The Eurasian and North American ice sheets at the Last and Penultimate glacial maxima: coupled atmosphere–ice sheet model sensitivity and calibration

The configuration of the Northern Hemisphere ice sheets during the Last and Penultimate Glacial Maxima (LGM; PGM) influenced millennial-scale climate changes, as well as solid Earth and sea level changes that occurred during the subsequent deglaciations, due to their effects on the atmosphere, ocean circulation, and the solid Earth. Thus, realistic simulations of these ice sheets are crucial for the initialisation of deglaciation experiments that can help improve our understanding of interactions between the climate, ice sheets and sea levels. Here, we produce the first large ensembles of complex coupled atmosphere–ice sheet model (FAMOUS-BISICLES) simulations of the PGM and LGM, varying 12 uncertain parameters that control the ice sheet albedo, ice dynamics and climate. We quantify the sensitivity to input parameters using Gaussian Process emulators to perform a Sobol sensitivity analysis. Albedo parameters have the largest influence on ice volumes for both ice sheets and time periods. Parameters controlling precipitation and sliding have a larger effect on Eurasian than North American ice sheet size due to the differences in geographical and climatic settings. Out of 120 parameter combinations, we find 4 that produce LGM and PGM ice volumes and extents compatible with palaeo-evidence. The resulting ice sheet configurations provide new and improved reconstructions of PGM Northern Hemisphere ice sheets for use as inputs in climate, ice sheet and sea level models.