Role of Model Initialisation for Projections of 21st Century Greenland Ice Sheet Mass Loss

ABSTRACT. Model simulations of the Greenland ice sheet contribution to 21st-century sea-level rise areperformed with a state-of-the-art ice-sheet model (Parallel Ice Sheet Model (PISM)). The climate-forcingfields are obtained from the European Union’s Seventh Framework Programme project ice2sea, in whichthree regional climate models are used to dynamically downscale two scenarios (A1B and E1) from twogeneral circulation models (ECHAM5 and HadCM3). To assess the sensitivity of the projections to themodel initial state, four initialization methods are applied. In these experiments, the simulatedcontribution to sea-level rise by 2100 ranges from an equivalent of 0.2 to 6.8cm. The largestuncertainties arise from different formulations of the regional climate models (0.8–3.9cm) and appliedscenarios (0.65–1.9cm), but an important source of uncertainty is the initialization method (0.1–0.8cm). These model simulations do not account for the recently observed acceleration of ice streamsand consequent thinning rates, the changing ice discharge that may result from the spatial and temporalvariability of ocean forcing, or the feedback occurring between ice-sheet elevation changes and climateforcing. Thus the results should be considered the lower limit of Greenland ice sheet contributions tosea-level rise, until such processes have been integrated into large-scale ice-sheet models.KEYWORDS:

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