Collapse and Rise
The West Antarctic Ice Sheet (WAIS) is thought to be inherently unstable and susceptible to rapid collapse if it reaches a certain warming threshold. Although such an event is considered unlikely, to predict the consequences of collapse it is important to know how much sea level would rise in such a case. The WAIS is thought to contain enough ice to raise sea level by 5 to 7 meters were it to collapse. Bamber et al. (p. 901, see the cover; see the Perspective by Ivins) have reassessed that number, on the basis of better data on the geometry of the WAIS, and conclude that its sudden collapse would raise sea level by about 3.2 meters, on average, with large and important regional variations. Although this is only about half as much as previously thought, its impact on coastal areas would still be devastating.
Science 15 May 2009:
Vol. 324. no. 5929, pp. 901 - 903
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Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet
Jonathan L. Bamber,1,* Riccardo E. M. Riva,2 Bert L. A. Vermeersen,2 Anne M. LeBrocq3
Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.
1 Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK.
2 Delft Institute of Earth Observation and Space Systems, Delft University of Technology, NL-2629 HS Delft, Netherlands.
3 Department of Geography, University of Durham, Durham DH1 3LE, U
Ice Sheet Stability and Sea Level
Erik R. Ivins
Volume changes in the Antarctic Ice Sheet are poorly understood, despite the importance of the ice sheet to sea-level and climate variability. Over both millennial and shorter time scales, net water influx to the ice sheet (mainly snow accumulation) nearly balances water loss through ice calving and basal ice shelf melting at the ice sheet margins (1). However, there may be times when parts of the West Antarctic Ice Sheet (WAIS) are lost to the oceans, thus raising sea levels. On page 901 of this issue, Bamber et al. (2) calculate the total ice volume lost to the oceans from an unstable retreat of WAIS, which may occur if the part of the ice sheet that overlies submarine basins is ungrounded and moves to a new position down the negative slope (see the figure).
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.