Even at today’s slightly elevated temperatures, with a rise of around half a degree centigrade, mountain glaciers are receding significantly, as also seem to be, locally, the margins of the ice in Greenland and Antarctica. The Greenland icecap is vulnerable, and its loss would mean a sea level rise of some 7 metres. As it creates its own regional climate, its loss may be effectively permanent. In Antarctica, the recent break-up of ice shelves has precipitated increased streaming of ice from much farther inland, which potentially represents the initiation of a phase of much more serious ice-sheet collapse.
This recently observed behaviour has shown clearly that ice-sheets are not relatively inert masses responding sluggishly to temperature change. Rather they are now perceived in much more dynamic terms, showing strong – and potentially dangerous – responses to small changes in external conditions. This would accord with geological evidence indicating past ice-sheet collapses, releasing ‘iceberg armadas’ and causing sea level rises of several metres in a decade.
Sources The state of the world’s ice masses is now being monitored with keen interest. The news from the ice front is not good. Some recent articles are:
- Arendt, A.A. et al. 2002. Rapid wastage of Alaska glaciers and their contribution to rising sea level. Science, vol. 297, pp. 382-386. (also discussed on pp. 350-351 of the same issue).
- De Angelis, H. & Skvarca, P. 2003. Glacier surge after ice sheet collapse. Science, vol. 299, pp. 1560-1562.
- Gregory, J.M., Huybrechts, P & Raper, S.C.B. 2004. Threatened loss of the Greenland ice-sheet. Nature, vol 428, p. 616.
- Schiermeier, J. 2004. A rising tide. Nature, vol. 428, p. 114-115.
- Shepherd, A. et al. 2003. Larsen Ice Shelf has progressively thinned. Science, vol. 302, pp. 856-859 (also discussed on p. 759 of the same issue).
- There is also a set of articles on this topic under the heading ‘Trouble in Polar Paradise’ in Science (2002, vol. 297, pp. 1489-1514).
This brief recent article on Heinrich events (ice-sheet collapses to produce ‘iceberg armadas’ ) provides entry to literature on this aspect of ice-sheet behaviour; interestingly, it suggests that a strongly tidal regime is sufficient to catalyse this phenomenon.
- Arbic, B.K. et al. 2004. Ocean tides and Heinrich events. Nature, vol. 432, p. 460.