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Harry Stern Principal Mathematician harry@apl.washington.edu Phone 206-543-7253 |
Biosketch
Harry Stern studies Arctic sea ice and climate using satellite data. Current interests include the changing sea ice habitat of polar bears and narwhals, and the history of Arctic exploration. He participated in the Around the Americas expedition, sailing through the eastern half of the Northwest Passage in 2009. He served as an Associate Editor for the Journal of Geophysical Research—Oceans (2007–2010). He helped to launch the annual Polar Science Weekend at Seattle's Pacific Science Center, and now runs the event. He has a B.S. in mathematics and M.S. in applied mathematics. He has been with the Polar Science Center since 1987 and with the University since 1980.
Education
B.S. Mathematics, Stanford University, 1980
M.S. Applied Mathematics, University of Washington, 1982
Projects
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RADARSAT Geophysical Processor System at the Polar Science Center |
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Arctic Surface Air Temperatures for the Past 100 Years Accurate fields of Arctic surface air temperature (SAT) are needed for climate studies, but a robust gridded data set of SAT of sufficient length is not available over the entire Arctic. We plan to produce authoritative SAT data sets covering the Arctic Ocean from 1901 to present, which will be used to better understand Arctic climate change. |
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Videos
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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. |
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A Look Back to Arctic Climate in the 18th Century Captain James Cook’s logs and maps give insight to late-18th century sea ice conditions north of Bering Strait. |
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15 Nov 2016
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Polar Science Center mathematician Harry Stern used these records to plot the sea ice edge that Cook encountered in 1778. These earliest records of summer ice extent in the Chukchi Sea underscore the dramatic recent changes in arctic climate. |
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Focus on Arctic Sea Ice: Current and Future States of a Diminished Sea Ice Cover APL-UW polar scientists are featured in the March edition of the UW TV news magazine UW|360, where they discuss their research on the current and future states of a diminished sea ice cover in the Arctic. |
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7 Mar 2012
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The dramatic melting of Arctic sea ice over the past several summers has generated great interest and concern in the scientific community and among the public. Here, APL-UW polar scientists present their research on the current state of Arctic sea ice. A long-term, downward trend in sea ice volume is clear. |
Publications |
2000-present and while at APL-UW |
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Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation Laidre, K.L., S.N. Atkinson, E.V. Regehr, H.L. Stern, E.W. Born, Ø. Wiig, N.J. Lunn, M Dyck, P. Heagerty, B.R. Cohen, "Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation," Global Change Biol., 26, 6251-6265, doi:10.1111/gcb.15286, 2020. |
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1 Nov 2020 ![]() |
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Kane Basin (KB) is one of the world's most northerly polar bear (Ursus maritimus) subpopulations, where bears have historically inhabited a mix of thick multiyear and annual sea ice year‐round. Currently, KB is transitioning to a seasonally ice‐free region because of climate change. This ecological shift has been hypothesized to benefit polar bears in the near‐term due to thinner ice with increased biological production, although this has not been demonstrated empirically. We assess sea‐ice changes in KB together with changes in polar bear movements, seasonal ranges, body condition, and reproductive metrics obtained from capturerecapture (physical and genetic) and satellite telemetry studies during two study periods (19931997 and 20122016). The annual cycle of sea‐ice habitat in KB shifted from a year‐round ice platform (~50% coverage in summer) in the 1990s to nearly complete melt‐out in summer (<5% coverage) in the 2010s. The mean duration between sea‐ice retreat and advance increased from 109 to 160 days (p = .004). Between the 1990s and 2010s, adult female (AF) seasonal ranges more than doubled in spring and summer and were significantly larger in all months. Body condition scores improved for all ages and both sexes. Mean litter sizes of cubs‐of‐the‐year (C0s) and yearlings (C1s), and the number of C1s per AF, did not change between decades. The date of spring sea‐ice retreat in the previous year was positively correlated with C1 litter size, suggesting smaller litters following years with earlier sea‐ice breakup. Our study provides evidence for range expansion, improved body condition, and stable reproductive performance in the KB polar bear subpopulation. These changes, together with a likely increasing subpopulation abundance, may reflect the shift from thick, multiyear ice to thinner, seasonal ice with higher biological productivity. The duration of these benefits is unknown because, under unmitigated climate change, continued sea‐ice loss is expected to eventually have negative demographic and ecological effects on all polar bears. |
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Estimating statistical errors in retrievals of ice velocity and deformation parameters from satellite images and buoy arrays Dierking, W., H.L. Stern, and J.K. Hutchings, "Estimating statistical errors in retrievals of ice velocity and deformation parameters from satellite images and buoy arrays," Cryosphere, 14, 2999-3016, doi:10.5194/tc-14-2999-2020, 2020. |
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15 Sep 2020 ![]() |
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The objective of this note is to provide the background and basic tools to estimate the statistical error of deformation parameters that are calculated from displacement fields retrieved from synthetic aperture radar (SAR) imagery or from location changes of position sensors in an array. We focus here specifically on sea ice drift and deformation. In the most general case, the uncertainties of divergence/convergence, shear, vorticity, and total deformation are dependent on errors in coordinate measurements, the size of the area and the time interval over which these parameters are determined, as well as the velocity gradients within the boundary of the area. If displacements are calculated from sequences of SAR images, a tracking error also has to be considered. Timing errors in position readings are usually very small and can be neglected. We give examples for magnitudes of position and timing errors typical for buoys and SAR sensors, in the latter case supplemented by magnitudes of the tracking error, and apply the derived equations on geometric shapes frequently used for deriving deformation from SAR images and buoy arrays. Our case studies show that the size of the area and the time interval for calculating deformation parameters have to be chosen within certain limits to make sure that the uncertainties are smaller than the magnitude of deformation parameters. |
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Interrelated ecological impacts of climate change on an apex predator Laidre, K.L., S. Atkinson, E.V. Regehr, H.L. Stern, E.W. Born, Ø. Wiig, N.J. Lunn, and M. Dyck, "Interrelated ecological impacts of climate change on an apex predator," Ecol. Appl., 30, e02071, doi:10.1002/eap.2071, 2020. |
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1 Jun 2020 ![]() |
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Climate change has broad ecological implications for species that rely on sensitive habitats. For some top predators, loss of habitat is expected to lead to cascading behavioral, nutritional, and reproductive changes that ultimately accelerate population declines. In the case of the polar bear (Ursus maritimus), declining Arctic sea ice reduces access to prey and lengthens seasonal fasting periods. We used a novel combination of physical capture, biopsy darting, and visual aerial observation data to project reproductive performance for polar bears by linking sea ice loss to changes in habitat use, body condition (i.e., fatness), and cub production. Satellite telemetry data from 43 (19911997) and 38 (20092015) adult female polar bears in the Baffin Bay subpopulation showed that bears now spend an additional 30 d on land (90 d in total) in the 2000s compared to the 1990s, a change closely correlated with changes in spring sea ice breakup and fall sea ice formation. Body condition declined for all sex, age, and reproductive classes and was positively correlated with sea ice availability in the current and previous year. Furthermore, cub litter size was positively correlated with maternal condition and spring breakup date (i.e., later breakup leading to larger litters), and negatively correlated with the duration of the ice‐free period (i.e., longer ice‐free periods leading to smaller litters). Based on these relationships, we projected reproductive performance three polar bear generations into the future (approximately 35 yr). Results indicate that two‐cub litters, previously the norm, could largely disappear from Baffin Bay as sea ice loss continues. Our findings demonstrate how concurrent analysis of multiple data types collected over long periods from polar bears can provide a mechanistic understanding of the ecological implications of climate change. This information is needed for long‐term conservation planning, which includes quantitative harvest risk assessments that incorporate estimated or assumed trends in future environmental carrying capacity. |
In The News
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Some polar bears in far north are getting short-term benefit from thinning ice UW News, Hannah Hickey A small subpopulation of polar bears lives on what used to be thick, multiyear sea ice far above the Arctic Circle. They are healthier as conditions are warming because thinning and shrinking multiyear sea ice is allowing more sunlight to reach the ocean surface, which makes the ecosystem more productive. photo: Carsten Egevang |
23 Sep 2020
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Polar bears are getting thinner and having fewer cubs CNN, Scottie Andrew The impact of the climate crisis is becoming more and more obvious to humans and their animal neighbors. But among all species, polar bears might be some of the hardest hit. |
14 Feb 2020
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Polar bears in Baffin Bay skinnier, having fewer cubs due to less sea ice UW News, Hannah Hickey Polar bears are spending more time on land than they did in the 1990s due to reduced sea ice, new University of Washington-led research shows. Bears in Baffin Bay are getting thinner and adult females are having fewer cubs than when sea ice was more available. |
12 Feb 2020
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