Sources of uncertainty in Greenland surface mass balance in the 21st century

Katharina M Holube,Tobias Zolles,Andreas Born

doi:10.5194/tc-16-315-2022

Abstract

Abstract. The surface mass balance (SMB) of the Greenland ice sheet is subject to considerable uncertainties that complicate predictions of sea level rise caused by climate change. We examine the SMB of the Greenland ice sheet in the 21st century with the Bergen Snow Simulator (BESSI) surface energy and mass balance model. To estimate the uncertainty of the SMB, we conduct simulations for four greenhouse gas emission scenarios using the output of a wide range of Earth system models (ESMs) from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to force BESSI. In addition, the uncertainty of the SMB simulation is estimated by using 16 different parameter sets in our SMB model. The median SMB across ESMs and parameter sets, integrated over the ice sheet, decreases over time for every emission scenario. As expected, the decrease in SMB is stronger for higher greenhouse gas emissions. The regional distribution of the resulting SMB shows the most substantial SMB decrease in western Greenland for all ESMs, whereas the differences between the ESMs are most pronounced in the north and around the equilibrium line. Temperature and precipitation are the input variables of the snow model that have the largest influence on the SMB and the largest differences between ESMs. In our ensemble, the range of uncertainty in the SMB is greater than in previous studies that used fewer ESMs as forcing. An analysis of the different sources of uncertainty shows that the uncertainty caused by the different ESMs for a given scenario is larger than the uncertainty caused by the climate scenarios. In comparison, the uncertainty caused by the snow model parameters is negligible, leaving the uncertainty of the ESMs as the main reason for SMB uncertainty.

Highlights

The Greenland ice sheet (GrIS) currently experiences a net mass loss through changes in surface mass balance (SMB) and dynamical processes such as solid ice discharge
The range in simulated SMB for different Earth system models (ESMs) increases, the range in input variables except precipitation does not seem to depend on the scenario (Fig. 1)
In the highemission scenario (SSP585), the surface mass loss accelerates and the integrated SMB is about −230 Gt yr−1 at the end of the 21st century, whereas in the low-emission scenario SSP126 the integrated SMB is only slightly lower than in the historical time period and is approximately constant (Table 1, Fig. 2)

Summary

Introduction

The Greenland ice sheet (GrIS) currently experiences a net mass loss through changes in surface mass balance (SMB) and dynamical processes such as solid ice discharge. In 2005–2017, the GrIS contributed almost as much to sea level rise as all glaciers worldwide (Sasgen et al, 2020). According to Slater et al (2020), the contribution of melt to sea level rise in 2007–2017 exceeded the highest estimates of the IPCC Fifth Assessment Report sea level predictions, whereas for dynamic ice loss the lower or middle estimates were met. The influence of SMB on the total mass loss becomes more important in the future because outlet glaciers will retreat above sea level (Fettweis et al, 2013). The uncertainty in ice discharge is not as substantial as the uncertainties of climate projections and in SMB (Aschwanden et al, 2019)

Methods

Results

Conclusion