A transient glacial cycle simulation with the coupled CESM1.2-PSUIM climate-ice-sheet model

Here we present first results from a series of transient glacial cycle simulations which were conducted with the Community Earth System model (CESM, version 1.2) coupled to the Penn State University ice sheet-ice-shelf Model (PSUIM). The coupling is achieved by applying CESM-simulated surface air temperature, precipitation, surface shortwave radiation and subsurface-ocean temperatures to the PSUIM. CESM is forced in return by PSUIM-simulated ice sheet cover, topography, and freshwater fluxes. The coupled model, which uses a ~ 4 degree horizontal resolution in the atmosphere and ocean and ~ 40 km for the ice-sheets in both hemispheres, includes representations of the lapse-rate, desert-elevation and albedo-dust feedbacks. The coupled model, which uses moderate bias corrections for temperature and precipitation, reproduces the ice sheet evolution over the last glacial cycle in reasonable agreement with paleo-climate data. In this presentation we will further highlight the sensitivity of simulated glacial variability to changes in key surface parameters as well to the individual orbital and greenhouse gas forcings. Our results reveal that only the combination of orbital and CO₂ forcings can generate the full glacial/interglacial amplitude. Single forcings are insufficient to generate glacial variability, which emphasizes the need to understand the mechanisms that led to the orbital pace-making of CO₂ during the Pleistocene.