Benjamin Smith Senior Principal Physicist Affiliate Associate Professor, Earth and Space Sciences bsmith@apl.washington.edu Phone 206-616-9176 |
Education
B.S. Physics, University of Chicago, 1997
M.S. Geology & Geophysics, University of Wisconsin - Madison, 1999
Ph.D. Earth & Space Sciences/Geophysics, University of Washington - Seattle, 2005
Projects
EDGE Earth Dynamics Geodetic Explorer EDGE is one of four missions proposed to the new NASA Earth Systems Explorers program. Each are receiving $5 million to conduct a one-year mission concept study, at the conclusion of which the space agency will choose two concepts to be developed fully and scheduled for launch in the early 2030s. |
14 May 2024
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Marine Ice Sheet Collapse in Thwaites Glacier Basin, West Antarctica Airborne and satellite observations of West Antarctic topography and glacier flow speeds are combined with a computer model simulating ocean-driven glacier melting to show that the ice sheet's collapse is already underway. The onset of rapid collapse may begin in two centuries or a millennium from now |
14 May 2014
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Videos
Polar Science Weekend @ Pacific Science Center This annual event at the Pacific Science Center shares polar science with thousands of visitors. APL-UW researchers inspire appreciation and interest in polar science through dozens of live demonstrations and hands-on activities. |
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10 Mar 2017
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Polar research and technology were presented to thousands of visitors by APL-UW staff during the Polar Science Weekend at Seattle's Pacific Science Center. The goal of is to inspire an appreciation and interest in science through one-on-one, face-to-face interactions between visitors and scientists. Guided by their 'polar passports', over 10,000 visitors learned about the Greenland ice sheet, the diving behavior of narwhals, the difference between sea ice and freshwater ice, how Seagliders work, and much more as they visited dozens of live demonstrations and activities. |
Clocking Greendland's Glaciers: Ice-sheet-wide velocity mapping |
5 Dec 2013
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Publications |
2000-present and while at APL-UW |
Quantifying volumetric scattering bias in ICESat-2 and Operation IceBridge altimetry over Greenland firn and aged snow Fair, Z., M. Flanner, T. Neumann, C. Vuyovich, B. Smith, and A. Schneider, "Quantifying volumetric scattering bias in ICESat-2 and Operation IceBridge altimetry over Greenland firn and aged snow," Earth Space Sci., 11, doi:10.1029/2022EA002479, 2024. |
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19 Jun 2024 |
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The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission has collected surface elevation measurements for over 5 years. ICESat-2 carries an instrument that emits laser light at 532 nm, and ice and snow absorb weakly at this wavelength. Previous modeling studies found that melting snow could induce significant bias to altimetry signals, but there is no formal assessment on ICESat-2 acquisitions during the melting season. We performed two case studies over the Greenland Ice Sheet to quantify bias in ICESat-2 signals over snow: one to validate Airborne Topographic Mapper (ATM) data against Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) grain sizes, and a second to estimate ICESat-2 bias relative to ATM. We used snow optical grain sizes derived from ATM and AVIRIS-NG to attribute altimetry bias to snowpack properties. For the first case study, the mean and standard deviation of optical grain sizes were 340 ± 65 μm (AVIRIS-NG) and 670 ± 420 μm (ATM). A mean altimetry bias of 4.81 ± 1.76 cm was found for ATM, with larger biases linked to increases in grain size. In the second case study, we found a mean grain size of 910 ± 381 μm and biases of 6.42 ± 1.77 cm (ICESat-2) and 9.82 ± 0.97 cm (ATM). The grain sizes and densities needed to recreate biases with a model are uncommon in nature, so we propose that additional surface attributes must be considered to characterize ICESat-2 bias over snow. The altimetry biases are within the accuracy requirements of the ICESat-2 mission, but we cannot rule out more significant errors over coarse-grained snow. |
Estimating differential penetration of green (532 nm) laser light over sea ice with NASA's Airborne Topographic Mapper: observations and models Studinger, M., B.E. Smith, N. Kurtz, A. Petty, T. Sutterly, and R. Tilling, "Estimating differential penetration of green (532 nm) laser light over sea ice with NASA's Airborne Topographic Mapper: observations and models," Cryophere, 18, 2625-2652, doi:10.5194/tc-18-2625-2024, 2024. |
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31 May 2024 |
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Differential penetration of green laser light into snow and ice has long been considered a possible cause of range and thus elevation bias in laser altimeters. Over snow, ice, and water, green photons can penetrate the surface and experience multiple scattering events in the subsurface volume before being scattered back to the surface and subsequently the instrument's detector, therefore biasing the range of the measurement. Newly formed sea ice adjacent to open-water leads provides an opportunity to identify differential penetration without the need for an absolute reference surface or dual-color lidar data. We use co-located, coincident high-resolution natural-color imagery and airborne lidar data to identify surface and ice types and evaluate elevation differences between those surfaces. The lidar data reveals that apparent elevations of thin ice and finger-rafted thin ice can be several tens of centimeters below the water surface of surrounding leads, but not over dry snow. These lower elevations coincide with broadening of the laser pulse, suggesting that subsurface volume scattering is causing the pulse broadening and elevation shift. To complement our analysis of pulse shapes and help interpret the physical mechanism behind the observed elevation biases, we match the waveform shapes with a model of scattering of light in snow and ice that predicts the shape of lidar waveforms reflecting from snow and ice surfaces based on the shape of the transmitted pulse, the surface roughness, and the optical scattering properties of the medium. We parameterize the scattering in our model based on the scattering length Lscat, the mean distance a photon travels between isotropic scattering events. The largest scattering lengths are found for thin ice that exhibits the largest negative elevation biases, where scattering lengths of several centimeters allow photons to build up considerable range biases over multiple scattering events, indicating that biased elevations exist in lower-level Airborne Topographic Mapper (ATM) data products. Preliminary analysis of ICESat-2 ATL10 data shows that a similar relationship between subsurface elevations (restored negative freeboard) and "pulse width" is present in ICESat-2 data over sea ice, suggesting that biased elevations caused by differential penetration likely also exist in lower-level ICESat-2 data products. The spatial correlation of observed differential penetration in ATM data with surface and ice type suggests that elevation biases could also have a seasonal component, increasing the challenge of applying a simple bias correction. |
Simulating the processes controlling ice-shelf rift paths using damage mechanics Huth, A., R. Dudu, B. Smith, and O. Sergienko, "Simulating the processes controlling ice-shelf rift paths using damage mechanics," J. Glaciol., EOR, doi:10.1017/jog.2023.71, 2023. |
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21 Sep 2023 |
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Rifts are full-thickness fractures that propagate laterally across an ice shelf. They cause ice-shelf weakening and calving of tabular icebergs, and control the initial size of calved icebergs. Here, we present a joint inverse and forward computational modeling framework to capture rifting by combining the vertically integrated momentum balance and anisotropic continuum damage mechanics formulations. We incorporate rift–flank boundary processes to investigate how the rift path is influenced by the pressure on rift–flank walls from seawater, contact between flanks, and ice mélange that may also transmit stress between flanks. To illustrate the viability of the framework, we simulate the final 2 years of rift propagation associated with the calving of tabular iceberg A68 in 2017. We find that the rift path can change with varying ice mélange conditions and the extent of contact between rift flanks. Combinations of parameters associated with slower rift widening rates yield simulated rift paths that best match observations. Our modeling framework lays the foundation for robust simulation of rifting and tabular calving processes, which can enable future studies on ice-sheet–climate interactions, and the effects of ice-shelf buttressing on land ice flow. |
Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020 Otosaka, I.N., and 67 others including I. Joughin, M.D. King, B.E. Smith, and T.C. Sutterley, "Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020," Earth Syst. Sci. Data, 15, 1297-1616, doi:10.5194/essd-15-1597-2023, 2023. |
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20 Apr 2023 |
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Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9 mm to global mean sea level, with the rate of mass loss rising from 105 Gt yr−1 between 1992 and 1996 to 372 Gt yr−1 between 2016 and 2020. In Greenland, the rate of mass loss is 169±9 Gt yr−1 between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86 Gt yr−1 in 2017 to 444 Gt yr−1 in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9 Gt yr−1) and, to a lesser extent, from the Antarctic Peninsula (13±5 Gt yr−1). East Antarctica remains close to a state of balance, with a small gain of 3±15 Gt yr−1, but is the most uncertain component of Antarctica's mass balance. |
Evaluating Greenland surface-mass-balance and firn-densification data using ICESat-2 altimetry Smith, B.E., B. Medley, X. Fettweis, T. Sutterley, P. Alexander, D. Porter, and M. Tedesco, "Evaluating Greenland surface-mass-balance and firn-densification data using ICESat-2 altimetry," Cryosphere, 17, 789-808, doi:10.5194/tc-17-789-2023, 2023. |
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16 Feb 2023 |
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Surface-mass-balance (SMB) and firn-densification (FD) models are widely used in altimetry studies as a tool to separate atmospheric-driven from ice-dynamics-driven ice-sheet mass changes and to partition observed volume changes into ice-mass changes and firn-air-content changes. Until now, SMB models have been principally validated based on comparison with ice core and weather station data or comparison with widely separated flight radar-survey flight lines. Firn-densification models have been primarily validated based on their ability to match net densification over decades, as recorded in firn cores, and the short-term time-dependent component of densification has rarely been evaluated at all. The advent of systematic ice-sheet-wide repeated ice-surface-height measurements from ICESat-2 (the Ice Cloud, and land Elevation Satellite, 2) allows us to measure the net surface-height change of the Greenland ice sheet at quarterly resolution and compare the measured surface-height differences directly with those predicted by three FD–SMB models: MARv3.5.11 and GSFCv1.1 and GSFCv1.2. By segregating the data by season and elevation, and based on the timing and magnitude of modelled processes in areas where we expect minimal ice-dynamics-driven height changes, we investigate the models' accuracy in predicting atmospherically driven height changes. We find that while all three models do well in predicting the large seasonal changes in the low-elevation parts of the ice sheet where melt rates are highest, two of the models (MARv3.5.11 and GSFCv1.1) systematically overpredict, by around a factor of 2, the magnitude of height changes in the high-elevation parts of the ice sheet, particularly those associated with melt events. This overprediction seems to be associated with the melt sensitivity of the models in the high-elevation part of the ice sheet. The third model, GSFCv1.2, which has an updated high-elevation melt parameterization, avoids this overprediction. |
Simulations of firn processes over the Greenland and Antarctic ice sheets: 19802021 Medley, B., T.A. Neumann, H.J. Zwally, B.E. Smith, and C.M. Stevens, "Simulations of firn processes over the Greenland and Antarctic ice sheets: 19802021," Cryosphere, 16, 3971-4011, doi:10.5194/tc-16-3971-2022, 2022. |
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6 Oct 2022 |
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Conversion of altimetry-derived ice-sheet volume change to mass requires an understanding of the evolution of the combined ice and air content within the firn column. In the absence of suitable techniques to observe the changes to the firn column across the entirety of an ice sheet, the firn column processes are typically modeled. Here, we present new simulations of firn processes over the Greenland and Antarctic ice sheets (GrIS and AIS) using the Community Firn Model and atmospheric reanalysis variables for more than four decades. A data set of more than 250 measured depthdensity profiles from both ice sheets provides the basis of the calibration of the dry-snow densification scheme. The resulting scheme results in a reduction in the rate of densification, relative to a commonly used semi-empirical model, through a decreased dependence on the accumulation rate, a proxy for overburden stress. The 19802020 modeled firn column runoff, when combined with atmospheric variables from MERRA-2, generates realistic mean integrated surface mass balance values for the Greenland (+390 Gt yr-1) and Antarctic (+2612 Gt yr-1) ice sheets when compared to published model-ensemble means. We find that seasonal volume changes associated with firn air content are on average approximately 2.5 times larger than those associated with mass fluxes from surface processes for the AIS and 1.5 times larger for the GrIS; however, when averaged over multiple years, ice and air-volume fluctuations within the firn column are of comparable magnitudes. Between 1996 and 2019, the Greenland Ice Sheet lost nearly 5% of its firn air content, indicating a reduction in the total meltwater retention capability. Nearly all (94%) of the meltwater produced over the Antarctic Ice Sheet is retained within the firn column through infiltration and refreezing. |
Ocean-induced melt volume directly paces ice loss from Pine Island Glacier Joughin, I., D. Shapero, P. Dutrieux, and B. Smith, "Ocean-induced melt volume directly paces ice loss from Pine Island Glacier," Sci. Adv., 7, doi:10.1126/sciadv.abi5738, 2021. |
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22 Oct 2021 |
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The spatial distribution of ocean-induced melting beneath buttressing ice shelves is often cited as an important factor controlling Antarctica’s sea-level contribution. Using numerical simulations, we investigate the relative sensitivity of grounded-ice loss to the spatial distribution and overall volume of ice-shelf melt over two centuries. Contrary to earlier work, we find only minor sensitivity to melt distribution (<6%), with a linear dependence of ice loss on the total melt. Thus, less complex models that need not reproduce the detailed melt distribution may simplify the projection of future sea level. The linear sensitivity suggests a contribution of up to 5.1 cm from Pine Island Glacier over the next two centuries given anticipated levels of ocean warming, provided its ice shelf does not collapse because of other causes. |
Abrupt Common Era hydroclimate shifts drive west Greenland ice cap change Osman, M.B., B.E. Smith, L.D. Trusel, S.B. Das, J.R. McConnell, N. Chellman, M. Arienzo, and H. Sodermann, "Abrupt Common Era hydroclimate shifts drive west Greenland ice cap change," Nat. Geosci., 14, 756-761, doi:10.1038/s41561-021-00818-w, 2021. |
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9 Sep 2021 |
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Ice core archives are well suited for reconstructing rapid past climate changes at high latitudes. Despite this, few records currently exist from coastal Greenlandic ice caps due to their remote nature, limiting our long-term understanding of past maritime and coastal climate variability across this rapidly changing Arctic region. Here, we reconstruct regionally representative glacier surface mass balance and climate variability over the last two thousand years (similar to 1692015 CE) using an ice core collected from the Nuussuaq Peninsula, west Greenland. We find indications of abrupt regional hydroclimate shifts, including an up to 20% decrease in average snow accumulation during the transition from the Medieval Warm Period (950-1250 CE) to Little Ice Age (14501850 CE), followed by a subsequent >40% accumulation increase from the early 18th to late 20th centuries CE. These coastal changes are substantially larger than those previously reported from interior Greenland records. Moreover, we show that the strong relationship observed today between Arctic temperature rise and coastal ice cap decay contrasts with that of the last millennium, during which periods of warming led to snowfall-driven glacial growth. Taken together with modern observations, the ice core evidence could indicate a recent reversal in the response of west Greenland ice caps to climate change. |
A generalized interpolation material point method for shallow ice shelves. 1: Shallow shelf approximation and ice thickness evolution Huth, A., R. Duddu, and B. Smith, "A generalized interpolation material point method for shallow ice shelves. 1: Shallow shelf approximation and ice thickness evolution," J. Adv. Model. Earth Syst., 13, doi:10.1029/2020MS002277, 2021. |
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1 Aug 2021 |
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We develop a generalized interpolation material point method (GIMPM) for the shallow shelf approximation (SSA) of ice flow. The GIMPM, which can be viewed as a particle version of the finite element method, is used here to solve the shallow shelf approximations of the momentum balance and ice thickness evolution equations. We introduce novel numerical schemes for particle splitting and integration at domain boundaries to accurately simulate the spreading of an ice shelf. The advantages of the proposed GIMPM-SSA framework include efficient advection of history or internal state variables without diffusion errors, automated tracking of the ice front and grounding line at sub-element scales, and a weak formulation based on well-established conventions of the finite element method with minimal additional computational cost. We demonstrate the numerical accuracy and stability of the GIMPM using 1-D and 2-D benchmark examples. We also compare the accuracy of the GIMPM with the standard material point method (sMPM) and a reweighted form of the sMPM. We find that the grid-crossing error is very severe for SSA simulations with the sMPM, whereas the GIMPM successfully mitigates this error. While the grid-crossing error can be reasonably reduced in the sMPM by implementing a simple material point reweighting scheme, this approach it not as accurate as the GIMPM. Thus, we illustrate that the GIMPM-SSA framework is viable for the simulation of ice sheet-shelf evolution and enables boundary tracking and error-free advection of history or state variables, such as ice thickness or damage. |
A generalized interpolation material point method for shallow ice shelves. 2: Anisotropic nonlocal damage mechanics and rift propagation Huth, A., R. Duddu, and B. Smith, "A generalized interpolation material point method for shallow ice shelves. 2: Anisotropic nonlocal damage mechanics and rift propagation," J. Adv. Model. Earth Syst., 13, doi:10.1029/2020MS002292, 2021. |
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1 Aug 2021 |
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Ice shelf fracture is responsible for roughly half of Antarctic ice mass loss in the form of calving and can weaken buttressing of upstream ice flow. Large uncertainties associated with the ice sheet response to climate variations are due to a poor understanding of these fracture processes and how to model them. Here, we address these problems by implementing an anisotropic, nonlocal integral formulation of creep damage within a large-scale shallow-shelf ice flow model. This model can be used to study the full evolution of fracture from initiation of crevassing to rifting that eventually causes tabular calving. While previous ice shelf fracture models have largely relied on simple expressions to estimate crevasse depths, our model parameterizes fracture as a progressive damage evolution process in three-dimensions (3-D). We also implement an efficient numerical framework based on the material point method, which avoids advection errors. Using an idealized marine ice sheet, we test the creep damage model and a crevasse-depth based damage model, including a modified version of the latter that accounts for damage evolution due to necking and mass balance. We demonstrate that the creep damage model is best suited for capturing weakening and rifting over shorter (monthly/yearly) timescales, and that anisotropic damage reproduces typically observed fracture patterns better than isotropic damage. Because necking and mass balance can significantly influence damage on longer (decadal) timescales, we discuss the potential for a combined approach between models to best represent mechanical weakening and tabular calving within long-term simulations. |
Ice-shelf retreat drives recent Pine Island Glacier speedup Joughin, I., D. Shapero, B. Smith, P. Dutrieux, and M. Barham, "Ice-shelf retreat drives recent Pine Island Glacier speedup," Sci. Adv., 7, doi:10.1126/sciadv.abg3080, 2021. |
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11 Jun 2021 |
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Speedup of Pine Island Glacier over the past several decades has made it Antarctica's largest contributor to sea-level rise. The past speedup is largely due to grounding-line retreat in response to ocean-induced thinning that reduced ice-shelf buttressing. While speeds remained fairly steady from 2009 to late 2017, our Copernicus Sentinel 1A/B-derived velocity data show a >12% speedup over the past 3 years, coincident with a 19-km retreat of the ice shelf. We use an ice-flow model to simulate this loss, finding that accelerated calving can explain the recent speedup, independent of the grounding-line, melt-driven processes responsible for past speedups. If the ice shelf’s rapid retreat continues, it could further destabilize the glacier far sooner than would be expected due to surface- or ocean-melting processes. |
The scientific legacy of NASA's Operation IceBridge MacGregor, J.A., and 46 others including B.E. Smith, "The scientific legacy of NASA's Operation IceBridge," Rev. Geophys., 59, doi:10.1029/2020RG000712, 2021. |
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1 Jun 2021 |
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The National Aeronautics and Space Administration (NASA)'s Operation IceBridge (OIB) was a 13-year (20092021) airborne mission to survey land and sea ice across the Arctic, Antarctic, and Alaska. Here, we review OIB's goals, instruments, campaigns, key scientific results, and implications for future investigations of the cryosphere. OIB's primary goal was to use airborne laser altimetry to bridge the gap in fine-resolution elevation measurements of ice from space between the conclusion of NASA's Ice, Cloud, and land Elevation Satellite (ICESat; 20032009) and its follow-on, ICESat-2 (launched 2018). Additional scientific requirements were intended to contextualize observed elevation changes using a multisensor suite of radar sounders, gravimeters, magnetometers, and cameras. Using 15 different aircraft, OIB conducted 968 science flights, of which 42% were repeat surveys of land ice, 42% were surveys of previously unmapped terrain across the Greenland and Antarctic ice sheets, Arctic ice caps, and Alaskan glaciers, and 16% were surveys of sea ice. The combination of an expansive instrument suite and breadth of surveys enabled numerous fundamental advances in our understanding of the Earth's cryosphere. For land ice, OIB dramatically improved knowledge of interannual outlet-glacier variability, ice-sheet, and outlet-glacier thicknesses, snowfall rates on ice sheets, fjord and sub-ice-shelf bathymetry, and ice-sheet hydrology. Unanticipated discoveries included a reliable method for constraining the thickness within difficult-to-sound incised troughs beneath ice sheets, the extent of the firn aquifer within the Greenland Ice Sheet, the vulnerability of many Greenland and Antarctic outlet glaciers to ocean-driven melting at their grounding zones, and the dominance of surface-melt-driven mass loss of Alaskan glaciers. For sea ice, OIB significantly advanced our understanding of spatiotemporal variability in sea ice freeboard and its snow cover, especially through combined analysis of fine-resolution altimetry, visible imagery, and snow radar measurements of the overlying snow thickness. Such analyses led to the unanticipated discovery of an interdecadal decrease in snow thickness on Arctic sea ice and numerous opportunities to validate sea ice freeboards from satellite radar altimetry. While many of its data sets have yet to be fully explored, OIB's scientific legacy has already demonstrated the value of sustained investment in reliable airborne platforms, airborne instrument development, interagency and international collaboration, and open and rapid data access to advance our understanding of Earth's remote polar regions and their role in the Earth system. |
Comparisons of satellite and airborne altimetry with ground-based data from the interior of the Antarctic ice sheet Brunt, K.M., B.E. Smith, T.C. Sutterly, N.T. Kurtz, and T.A. Neumann, "Comparisons of satellite and airborne altimetry with ground-based data from the interior of the Antarctic ice sheet," Geophys. Res. Lett., 48, doi:10.1029/2020GL090572, 2021. |
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28 Jan 2021 |
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A series of traverses has been conducted for validation of the National Aeronautics and Space Administration Ice, Cloud, and land Elevation Satellite 2 (ICESat‐2) on the flat interior of the Antarctic ice sheet. Global Navigation Satellite System data collected on three separate 88S Traverses intersect 20% of the ICESat‐2 reference ground tracks and have precisions of better than ±7 cm and biases of less than ~4 cm. Data from these traverses were used to assess heights from ICESat‐2, CryoSat‐2, and Airborne Topographic Mapper (ATM). ICESat‐2 heights have better than ±3.3 cm bias and better than ±7.2 cm precision. ATM heights have better than 9.3 cm bias and better than ±9.6 cm precision. CryoSat‐2 heights have 38.9 cm of bias and ±47.3 cm precision. These best case results are from the flat ice‐sheet interior but provide a characterization of the quality of satellite and airborne altimetry. |
Brief communication: Heterogenous thinning and subglacial lake activity on Thwaites Glacier, West Antarctica Hoffman, A.O., K. Christianson, D. Shapero, B.E. Smith, and I. Joughin, "Brief communication: Heterogenous thinning and subglacial lake activity on Thwaites Glacier, West Antarctica," Cryosphere, 14, 4603-4609, doi:10.5194/tc-14-4603-2020, 2020. |
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18 Dec 2020 |
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A system of subglacial lakes drained on Thwaites Glacier from 2012-2014. To improve coverage for subsequent drainage events, we extended the elevation and icevelocity time series on Thwaites Glacier through austral winter 2019. These new observations document a second drainage cycle in 2017/18 and identified two new lake systems located in the western tributaries of Thwaites and Haynes glaciers. In situ and satellite velocity observations show temporary < 3% speed fluctuations associated with lake drainages. In agreement with previous studies, these observations suggest that active subglacial hydrology has little influence on thinning and retreat of Thwaites Glacier on decadal to centennial timescales. |
Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes Smith, B., and 14 others, "Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes," Science, 368, 1239-1242, doi:10.1126/science.aaz5845, 2020. |
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12 Jun 2020 |
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Quantifying changes in Earth's ice sheets, and identifying the climate drivers, is central to improving sea-level projections. We provide unified estimates of grounded and floating ice mass change from 2003 to 2019 using NASA's ICESat and ICESat-2 satellite laser altimetry. Our data reveal patterns likely linked to competing climate processes: Ice loss from coastal Greenland (increased surface melt), Antarctic ice shelves (increased ocean melting), and Greenland and Antarctic outlet glaciers (dynamic response to ocean melting), was partially compensated by mass gains over ice sheet interiors (increased snow accumulation). Losses outpaced gains, with grounded-ice loss from Greenland (200 Gt a1) and Antarctica (118 Gt a1) contributing 14 mm to sea level. Mass lost from West Antarctica's ice shelves accounted for over 30% of that region's total. |
Mass balance of the Greenland Ice Sheet from 1992 to 2018 Shepherd, A., and 87 others including B. Smith, I. Joughin, and T. Sutterley, "Mass balance of the Greenland Ice Sheet from 1992 to 2018," Nature, 579, 233-239, doi:10.1038/s41586-019-1855-2, 2020. |
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12 Mar 2020 |
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The Greenland Ice Sheet has been a major contributor to global sea-level rise in recent decades and it is expected to continue to be so. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric 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 conditions and ocean temperatures fell at the terminus of Jakobshavn Isbrae. 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 scenario, which forecast an additional 70 to 130 millimetres of global sea-level rise by 2100 compared with their central estimate. |
A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity Joughin, I., D.E. Shean, B.E. Smith, and D. Floricioiu, "A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity," Cryosphere, 14, 211-227, doi:10.5194/tc-14-211-2020, 2020. |
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24 Jan 2020 |
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The speed of Greenland's fastest glacier, Jakobshavn Isbræ, has varied substantially since its speed-up in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speed-up and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 20162017 and 20172018, concurrent with terminus advances ~6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean's dominant influence on Jakobshavn Isbræ is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations approach flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds were slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending. |
Assessment of ICESat-2 ice sheet surface heights, based on comparison over the interior of the Antarctic Ice Sheet Brunt, E.M., T.A. Neumann, and B.E. Smith, "Assessment of ICESat-2 ice sheet surface heights, based on comparison over the interior of the Antarctic Ice Sheet," Geophys. Res. Lett., 46, 13,072-13,078, doi:10.1029/2019GL084886, 2019. |
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28 Nov 2019 |
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We collected kinematic Global Navigation Satellite Systems (GNSS) surface height data, on a 750‐km ground‐based traverse of the flat interior of the Antarctic ice sheet, for comparison with Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2) surface heights. Vertical errors in the GNSS data are estimated to be 5.6 cm, comparable to results from a previous traverse and with year‐to‐year comparisons. Comparisons of the GNSS heights and 6 months of ICESat‐2 ATL03 photon‐based heights and ATL06 segment‐based heights indicate that the accuracy and precision of ICESat‐2 data are comparable to that of results from the ICESat mission: ATL03 is currently accurate to better than 5 cm with better than 13 cm of surface measurement precision, while ATL06 is currently accurate to better than 3 cm with better than 9 cm of surface measurement precision. |
Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers Lilien, D.A., I. Joughin, B. Smith, and N. Gourmelen, "Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers," The Cryosphere, 13, 2817-2834, doi:10.5194/tc-13-2817-2019, 2019. |
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5 Nov 2019 |
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Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson ice shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e., that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained, elevated melt at the grounding line was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier's trough appears likely. Given the rapid progression of grounding-line retreat in the model simulations, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus. |
Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica Shean, D.E., I.R. Joughin, P. Dutrieux, B.E. Smith, and E. Berthier, "Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica," Cryosphere, 13, 2633-2656, doi:10.5194/tc-13-2633-2019, 2019. |
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10 Oct 2019 |
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Ocean-induced basal melting is responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution digital elevation models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 20022015 DEM and altimetry data. We implemented a Lagrangian elevation change (Dh∕Dt) framework to estimate ice shelf basal melt rates at 32256 m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG ice shelf and lower catchment from 2008 to 2015. We document the evolution of Eulerian elevation change (dh∕dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 20082015 period were ~8293 Gt yr-1, with ~200250 m yr-1 basal melt rates within large channels near the grounding line, ~1030 m yr-1 over the main shelf, and ~010 m yr-1 over the North shelf and South shelf, with the notable exception of a small area with rates of ~50100 m yr-1 near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt-rate observations. We also document the relative melt rates for kilometer-scale basal channels and keels at different locations on the ice shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice–ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica. |
Measuring height change around the periphery of the Greenland Ice Sheet with radar altimetry Gray, L., and 10 others including I. Joughin and B. Smith, "Measuring height change around the periphery of the Greenland Ice Sheet with radar altimetry," Front. Earth Sci., 7, 146, doi:10.3389/feart.2019.00146, 2019. |
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11 Jun 2019 |
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Ice loss measurements around the periphery of the Greenland Ice Sheet can provide key information on the response to climate change. Here we use the excellent spatial and temporal coverage provided by the European Space Agency (ESA) CryoSat satellite, together with NASA airborne Operation IceBridge and automatic weather station data, to study the influence of changing conditions on the bias between the height estimated by the satellite radar altimeter and the ice sheet surface. Surface and near-surface conditions on the ice sheet periphery change with season and geographic position in a way that affects the returned altimeter waveform and can therefore affect the estimate of the surface height derived from the waveform. Notwithstanding the possibility of a varying bias between the derived and real surface, for the lower accumulation regions in the western and northern ice sheet periphery (< ~1 m snow accumulation yearly) we show that the CryoSat altimeter can measure height change throughout the year, including that associated with ice dynamics, summer melt and winter accumulation. Further, over the 9-year CryoSat lifetime it is also possible to relate height change to change in speed of large outlet glaciers, for example, there is significant height loss upstream of two branches of the Upernavik glacier in NW Greenland that increased in speed during this time, but much less height loss over a third branch that slowed in the same time period. In contrast to the west and north, winter snow accumulation in the south-east periphery can be 2 3 m and the average altimeter height for this area can decrease by up to 2 m during the fall and winter when the change in the surface elevation is much smaller. We show that vertical downward movement of the dense layer from the last summer melt coupled with overlying dry snow, are responsible for the anomalous altimeter height change. However, it is still possible to estimate year-to-year height change measurements in this area by using data from the late-summer to early-fall when surface returns dominate the altimeter signal. |
Regularized Coulomb friction laws for ice sheet sliding: Application to Pine Island Glacier, Antarctica Joughin, I., B.E. Smith, and C.G. Schoof, "Regularized Coulomb friction laws for ice sheet sliding: Application to Pine Island Glacier, Antarctica," Geophys. Res. Lett., 46, 4764-4771, doi:10.1029/2019GL082526, 2019. |
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16 May 2019 |
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The choice of the best basal friction law to use in ice‐sheet models remains a source of uncertainty in projections of sea level. The parameters in commonly used friction laws can produce a broad range of behavior and are poorly constrained. Here we use a time series of elevation and speed data to examine the simulated transient response of Pine Island Glacier, Antarctica, to a loss of basal traction as its grounding line retreats. We evaluate a variety of friction laws, which produces a diversity of responses, to determine which best reproduces the observed speedup when forced with the observed thinning. Forms of the commonly used power law friction provide much larger modeldata disagreement than less commonly used regularized Coulomb friction in which cavitation effects yield an upper bound on basal friction. Thus, adoption of such friction laws could substantially improve the fidelity of large‐scale simulations to determine future sea level. |
The Reference Elevation Model of Antarctica Howat, I.M., C. Porter, B.E. Smith, M.-J. Noh, and P. Morin, "The Reference Elevation Model of Antarctica," Cryosphere, 13, 665-674, doi:10.5194/tc-13-665-2019, 2019. |
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26 Feb 2019 |
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The Reference Elevation Model of Antarctica (REMA) is the first continental-scale digital elevation model (DEM) at a resolution of less than 10 m. REMA is created from stereophotogrammetry with submeter resolution optical, commercial satellite imagery. The higher spatial and radiometric resolutions of this imagery enable high-quality surface extraction over the low-contrast ice sheet surface. The DEMs are registered to satellite radar and laser altimetry and are mosaicked to provide a continuous surface covering nearly 95% the entire continent. The mosaic includes an error estimate and a time stamp, enabling change measurement. Typical elevation errors are less than 1 m, as validated by the comparison to airborne laser altimetry. REMA provides a powerful new resource for Antarctic science and provides a proof of concept for generating accurate high-resolution repeat topography at continental scales. |
Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming Trusel, L.D., and 8 other including B.E. Smith, "Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming," Nature, 564, 104-108, doi:10.1038/s41586-018-0752-4, 2018. |
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5 Dec 2018 |
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The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise, with recent ice mass loss dominated by surface meltwater runoff. Satellite observations reveal positive trends in GrIS surface melt extent, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350 years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates and satellite-derived melt duration across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions. |
Greenland Ice Mapping Project: Ice flow velocity variation at sub-monthly to decadal timescales Joughin, I., B.E. Smith, and I. Howat, "Greenland Ice Mapping Project: Ice flow velocity variation at sub-monthly to decadal timescales," Cryosphere, 12, 2211-2227, doi:10.5194/tc-12-2211-2018, 2018. |
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11 Jul 2018 |
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We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results. |
GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica Shean, D.E., K. Christianson, K.M. Larson, S.R.M. Ligtenberg, I.R. Joughin, B.E. Smith, C.M. Stevens, M. Bushuk, and D.M. Holland, "GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica," Cryosphere, 11, 2655-2674, doi:10.5194/tc-11-2655-2017, 2017. |
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21 Nov 2017 |
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In the last 2 decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to marine ice-sheet instability and ice-shelf basal melt. To better understand these processes, we combined 20082010 and 20122014 GPS records with dynamic firn model output to constrain local surface and basal mass balance for PIG. We used GPS interferometric reflectometry to precisely measure absolute surface elevation (zsurf) and Lagrangian surface elevation change (Dzsurf∕ Dt). Observed surface elevation relative to a firn layer tracer for the initial surface (zsurf zsurf0′) is consistent with model estimates of surface mass balance (SMB, primarily snow accumulation). A relatively abrupt ~0.20.3 m surface elevation decrease, likely due to surface melt and increased compaction rates, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dzsurf∕ Dt trends (1 to 4 m yr-1) for the PIG shelf sites are all highly linear. Corresponding basal melt rate estimates range from ~10 to 40 m yr-1, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo digital elevation model (DEM) records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (i.e., transverse surface depressions, rifts). Basal melt rates for the 20122014 period show limited temporal variability despite large changes in ocean temperature recorded by moorings in Pine Island Bay. Our results demonstrate the value of long-term GPS records for ice-shelf mass balance studies, with implications for the sensitivity of iceocean interaction at PIG. |
Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland Moon, T., I, Joughin, and B. Smith, "Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland," J. Geophys. Res., 120, 818-833, doi:10.1002/2015JF003494, 2015. |
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13 May 2015 |
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Glacier ice discharge, which depends on ice velocity and terminus fluctuations, is a primary component of Greenland Ice Sheet mass loss. Some research suggests that ice melange influences terminus calving, in turn affecting glacier velocity. The details and broad spatiotemporal consistency of these relationships, however, is undetermined. Focusing on 16 northwestern Greenland glaciers during 2009 through summer 2014, we examined seasonal surface velocity changes, glacier terminus position, and sea ice and ice melange conditions. For a longer-term analysis, we also produced extended records of four glaciers from 1999 to 2014. There is a strong correspondence between seasonal near-terminus sea ice/melange conditions and terminus change, with rigid ice melange conditions associated with advance and open water associated with retreat. Extended sea ice-free periods and reduced rigid melange are also linked with anomalously large terminus retreat. In all but one case, sustained multiyear retreat of greater than 1 km during both the 15-year and 6-year records was accompanied by interannual velocity increases. Seasonal velocity patterns, however, correspond more strongly with runoff changes than terminus behavior. Projections of continued warming and longer sea ice-free periods around Greenland indicate that notable retreat over wide areas may continue. This sustained retreat likely will contribute to multiyear speedup. Longer melt seasons and earlier breakup of melange may also alter the timing of seasonal ice flow variability. |
Marine ice sheet collapse potentially underway for the Thwaites Glacier Basin, West Antarctica Joughin, I., B.E. Smith, and B. Medley, "Marine ice sheet collapse potentially underway for the Thwaites Glacier Basin, West Antarctica," Science, 344, 735-738, doi: 10.1126/science.1249055, 2014 |
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16 May 2014 |
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Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigate the sensitivity of Thwaites Glacier to ocean melt and whether unstable retreat is already underway. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (<0.25 mm per year sea level) over the 21st Century, but generally increase thereafter. Except possibly for the lowest-melt scenario, the simulations indicate early-stage collapse has begun. Less certain is the timescale, with onset of rapid (> 1 mm per year of sea-level rise) collapse for the different simulations within the range of two to nine centuries. |
Transition of flow regime along a marine-terminating outlet glacier in East Antarctica Callens, D., K. Matsuoka, D. Steinhage, B. Smith, E. Witrant, and F. Pattyn, "Transition of flow regime along a marine-terminating outlet glacier in East Antarctica," Cryosphere, 8, 867-875, doi:10.5194/tc-8-867-2014, 2014. |
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13 May 2014 |
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We present results of a multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (>2000 m) than previously thought. With a discharge estimate of 13%u201314 Gt yr%u22121, West Ragnhild Glacier thus becomes of the three major outlet glaciers in Dronning Maud Land. Its bed topography is distinct between the upstream and downstream section: in the downstream section (<65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level, while the upstream region is more mountainous. Spectral analysis of the bed topography also reveals this clear contrast and suggests that the downstream area is sediment covered. Furthermore, bed-returned power varies by 30 dB within 20 km near the bed flatness transition, suggesting that the water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~250 m yr%u22121) can only be explained through very low basal friction, leading to a substantial amount of basal sliding in the downstream 65 km of the glacier. All the above lines of evidence (sediment bed, wetness and basal motion) and the relatively flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region, which are more stable due to their bed geometry (e.g. Shirase Glacier). |
Further speedup of Jakobshavn Isbrae Joughin, I., B.E. Smith, D.E. Shean, and D. Floricioiu, "Further speedup of Jakobshavn Isbrae," The Cryosphere, 8, 209-214, doi:doi:10.5194/tc-8-209-2014, 2014. |
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3 Feb 2014 |
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We have extended the record of flow speed on Jakobshavn Isbrae through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% greater than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as great as that in the mid-1990s, while the peak summer speeds are more than a factor of four greater. These speeds were achieved as the glacier terminus appears to have retreated to the bottom of an over-deepened basin with a depth of ~ 1300 m below sea level. The terminus is likely to reach the deepest section of the trough within a few decades, after which it could rapidly retreat to the shallower regions ~ 50 km farther upstream, potentially by the end of this century. |
Ice-sheet mass balance and climate change Hanna, E., and 11 others, including B. Smith, "Ice-sheet mass balance and climate change," Nature, 498, 51-59, doi:10.1038/nature12238, 2013. |
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6 Jun 2013 |
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Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain. |
A reconciled estimate of ice-sheet mass balance Shepherd, A., and 46 others, including I. Joughin and B. Smith, "A reconciled estimate of ice-sheet mass balance," Science, 338, 1183-1189, doi:10.1126/science.1228102, 2012. |
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30 Nov 2012 |
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We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methodsespecially in Greenland and West Antarcticaand that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by 142 ± 49, +14 ± 43, 65 ± 26, and 20 ± 14 gigatonnes year-1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year-1 to the rate of global sea-level rise. |
Glaciology: Repeat warming in Greenland Smith, B.E., "Glaciology: Repeat warming in Greenland," Nature Geosci., 5, 369-370, doi:10.1038/ngeo1488, 2012. |
27 May 2012 |
Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis Joughin, I., B.E. Smith, I.M. Howat, D. Floriciolu, R.B. Alley, M. Truffer, and M. Fahnestock, "Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis," J. Geophys. Res., 117, doi:10.1029/2011JF002110, 2012. |
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25 May 2012 |
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Using new data, we build upon the nearly two-decade long record of observations from Jakobshavn Isbrae to investigate the processes driving its dynamic evolution. While winter flow speed has not increased substantially over the last three winters, there remains a strong seasonal variation in flow speed that coincides with a cycle of summer thinning and winter thickening. We relate changes in glacier speed to geometry through variations in basal traction and horizontal stresses, using ice-flow models constrained by satellite and airborne observations. These results suggest that the bed provides little flow resistance along the main trough within about 20 km of the terminus. While the loss of buttressing from the retreat of grounded and floating ice likely contributed to the initial speedup, other processes are of comparable significance at seasonal to decadal time scales. From analysis of the models, we hypothesize that thinning-induced change in basal effective pressure is the dominant process influencing near-terminus behavior, while diffusive processes drive the upstream response. The apparent need for the terminus to thin to near flotation before it can calve may limit the rate at which retreat occurs. Our analysis of the processes controlling the speed suggests little potential for further large acceleration. Thinning and elevated speeds may continue at rates similar to present, however, putting the glacier on course to retreat to the head of its deep trough in about a century, at which point it likely would stabilize with a thinner terminus. |
21st-century evolution of Greenland outlet glacier velocities Moon, T., I. Joughin, B. Smith, and I. Howat, "21st-century evolution of Greenland outlet glacier velocities," Science, 336, 576-578, doi:10.1126/science.1219985, 2012. |
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4 May 2012 |
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Earlier observations on several of Greenland%u2019s outlet glaciers, starting near the turn of the 21st century, indicated rapid (annual-scale) and large (>100%) increases in glacier velocity. Combining data from several satellites, we produce a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200 ) of Greenland%u2019s major outlet glaciers, revealing complex spatial and temporal patterns. Changes on fast-flow marine-terminating glaciers contrast with steady velocities on ice-shelf%u2013terminating glaciers and slow speeds on land-terminating glaciers. Regionally, glaciers in the northwest accelerated steadily, with more variability in the southeast and relatively steady flow elsewhere. Intraregional variability shows a complex response to regional and local forcing. Observed acceleration indicates that sea level rise from Greenland may fall well below proposed upper bounds. |
Changes in the dynamics of marine terminating outlet glaciers in west Greenland (2000-2009) McFadden, E.M., I.M. Howat, I. Joughin, B.E. Smith, and Y. Ahn, "Changes in the dynamics of marine terminating outlet glaciers in west Greenland (2000-2009)," J. Geophys. Res., 116, doi:10.1029/2010F001757, 2011. |
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23 Jun 2011 |
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Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a rapid and complex response to external forcing. Despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along Greenland's northwestern margin, it is unclear whether west Greenland glaciers have undergone the synchronous speed-up and subsequent slow-down as observed in southeastern glaciers earlier in the decade. To investigate changes in west Greenland outlet glacier dynamics and the potential controls behind their behavior, we derive time series of front position, surface elevation, and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west Greenland from 2000 to 2009. Using these data, we look for relationships between retreat, thinning, acceleration, and geometric parameters to determine the first-order controls on glacier behavior. Our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales, though nearly all glaciers retreated and thinned over the decade. We found no direct relationship between retreat, acceleration, and external forcing applicable to the entire region. In regard to geometry, we found that, following retreat, (1) glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and (2) thinning rates declined more quickly for glaciers with steeper slopes. Overall, glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front, but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west Greenland. |
Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade. Price, S.F., A.J. Payne, I.M. Howat, and B.E. Smith, "Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade." P. Natl. Acad. Sci. USA, 108, 8978-8983, doi:10.1073/pnas.1017313108, 2011. |
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31 May 2011 |
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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 Isbrae, 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 plus/minus 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 plus/minus 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. |
Light propagation in firn: Application to borehole video Fudge, T.J., and B.E. Smith, "Light propagation in firn: Application to borehole video," J. Glaciol., 56, 614-624, doi:10.3189/002214310793146205, 2010. |
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1 Oct 2010 |
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Borehole optical stratigraphy (BOS) is a borehole video system and processing routine for investigating polar firn. BOS records brightness variations in the firn and is effective at identifying stratigraphic markers. BOS brightness logs have been used to count annual layers and measure vertical strain, even though a specific cause of the brightness variations has not been determined. Here we combine two models of light transport to examine potential errors with BOS and identify improvements which will allow the system to estimate optical grain size. We use a Monte Carlo radiative transfer model to estimate the influence of firn microstructure variations on borehole reflectance. We then use a ray-tracing algorithm to model the multiple reflections within the borehole that cause measured brightness variations. |
Greenland flow variability from ice-sheet-wide velocity mapping Joughin, I., B.E. Smith, I.M. Howat, T. Scambos, and T. Moon, "Greenland flow variability from ice-sheet-wide velocity mapping," J. Glaciol., 56, 415-430, doi:10.3189/002214310792447734, 2010. |
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1 Aug 2010 |
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Using RADARSAT synthetic aperture radar data, we have mapped the flow velocity over much of the Greenland ice sheet for the winters of 2000/01 and 2005/06. These maps provide a detailed view of the ice-sheet flow, including that of the hundreds of glaciers draining the interior. The focused patterns of flow at the coast suggest a strong influence of bedrock topography. Differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes. The overall pattern is one of speed-up accompanied by terminus retreat, but there are also several instances of surge behavior and a few cases of glacier slowdown. Comprehensive mappings such as these, at regular intervals, provide an important new observational capability for understanding ice-sheet variability. |
An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008) Smith, B.E., H.A. Fricker, I.R. Joughin, and S. Tulaczyk, "An inventory of active subglacial lakes in Antarctica detected by ICESat (2003-2008)," J. Glaciol., 55, 573-595, doi:10.3189/002214309789470879, 2009. |
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1 Sep 2009 |
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Through the detection of surface deformation in response to water movement, recent satellite studies have demonstrated the existence of subglacial lakes in Antarctica that fill and drain on timescales of months to years. These studies, however, were confined to specific regions of the ice sheet. Here we present the first comprehensive study of these 'active' lakes for the Antarctic ice sheet north of 86°S, based on 4.5 years (2003-08) of NASA's Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Our analysis has detected 124 lakes that were active during this period, and we estimate volume changes for each lake. The ICESat-detected lakes are prevalent in coastal Antarctica, and are present under most of the largest ice-stream catchments. Lakes sometimes appear to transfer water from one to another, but also often exchange water with distributed sources undetectable by ICESat, suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow. Thus, these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds, but also may withdraw water at other times to slow flow. |
Continued evolution of Jakobshavn Isbrae following its rapid speedup Joughin, I., I. Howat, M. Fahnestock, B. Smith, W. Krabill, R. Alley, H. Stern, and M. Truffer, "Continued evolution of Jakobshavn Isbrae following its rapid speedup," J. Geophys. Res., 113, doi:10.1029/2008JF001023, 2008. |
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28 Oct 2008 |
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Several new data sets reveal that thinning and speedup of Jakobshavn Isbrae continue, following its recent rapid increase in speed as its floating ice tongue disintegrated. The present speedup rate of 5% a-1 over much of the fast-moving region appears to be a diffusive response to the initial much larger speedup near the front. There is strong seasonality in speed over much of the fast-flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short (typically ~6 km) floating ice tongue. This modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003. Analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving. Major calving only resumes in late winter when much of this ice clears from the fjord. The collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea-ice concentration in Disko Bay. This decline may have extended the length of the calving season for several consecutive years, leading to the ice tongue's collapse. |
Seasonal speedup along the western flank of the Greenland ice sheet Joughin, I., S.B. Das, M.A. King, B.E. Smith, I.M. Howat, and T. Moon, "Seasonal speedup along the western flank of the Greenland ice sheet," Science, 320, 791-883, 2008. |
More Info |
9 May 2008 |
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It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow. |
In The News
UW-led project to study ozone, atmospheric layers a finalist for next-generation NASA satellite UW News, Hannah Hickey A project led by the University of Washington to better understand our atmosphere's complexity is a finalist for NASA's next generation of Earth-observing satellites. The four teams that reached the proof-of-concept stage will spend the next year refining their proposals. NASA will then review the concept study reports and select two for implementation. |
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Edge of Pine Island Glacier’s ice shelf is ripping apart, causing key Antarctic glacier to gain speed UW News, Hannah Hickey For decades, the ice shelf helping to hold back one of the fastest-moving glaciers in Antarctica has gradually thinned. Analysis of satellite images reveals a more dramatic process in recent years: From 2017 to 2020, large icebergs at the ice shelf’s edge broke off, and the glacier sped up. |
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Shrinking ice sheets lifted global sea level 14 millimeters Eos (American Geophysical Union), Tim Hornyak Researchers measure both grounded and floating ice sheets using satellite data spanning a 16-year period. |
15 May 2020
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NASA: 318 gigatons of ice are melting in Antarctica and Greenland each year Tech Times, Giuliano J. The results of a new study reveal that the ice sheet in Antarctica's interior is getting thicker because of increased snowfall. However, the warming of the ocean has also caused ice meltdowns in the Antarctic Peninsula and West Antarctica, which outweigh the gains in the interior. |
3 May 2020
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NASA space lasers offer 'fantastically detailed' look at the world's ice loss Gizmodo, Yessenia Funes A new study shows increased snow accumulation isn’t enough to offset massive ice losses in Greenland and Antarctica. Greenland has shed an average of 200 gigatons of ice a year, and Antarctica has lost an average of 118 gigatons of ice a year. That's contributed to more than half an inch of sea level rise over the past 16 years alone |
2 May 2020
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In just 16 years, Antarctica and Greenland have lost enough ice to fill Lake Michigan CBS News, Sophie Lewis Antarctica and Greenland have lost thousands of gigatons of ice in the last 16 years alone. According to new data from NASA, that ice melt has contributed to more than half an inch of sea level rise around the world. |
1 May 2020
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New satellite gives clearest view yet of polar ice melt Scientific American, Chelsea Harvey A cutting-edge NASA satellite has provided one of the most detailed looks yet at glaciers in Greenland and Antarctica. The findings are clearer than ever: Both ice sheets are losing billions of tons of mass into the ocean each year, contributing significantly to global sea-level rise. |
1 May 2020
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Ocean warming is causing massive ice sheet loss in Greenland and Antarctica, NASA study shows CNN, Mallika Kallingal The Earth is losing ice at a record speed chiefly due to warming from the ocean caused by climate change. |
1 May 2020
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Satellites map melting ice sheets Cosmos, Nick Carne Ice sheet losses from Greenland and Antarctica have outpaced snow accumulation and contributed around 14 millimetres to sea level rise over the past 16 years, a new analysis of data from NASA’s laser-shooting satellites has revealed. |
1 May 2020
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A new way of measuring ice melt in Antarctica, Greenland sounds alarm about global sea level rise CNBC, Emma Newburger Analysis of satellite altimeter measurements taken over a span of 16 years gives scientists confidence that the changes observed in the ice sheets of Antarctica and Greenland are the results of long-term changes in the climate. |
30 Apr 2020
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A satellite lets scientists see Antarctica's melting like never before The New York Times, Kendra Pierre-Louis, Henry Fountain, Denise Lu New data from space is providing the most precise picture yet of Antarctica’s ice, where it is accumulating most quickly and disappearing at the fastest rate, and how the changes could contribute to rising sea levels. |
30 Apr 2020
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First results from NASA's ICESat-2 map 16 years of melting ice sheets UW News, Hannah Hickey Using the most advanced Earth-observing laser instrument NASA has ever flown in space, a team of scientists led by the University of Washington has made precise measurements of how the Greenland and Antarctic ice sheets have changed over 16 years. |
30 Apr 2020
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ICESat-2 laser-scanning satellite tracks how billions of tons of polar ice are lost GeekWire, Alan Boyle A satellite mission that bounces laser light off the ice sheets of Antarctica and Greenland has found that hundreds of billions of tons’ worth of ice are being lost every year due to Earth’s changing climate. |
30 Apr 2020
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NASA space lasers track melting of Earth's ice sheets BBC, Jonathan Amos Scientists have released a new analysis of how the Greenland and Antarctic ice sheets have changed, from 2003 to 2019. The study shows that ice losses from melting have outpaced increases in snowfall, resulting in a 14 mm rise in global sea levels over the period. |
30 Apr 2020
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Study reveals massive yearly ice loss in the Antarctic and Greenland New Atlas, Anthony Wood A new paper has revealed that Greenland and the Antarctic have lost a staggering amount of mass from their ice sheets over the last 16 years thanks to climate change, and that the melting has contributed to sea level rise. |
30 Apr 2020
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Key data for NASA's ice-monitoring satellite in trouble thanks to shutdown Gizmodo, Maddie Stone the spring campaign for NASA’s Operation IceBridge a series of airborne flights over the Arctic and Antarctic the space agency has been conducting since 2009 would likely be delayed thanks to President Trump’s fictitious crisis at the U.S. southern border. |
23 Jan 2019
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Shutdown imperils NASA's decadelong ice-measuring campaign Science, Paul Voosen The partial U.S. government shutdown threaten to shorten IceBridge missions, a decadelong NASA aerial campaign meant to secure a seamless record of ice loss. Ben Smith comments that this will imperil the plan to collect overlapping data with the new ice-monitoring satellite called the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). |
18 Jan 2019
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14 Dec 2018
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NASA's IceSat space laser makes height maps of Earth BBC News, Jonathan Amos One of the most powerful Earth observation tools ever put in orbit is now gathering data about the planet. The great advantage of the new laser system is that it can detect behaviour in areas that have been beyond the vision of previous satellites. "We're resolving every valley in the mountains," said team-member Ben Smith. |
11 Dec 2018
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Scary warming at poles showing up at weird times, places The New York Times Scientists are seeing surprising melting in Earth's polar regions at times they don't expect, like winter, and in places they don't expect, like eastern Antarctica. NASA's newest space-based radar, Icesat 2, in its first couple of months has already found that the Dotson ice shelf in Antarctica has lost more than 390 feet (120 meters) in thickness since 2003, said radar scientist Ben Smith. |
11 Dec 2018
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UW polar scientists advised NASA on upcoming ICESat-2 satellite UW News, Hannah Hickey NASA plans to launch a new satellite this month that will measure elevation changes on Earth with unprecedented detail. Once in the air, it will track shifts in the height of polar ice, mountain glaciers and even forest cover around the planet. Two University of Washington polar scientists are advising the ICESat-2 mission, provided expertise on the massive glaciers covering Antarctica and Greenland, and sea surface height in the Arctic and other oceans. |
10 Sep 2018
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UW scientists working with NASA to monitor Earth's ice loss KING 5, Glenn Farley This Saturday, NASA will launch a high-resolution satellite designed primarily to measure the status of the world's ice. |
10 Sep 2018
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Hidden lakes drain below West Antarctica's Thwaites Glacier UW News and Information, Hannah Hickey Thwaites Glacier on the edge of West Antarctica is one of the planet’s fastest-moving glaciers. Research shows that it is sliding unstoppably into the ocean, mainly due to warmer seawater lapping at its underside. |
8 Feb 2017
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What Antarctica's incredible "growing" icepack really means National Geographic, Brian Clark Howard Are the Antarctic's ice sheets shrinking or growing? And what does that mean for global sea-level rise? Ben Smith, who was not involved with the study, notes that the technology used to collect surface elevation measurements might not be up to the task of distinguishing snowpack volume based on differences of one or two centimeters. |
3 Nov 2015
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Antarctica accumulates more ice than it melts Business Insider, Rebecca Harrington The snow that falls on Antarctica every year is accumulating as ice faster than it's melting on the continent, a new study from NASA found. Ben Smith, not involved in the study, notes that precise records of snow accumulation are needed to fully understand the nature of the net ice gains and losses. |
2 Nov 2015
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This is the new worst-case scenario for ice loss in Antarctica Slate, Eric Holthaus With the most ice on Earth, Antarctica holds the key to the world's coastal fate. But up until now, there hasn't been a reliable upper bounds on how much Antarctica as a whole may contribute to global sea level rise over the relatively short term of the next several decades. |
14 Aug 2014
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Collapse or catastrophe? The Economist The West Antarctic ice sheet looks doomed eventually. Glaciologists use the word "collapse" to describe a shift towards an irretrievable loss of an ice sheet. There is, reckons Dr Joughin, probably nothing that can now be done to save the Thwaites glacier. |
17 May 2014
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Antarctic ice sheet slipping into the sea National Public Radio: Science Friday, Ira Flatow Two studies out this week confirm that the glaciers of West Antarctica have begun to slip into the Amundsen Sea. Scientists estimate it could take 200 years for the ice sheet to completely melt. Glaciologist Ian Joughin tells us what this could mean for rising sea levels. |
16 May 2014
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Antarctic glaciers melting 'passed point of no return' USA Today, Traci Watson The vast glaciers of western Antarctica are rapidly melting and losing ice to the sea and almost certainly have 'passed the point of no return,' according to new work by two separate teams of scientists. |
13 May 2014
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New study: Glacial collapse in Antarctica 'unstoppable' KUOW Radio, Steve Scher, Ashley Ahearn, and Posey Gruener New research from the University of Washington and other institutions provides detailed predictions for the collapse of an ice shelf in West Antarctica. When the Thwaites Glacier melts, it could trigger even more extreme sea level rise than scientists previously thought. |
13 May 2014
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UW researchers: Polar ice sheet doomed, but how soon? The Seattle Times, Craig Welch It%u2019s too late to halt the collapse of the West Antarctic ice sheet into the sea, triggering several feet of sea-level rise, scientists have found. But UW researchers say the speed of that collapse depends on our response to climate change. |
13 May 2014
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Antarctic glacier loss is 'unstoppable,' study says Time, Bryan Walsh The Intergovernmental Panel on Climate Change had projected that sea level will rise by about 35.5 in (98 cm) at most by 2100, but that prediction will likely need to be revisited in the wake of these new studies. |
12 May 2014
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Irreversible collapse of Antarctic glaciers has begun, studies say Los Angeles Times, Scott Gold A slow-motion and irreversible collapse of a massive cluster of glaciers in Antarctica has begun, and could cause sea levels to rise across the planet by another 4 feet within 200 years, scientists concluded in two studies released Monday. |
12 May 2014
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Melting of Antarctic ice sheet might be unstoppable National Public Radio, Scott Neuman Scientists have long worried about climate change-induced melting of the huge West Antarctic Ice Sheet. Now they say that not only is the disintegration of the ice already underway, but that it's likely unstoppable. |
12 May 2014
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NASA spots worrisome Antarctic ice sheet melt The Washington Post The huge West Antarctic ice sheet is starting a glacially slow collapse in an unstoppable way, two new studies show. Alarmed scientists say that means even more sea level rise than they figured. |
12 May 2014
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Scientists warm of melting ice sheet, rising sea level The Wall Street Journal, Robert Lee Hotz Six rapidly melting glaciers in Antarctica are destabilizing one of the world's largest ice sheets, a process which, if unchecked, could release enough water to raise sea levels world-wide significantly in centuries to come. |
12 May 2014
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Scientists warn of rising oceans from polar melt The New York Times, Justin Gillis and Kenneth Chang A large section of the mighty West Antarctica ice sheet has begun falling apart and its continued melting now appears to be unstoppable, two groups of scientists reported. |
12 May 2014
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Studies: Seas to rise up to 10 feet from 'unstoppable' glacier melt U.S. News and World Report, Alan Neuhauser A huge swath of the West Antarctic ice sheet has "passed the point of no return," a pair of new science reports say, melting far faster than expected in an "irreversible decline" that will raise the world%u2019s oceans by anywhere from 4 to 10 feet. |
12 May 2014
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West Antarctic glacier loss: 'We have passed the point of no return' Christian Science Monitor, Pete Spotts Two studies released Monday signal that five glaciers in West Antarctica are undergoing irreversible decline over the next several hundred years, signaling sea level-rise of nearly four feet. |
12 May 2014
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West Antarctic ice sheet collapse is under way UW News and Information, Hannah Hickey University of Washington researchers used detailed topography maps and computer modeling to show that the collapse of the West Antarctic ice sheet appears to have already begun. The fast-moving Thwaites Glacier will likely disappear in a matter of centuries, researchers say, raising sea level by nearly 2 feet. |
12 May 2014
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West Antarctic ice sheet's collapse triggers sea level warning NBC News, Alan Boyle Two teams of scientists say the long-feared collapse of the West Antarctic Ice Sheet has begun, kicking off what they say will be a centuries-long, "unstoppable" process that could raise sea levels by as much as 15 feet. |
12 May 2014
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Western Antarctic ice sheet collapse has already begun, scientists warn The Guardian, Suzanne Goldenberg Two separate studies confirm loss of ice sheet is inevitable, and will cause up to 4m of additional sea-level rise. This collapse will change the coastline of the whole world. |
12 May 2014
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Glacier that sank the Titanic is really on the move, say scientists The Christian Science Monitor, Sudeshna Chowdhury Jakobshavn Glacier has bagged the tile of Greenland's Fastest Glacier in Greenland: In the summer of 2012 it reached a record speed of over 150 feet per day. |
4 Feb 2014
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Greenland glacier hits speed record BBC News, Paul Rincon A river of ice in Greenland has become the fastest-flowing glacier currently known in the world, a study suggests. Ian Joughin and Ben Smith of the University of Washington's Polar Science Center in Seattle analysed pictures from the German TerraSAR-X satellites to measure the speed of the glacier. |
4 Feb 2014
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Greenland's fastest glacier sets new speed record UW News and Information, Hannah Hickey The latest observations of Jakobshavn Glacier show that Greenland's largest glacier is moving ice from land into the ocean at a speed that appears to be the fastest ever recorded. |
3 Feb 2014
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UW researchers mapping changes in glacier ice KING5 News, Seattle, Adam Mertz University of Washington researchers are working with NASA to create digital maps of glaciers in Greenland. |
25 Nov 2013
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Post-shutdown, UW Arctic research flights resume UW News and Information, Hannah Hickey After a couple of stressful weeks during the federal government shutdown, University of Washington researchers are back at work monitoring conditions near the North Pole. November has been busy for UW scientists studying winter storms, glacier melt and floating sea ice. |
18 Nov 2013
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International study provides more solid measure of shrinking in polar ice sheets UW News and Information, Hannah Hickey Dozens of climate scientists have reconciled their measurements of ice sheet changes in Antarctica and Greenland during the past two decades. The results, published Nov. 29 in the journal Science, roughly halve the uncertainty and discard some conflicting observations. |
29 Nov 2012
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80-year-old aerial images show retreat of Greenland glaciers Los Angeles Times, Thomas H. Maugh II Long-abandoned 80-year-old aerial photographs found in a Danish basement document the unexpectedly rapid response of Greenland glaciers to changes in average temperatures. |
30 May 2012
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Data sheds light on speed of Greenland's glaciers BBC News, Mark Kinver Greenland's glaciers are not speeding up as much as previously thought, researchers have estimated. A team of US researchers based their findings on data stretching back to 2000-2001, collected from more than 200 outlet glaciers. "So far, on average, we are seeing about a 30% speed-up in 10 years," observed lead author Twila Moon. |
4 May 2012
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Greenland ice melt could raise seas less than feared, study says CNN, Matt Smith Greenland's glaciers are sliding into oceans at a faster pace than previously known, but they may contribute less to an expected rise in global sea level than feared, scientists reported Thursday. |
4 May 2012
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Greenland glaciers shrinking quickly, but not worst case The Washington Post (Associated Press) Greenland's glaciers are hemorrhaging ice at an increasingly faster rate but not at the breakneck pace that scientists once feared, a new study says. |
3 May 2012
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Greenland's ice melting more slowly than expected NPR 'All Things Considered', RIchard Harris The flow of Greenland glaciers to the sea has increased by 30 percent over the past decade. But Polar Science Center researchers report in Science that they aren't seeing a runaway meltdown of Greenland that some have feared. |
3 May 2012
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Increasing speed of Greenland glaciers gives new insight for rising sea level UW Today, Vince Stricherz Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland's contribution to rising sea level in the 21st century might be significantly less than the upper limits some scientists thought possible, a new study shows. |
3 May 2012
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Sea-level rise 'may not be as high as worst-case scenarios have predicted' The Guardian, Damian Carrington New research published in Science suggests that Greenland's glaciers are slipping into the sea more slowly than was previously thought. But scientists warn that ice loss still sped up by 30% and is driving rises in sea levels that endanger low-lying coasts around the world. |
3 May 2012
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Go to the poles in your imagination at annual Polar Science Weekend University Week Hands-on exhibits, UW polar experts and a bit of imagination will transport you and your family to the extreme environments of the Arctic and Antarctica later this month during Polar Science Weekend at Pacific Science Center. |
11 Feb 2010
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