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The response of the Greenland ice sheet to climate changes in the 21st century by interactive coupling of an AOGCM with a thermomechanical ice sheet model

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Huybrechts, P. , Janssens, I. , Poncin, C. and Fichefet, T. (2001): The response of the Greenland ice sheet to climate changes in the 21st century by interactive coupling of an AOGCM with a thermomechanical ice sheet model , International symposium on Ice Cores and Climate, Kangerlussuaq (Greenland)August 2001. .
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Abstract:

We present results from a climate change experiment obtained from an atmosphere-ocean general circulation model that is fully interactively coupled with a three-dimensional model of the Greenland ice sheet. The experiment covers the period 1970-2100 and is driven by the IPCC SRES B2 scenario. The Greenland model is a thermomechanic high-resolution (20 km) 3D model coupled with a visco-elastic bedrock model. The melt-and-runoff model is based on the positive-degree day method with parameters obtained from a new calibration on available data and includes meltwater retention in the snowpack and the formation of superimposed ice. The AOGCM is a coarse resolution model without flux correction. Its atmospheric component is based on version 5.2 of the AGCM developed at the "Laboratoire de Météorologie Dynamique" of the CNRS (Paris). The OGCM is a primitive-equation, free surface model incorporating sea-ice developed at Louvain-la-Neuve (CLIO). The ice sheet model uses temperature and precipitation perturbations provided by the AOGCM and provides the spatial and temporal distribution of the fresh water released back into the ocean to investigate its effects on the thermohaline circulation in the North Atlantic.Various terms of the mass-balance such as runoff from the ice sheet, runoff from land, calving and basal melt are calculated for a control experiment arising from the background evolution in response to the last glacial cycle, and for a climatically forced experiment. For the 21st century, we find that the annually averaged temperature forcing increases from 3*C in south Greenland to more than 6*C in the northern parts of the ice sheet, while the mean precipitation increases by between 30 and 50 %. The total fresh water flux approximately doubles over this period due to increased runoff from the ice sheet and the ice-free land, whereas the calving rate is found to decrease by 25% over the same period. The ice sheet shrinks equivalent to about 3 cm of sea-level rise. The contribution from the background evolution is not more than 5 %. We did not find significant changes of the thermohaline circulation and the general patterns of climatic change as compared to a control run with the AOGCM using a constant Greenland fresh water flux.

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