Abstract

Abstract. Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i) the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii) the modeled present-day elevation at GRIP; and (iii) the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4–4.4 m sea level equivalent, with a more likely range of about 3.7–4.4 m sea level if the GRIP δ18O isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.

Highlights

  • Prediction of the future response of the Greenland Ice Sheet (GIS) to global warming is of great practical importance since the GIS can contribute up to 7 m to global sea level rise

  • Several key model parameters were perturbed to produce an ensemble of model versions, which were constrained using information about the ice sheet for the Eemian Interglacial and the present day

  • We have shown that even modest variations of a single model parameter lead to large uncertainties in the simulated volume of the Eemian GIS

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Summary

Introduction

Prediction of the future response of the Greenland Ice Sheet (GIS) to global warming is of great practical importance since the GIS can contribute up to 7 m to global sea level rise. On short (centennial) time scales, the response of GIS is primarily controlled by changes in surface mass balance (which can be modeled relatively accurately) and by changes in fast flow (which is still poorly understood). On millennial time scales, when the GIS can lose a considerable portion of its volume, the situation is complicated by a number of climate-ice sheet feedbacks. A study of past climate changes, and the response of the ice sheet to these changes, could help improve and better constrain ice sheets models

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