CONSTRAINING LAST GLACIAL MAXIMUM SIMULATIONS USING A SIMPLE POSITIVE-DEGREE-DAY ICE SHEET MODEL

Comparisons of temperature and precipitation from climate simulations with terrestrial records from the Last Glacial Maximum (LGM) serve to validate climate models and provide insights into ecological responses to ice-age climate. A complimentary data-model comparison can be accomplished using climate model output to drive an ice sheet model to simulate the Laurentide Ice Sheet (LIS), which was a dominant control of LGM climate over North America and beyond. We apply the Community Ice Sheet Model (CISM) Glimmer, a simple positive-degree-day (PDD) model, to simulate the LIS as driven by temperature and precipitation from LGM climate simulations that include our coupled global climate model (GENMOM) and seven models from phase 3 of the Palaeoclimate Modelling Intercomparison Project. A range of possible ice sheets is created by Glimmer through exploring the PDD parameter space. We used the ice sheet area from the ICE6G reconstruction as a metric to evaluate which combinations of climate models and PDD parameterizations yielded realistic configurations of the LIS. Six of the eight climate models produced reasonable ice sheets with areas within ±10% of ICE6G and a mean volume of 33.8±3.0 10⁶km³. The two models that fail to produce the LIS (CNRM-CM5 and MRI-CGCM3) have summer temperatures that are too warm to support year-round ice.