Sensitivity of the Greenland mass and energy balance to uncertainties in key model parameters

Abstract. We investigate the sensitivity of a glacier surface mass and energy balance model using a variance based analysis, for two distinct periods of the last glacial cycle: present day climate and the Last Glacial Maximum (LGM). The results can be summarized in three major findings: The sensitivity towards individual model parameters and parameterizations is neither invariant in space nor in time. The model is most sensitive to uncertainty related to down-welling long-wave radiation. Turbulent latent heat flux has a sizable contribution to the surface mass balance uncertainty in central Greenland today and over the entire ice sheet during the cold climate of the LGM, in spite of its low impact on the overall surface mass balance of the Greenland ice sheet in modern climate. We conclude that quantifying the model sensitivity is very helpful for the subsequent tuning of free model parameters, because it clarifies the relative importance of individual parameters and highlights interactions between them that need to be considered.