Carbon-climate feedback responses to spatial aerosol model implementation variations

Abstract Aerosols have played an important role in defining the climate over the historical period, due to their net cooling effect in the atmosphere. However, as their emissions are expected to decrease in upcoming decades, they will be associated with reduced cooling, i.e. future warming, of the planet. Despite their importance and high uncertainty associated with their radiative forcing, aerosols inclusion in simple climate models, impact models and carbon-based climate assessment metrics requires simplifications and assumptions. Typically, interactions between physical and biogeochemical processes are disregarded by such. By varying the spatial implementation of aerosols in an intermediate complexity model we explore the variability in Earth system responses under an ambitious mitigation scenario due to aerosols-radiation interactions. When aerosols are implemented disregarding their spatial distribution, surface air temperature is higher by almost 0.1 °C when compared to a regionally heterogeneous implementation, corresponding to an uncertainty of ca . 200 GtCO 2 of remaining carbon budgets. The main processes driving these responses are the land surface temperature and its effect on soil respiration, as well as changed ocean heat fluxes due to differences in incoming shortwave radiation at the surface. The spatial distribution of aerosols triggers important climate-carbon feedbacks, which should be specifically considered when assessing climate evolution and simulated Earth system responses. Even if aerosol-cloud interactions aren’t explored, the results already indicate that aerosols should be deliberately accounted for in simple models and assessment tools, as their triggered feedbacks will be instrumental in defining pathways for temperature stabilisation and evaluating, for example, remaining carbon budgets.