An assessment of uncertainties in using volume-area modelling for computing the twenty-first century glacier contribution to sea-level change

Abstract

Abstract.A large part of present-day sea-level change is formed by the melt of glaciers and ice caps (GIC). This study focuses on the uncertainties in the calculation of the GIC contribution on a century timescale. The model used is based on volume-area scaling, combined with the mass balance sensitivity of the GIC. We assess different aspects that contribute to the uncertainty in the prediction of the contribution of GIC to future sea-level rise, such as (1) the volume-area scaling method (scaling factor), (2) the glacier data, (3) the climate models, and (4) the emission scenario. Additionally, a comparison of the model results to the 20th century GIC contribution is presented.We find that small variations in the scaling factor cause significant variations in the initial volume of the glaciers, but only limited variations in the glacier volume change. If two existing glacier inventories are tuned such that the initial volume is the same, the GIC sea-level contribution over 100 yr differs by 0.027 m or 18 %. It appears that the mass balance sensitivity is also important: variations of 20 % in the mass balance sensitivity have an impact of 17 % on the resulting sea-level projections. Another important factor is the choice of the climate model, as the GIC contribution to sea-level change largely depends on the temperature and precipitation taken from climate models. Connected to this is the choice of emission scenario, used to drive the climate models. Combining all the uncertainties examined in this study leads to a total uncertainty of 0.052 m or 35 % in the GIC contribution to global mean sea level. Reducing the variance in the climate models and improving the glacier inventories will sigCorrespondence to: A. B. A. Slangen (a.slangen@uu.nl) nificantly reduce the uncertainty in calculating the GIC contributions, and are therefore crucial actions to improve future sea-level projections.

Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?

“…[SMB per unit area is also affected, but less strongly, by surface lowering (Paul 2010;Huss et al 2012). ] The model of Slangen and van de Wal (2011), which uses power-law scaling of the volume for evolution of the area, gives results that favor a roughly constant rate of global glacier mass loss during the twentieth century. Further indirect support for this explanation is that a similar balance of opposing tendencies (more intense mass loss per unit area, accompanied by declining area) leads to a fairly constant rate of glacier mass loss, despite a warming global climate, throughout the twenty-first century in the projections of Radi c and Hock (2011, their Fig.…”

An upper-bound estimate for the accuracy of glacier volume–area scaling

“…Despite this wealth of approaches, many studies -especially those focusing on sea level change, mountain hydrology, and other climate change impacts -have been using, and still use, simpler approaches, mostly based on empirical relations between glacier volume and area (e.g. Van de Wal and Wild, 2001;Comeau et al, 2009;Radić and Hock, 2010;Marshall et al, 2011;Hagg et al, 2013;Grinsted, 2013). This is either due to the lack of necessary data sets, the large spatial scale considered, or the convenience of simpler methods.…”

“…Analysis of the second application is of particular interest since the vast majority of the projections concerning the contribution of mountain glaciers and ice caps to future sea level rise in the fifth assessment report of the Intergovernmental Panel on Climate Change is based thereupon (e.g. Slangen and van de Wal, 2011;Marzeion et al, 2012;Radić et al, 2013;Giesen and Oerlemans, 2013). In the following, the accuracy that can be expected from both applications is analyzed separately.…”

“…Granshaw and Fountain, 2006;Moore et al, 2009;Hagg et al, 2013), or (2) a volume change between two points in time is calculated by using a mass balance model, and the scaling relation is inverted in order to update glacier area (e.g. Raper et al, 2000;Van de Wal and Wild, 2001;Radić et al, 2007Radić et al, , 2008Möller and Schneider, 2010;Marshall et al, 2011;Cogley, 2011). Analysis of the second application is of particular interest since the vast majority of the projections concerning the contribution of mountain glaciers and ice caps to future sea level rise in the fifth assessment report of the Intergovernmental Panel on Climate Change is based thereupon (e.g.…”

“…Although Bahr et al (1997) provided the physical basis for this relation, and its performance has already been addressed in the context of glacier volume projections (e.g. Radić et al, 2007Radić et al, , 2008Bahr et al, 2009;Slangen and van de Wal, 2011), the appropriateness of volume-area scaling is currently highly debated. Recently, Adhikari and Marshall (2012) used higher-order mechanics for showing how estimated scaling parameters evolve over time if considering transient glacier states, confirming the results by Radić et al (2007), whereas Huss and Farinotti (2012) pointed out that parameters can also vary spatially on a continental scale.…”