Description: A two-fold method with two aerosol models and three Earth System Models (ESM) was used to simulate climate impacts of solar radiation modification (SRM) by continuous equatorial injections with six different injection rates ranging from 2 to 100 Tg(S)/yr. Aerosol optical properties were simulated with modal (M7) and sectional (SALSA) aerosol modules within the ECHAM-HAMMOZ aerosol-chemistry-climate model. Simulated optical properties were implemented to MPI-ESM, CESM, and EC-Earth to produce consistent perturbation on radiation. Based on the ECHAM-HAMMOZ simulation , the shortwave radiative forcing was 45 %–85 % more negative in SALSA than in M7 with the corresponding injection rate while the longwave radiative forcing was 33 %–67 % larger in M7. These differences were translated into large differences in the estimated temperature and precipitation changes in ESM simulations: 20 Tg(S)/yr injection rate led to only 1.8K global mean cooling while EC-Earth - SALSA combination produced 5 K change. In ideal scenarios where SRM was used to compensate for radiative forcing of 530 ppm atmospheric CO2 concentration, global mean precipitation reduction varied between models from -0.5 to - 2.5 %. These precipitation changes were explained with the fast precipitation response due to radiation changes caused by the SRM and CO2. These results highlight the importance of simulating aerosol microphysics when estimating climate impacts of stratospheric sulfur intervention, but also reveal gaps in our understanding and uncertainties which are still existing related SRM.

Description: Stratospheric aerosols play a key role in atmospheric chemistry and climate. They are considered a catalyst for ozone depletion, serve as condensation nuclei for polar stratospheric cloud formation, and, in large amounts, have a short-term impact on the Earth's radiative budget. The aerosol effects depend strongly on the aerosol particle size distribution (PSD). Despite its importance, available observations on PSD are rather limited, restricting the knowledge of chemical and climate aerosol feedback mechanisms. We present a novel aerosol climatology including the PSD, the effective radius, and the extinction coefficient from limb observations of SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) operated aboard Envisat between 2002 and 2012. The aerosol climatology is successfully evaluated with in-situ balloon-borne measurements from Wyoming and global aerosol products from different satellite instruments (SAGE II, SAGE III, OSIRIS). The data set significantly expands the limited knowledge of stratospheric aerosol properties and serves to a better understanding of aerosol microphysical processes. We demonstrate its potential by comparing the simulated and observed aerosol plume evolution after the volcanic eruptions of Manam (Jan 2005) and Sarychev (Jun 2009).