Regular readers will know that I’ve been keeping a close eye on this year’s Arctic summer, and the record minimum sea ice extent reached last month (nice NASA picture here). The ice area is increasing now, but is still about 1m km2 below the same time last year. I might have to increase my bet… If all the summer Arctic sea ice disappears quickly, it won’t have any impact on sea level, but if the ice on land – mountain glaciers and the great ice sheets of Greenland and the Antarctic – melts, sea level will rise. During the last interglacial, about 125,000 years ago, global temperature was a degree or two warmer than today and sea level was about 5m higher. Some of that extra water came from Greenland and Antarctica.
When I was writing Hot Topic, the latest information suggested that Greenland was losing about 200 km3 (cubic kilometres) of ice every year, and Antarctica about 150 km3 (HT, p45). But time goes on, and the world warms. A study to be published in Geophysical Research Letters suggests that the glaciers of southeast Greenland are now losing 300 km3 of ice per year, a 400% increase in melt rate since 2004. AFP reports:
“Until 2004, the glacier mass in the southeastern part of the island lost about 50 to 100 cubic kilometres (12 to 24 cubic miles) per year. After this date, the melting rate accelerated to 300 cubic kilometres per year. It’s a jump of 400 percent, which is very worrying,†National Space Center head researcher and project chief Abbas Khan told AFP. […] The measurements indicated that the mountains hugging glaciers in the southeastern part of Greenland rose four to five centimetres (1.5 to two inches) per year, and that the banks of the glaciers thinned 100 metres per year.
What’s this got to do with the Arctic sea ice? If the summer sea ice continues to decline, Greenland will find itself experiencing warmer summers. More heat, more melt. And if the loss of ice can jump by 400% in a few years, who knows what will happen in the future. It’s only one study, and it’ll be interesting to see if the latest satellite data match up, but it’s certainly – as Khan – says, worrying. (Khan, S. A., J. Wahr, L. A. Stearns, G. S. Hamilton, T. Van Dam, K. M. Larson, and O. Francis (2007), Elastic uplift in southeast Greenland due to rapid ice mass loss, Geophys. Res. Lett., doi:10.1029/2007GL031468, in press.)
Meanwhile, NOAA in the US has released its first annual update on the state of the Arctic. The Arctic “report card†flags significant changes in oceans and atmosphere around the North Pole, but provides a somewhat less alarming view of events in Greenland. From the NOAA press release:
“The purpose of the Report Card is to provide a concise, scientifically credible and accessible source of information on recent changes in the Arctic,†says Jacqueline Richter-Menge, the chief editor of the project, from the US Army Cold Regions Research and Engineering Laboratory. A lead author, James Overland, a scientist at NOAA’s Pacific Marine Environmental Laboratory in Seattle, Wash., has identified a wind circulation pattern blowing more warm air towards the North Pole, compared to the circulation patterns in the 20th century. The fate of the Greenland ice sheet represents large uncertainty. “Recent ice loss is about the same as in the early 20th century, but one cannot exclude a potentially faster response, as mechanisms remain incompletely understood,†wrote the team headed by Edward Hanna of the University of Sheffield, United Kingdom.