Greenland Ice Sheet Changes Are Normal; No Evidence Of Long-Term Climate Changes, Researchers Say

In a paper that will appear in the Aug. 24 edition of Nature, Davis and his co-investigators will report that changes in the ice sheet's upper elevations, areas above 6,000 feet, are caused by natural variations in snow accumulation over time.

"When we released our original findings, they were somewhat controversial," said Davis, an associate professor of electrical engineering who has been using remote-sensing satellites to study changes in the ice sheet since 1990. "Our data indicated that overall, the ice sheet was maintaining a constant elevation, but we found great variability over short distances, with substantial thickening in some areas and strong thinning in other areas."

Shortly after his study was released, Davis and a group of researchers led by Joe McConnell, an associate research professor at the Desert Research Institute in Reno, Nev., joined together to investigate the cause of the variability in elevation.

Using ice cores, each 45 to 400 feet deep, that were collected from 12 locations around the southern Greenland ice sheet above 6,000 feet, the researchers measured variations in the concentrations of dust and chemical compounds such as hydrogen peroxide, calcium and ammonium. The researchers used this analysis to determine the amount of snow that accumulated each year over the time span of the cores.

"Analyzing ice cores is similar to studying tree rings," Davis said. "Just as the distance between a tree's rings represents its growth that year, the amount of ice between layers of certain compounds indicates that year's accumulation in that location."

Ice core analysis and modeling revealed that areas where elevation changed dramatically had a corresponding variation in snowfall during the study period. Further analysis indicated these snowfall variations were consistent with natural fluctuations over decades. This proves the elevation changes across southern Greenland that Davis discovered in his earlier study were not unusual.

Just last month, two other studies were reported that support Davis and his co-investigators' findings. These studies also found that, overall, the ice sheet's upper elevations were relatively stable. However, one of these studies found that most of the lower elevations of the ice sheet were thinning rapidly, with rates exceeding three feet a year in some locations along the edges.

"Although there doesn't appear to be any changes in southern Greenland's upper elevations that can be associated with global warming, dramatic lower elevation thinning has been documented," Davis said. "While this thinning seems to have had no effect on the upper elevations so far, more study is needed to determine its cause and the possible impact on the ice sheet's contribution to sea-level rise in the future."

Other universities who participated in the study include: the University of Washington, Ohio State University, the University of Arizona and the University of Nebraska. Funding was provided by grants from NASA and the National Science Foundation.