FutGreenlandice · Future evolution of the Greenland ice sheet and associated impacts: Studies with an advanced Earth System model

Future evolution of the Greenland ice sheet and associated impacts: Studies with an advanced Earth System model

One of the major impacts of anthropogenic climate change is sea level rise. Reliable estimates of the contribution of ice sheets to future sea level rise are important to policy makers and the civil society. Remote sensing measurements from the recent decades indicate a positive increasing contribution to sea level rise from the ice sheets of Greenland and Antarctica. In the case of Greenland, the current contributions from enhanced ice discharge to the oceans and increased surface melt have been estimated to be of similar importance (van den Broeke et al., 2009). In addition to sea level rise, ice sheet change might produce an impact on the global climate through modified freshwater fluxes in the areas of deep-water convection. Also, ice sheets modify local and largescale climate through changes in surface albedo and in their own topography. Ice sheets, unlike ocean circulation, sea-ice, interactive vegetation, or the carbon cycle, are not yet standard components of climate models. First attempts have been done in this direction with several climate models, and it is foreseeable that in several years ice sheets will be included as interactive components of most models. Within this project, the first successful attempt of simulating ice sheet surface mass balance with a global climate model has been performed. Up to date, global climate models have not been considered suitable to model ice sheet surface mass balance, due to model biases and insufficient resolution. Regional climates are the state-of-the-art in simulating ice sheet surface mass balance. The main outcome of this project is the first simulations with the global climate CESM (http://www.cesm.ucar.edu/) including a new land ice component. This project has also been key in the implementation of this new land ice component. The results on the mass balance of the Greenland ice sheet have been presented in international conferences and workshops, and in three manuscripts aimed at a Special Collection of the Journal of Climate on CESM. Owing to realistic modeling of present-day climate and snow processes including albedo evolution and meltwater refreezing, and to an adequate downscaling method, CESM has been shown to realistically simulate GIS surface climate and SMB. The CESM results for 1960-2005 have been shown to agree well with in-situ and remote sensing data, as well as state-ofthe-art regional models. The first projections with CESM of the future contribution of the Greenland ice sheet to 21st century sea level rise have been done. Under RCP8.5 forcing, the simulated GIS SMB decreases from 372±100 Gt yr-1 in 1980-99 to -78±143 Gt yr-1 in 2080-99. 2080-99 near-surface temperatures over the GIS increase by 4.7 K (annual mean) with respect to 1980-99, which is 1.3 times the simulated global increase (+3.7 K). Snowfall increases by 18%, and surface melt doubles. The ablation area, e.g. the area with net surface mass loss, increases from 9% of the GIS in 1980-99 to 28% in 2080-99 (Fig.1).

Data: CORDIS, © European Union