Atmospheric dynamics supporting the Alpine glaciers at the Last Glacial Maximum assessed with a high-resolution regional climate model

The Last Glacial Maximum (LGM) is a global event that occurred 26 to 21 ka BP and was characterized by lower temperatures (3 to 6 °C globally) and different precipitation regimes. The environment was marked by extended glaciers which released a large set of morphologies as the systems of well-preserved moraines in the alpine foreland that testify the advanced phases of the alpine glaciers during the LGM. Mountain glaciers, quickly responding to temperature and precipitation variations, are considered excellent indicators of climate change. Here we focus on the European Alps and attempt to unveil the physical processes that sustained the glacier extent during the LGM using a multiple regional climate model (RCM) nesting approach. Toward this goal, we completed and intercompared two high-resolution (12 km) RCM simulations, one for the steady-state LGM standard (21 ka BP) and one for pre-industrial (PI) conditions. We also calculated the LGM and PI environmental equilibrium line altitude (envELA) for the whole Alpine chain starting from physically-based summer temperature a total annual precipitation. Precipitation and temperature patterns show good consistency with proxy records and other RCM studies. In particular, our results present a predominance of convection over stratiform precipitation during summer, as well as increased southwesterly stratiform precipitation in the southern alpine region compared to the PI. Frequent summer snowfall, extending to low elevations, where caused by this precipitation pattern, along with lower temperatures, and led to a substantial drop in the ELA. Our model-based evaluation of the LGM ELA showed unprecedented consistency with the estimated LGM Alpine glacier reconstructions, further proving the great potential of this method for paleoclimate applications.