Greenland is not only still losing ice to the sea but the rate has accelerated in the last decade, an international group of scientists has highlighted this week. As a consequence, while the increased loss had previously mainly been happening in Greenland’s south, ice is also now noticeably disappearing more rapidly from its north-west coast.
[Updated 20 Feb 2014] I have updated the animated movie of the spread of ice loss into northwest Greenland observed by satellite so that it now reaches from 2003 through to 2011 as the link to the old movie died. The colour scale shows ice thickness in centimetres.
“These changes on the Greenland ice sheet are happening fast, and we are definitely losing more ice mass than we had anticipated,” said team-member Isabella Velicogna of the University of California, Irvine. The team, led by Shfaqat Abbas Khan of the Danish National Space institute, used satellite and GPS data to measure the ice sheet that covers around 80% of Greenland’s surface. In the study, published in Geophysical Research Letters, they looked at the vertical movement of the land underneath the ice sheet. Ice sheets’ weight pushes the Earth’s surface beneath them down towards its core, but when the ice melts the surface can rebound back.
The measurements showed that ice loss has increased from north-west Greenland since 2005. “This was undocumented before this study,” said team member John Wahr from the University of Colorado, Boulder. “Our speculation is that some of the big glaciers in this region are sliding downhill faster and dumping more ice in the ocean.” Meanwhile, although changes at the south coast slowed down again in 2006 after speeding up rapidly in 2004, they are still losing ice faster than they were in 2003. “Even if glaciers in this region have stabilized and are not accelerating further, they are continuing to contribute significantly to sea level rise,” the team writes.
Greenland holds about 20 percent of the world’s ice, the equivalent of nearly 6.5 metres of global sea rise. Last year Velicogna showed that between April 2002 and February 2009, the Greenland ice sheet shed roughly 385 cubic miles of ice. The mass loss is equivalent to about 0.5 millimetres of global sea-level rise per year. “Greenland’s main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade,” the team notes in its latest paper.
Elsewhere, the Guardian this week reported on another Geophysical Research Letters paper that may help improve the understanding of exactly how Arctic sea ice is disappearing. In September 2007, Arctic sea ice extent reached its lowest value since satellite measurements began in 1979, say Masayo Ogi and her co-authors. This was much lower than any models had previously predicted. The steady loss has previously been blamed on warmer seas, warming from the atmosphere and the effect of wind.
Now, Ogi and her co-workers say that the wind accounts for half the variation in change between one year’s ice extent and the next in a paper published online in advance of printing. “It also explains roughly 1/3 of the downward linear trend of sea ice extent over the past 31 years,” the US and Japanese researchers note. They find that in the winter prior to a year where there is a loss of ice there are especially strong winds blowing from the north. The winds funnel down through a channel called the Fram Strait between Greenland and the Norwegian island of Spitsbergen. “This pattern suggests an enhanced rate of flow of sea ice out through Fram Strait,” Ogi and colleagues write.
The team found a strong link between wind direction and ice cover from 1997 to 2009. 2007’s record low was accompanied by the largest increase in winds during the summer, and a moderate increase in winter. “In contrast, in 1996 when the record-high [ice cover] maximum was observed, both winter and summer exhibited near-record low [winds],” the team said.