Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology1, raising global sea level2 and elevating natural hazards3. Yet, owing to the scarcity of constrained mass loss observations, glacier evolution during the satellite era is known only partially, as a geographic and temporal patchwork4,5. Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. Using largely untapped satellite archives, we chart surface elevation changes at a high spatiotemporal resolution over all of Earth’s glaciers. We extensively validate our estimates against independent, high-precision measurements and present a globally complete and consistent estimate of glacier mass change. We show that during 2000–2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise6. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately7–9. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain10. We anticipate our highly resolved estimates to advance the understanding of drivers that govern the distribution of glacier change, and to extend our capabilities of predicting these changes at all scales. Predictions robustly benchmarked against observations are critically needed to design adaptive policies for the local- and regional-scale management of water resources and cryospheric risks, as well as for the global-scale mitigation of sea-level rise. Analysis of satellite stereo imagery uncovers two decades of mass change for all of Earth’s glaciers, revealing accelerated glacier shrinkage and regionally contrasting changes consistent with decadal climate variability.

Accelerated global glacier mass loss in the early twenty-first century

The Greenland Ice Sheet has been a major contributor to global sea-level rise in recent decades1,2, and it is expected to continue to be so3. Although increases in glacier flow4-6 and surface melting7-9 have been driven by oceanic10-12 and atmospheric13,14 warming, the magnitude and trajectory of the ice sheet's mass imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet's volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. The ice sheet was close to a state of balance in the 1990s, but annual losses have risen since then, peaking at 345 ± 66 billion tonnes per year in 2011. In all, Greenland lost 3,902 ± 342 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.8 ± 0.9 millimetres. Using three regional climate models, we show that the reduced surface mass balance has driven 1,964 ± 565 billion tonnes (50.3 per cent) of the ice loss owing to increased meltwater runoff. The remaining 1,938 ± 541 billion tonnes (49.7 per cent) of ice loss was due to increased glacier dynamical imbalance, which rose from 46 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. The total rate of ice loss slowed to 222 ± 30 billion tonnes per year between 2013 and 2017, on average, as atmospheric circulation favoured cooler conditions15 and ocean temperatures fell at the terminus of Jakobshavn Isbrae16. Cumulative ice losses from Greenland as a whole have been close to the rates predicted by the Intergovernmental Panel on Climate Change for their high-end climate warming scenario17, which forecast an additional 70 to 130 millimetres of global sea-level rise by 2100 compared with their central estimate.

/pdf/mass-balance-of-the-greenland-ice-sheet-from-1992-to-2018-2ir4asxtop.pdf

Mass balance of the Greenland Ice Sheet from 1992 to 2018

. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in
response to different climate scenarios and assess the mass loss that would contribute to
future sea level rise. However, there is currently no consensus on estimates of the future mass
balance of the ice sheet, primarily because of differences in the representation of physical
processes, forcings employed and initial states of ice sheet models. This study presents
results from ice flow model simulations from 13 international groups focusing on the evolution
of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model
Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the
Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate
model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response
to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent
(SLE) under Representative Concentration
Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with
constant climate conditions and should therefore be added to the mass loss contribution under
climate conditions similar to present-day conditions over the same period. The simulated evolution of the
West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and
8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing
the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf
collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of
ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice
shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the
calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities
and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based
on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to
simulations done under present-day conditions for the two CMIP5 forcings used and display
limited mass gain in East Antarctica.

/pdf/ismip6-antarctica-a-multi-model-ensemble-of-the-antarctic-2dsknrpr7o.pdf

ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century

Fluctuations in Antarctic Ice Sheet elevation and mass occur over a variety of timescales, owing to changes in snowfall and ice flow. Here, we disentangle these signals by combining 25 years of satellite radar altimeter observations and a regional climate model. From these measurements, patterns of change that are strongly associated with glaciological events emerge. While the majority of the ice sheet has remained stable, 24% of West Antarctica is now in a state of dynamical imbalance. Thinning of the Pine Island and Thwaites glacier basins reaches 122 m in places, and their rates of ice loss are now five times greater than at the start of our survey. By partitioning elevation changes into areas of snow and ice variability, we estimate that East and West Antarctica have contributed ‐1.1±0.4 and +5.7±0.8 mm to global sea level between 1992 and 2017.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082182

Trends in Antarctic Ice Sheet Elevation and Mass

........................................................................................................Siii

/pdf/state-of-the-climate-in-2019-2v04z6ei2d.pdf

State of the Climate in 2019

BOOK © E SA 2 01 8 24–29 September 2018 | Ponta Delgada, São Miguel Island Azores Archipelago, Portugal → 25 YEARS OF PROGRESS IN RADAR

/pdf/25-year-time-series-of-multiple-satellite-ice-sheet-changes-22dn45cx3t.pdf

25 Year Time Series of Multiple-Satellite Ice Sheet Changes: the ESA Climate Change Initiative

25 years of elevation changes of the Greenland Ice Sheet from ERS, Envisat, and CryoSat-2 radar altimetry

We use satellite radar interferometry to investigate changes in the location of the Petermann Glacier grounding line between 1992 and 2011. The grounding line location was identified in 17 quadruple-difference interferograms produced from European Remote Sensing (ERS)-1/2 data – the most extensive time series assembled at any ice stream to date. There is close agreement (20.6 cm) between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the Arctic Ocean Dynamics-based Tide Model 5 (AODTM-5) Arctic tide model. Over the 19 a period, the groundling line position varied by 470 m, on average, with a maximum range of 7.0 km observed on the north-east margin of the ice stream. Although the mean range (2.8 km) and variability (320 m) of the grounding line position is considerably lower if the unusually variable north-east sector is not considered, our observations demonstrate that large, isolated movements cannot be precluded, thus sparse temporal records should be analysed with care. The grounding line migration observed on Petermann Glacier is not significantly correlated with time (R2 = 0.22) despite reported ice shelf thinning and episodes of large iceberg calving, which suggests that unlike other ice streams, on the south-west margin of the Greenland ice sheet, Petermann Glacier is dynamically stable.

/pdf/grounding-line-migration-from-1992-to-2011-on-petermann-imihp62psd.pdf

Grounding line migration from 1992 to 2011 on Petermann Glacier, North-West Greenland

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Trends in Antarctic Ice Sheet Elevation and Mass

25 Year Time Series of Multiple-Satellite Ice Sheet Changes: the ESA Climate Change Initiative

25 years of elevation changes of the Greenland Ice Sheet from ERS, Envisat, and CryoSat-2 radar altimetry

Grounding line migration from 1992 to 2011 on Petermann Glacier, North-West Greenland