Quantifying and understanding uncertainties in regional impacts of solar geoengineering

The emerging regional climate discrepancies in global climate models raise questions about our ability to predict regional impacts of solar geoengineering scenarios. Our mechanistic understanding of regional impacts of solar geoengineering is also not as advanced as for climate change due to greenhouse gases and tropospheric aerosols. Therefore, we have recently started creating a perturbed parameter ensemble (PPE) to quantify structural uncertainties and thereby address the knowledge gaps that have emerged as regional climate discrepancies have accumulated. The PPE is based on a Geoengineering Model Intercomparison Project (GeoMIP) scenario involving stratospheric aerosol injection (SAI), which uses a prescribed artificial layer of sulfate aerosol to reduce the global temperature.

This project uses the new MPI-M CMIP7 ICON XPP model (Müller et al, 2025), an Earth system model with a horizontal resolution of 80 km for the atmosphere and 20 km for the ocean. The optical properties of the stratospheric aerosol layer for SAI are prescribed in ICON. These properties were previously simulated using the ECHAM-HAM aerosol microphysical model. Sulfur was injected into the stratosphere at two points: 30° N and 30° S.

For the PPE, we will vary the tuning variables for cloud physics, turbulence, and radiation. We will use a Latin hypercube to calculate the perturbation of these variables. This will result in approximately 100 simulations. Additionally, we plan to perform a perturbation of the initial state for each PPE member. The PPE is currently in an early stage of development. Therefore, we plan to present our project and preliminary results. We would like to discuss various focal points of PPE evaluation with interested colleagues at the EGU.