Scientists Survey Antarctic and Greenland Ice Loss

An international team of scientists has produced the most accurate assessment of ice losses from Greenland and Antarctica. In a landmark study, published on 30 November in the journal Science, the researchers show that melting of the Antarctic and Greenland ice sheets has contributed 11.1 millimeters to global sea levels since 1992. This amounts to one fifth of all sea-level-rise over the survey period (1992 – present day). Researchers from British Antarctic Survey and the University of Bristol describe how analysis of millions of NASA satellite measurements from both of these vast ice sheets shows that the most profound ice loss is a result of glaciers speeding up where they flow into the sea. The authors conclude that this ‘dynamic thinning’ of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic coastlines, is penetrating far into the ice sheets’ interior and is spreading as ice shelves thin by ocean-driven melt. Ice shelf collapse has triggered particularly strong thinning that has endured for decades. The scientists compared the rates of change in elevation of both fast-flowing and slow-flowing ice. In Greenland for example they studied 111 fast-moving glaciers and found 81 thinning at rates twice that of slow flowing ice at the same altitude. They found that ice loss from many glaciers in both Antarctica and Greenland is greater than the rate of snowfall further inland. In Antarctica some of the fastest thinning glaciers are in West Antarctica (Amundsen Sea Embayment) where Pine Island Glacier and neighboring Smith and Thwaites Glacier are thinning by up to 9 meters per year. The team used data from NASA’s high-resolution ICESat (Ice, Cloud and Land Elevation Satellite). Launched in January 2003, ICESat was sent into a polar orbit to examine changes in the world's ice and land masses — particularly ice mass balance — as well cloud and aerosol height. The satellite’s lasers have measured the surface elevation of the Earth’s ice sheets with unprecedented accuracy. The satellite’s repeated passes over both poles create a wide net of coverage, and contribute to a long-term time series of topographic changes. For the first time scientists can see the elevation change over the whole of the Antarctic Peninsula, and that glaciers in this area have the highest rates of thinning recorded in Antarctica or Greenland.