Date: Thu, 29 Jan 1998 08:33:33 +0000 From: Mark Jones <Jones_M-AT-netcomuk.co.uk> Subject: M-I: Ice-sheet disintegrates The British Antarctic Survey has just announced the collapse of the Larsen 'B' ice-shelf. While not unexpected, this disintegration of a piece of the Antarctic ice-sheet the size of south-east England is a catastrophe with no precedent in recorded history. It will affect the global ocean circulation and may impede the Gulf Stream; but the consequences could be worse even than that. Quote below is from Issue 36 of 'Globe', the UK government Global Environmental Research council journal, issue 36: A particular feature of the Antarctic ice sheet (compared to Greenland) is the presence of large floating ice shelves around its edge. There is currently great interest in the recent disintegrations of ice shelves in the Antarctic Peninsula and discharges of enormous icebergs from the Filchner-Ronne and Ross ice shelves. Dr David Vaughan and Dr Chris Doake (BAS) catalogued the variation in ice shelves around the Antarctic Peninsula, based on data from historical records, aerial photographs and satellite images. They found that around 8000 km2 of ice shelf in the Antarctic Peninsula had been lost since the 1950s - evidence of the considerable change in mass balance possible in a short period. They demonstrated for the first time that there exists a climatic limit of viability for ice shelves, that has been pushed southwards by the warming experienced over the past few decades (2.5oC over the past 50 years). The observation implies that marginal ice shelves in the Antarctic Peninsula are vulnerable to even brief periods of climate warming - and that ice shelves are very sensitive indicators of warming. The warming to date has taken many ice shelves above this critical temperature level, and many of them (eg Wordie Ice Shelf, the ice shelf in Prince Gustav Channel and Larsen A Ice Shelf) have been lost. The last remains of the Larsen A shelf broke up quickly in 1995, when an area the size of Surrey disappeared in a few weeks. The warming could well be a natural oscillation of climate and as yet its continuance or otherwise cannot be predicted. If it continues though, then the Larsen B Ice Shelf would be next in line for disintegration. Over the past two to three years large cracks have appeared in it although these do not necessarily presage an imminent break-up. Even if the warming did not spread further, other ice-shelves may still disappear due to a lag between temperature rise and its effects. A further warming of 10oC would be needed before the more southerly Filchner-Ronne and Ross ice shelves, are threatened. Their significance is that they may stabilise the West Antarctic ice sheet which itself contains enough water to raise sea level by about 5m. A catastrophic rise in sea level would result from surging of the West Antarctic Ice Sheet. IPCC 1995 comments that there are great uncertainties over the probability of this happening, but the likelihood of a major sea level rise by the year 2100 due to the collapse of the West Antarctic Ice Shelf is considered low. [But what the IPCC did not expect for another century may now be happening now] --- from list marxism-international-AT-lists.village.virginia.edu ---
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