File spoon-archives/marxism-international.archive/marxism-international_1998/marxism-international.9801, message 442


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]


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