Continued monitoring of the ice sheet, for example by using existing and future space-borne laser- and radar-altimeters (ICESAT/GLAS; CRYOSAT), is likely to improve our knowledge of the current volume change of the Greenland Ice Sheet. Combining this information with high-accuracy space-borne measurements of changes of the gravity field (GRACE) should allow discrimination between ice-sheet volume change and ice-sheet mass change.
In order to improve estimates of future mass-balance changes, the following studies should also be given high priority: (i) better understanding of albedo changes and feed-back mechanisms; (ii) studies of outlet glacier dynamics with emphasis on their potential for triggering persistent, fast changes in ice-sheet volume; and (iii) improving ice-dynamic models for determining the long-term response of the ice sheet to past climate change.
It is important to stress that although the use of remote-sensing measurements for studying changes of the Greenland Ice Sheet will increase in importance in the future, there will still be a large demand for in situ measurements for calibration/validation pur poses. It also should be emphasized that future mass-balance changes are strongly dependent on future changes of climate. As a consequence, our ability to predict future mass-balance changes of the Greenland Ice Sheet is closely linked to the ability of general atmosphere and ocean circulation models to predict future changes in regional climate over Greenland. Recent GCM model runs, for example, predict a larger increase in accumulation rate over Greenland associated with a temperature increase than did previous studies (Van de Wal et al., 2001). If true, this will to a large extent compensate for the increased runoff resulting from the predicted climate warming.
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