A new study of the mass of ice capping Greenland reveals that the giant ice sheet burying the island has rapidly lost mass in recent years due to melting and iceberg calving. Between 2003 and 2005, the island’s low coastal areas shed 155 gigatons (41 cubic miles) of ice per year, while snow accumulation in the interior of the ice sheet was only 54 gigatons per year. The amount of ice lost in two years is roughly the same as the amount of water that flows through the Colorado River in 12 years. “In the 1990s, the ice was very close to balance with gains at about the same level as losses. That situation has now changed significantly,” said lead researcher Scott Luthcke of the Planetary Geodynamics Laboratory at NASA’s Goddard Space Flight Center.
The research was based on observations made by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. This image illustrates where Greenland gained mass during the study period and where it lost mass. While the equivalent of 10 to 15 centimeters of water per year accumulated over the core of the island (red and orange areas), an even larger area experienced losses (blue) of between 5 and 25 centimeters per year. Losses were highest over southeastern Greenland.
The GRACE satellites sense changes in mass beneath them by responding to changes in gravitational force (the gravitational force an object exerts on other objects increases with mass). As the twin satellites orbit the Earth in tandem, the distance between them changes based on changes in the gravitational force below. The gravitational force changes as a result of changes in the concentration of mass on the Earth below.
The study was based on data collected over Greenland every 10 days. Scientists divided the island into separate drainage basins, based on which direction the ice sheet flows from the interior toward the coasts. They further divided the basins into high- and low-elevation terrain. While the two northernmost basins were in balance—snow accumulation equal to melting and iceberg loss—the southeastern basins experienced a rapid decline in ice mass, especially at low elevations. Overall, Greenland lost 20 percent more mass than it received in snowfall each year. These results are consistent with overall trends in ice loss that other types of observations of Greenland have documented, including radar-based estimates of accelerating glacier flow off the ice sheet.
According to one of the study’s authors, Jay Zwally of NASA’s Goddard Space Flight Center, “This is a very large change in a very short time. In the 1990s, the ice sheet was growing inland and shrinking significantly at the edges, which is what climate models predicted as a result of global warming. Now the processes of mass loss are clearly beginning to dominate the inland growth, and we are only in the early stages of the climate warming predicted for this century.”
To read the full NASA press release on this study, which will be published on October 19, 2006, in the online edition of the journal Science,please read Greenland Ice Sheet On A Downward Slide.
NASA image courtesy Scott Luthcke