Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade

Abstract

We use a three-dimensional, higher-order ice flow model and a realistic initial condition to simulate dynamic perturbations to the Greenland ice sheet during the last decade and to assess their contribution to sea level by 2100. Starting from our initial condition, we apply a time series of observationally constrained dynamic perturbations at the marine termini of Greenland's three largest outlet glaciers, Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. The initial and long-term diffusive thinning within each glacier catchment is then integrated spatially and temporally to calculate a minimum sea-level contribution of approximately 1 ± 0.4 mm from these three glaciers by 2100. Based on scaling arguments, we extend our modeling to all of Greenland and estimate a minimum dynamic sea-level contribution of approximately 6 ± 2 mm by 2100. This estimate of committed sea-level rise is a minimum because it ignores mass loss due to future changes in ice sheet dynamics or surface mass balance. Importantly, > 75% of this value is from the long-term, diffusive response of the ice sheet, suggesting that the majority of sea-level rise from Greenland dynamics during the past decade is yet to come. Assuming similar and recurring forcing in future decades and a self-similar ice dynamical response, we estimate an upper bound of 45 mm of sea-level rise from Greenland dynamics by 2100. These estimates are constrained by recent observations of dynamic mass loss in Greenland and by realistic model behavior that accounts for both the long-term cumulative mass loss and its decay following episodic boundary forcing.

Fig. 1.

Map view of (A) the target balance velocity field (27) and (B) the modeled, depth-averaged speed on a log ₁₀ scale. JI, HG, and KG label the locations of the outlet glaciers modeled here. The velocity field in B is used as the initial condition for perturbation experiments.

Fig. 2.

Model output for the first 10 y of the perturbation experiments showing (A) the model discharge anomaly (km³ y^-1) versus time and (B) the resulting rate of SLR. Squares in (A) mark discharge observations (13).

Fig. 3.

Observed (lines) and modeled (symbols) thinning rates along center line profiles of JI (circles), HG (triangles), and KG (squares). Modeled values are from several years after the start of the perturbation experiments, as discussed in the text. The outlet glacier front, ignoring growth and decay of any seasonal ice tongue, is at 0 km on the horizontal axis. Note that for JI, the modeled thinning profile has been scaled by the maximum observed thinning rates along the profile.

Fig. 4.

(A) Cumulative SLR curves over 100 y for JI, HG, KG, and their total, and (B) scaled, cumulative sea-level rise curves for the GIS until 2100. In A the solid black line is the sum of the colored lines for the three individual outlets. The dashed-black line is similar but assumes that perturbations on JI, HG, and KG occurred simultaneously starting in 2000. In B, the lightly shaded red lines marked σ denote an estimate for the uncertainty, which is ± 35%, as discussed in the text (see also Fig. S3).