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

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, 5 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 constant), (2) the choice of glacier inventory, (3) the imbalance of glaciers with climate, (4) the mass balance sensitivity, and (5) the climate models. Additionally, a comparison of the model 10 results to the 20th century GIC contribution is presented. We find that small variations in the scaling constant 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. It appears that the mass 15 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. Combining all the uncertainties examined in this study leads to a total uncertainty of 4.5 cm or 30% 20 in the GIC contribution to global mean sea level. Reducing the variance in the climate models and improving the glacier inventories will significantly reduce the uncertainty in calculating the GIC contributions, and are therefore crucial actions to improve future sea-level projections.