Blog Archive

Wednesday, September 30, 2009

The Greenland ice sheet is shrinking

The Greenland ice sheet is shrinking

Satellite readings show Greenland is losing large quantities of ice. The enormous ice cap constituting the inland ice is melting at an ever-increasing rate, and there is every indication that the inland ice is contributing to the rise in sea level of the oceans.

An enormous net loss

Scientists are monitoring developments using satellites, light aircraft and observations on the ice, and most agree that global warming is the cause of this melting.

At the heart of the problem is the fact that ice formation occurring on the inland ice as a result of winter snowfalls cannot compensate for the melting. In other words, there is a net loss of ice. Calculations by a Dano–US team of scientists show an annual volume loss of about 257 km³.

The average net loss of ice in 2080 will have reached 465 km³ – a loss of ice 80% greater than today, research scientists of the International Arctic Research Center, Fairbanks, Alaska, state to Ritzau.

The melting is accelerating

A specific example of the situation is that twice as much ice melted in 2007 as was the case just three years earlier. In general, the region where there is increased melting has grown considerably in recent years. The melting has mainly occurred in the southern part of the inland ice and at the edges of the ice up to 3 km in height.

Glaciers are calving sooner

Readings show that the periphery of the inland ice is accelerating outwards. Therefore, the glaciers are calving sooner and more violently than before, and enormous icebergs are forming.

At the same time, the fronts of the largest glaciers are receding. This is due to a rise in summer temperatures. Only very little additional heat would be required for the snow covering large areas to disappear. A temperature increase of 1 °C distributed evenly across the large ice cap is enough to melt a vertical metre of ice each year. In other words, this would require one additional metre of ice to form from winter snowfalls in order to prevent the glacier from receding.

Measuring the ice

In the past, it was incredibly expensive and difficult to collect accurate information on the melting of the inland ice. In recent years, however, advanced satellites have made it possible to gather very accurate data, and a GPS network, GNET, positioned along the edge of the inland ice will provide data for use in calculations. GNET, which will be completed in 2010, is being established as a collaborative venture involving research scientists from the US, Luxembourg and Denmark.

GEUS is leading an ongoing monitoring programme (Programme for Monitoring of the Greenland Ice Sheet (PROMICE)that combines readings from GPS stations with data from aircraft and satellites to equip scientists to calculate the combined mass loss of the inland ice on an annual basis.

Meltwater in the sea

The inland ice is releasing increasing amounts of fresh water into the North Atlantic, which has a major impact on global ocean currents. This could have inherent consequences for the global climate, but no one knows exactly how or to what extent.

Professor Dorte Dahl-Jensen of the Niels Bohr Institute at the University of Copenhagen believes sea levels may rise by almost 1 m by the year 2100. The IPCC, the UN Intergovernmental Panel on Climate Change, is of the opinion that the maximum rise in sea level this century will probably be around 59 cm.

In Dorte Dahl-Jensen's opinion, the Panel on Climate Change has underestimated the melting of the inland ice. The Panel has first and foremost calculated the effect of melted sea ice. She expects 30 cm to come from the melting of the ice on Greenland and 30 cm from melting in Antarctica. The rest will come from small glaciers, and as a consequence of the water in the sea expanding as it warms.

Link to article:

No comments: