ALBERT

Description: Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea-level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers as well as the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of the two ice sheets, which combined represent a sea-level rise potential of ∼65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks.

Description: The solid earth influences ice sheet dynamics by controlling bedrock deformation and hence surface elevation and grounding line position. These in turn determine surface and basal melt. Ice-sheet models typically include models to compute bedrock deformation with a constant mantle viscosity (or similar parameter), whereas mantle viscosity can vary strongly underneath the ice sheets. Here we use a recently developed model that couples an ice-sheet model (ANICE) to a finite-element based GIA model that includes 3D variations in viscosity derived from seismic measurements. We investigate the effect of mantle viscosity variations on the evolution of the last glacial ice sheets in Antarctica and Greenland. In Antarctica, the main feedback mechanism is the effect of bedrock elevation on local sea level and grounding line position. In particular, uplifting bedrock in marine ice sheets reduces ice sheet loss during deglaciation. Results show a grounding line position that is 500 km more outwards when including 3D variations in mantle viscosity compared to a homogeneous viscosity. In Greenland, the main feedback is the effect of bedrock elevation on the surface elevation and hence surface melt. We show that this feedback mainly manifests in north-west Greenland where the mantle viscosity is above average. The higher mantle viscosity leads to higher ice sheet elevation at last glacial maximum, which leads to less surface melt during deglaciation. The results underline the importance of including 3D viscosity in modeling ice sheet evolution.