Climatic Control of Ice Shelves

David G. Vaughan, British Antarctic Survey
Natural Environment Research Council
Madingley Road, Cambridge, CB3 0ET, United Kingdom.

Recent rapid regional (RRR) warming on the Antarctic Peninsula has caused: retreat of glaciers; reduction of snow cover; and where summer melting does not occur, increased precipitation has caused marginal thickening of the ice sheet. Furthermore, a consequence of warming on the Antarctic Peninsula originally predicted by Mercer in 1978, the retreat of ice shelves, is now well underway. I will review recent progress in understanding how climate controls the evolution of ice shelves around the Antarctic Peninsula.

Seven ice shelves around the Antarctic Peninsula retreated during the latter part of the 20th Century - all were close to an apparent limit of viability marked by the January 0^oC isotherm. RRR warming appears to have driven the limit of viability further south resulting in the loss of marginal ice shelves since the 1950s; ice shelves not close to the limit of viability have generally maintained their size. In each case, retreat began with a progressive and continued retreat of the ice front over many years. In a few cases progressive retreat eventually gave way to a catastrophic collapse that appears to be related to a structural instability. Most recently, Wilkins Ice Shelf, and Larsen Ice Shelf - B have begun to retreat and are now close to a configuration that is probably unstable and may well lead to collapse. While the geographic juxtaposition of retreating ice shelves and climatic warming is strong evidence of a causal connection, we are as yet uncertain of which physical process makes ice shelves so vulnerable to summer melting. I will review the mechanisms that have been proposed and discuss how we might discriminate between their effects.

Although the loss of ice shelves around the Antarctic Peninsula has little direct impact on wildlife, sea level, or climate, the pattern of recent retreat shows that ice shelves are sensitive indicators of climate, may well serve as important proxy of climatic conditions, and are a reminder of the potential sensitivity of non-linear environmental responses to climate change.