Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

Here, we present the first simulation with the Community Earth System Model (CESM), which includes an interactive carbon cycle, that covers the last millennium. The simulation is continued to the end of the twenty-first century.

Besides state-of-the-art forcing reconstructions, we apply a modified reconstruction of total solar irradiance to shed light on the issue of forcing uncertainty in the context of the last millennium. Nevertheless, we find that structural uncertainties between different models can still dominate over forcing uncertainty for quantities such as hemispheric temperatures or the land and ocean carbon cycle response. Compared to other model simulations, we find forced decadal-scale variability to occur mainly after volcanic eruptions, while during other periods internal variability masks potentially forced signals and calls for larger ensembles in paleoclimate modeling studies.