Climate Impacts of Space-Based Solar Geoengineering: EC-Earth Simulations with a Planetary Sunshade System

This work investigates the climate impacts of non-uniform radiative forcing associated with a Planetary Sunshade System, a space-based solar geoengineering concept based on a distributed swarm of Solar-Sail Satellites partially or fully assembled in the vicinity of the L1 point of the Sun–Earth/Moon Center of Mass system. Previous climate-modeling studies, including the GeoMIP experiments G1, G1ext, G2 and G6Solar, have focused on instantaneous or gradual uniform variations of the solar constant, without addressing space- and time-dependent radiative forcing arising from differential shading. The proposed framework enables the generation of latitude and season dependent shading patterns and provides a consistent methodology to compute both the natural insolation field and the sunshade-modified insolation. The non-uniform radiation pattern is implemented within the EC-Earth3 General Circulation Model. Both atmosphere-only and fully coupled atmosphere–ocean configurations can be considered, allowing the separation of fast atmospheric adjustments from slower ocean-mediated climate responses. Time-dependent variations associated with the elliptic motion of the primaries and natural fluctuations of the solar constant can also be taken into account. Long-term simulations can be performed under different emission scenarios, with particular attention to transient behaviour and quasi-equilibrium conditions in both atmosphere-only and coupled configurations. The analysis highlights the response of key climate variables, including surface temperature and large-scale circulation. Practical implementation aspects are discussed using EC-Earth3 as a reference, detailing how radiative forcing modifications can be introduced in the Fortran-based model code, as well as the diagnostics required to verify consistency and validate the imposed non-uniform forcing.