Sensitivity of Greenland Ice Sheet Projections to Model Formulations

Abstract

ABSTRACT. Physically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6-18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14-31% higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise

“…We tested this concept by repeating our experiments using the VUB-GISM-HO model with SMB determined interactively, using a degree-day model (DDM) (26). Experiments allowed DDM-derived SMB to evolve freely between 2000 and 2200 or held SMB fixed at its DDM-derived value for 2000.…”

“…The parameterization was implemented in four different icesheet models: Vrije Universiteit Brussel Greenland Ice Sheet Model (VUB-GISM-HO) (25,26), Elmer/Ice (27), Community Ice Sheet Model (CISM) 2.0 (28), and Model for Prediction Across Scales (MPAS)-Land Ice (29), all of which have higherorder flow physics in which the representation of an ice mass's internal stress distribution is complete or almost complete and no a priori assumption of a local stress balance is made. Details of the individual models, including initialization strategy and numerical implementation, are provided in SI Text.…”

Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries

“…4) demonstrates the significant and immediate effect of an abrupt change to the transmissive 'membrane' stresses acting across the grounding line on flow dynamics, highlighting the importance of explicitly including variations in the lateral transmissive stresses in model studies. While a number of modelling studies have been published that account for changes in backstress, which can propagate upstream through transmissive horizontal lateral stresses (Joughin and others, 2010;Favier and others, 2014;De Rydt and others, 2015), there are many studies that use a 'flowline' approach (Nick andothers, 2009, 2012;Gladstone and others, 2012;Goelzer and others, 2013). It has been shown that flowline models are deficient in some circumstances including those more complex settings where buttressing effects are important (Gudmundsson and others, 2012;Gudmundsson, 2013).…”

A simple equation for the melt elevation feedback of ice sheets

“…If and when this temperature threshold is passed depends critically on past and future greenhouse gas emissions Goelzer et al, 2013;Gregory et al, 2004a;Rae et al, 2012). Even if emissions were reduced to zero, temperatures would not drop significantly for thousands of years because of the long lifetime of anthropogenic CO 2 in the atmosphere and reduced oceanic heat uptake if oceanic convection is extenuated (Allen et al, 2009;Solomon et al, 2009;Zickfeld et al, 2013).…”