Glaciers melting faster than expected


THE EDGES of the world's two greatest stores of land ice are melting away and it seems there is very little we can do about it.

Glaciers at the coastal margins of Greenland and Antarctica are losing ice much faster than scientists realised, dumping cubic kilometres of water each year into the world's oceans.

This process will in time see island nations such as the Maldives disappearing under water as sea levels rise. Just as frightening, however, is the scientists' observation that our climate doesn't have to get any warmer for this rapid ice loss to continue.

Dr Hamish Prichard of the British Antarctic Survey and colleagues from the University of Bristol provided a completely new view of "dynamic thinning" at the edges of the Greenland and Antarctic glaciers. They used data provided by Nasa's ICESat (Ice, Cloud and land Elevation Satellite) and publish their alarming findings this morning in the journal Nature.

One of their main findings is that the process is widespread, occurring at locations right around both landmasses. This includes specific locations in eastern Antarctica, long considered untouched by climate-driven melting.

Rapid thinning is taking place at all latitudes, both closer to and distant from the two poles. And in some cases the losses are dramatic, Dr Prichard told The Irish Times.

Thinning of between two and four metres per year is commonplace, while the Pine Island, Smith and Thwaites glaciers in west Antarctica are thinning by up to nine metres per year, he said.

The Crane glacier which flows into the sea behind the now broken-up Larsen B ice shelf is thinning by a spectacular 70 metres a year, he said. The floating Larsen B ice shelf served to hold back the Crane glacier, slowing its flow, but with this now substantially gone there is nothing to slow the loss of ice. "It is like a cork coming out of a bottle," Dr Prichard said.

There are several processes causing this and unfortunately they are not wholly dependent on a continued rise in global temperatures, the authors suggest.

In most cases the losses have more to do with a faster flow of ice into the sea rather than actual melting because of climate change.Unfortunately there is a feedback effect, with ice loss speeding more ice loss. "It is widespread and once it starts it spreads," Dr Prichard said.

The researchers also found that the thinning can extend back along the glacier for hundreds of kilometres inland. "This kind of ice loss is so poorly understood that it remains the most unpredictable part of future sea level rise," Dr Prichard said.

The Intergovernmental Panel on Climate Change which is guiding international studies on the issue will need to take this faster ice loss into account when it makes sea level rise predictions, he said.

These currently indicate a rise of between 18 and 59 cm by 2100. Dynamic thinning could actually mean rises of a metre or more as the process accelerates.