Joint Seminar: Interactions of melting ice sheets with the global climate
Freshwater fluxes from ice sheets are projected to increase in the coming centuries due to anthropogenic warming, changing ocean stratification, atmosphere-ocean heat exchange, and ocean circulation. Surface atmospheric cooling and subsurface ocean warming induced by ice sheet freshwater are associated with negative and positive feedbacks respectively for the retreat of ice sheets, but uncertainties persist regarding their relative strength and combined effect. Existing studies drew contradictory conclusions regarding the sign of the net feedback under future warming, however, feedbacks could not be modeled in a temporally realistic way in these "offline-coupled" ice sheet-climate models. Here we assess feedbacks associated with ice sheet freshwater discharge in a quasi-synchronously coupled ice sheet-climate model, considering a variety of greenhouse gas emission scenarios and model equilibrium climate sensitivities (ECS). In simulations with increasing CO2 levels, surface cooling induced by ice sheet freshwater slows the retreat of both ice sheets, but for Antarctica the positive feedback associated with subsurface warming prevails in most scenarios. For scenarios with high emission and a high model ECS, where the West Antarctic Ice Sheet (WAIS) is modeled to collapse in the next few centuries, the negative cooling feedback dominates, delaying and slowing the collapse substantially. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet's retreat via the Bipolar Seesaw. These results demonstrate that ice sheet-climate interactions via freshwater flux, currently absent in most comprehensive climate models, are crucial for assessing future ice sheet retreat and associated sea-level rise. Next-generation models with fully interactive ice sheet components are expected to project a generally faster sea level rise under anthropogenic warming, at least in the early stages of WAIS retreat before the catastrophic collapse.
Date
15.07.2025
Time
15:15 h
Place
- DKRZ room 034
- Hamburg