Ecosystem Climate Sensitivities Drive the Divergence in Aerosol-Induced Carbon Uptake Across CMIP6 Models

Abstract. Anthropogenic aerosols significantly affect the terrestrial carbon cycle. Many models have been developed to simulate the effects of aerosols on regional ecosystem productivity. However, the differences among models in simulating the impacts of aerosols on gross primary production (GPP) remain unclear. To investigate the response of GPP to aerosol loadings among different models, we analyzed historical and hist-piAer simulations from five Earth System Models (ESMs) in Coupled Model Intercomparison Project Phase 6 (CMIP6). The results showed that all models captured the decrease in GPP (mean: –0.059 gC m^–2d^–1) and the magnitudes of aerosol-induced GPP changes varied greatly (–0.019 to –0.077 gC m^–2d^–1;). To analyze the roles of aerosol representations and model sensitivities to climatic factors across ESMs, we developed a biophysical attribution framework. Our results showed that inter-model discrepancies in simulating the effects of aerosols on GPP were primarily driven by the differences in ecosystem climate sensitivities across ESMs, especially the response of photosynthesis to radiation and temperature. These findings are very important for fully understanding the impacts of human activities on the terrestrial ecosystem carbon cycle.