Diminishing Sea-Ice Extent and Thickness in the Arctic Ocean
Rapid changes are occurring to Arctic sea ice thickness and extent. We survey the reasons for them, and the methods being used to monitor the changing thickness. Through the late twentieth century Arctic sea ice extent shrank at a relatively modest rate o
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Diminishing Sea-Ice Extent and Thickness in the Arctic Ocean Peter Wadhams
Abstract Rapid changes are occurring to Arctic sea ice thickness and extent. We survey the reasons for them, and the methods being used to monitor the changing thickness. Through the late twentieth century Arctic sea ice extent shrank at a relatively modest rate of 3–4% per decade (annually averaged) but after 1996 this speeded up to 10% per decade and in summer 2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million sq km. Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially rapid loss of mass from pressure ridges. The summer 2007 event may have arisen from an interaction between the long-term retreat and more rapid thinning rates. We review thickness monitoring techniques which show the greatest promise on different spatial and temporal scales, and for different purposes, and we show results from some recent work from submarines.
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Sea-Ice Thinning and Retreat
The present thinning and retreat of Arctic sea ice is one of the most serious geophysical consequences of global warming and is causing a major change to the face of our planet. A challenging characteristic of the behaviour is that both the rate of retreat (especially in summer) and the rate of thinning in all seasons have greatly exceeded the predictions of most models. A further challenge comes from the fact that Antarctic sea ice extent is currently expanding, at about half the rate that Arctic extent is diminishing [8].
P. Wadhams (*) Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, UK e-mail: [email protected] P.A. Berkman and A.N. Vylegzhanin (eds.), Environmental Security in the Arctic Ocean, NATO Science for Peace and Security Series C: Environmental Security, DOI 10.1007/978-94-007-4713-5_4, © Springer Science+Business Media Dordrecht 2013
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P. Wadhams
Although sea ice in the Arctic Ocean has been in slow retreat since the 1950s at a rate of 2.8–4.3% per decade [1] as measured since 1979 from passive microwave satellites [23], the annual-averaged rate speeded up to 10.7% per decade from 1996 onwards [8], while the summer extent has shrunk even faster. In September 2007 the area reached 4.1 million km2, a record low [22, 33] and more than one million km2 less than in the previous record year of 2005 [32]. Although the area stabilised in 2008–2011 the continuing decline in multi-year ice fraction suggests that the total Arctic ice volume in late summer has continued to decrease. New model predictions, tuned to match these recent changes, predict disappearance of the summer sea ice within 20–30 years [52]. At the same time, submarine sonar measurements have shown that the ice has been thinning much more rapidly, by some 43% in the 25 years between the early 1970s and late 1990s [27, 28, 42, 43, 53]. The thinning rate implies that at some critical date the annual cycle of thickness
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