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Ice loss from the Greenland ice sheet is one of the largest sources of contemporary sea-level rise (SLR). While process-based models place timescales on Greenland’s deglaciation, their confidence is obscured by model shortcomings including imprecise atmospheric and oceanic couplings. Here, we present a complementary approach resolving ice sheet disequilibrium with climate constrained by satellite-derived bare-ice extent, tidewater sector ice flow discharge and surface mass balance data. We find that Greenland ice imbalance with the recent (2000–2019) climate commits at least 274 ± 68 mm SLR from 59 ± 15 × 103 km2 ice retreat, equivalent to 3.3 ± 0.9% volume loss, regardless of twenty-first-century climate pathways. This is a result of increasing mass turnover from precipitation, ice flow discharge and meltwater run-off. The high-melt year of 2012 applied in perpetuity yields an ice loss commitment of 782 ± 135 mm SLR, serving as an ominous prognosis for Greenland’s trajectory through a twenty-first century of warming., Physical and Space Geodesy

Since the mid-19th century, most glaciers have been losing area and volume. This loss of area has not been homogeneous in time and space, and direct observations are sparse, making regional and global estimates of glacier change difficult. This paper focuses on developing a single index for monitoring glacier change, one that would be particularly useful for remote-sensing applications. We combine the results of direct glacier mass-balance observations B, total glacier area S and accumulation area S-c derived from maps or remotely sensed images. Using the accumulation-area ratio (AAR = S-c/S), we note the differences between observed AAR, time-averaged < AAR > and the equilibrium state AAR(0), as determined by its value at B = 0 from a regression of B(AAR). We suggest that alpha(d) = (< AAR > - AAR(0))/ AAR(0) quantifies the difference between the currently observed state of glaciers and their equilibrium state and measures the delay in the dynamic response of S relative to the climatic response of S-c. Using all available observations for the period 1961-2004, alpha(d) approximate to -65% for tropical glaciers, which implies their rapid shrinkage as S continues to decrease and 'catch up' with S-c. During the same period, mid-latitude and polar glaciers show less negative values Of alpha(d). Of 86 glaciers from all latitudes and regions, only 11 show positive alpha(d) at any time between 1961 and 2004. Averaged over 1961-2004, alpha(d) is -15.1 +/- 2.2%, and < B > is -360 +/- 42 mm a(-1) w.e. Values for AAR(0) range between about 40% and 80%, but the bulk of the equilibrium values are between 50% and 60%. The average AAR(0) is 57.9 +/- 0.9% and has remained stable over time (the equilibrium AAR has not changed with climate). Overall, the observed negative alpha(d) suggests a committed retreat of glaciers and their continuing contribution to sea level even if global temperature is held constant., MASS-BALANCE; CLIMATE