Investigating the Dynamic Response of the Greenland Ice Sheet to Climate Forcing using a Geophysical, Remote-Sensing and Numerical Modelling Framework

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Summary An increasing number of scientific studies show that human activities, e.g. burning of fossil fuels, have increased the concentration of heat-trapping gasses in the atmosphere. It is estimated that global temperatures will increase by 2-5 degrees C during this century if we continue to add carbon dioxide and other 'greenhouse' gasses to the atmosphere. In the Arctic, warming is expected to be even faster and mean annual temperature may increase by 4-7 degrees C. The implications of global warming are of immense proportions because glaciers and ice sheets will melt faster and become increasingly prone to collapse. In Greenland, discharge from outlet glaciers is responsible for about half the annual loss of ice. The other lost half is due to runoff of surface meltwater. The combined effect of iceberg discharge and surface melt are currently greater than the total amount of snowfall falling onto the Greenland Ice Sheet. This ice sheet is therefore shrinking while releasing freshwater into the Atlantic Ocean. The imbalance amounted to -90 cubic km per year for 1996 and increased to -140 cubic km per year by 2000. In 2005, this imbalance may have increased to as much as -220 cubic km per year. The size of the Greenland Ice Sheet is thus diminishing at what appears to be a growing rate. Worldwide concern is associated with this trend because ice-sheet decay results in global sea-level rise and possibly even an obstruction of oceanic circulation, which in key places - such as the North Atlantic - is sensitive to freshwater released from melting ice masses. The Greenland Ice Sheet rests on bedrock above or close to sea level. Glaciologists have for years assumed that such position would be stable and that demise of the ice sheet would require thousands of years even under extreme global warming scenarios. This assumption may need revision. It was shown recently that surface meltwater could penetrate through over 1km of ice to the base of the Greenland Ice Sheet and cause ice-flow speed-up due to faster basal sliding. This mechanism is potentially dangerous because accelerated ice flow leads to thinning, which in turn leads to an increase in surface melt since a larger part of the ice sheet moves into lower and warmer elevations. The Greenland Ice Sheet may therefore be far more prone to decay than it was assumed in earlier projections of global warming. However, up until now the mechanisms by which this dynamic response between surface melt and ice flow have only been generally understood and the present generation of climate-ice sheet models which are used to forecast future sea-level change do not include them in any rigorous manner. This is particularly true in respect of: 1) the extent to which the surface, interior and basal water-plumbing and ice flow systems can moderate, amplify and transmit the dynamic response away into the interior of the ice sheet thereby drawing the inland ice reservoir down and, 2) the extent to which future changes in Greenland temperatures may increase both the area and length of time of which the ice sheet directly experiences these effects. This project directly addresses both of these shortcomings in current models and will implement a set of fieldwork, satellite remote-sensing and comprehensive Greenland Ice Sheet modelling simulations that will fully assess and implement those 'dynamical processes related to ice flow not included in current models... (which) could increase the vulnerability of the ice sheets to warming, increasing future sea-level rise.' (IPCC, WG1 - 2007).