GREEN RISE

The Greenland glacial system (GGS) consists of the ice sheet, the outlet glacier system, fjords into which most of the outlet glaciers terminate, the sub- and englacial hydrological system and the surface snow pack. Understanding the dynamics of the GGS, and being able to model these realistically, is an issue of great importance due to the potential of the Greenland Ice Sheet (GIS) to contribute significantly to future sea level rise. The GIS contains enough ice to raise global sea level by 7 m. Observational data suggest that during the past decade mass losses of the GIS significantly accelerated. The GIS contribution to sea level rise may become even more important in the future, yet sea level rise projections remain rather uncertain due to poor understanding of the ice sheet dynamics, in particular the role of fast processes associated with the ice streams, outlet glaciers, and their interaction with the ocean. Achieving progress in modelling of the entire GGS is thus crucial to improving future sea level rise projections. In the past decade considerable progress has been made in the development of models of individual elements of the GGS, such as regional climate models and 3-D ice sheet models. However, a comprehensive model of the entire GGS system does not yet exist. Coupling of state-of-the-art models for all relevant components of the GGS is eventually desirable, but currently computationally too expensive and therefore impractical. Here, we propose an alternative approach based on the use of intermediate complexity modelling components. Such an approach will allow us to design a computationally-efficient modelling tool suitable for performing a large ensemble of simulations of the GGS response to climate change, thus contributing significantly to the assessment of the risk of future sea-level rise.

The principal project objective is to gain a better understanding of the GIS response to future climate change and to improve the accuracy of the projections of its contribution to global sea level rise for time scales from decades to millennia. In summary: • We will develop a novel generic 1-D outlet glacier-fjord model and will couple it with an existing 3-D thermo-mechanical ice-sheet model and a regional climate model of inter¬mediate complexity. • With this new tool, we will study the role of fast processes (ice streams and outlet glaciers) and the ice sheet-ocean interaction for the GIS response to climate change on different time scales. • We will analyse the major sources of uncertainties in the GIS response to climate change and how to use available observational and paleoclimatic constraints to reduce these uncertainties. • We will perform large ensembles of model simulations covering a broad range of plausible GHG emission/climate change scenarios to assess the contribution of the GIS to future sea level rise, with an emphasis on constraining the upper bound and the possibility of irreversible changes.