The Western Antarctic carries a blanket of ice in places more than two kilometres thick. Despite its volume and thickness, recent research suggests its future is alarmingly precarious.
It is riven by "ice streams" which flow along like solid rivers, rushing to the sea at a pacey 100 metres a year. The continent's ice cover used to sit on the sea floor, a full 1,300 kilometres beyond the coastline, but the ice just off the edge of the western continent now floats on the sea, evidence of a remarkable retreat.
The current issue of the journal, Science, carries three research reports on the West Antarctic ice sheet and the consistent themes are change and collapse. The new work predicts that the sheet, in constant decline for the past 20,000 years, could be gone in the next 7,000. And this may be inevitable, no matter what we might do about global warming.
"Collapse appears to be part of an ongoing natural cycle, probably caused by rising sea levels initiated by the melting of the northern hemisphere ice sheets at the end of the last ice age," said Dr Howard Conway, of the University of Washington, a lead author on one of the reports.
A distinction must be made between the sheets - ice which is grounded either on the Antarctic land mass or just offshore on the seabed - and the continent's ice shelves, projections of thick floating ice that reach out for hundreds of miles depending on the season.
The shelves have no bearing on sea level change because their influence is already apparent, in the same way as ice in a glass of water pushes up the water to a given level. The sheet ice is different, however. If it collapsed, it would produce a tremendous fresh water pulse that could raise sea levels by five to six metres, more than enough to swamp island and coastal communities.
The scientists writing in Science were using different methods to study what has happened in the past as a way to understand what might happen in the future.
Dr Ian Joughin from the Jet Propulsion Laboratory in California and colleagues from NASA, the University of Texas, the Canadian Centre for Remote Sensing and from General Sciences Corporation were using satellite-based radar interferometry to study ice motion at the surface. In particular, they examined the many ice streams which criss-cross the continent, many of which empty into the Ross Sea. "Although the possibility of a catastrophic collapse of the ice sheet is under debate, field and satellite observations have established that substantial changes are occurring in West Antarctica, particularly in the ice streams," they write.
The streams deliver ice from inland to the coasts along solid rivers which tend to be 10 to 20 kilometres across and which can move an order of magnitude faster than surrounding ice. They travel at between 25 metres and 100 metres on average a year and their positions correlate well with valleys and ground level formations deep under the ice.
While some streams show signs of blocking, causing ice levels to thicken, most help to drain away ice, causing a significant thinning of ice cover on the continent. The streams are carrying away ice over vast areas that can drop by a metre a year, they report.
Dr Conway and colleagues from the University of Washington, the University of Main and Woods Hole Oceanographic Institution used different techniques to study past "grounding-line retreat" of the ice sheet in order to provide suggestions about its future.
The retreat, they said, has been in evidence since the early Holocene. They found historical indications of both fast and slow ice stream movement. They said that as recently as 7,500 years ago large coastal land areas including McMurdo Sound became free of ice, as evidenced by mollusc colonisation and the formation of raised beaches along the southern Scott Coast. These raised by about 25-30 metres as the ice burden was removed and the land rebounded back as a result.