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Abstract

Surface crevassing on the Greenland Ice Sheet is a large source of uncertainty in processes controlling mass loss due to a lack of comprehensive observations of their location and evolution through time. Here we use high-resolution digital elevation models to map the three-dimensional volume of crevasse fields across the Greenland Ice Sheet in 2016 and 2021. We show that, between the two years, large and significant increases in crevasse volume occurred at marine-terminating sectors with accelerating flow (up to +25.3 ± 10.1% in the southeast sector), while the change in total ice-sheet-wide crevasse volume was within measurement error (+4.3 ± 5.9%). The sectoral increases were offset by a reduction in crevasse volume in the central west sector (−14.2 ± 3.2%), particularly at Sermeq Kujalleq (Jakobshavn Isbræ), which exhibited slowdown and thickening over the study period. Changes in crevasse volume correlate strongly with antecedent discharge changes, indicating that the acceleration of ice flow in Greenland forces significant increases in crevassing on a timescale of less than five years. This response provides a mechanism for mass-loss-promoting feedbacks on sub-decadal timescales, including increased calving, faster flow and accelerated water transfer to the bed.

Abstract

Global mean sea surface temperature (GMSST) is a fundamental diagnostic of ongoing climate change, yet there is incomplete understanding of multi-decadal changes in warming rate and year-to-year variability. Exploiting satellite observations since 1985 and a statistical model incorporating drivers of variability and change, we identify an increasing rate of rise in GMSST. This accelerating ocean surface warming is physically linked to an upward trend in Earth's energy imbalance (EEI). We quantify that GMSST has increased by 0.54 0.07 K for each GJ m–2 of accumulated energy, equivalent to 0.17 ± 0.02 K decade‒1 (W m‒2)‒1. Using the statistical model to isolate the trend from interannual variability, the underlying rate of change of GMSST rises in proportion with Earth's energy accumulation from 0.06 K decade–1 during 1985–89 to 0.27 K decade–1 for 2019–23. While variability associated with the El Niño Southern Oscillation triggered the exceptionally high GMSSTs of 2023 and early 2024, 44% (90% confidence interval: 35%–52%) of the +0.22 K difference in GMSST between the peak of the 2023/24 event and that of the 2015/16 event is unexplained unless the acceleration of the GMSST trend is accounted for. Applying indicative future scenarios of EEI based on recent trends, GMSST increases are likely to be faster than would be expected from linear extrapolation of the past four decades. Our results provide observational evidence that the GMSST increase inferred over the past 40 years will likely be exceeded within the next 20 years. Policy makers and wider society should be aware that the rate of global warming over recent decades is a poor guide to the faster change that is likely over the decades to come, underscoring the urgency of deep reductions in fossil-fuel burning.