Dramatic Change in West Antarctic Ice Could Produce 16ft Rise in Sea Levels 

MICHAEL McCARTHY / The Independent (UK) 2feb2005

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British scientists have discovered a new threat to the world which may be a result of global warming. Researchers from the Cambridge-based British Antarctic Survey (BAS) have discovered that a massive Antarctic ice sheet previously assumed to be stable may be starting to disintegrate, a conference on climate change heard yesterday. Its collapse would raise sea levels around the earth by more than 16 feet.

BAS staff are carrying out urgent measurements of the remote points in the West Antarctic Ice Sheet (WAIS) where they have found ice to be flowing into the sea at the enormous rate of 250 cubic kilometres a year, a discharge alone that is raising global sea levels by a fifth of a millimetre a year.

Professor Chris Rapley, the BAS director, told the conference at the UK Meteorological Office in Exeter, which was attended by scientists from all over the world, that their discovery had reactivated worries about the ice sheet's collapse.

Only four years ago, in the last report of the UN's Intergovernmental Panel on Climate Change (IPCC), worries that the ice sheet was disintegrating were firmly dismissed.

Professor Rapley said: "The last IPCC report characterised Antarctica as a slumbering giant in terms of climate change. I would say it is now an awakened giant. There is real concern."

He added: "The previous view was that WAIS would not collapse before the year 2100. We now have to revise that judgement. We cannot be so sanguine." Collapse of the WAIS would be a disaster, putting enormous chunks of low-lying, desperately poor countries such as Bangladesh under water - not to mention much of southern England.

The conference has been called by Tony Blair as part of Britain's efforts to increase the pace of international action on climate change, in a year when the UK is heading the G8 group of industrialised nations and the European Union.

Mr Blair has asked it to explore the question of how much climate change the world can take before the consequences are catastrophic for human society and ecosystems.

Yesterday, it heard several alarming new warnings of possible climate-related catastrophic events, including the failure of the Gulf Stream, which keeps the British Isles warm, and the melting of the ice sheet covering Greenland.

But it was the revelations of Professor Rapley, head of one of the world's most respected scientific bodies, which were the most dramatic, as they reopened a concern many scientists assumed had been laid to rest.

Antarctica as a whole is a land covered by very thick ice, but the ice sheet covering the eastern half of the continent is very stable as it sits on rocks that are well above sea level.

Worries about the ice covering the western half first surfaced more than 25 years ago when it was realised that the base rocks are actually well below the level of the sea.

In some circumstances, it was feared, such as a melting of the edge of the ice sheet from rising temperatures, sea water could get under it and eventually lead to its collapse.

Yet the 2001 IPCC report, the principal consensus view of the international community of climate scientists, thought that very unlikely, and said such a collapse was improbable before the end of the current century, or even for 1,000 years.

What puts a very big question mark over this, Professor Rapley said, was the recent discovery of the extremely rapid discharge of ice into the Amundsen sea from the WAIS at three remote ice streams, Pine Island, Thwaites, and another unnamed site.

"There is a very dramatic discharge from this region which, five years ago when the IPCC report was written, we just didn't know about," he said. "What we have found completely opens up the whole debate." It had only been recently discovered, he said, because the area was so remote. But BAS scientists, with US help, had established a base in the area to investigate. Professor Rapley said there was some evidence that the discharge was a relatively recent phenomenon and it might be caused by rising ocean temperatures.

Margaret Beckett, the Environment Secretary, who opened the conference, added another ominous prediction when she said that major global warming impacts on the world in the next 20 to 30 years could not be avoided. Whatever we do, potentially disastrous world temperature rises will take place because they are already "built into the system," she said.

Her forecast that we are powerless to prevent major damage from climate change is accepted by scientists but it is rare for such a frank admission from a politician. It reflects the concern at a high level.

It was amplified by senior climate researchers, who said the amount of future warming to which the world is firmly committed, because of greenhouse gases that have already been put into the atmosphere, will be enough to threaten the survival of many ecosystems and wildlife species such as polar bears and penguins.

"I believe that most of the warming we are expecting over the next few decades is now virtually inevitable, and even in this time frame we may expect a significant impact," Mrs Beckett said.

source: http://news.independent.co.uk/world/environment/story.jsp?story=606845 2feb2005

New concerns on the stability of the west Antarctic ice sheet

GINO CASASSA / The Environment Times 3sep03

A periodic publication by UNEP/GRID-Arendal

Increased global temperatures are taking their toll on the Antarctic ice shelves. Here are eight points of concerns regarding the west Antarctic Ice Sheet.

1. Antarctica accounts for 91 percent of the total mass of ice on the Earth, contained in a vast ice sheet up to 4.6 kilometres thick. If the Antarctic ice were to melt entirely, it would raise global sea level by 55 metres, a truly catastrophic scenario. Thankfully, this full-scale melt-down of the Antarctic ice is unlikely to occur over the East Antarctic Ice Sheet (EAIS), which accounts for 50 metres of global sea level and is considered stable because its bed lies well over sea level.

2. Some believe that the interior of the Antarctic continent is too cold to be affected by potential melting produced by surface warming of a few degrees expected to occur from over the next century. On the contrary, parts of inland Antarctica, such as the South Pole, are growing because of enhanced snow precipitation in a warmer atmosphere, which can retain higher humidity.

3. However global warming is already having a discernable effect on the fringes of the continent, as evidenced by the dramatic break-up of the Larsen A ice shelf and other smaller floating ice shelves on the Antarctic Peninsula, where summer temperatures are frequently above zero.

4. There is evidence that these peripheral changes are having a strong effect on glaciers of the inland Antarctic ice due to ice dynamics. The glaciers that used to feed Larsen A ice shelf have accelerated threefold after the collapse of the ice shelf, suggesting that the ice shelves have a critical role in restraining the flow of the inland ice. A similar behaviour might be occurring on the Amundsen Sea sector of the west Antarctic Ice Sheet (WAIS), where Pine Island and Thwaites glaciers have lost significant portions of their fringing ice shelves, and show signs of recent acceleration. This ice sheet is a fraction of the size of the dominating east Antarctic ice sheet, but its mass is still great enough to raise global sea-level by five meters.

5. The east Antarctic ice sheet is known as a continental ice sheet since it is supported by land above sea level. Unlike its eastern sister, the western ice sheet is a marine ice sheet which is grounded on bedrock well below sea level. In addition, the underlying bedrock in many areas has a downward slope away from the coastline. This circumstance could result in a run-away effect leading to total collapse should the edges of the ice sheet start to retreat due to an initial trigger such as atmospheric and/or oceanic warming. The western ice sheet would therefore largely disappear if the ice would melt

6. The west ice sheet has been the subject of considerable research over the last 25 years.
Theoretical: Modelling has been developed to understand the nature of potential instability of West ice sheet, and the roles that ice shelves play in stabilizing the ice sheets. Differing views exist on the importance of the buttressing effect of ice shelves. Early models predicted an important stabilizing role of ice shelves, but later more sophisticated models suggested an insignificant role of ice shelves. There is now compelling evidence that shows the relevant stabilizing role of ice shelves, and in a few cases this new information is already being incorporated into the models.
Experimental: Of the major glaciers – ice streams – in the Antarctic Peninsula and in western Antarctica studies are being conducted to detect whether they are speeding up or slowing down. Results in the west ice sheet are contradictory. Ice streams in the Ross Sea sector are slowing down while the glaciers in the Weddell Sea are in near steady state.
Overall conclusion reached by the scientific community by the mid-1990s was that the west ice sheet appeared to be relatively stable, and any retreat of the ice sheet would occur relatively slowly over hundreds or thousands of years, despite loss of ice shelves.

7. Over the last few years, new evidence that changes may indeed be happening faster than previously thought has emerged:
Recent satellite image analyses show that the ice streams in the Amundsen region are clearly retreating, thinning and accelerating, particularly Thwaites and Pine Island glaciers;
New theoretical models suggest that ice shelves are important for the stability of ice sheets;
Small glaciers on the Antarctic Peninsula have speeded up greatly following the collapse of the Larsen A ice shelf.

8. A new urgency has been injected into the study of the stability of West ice sheet. A team from the Center for Scientific Studies of Santiago (CECS), NASA and the German Geological Survey (BGR) plans a new series of investigations, concentrating on the Amundsen Sea region in 2004/2005.

GINO CASASSA is Head of the Glaciology and Climate Change Laboratory at Centro de Estudios Científicos in Valdivia, Chile. He is the glaciology representative of Chile’s Scientific Committee for Antarctic Research (SCAR), and member of the International Council of Scientific Unions (ICSU) Planning Group for the International Polar Year 2007. He is currently also the head of the Andean Working Group on Glacier Mass Balance sponsored by the International Commission on Snow and Ice/International Association of Hydrological Sciences.