Project plan

The first phase focuses on data acquisition and preparation. This involves collecting satellite (e.g., CALIPSO, EarthCARE, Aeolus, TROPOMI) and ground-based (e.g., ACTRIS, BSRN, AERONET) observations to characterise natural analogues such as volcanic eruptions (e.g., Pinatubo, Calbuco) and ship-track aerosols. These datasets provide essential inputs to constrain microphysical and optical properties of aerosols and clouds relevant to SRM analogues.

The second phase consists of data exploitation and analysis, where advanced radiative transfer modelling (using tools like DOME and pyDOME) will simulate radiation fields at the top and bottom of the atmosphere. These simulations will incorporate realistic aerosol and cloud properties, validated against satellite and ground-based measurements. Special attention will be given to the vertical profiling of aerosols and clouds, particularly in the stratosphere and marine boundary layer.

The third phase focuses on development and validation of SRM observational proxies. This includes investigating satellite-derived metrics (e.g., aerosol layer height, UV absorbing aerosol index) and their sensitivity to SRM-relevant perturbations. The impact of aviation-induced cirrus modification will also be analysed using lidar-based polarization data (PLDR) and linked to cirrus cloud formation processes.

The fourth phase is dedicated to sensitivity studies and scenario simulations. The radiative impact of SRM scenarios will be tested under a range of atmospheric conditions using advanced sensitivity analyses and phase function corrections. These outcomes feed into global and regional climate simulations using the ICON atmospheric model, aligned with GeoMIP/CMIP6 protocols, to evaluate broader climatic consequences such as temperature anomalies, teleconnection shifts, and extreme weather impacts.

A final integrative activity will synthesise all results, facilitating the development of monitoring and attribution requirements for a dedicated SRM satellite mission. Cross-cutting actions include validation campaigns (e.g., PANGEA/ASKOS) and the assessment of uncertainties associated with SRM interventions.

Overall, ACtIon4Cooling combines high-resolution observations, radiative transfer theory, and climate modelling to build a robust scientific basis for assessing the feasibility, effectiveness, and risks of SRM strategies.