ice in the Pine Island Glacier, which lies in the Antarctic Ice sheet is melting and raising the sea level. This is the first evidence of glacial melting raising the sea levels. "In terms of ice discharge, this is nothing like anyone has seen before," says Andrew Shepherd, researcher at the Centre for Polar Observation and Modelling, University College London. The glacier usually transports 69 cubic km of ice each year from of the West Antarctic Ice Sheet (wais). Researchers monitored the glacier using satellite altimetry to measure changes in elevation and satellite interferometry to measure ice velocity. It showed that the glacier had thinned by as much as 1.6 metre per year between 1992 and 1999, affecting 150 km of the inland glacier. The glacier is currently loosing about four billion tonne of ice to the ocean.
"The vast majority of freshwater is locked in Antarctica and this is the first time we have seen an Antarctic glacier retreating. The concerns for sea level rise are real in that respect," says Shephard. The wais contains enough water to raise the global sea level by a catastrophic five metre. If glacier continues to melt away at the current rate it could melt in entirety in just 600 years and raise sea level by 0.6 cm. But Shepherd points out the melting glacier could also effect the drainage basin, which contains enough ice to raise sea level by another 50 cm. It is not yet certain whether the glacier's retreat is a process that will accelerate or stabilize (Science , Vol 291, No 5505).
Modelling studies that have predicted rise in sea temperatures have produced patterns of thinning similar to those observed now. They are simple models but tell us that changes at the margins of the ice sheet can be transmitted inland causing tremendous changes in sea level. But David Vaughan, glaciologist at the British Antarctic Survey, England, says it is not yet clear whether the changes seen in the Antarctic ice sheet are related to human-induced climate change or not.