Ice sheet complexity leaves sea level rise uncertain

Ice shed from the giant sheets covering Antarctica and Greenland is responsible for just 12% of the current rate of global sea level rise, according to a new review.

The authors emphasise that it is now clear that the ice caps are losing ice faster than it is being replenished by snowfall. But exactly why this is happening remains unknown, making it difficult to predict the extent of future sea level rises.

The remaining 88% of the current rise is due to the expansion of water as it warms, and melting from mountain glaciers and ice caps outside Greenland and Antarctica. Yet the shrinking of Greenland and Antarctica remains crucial because together they hold enough water to make sea levels rise by 70 metres, submerging vast swathes of land and displacing millions.

Over the past 10 years, satellite measurements have vastly improved the quality of data detailing changes in the ice sheets, say Duncan Wingham from University College London and Andrew Shepherd from the University of Edinburgh, both in the UK.

Having reviewed the latest data, the pair conclude that losses from the ice sheets of Greenland and Antarctica contribute 0.35 millimetres per year to the total rate of sea level rise, estimated at 3 mm per year.

This contribution is close to the Intergovernmental Panel on Climate Change's latest estimate of 0.41 mm from the Greenland and Antarctic ice sheets. According to the IPCC, measurements since 1993 show that the thermal expansion of water is responsible for 1.6 mm of the annual rise and other melting glaciers and ice caps for 0.77 mm.

from New Scientist