process chain and has been shown to be subject to large and persistent uncertainties. Moreover, significant structural limitations remain, in particular related to the intrinsic sub-grid scale coupling of aerosols and clouds. The emergence of global km-scale models provides an opportunity to overcome some of these limitations and to explore previously unresolved aerosol phenomena explicitly, including aerosol-convection interactions. In this presentation, I will review and highlight the potential of global km-scale climate models to make progress on our understanding of cloud-aerosol interactions, with a particular focus on aerosol-convection interactions. Starting from regional km-scale simulations using ICON with idealised aerosol perturbations from the MACv2-SP plume model, we show the potential and challenges to transition this work to global km-scale modelling. This work motivates our development of the reduced complexity aerosol model HAM-lite, suitable for long-term global km-scale climate modelling. After a brief overview of the technical development, I will showcase some of our early results, hopefully triggering a good discussion!