Rapid Arctic ice loss confirmed
New measurements of the Greenland ice sheet by the two GRACE satellites confirm that the glaciers are melting at an accelerated rate again this year: The ice losses from May 2004 to April 2006 are 250 percent higher compared to the period between April 2002 and April 2004.
According to Isabella Velicogna and John Wahr of the University of Colorado at Boulder, this accelerated meltdown is mostly concentrated in the south of the island, where the average temperature has warmed by 4.4 Kelvin since 1990. The Kangerdlugssaq and Helheim glaciers are now flowing towards the sea at twice the speed they were five years ago, as the resulting meltwater reduces the braking surface friction. All in all, the entire Greenland ice sheet lost around 680 cubic kilometers of ice in the last two years, which flowed off as fresh water into the North Atlantic and Arctic Seas.
The two GRACE satellites (Gravity Recovery and Climate Experiment) fly over the Earth 16 times a day at an altitude of 500 kilometers and a distance of 220 kilometers from each other, measuring changes in the planet's gravitational field. If the earth's gravity changes locally - for example due to the melting of glaciers or increased water ingress into the ocean - this deflects the leading satellite slightly off course, which is ultimately recorded by its subsequent colleague. The recording devices work so sensitively that even deviations of just one micrometer are noticed.
The ASAR satellite (Avanced Synthetic Aperture R adar) from the European space agency Esa has now also taken the first images of ice-free areas north of Spitsbergen and Siberia, which have always been covered by permanent sea ice since records began. About five to ten percent of the Arctic permanent ice that was still there in summer was torn apart by strong storms in late summer, pushed aside, and an area of sea the size of the British Isles was uncovered. Since the early 1980s, the area of permanent sea ice around the North Pole has decreased from 8 to 5.5 million square kilometers.
