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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

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, EOR, doi:10.1126/science.aaz5845, 2020.

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30 Apr 2020

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 a–1) and Antarctica (118 Gt a–1) 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

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.

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In The News

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

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

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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