Sensitivity of the modeled present-day Greenland Ice Sheet to climatic forcing and spin-up methods and its influence on future sea level projections

Abstract

[1] The accuracy of the modeled present-day Greenland Ice Sheet (GrIS) is crucial for future projections of GrIS changes. In this study, we present a detailed evaluation of the modeled present-day GrIS sensitivity to different present-day climatology data sets and spin-up methods and further assess the influence of the modeled present-day GrIS on future sea level projections. Our study demonstrates that with present-day climatology data sets derived from the Regional Atmospheric Climate Model (RACMO2), the modeled ice volume, area, and elevation of the GrIS agree substantially better with observations compared to simulations with present-day climatology data sets from temperature parameterizations and ERA-interim reanalysis. With transient spin-up, the simulated rates of ice elevation changes for the 1993-2010 period are closer to observations than those with steady state spin-up. These results indicate that the RACMO2 forcing and transient spin-up may be preferable for use in the ice sheet model. Moreover, our results reveal that the present-day climatology data sets and spin-up methods affect future sea level projections. Using transient spin-up, the ice sheet model estimates a range of 26 mm in projected sea level rise by 2098 under the A1B emissions scenario, due to different present-day climatology data sets. Compared to the results with transient spin-up, the estimated sea level rise by 2098 is reduced by 5-21 mm with steady state spin-up. This discrepancy is attributed mainly to differences in ice thickness and ice velocity between the modeled present-day GrIS with transient and steady state spin-ups and the effect of paleoclimatic changes with transient spin-up.Citation: Yan, Q., Z. Zhang, Y. Gao, H. Wang, and O. M. Johannessen (2013), Sensitivity of the modeled present-day Greenland Ice Sheet to climatic forcing and spin-up methods and its influence on future sea level projections, J. Geophys.

The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet

“…Given these uncertainties amongst climate models and the large sensitivity of the ice sheet model to climate forcing fields (e.g. Charbit et al, 2007;Quiquet et al, 2012;Yan et al, 2013), it is difficult to calibrate the mechanical parameters independently from those of the SMB, in particular for Northern Hemisphere ice sheets. For these reasons, here we suggest a simple calibration methodology for the Antarctic ice sheet in which the model is run for 100 kyr under a perpetual modern climate forcing until equilibrium.…”

Using results from the PlioMIP ensemble to investigate the Greenland Ice Sheet during the mid-Pliocene Warm Period

“…Koenig et al, 2011) and multiple versions of CAM (Community Atmosphere Model; e.g. Yan et al, 2014). Although all available simulations suggest that the GrIS was reduced in size during the mPWP, the model dependency of the results is yet to be robustly assessed.…”

Application of GRACE to the assessment of model-based estimates of monthly Greenland Ice Sheet mass balance (2003–2012)

“…In terms of ice sheet model spinup, a number of studies have been conducted to determine the sensitivity of model results to the model setup and spinup methods (e.g., Rogozhina et al, 2011;Gillet-Chaulet et al, 2012;Aschwanden et al, 2013;Goelzer et al, 2013;Greve and Herzfeld, 2013;Yan et al, 2013;Saito et al, 2016). Overall, such studies conclude that results are indeed sensitive to the spinup procedures.…”

“…In addition, physically based models of surface processes are difficult to evaluate due to the scarcity of continentalwide data for SMB model validation . As a consequence, while on broad regional scales SMB errors are relatively well documented, local partitioning of Greenland's MB between SMB and discharge -and associated uncertainties -remains difficult to quantify accurately (Howat et al, 2007;Pritchard et al, 2009;Kjaer et al, 2012;Yan et al, 2013;Khan et al, 2014).…”

“…However, model-based estimates of Greenland MB are associated with large uncertainties that are difficult to quantify. For instance, simulation results are dependent on spinup procedure, treatment of boundary conditions/model forcing, implementation of sliding laws, spatial resolution, and choice of ice flow equations (e.g., Nowicki et al, 2013;Goelzer et al, 2013;Greve and Herzfeld, 2013;Aschwanden et al, 2013;Yan et al, 2013;Aðalgeirsdóttir et al, 2014), to name a few. Thus, in order to assess the uncertainties associated with a particular ice sheet model simulation, it is necessary to specifically quantify uncertainties associated with the representation of ice dynamic processes -i.e., basal lubrication due to surface runoff reaching the bed (Schoof, 2010;Bartholomew et al, 2012;Tedesco et al, 2012;Joughin et al, 2013), warming of ice due to runoff refreeze (Fausto et al, 2009;Phillips et al, 2010Phillips et al, , 2013, ice/ocean interaction including grounding line retreat (Holland et al, 2008;Rignot et al, 2010;Chauche et al, 2014), changes to flow resistance at the calving front (Nick et al, 2010;Walter et al, 2012), as well as limitations in model spinup and errors in SMB.…”