Rapid growth of land ice due to summer snowfall

The study simulates the build-up of the North American ice sheet before the LGM and shows which factors influenced its growth. By developing a new Earth system model that included ice sheets into simulations, it was possible to adequately capture the necessary complexity of the system. “This new feature in our model system enables ice-sheet feedbacks which are not included yet in the current scenarios,“ explains Lu Niu, first author of the publication and scientist at the AWI.

In particular, the research team investigated the period of pronounced ice growth into the LGM: During this time, the volume of the continental ice increased by approximately 50 meters, which was equivalent to a sea level drop of around the same amount. The results show that the rapid expansion of the North American ice sheet can be explained by summer snowfall, which was caused by the transport of moisture from warmer lower latitudes of the Atlantic into the interior of the North American continent. “This mechanism not only led to more ice, but also greater snow cover over North America, which reflected sunlight more effectively and thus additionally reduced melting,“ adds Gregor Knorr,  co-author of the study. These feedbacks highlight the complexity of possible Earth system interactions that might also play a role for future changes of the Antarctic and Greenland ice sheets.

From the past, insights can be gained into how processes in the atmosphere can affect and change today's ice sheets and sea level. “Coupled ice sheet-climate models will set a new standard for sea-level projections under warming conditions,” emphasizes Gerrit Lohmann, Head of the Paleoclimate Dynamics Section at the AWI and co-author of this study. The research is part of a large German research project PalMod with the aim of simulating the last 120,000 years into the future.