Simulations of North American ice sheet at the LGM with FAMOUS-BISICLES and its sensitivity to global temperatures

Understanding the response of ice sheets to global temperature changes is a critical issue for the climate community. To accurately simulate future ice sheet evolution, we need to know the strength of feedbacks between the climate and ice sheets. Testing the ability of coupled climate-ice sheet models to simulate past ice sheet extent can provide a way to evaluate the models and ground truth projections. One example is the Last Glacial Maximum (LGM), when huge ice sheets covered the Northern Hemisphere, especially over the North America. Here, we performed simulations of the North American ice sheet and climate of the LGM with a recently updated ice sheet-atmosphere coupled model Famous-Ice (Smith et al. 2021, Gregory et al. 2020). The model consists of a low-resolution atmospheric general circulation model Famous (Smith et al. 2008) and an ice sheet model BISICLES (Cornford et al. 2013). It calculates the surface mass balance over ice sheets based on an energy budget scheme and incorporates an updated albedo scheme, which accounts for albedo changes associated with modifications in surface air temperature, grain size and density of the snow. The atmospheric model reproduces the surface mass balance of the modern Greenland ice sheet reasonably well (Smith et al. 2021). Simulations of projections of future sea-level rise (Gregory et al. 2020) and the LGM (Gandy et al. in prep) have also been performed with Famous-Ice using a different ice sheet model GLIMMER.

We present simulations of the LGM with interactive ice sheets in North America and Greenland using FAMOUS-BISICLES. Uncertain input parameters controlling the surface temperatures and ice albedo are varied in our simulations. The global temperature is specified by applying fixed sea surface temperature in the atmospheric model producing a global cooling that ranges from -3K to -6.5K in the simulations. The bare ice minimum albedo is varied from 0.2 to 0.7, which corresponds to the range in PMIP3 models. Our results show a better representation of North American ice sheet when forced with a colder LGM (-6.5K) and high bare ice albedo. We will further discuss potential roles of model biases and compare our results with simulations performed with FAMOUS-GLIMMER (Gandy et al. in prep).