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Benjamin Smith

Principal Physicist

Affiliate Associate Professor, Earth and Space Sciences

Email

bsmith@apl.washington.edu

Phone

206-616-9176

Department Affiliation

Polar Science Center

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

Publications

2000-present and while at APL-UW

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

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," The Cryosphere, 14, 211-227, doi:10.5194/tc-14-211-2020, 2020.

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24 Jan 2020

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 2016–2017 and 2017–2018, 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

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.

More Publications

In The News

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

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

UW glaciologist gets first look at NASA's new measurements of ice sheet elevation

UW News, Hannah Hickey

Less than three months into its mission, NASA's Ice, Cloud and land Elevation Satellite-2, or ICESat-2, is already exceeding scientists’ expectations. Benjamin Smith, a member of the ICESat-2 science team, shared the first look at the satellite's performance at the American Geophysical Union's annual meeting Dec. 11 in Washington, D.C.

14 Dec 2018

More News Items

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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