Climate Science

Twinned Thinning

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Science  14 Jan 2005:
Vol. 307, Issue 5707, pp. 182
DOI: 10.1126/science.307.5707.182c

The response of the West Antarctic Ice Sheet (WAIS) to global warming is of great concern because, if it were to melt completely, it is large enough to raise sea level by approximately 7 m. Such massive melting is unlikely to occur soon; nevertheless, there is still the potential for a marked increase in the rate of sea level rise due to accelerated ice loss. The great majority of the ice mass lost presently from the WAIS flows to the sea as ice streams, of which that of Pine Island Glacier is the most important. The Pine Island Glacier, and the adjoining ice shelves of Pine Island Bay, have thinned significantly over the past 3 decades. In two related papers, the extents, causes, and effects of these changes are examined. Shepherd et al. use satellite data altimetry to document how ice shelves in that region have thinned, and they attribute the thinning to melting cased by the action of ocean currents that are 0.5°C warmer than freezing on average. The pattern of shelf thinning mirrors that of their grounded tributaries, suggesting that Antarctic ice is more sensitive to changing climates than previously thought. Payne et al. test the hypothesis that these changes are triggered by the adjoining ocean, using a numerical ice-flow model to simulate its effects on the dynamics of the Pine Island Glacier. They confirm the idea that recent increases in local ocean temperature are the cause of the observed thinning and find that the thinning of coastal ice shelves is transmitted rapidly to the grounded ice streams above, revealing a tight coupling between the ice sheet interior and surrounding ocean. — HJS

Geophys. Res. Lett. 31, 10.1029/2004GL021106; 10.1029/2004GL021284 (2004).

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