An ice sheet–climate change connection?

The ice sheet in northwest Greenland has been thinning over the past 40 years, say researchers Stan Paterson of Paterson Geophysics in Heriot Bay, British Columbia, and Niels Reeh of the Technical University of Denmark, in Lyngby, who report thinning rates that are significantly faster and extend to higher elevations than have been anticipated from previous studies.

The researchers’ findings are based on direct measurements of surface elevation changes over the period 1954–1995 on a traverse across the north Greenland ice sheet. In contrast to the significant thinning on the west side of the ice sheet, some thickening of the north ice stream has occurred on the eastern part of the transect, but there has been little change across the midsection.

Accounting for climate change effects on sea level rise requires a good understanding of the thermal expansion of oceans, glacial melting, and changes in ice caps and sheets. The new findings fill a significant void: The largest uncertainties in forecasting sea level changes are associated with estimates of the mass balance of the Greenland and Antarctica ice sheets.

The reported observations, say Paterson and Reeh, span a long enough period of time to assure that what they determined is ice sheet thinning and not fluctuations in snow cover. Because of the complexity of the processes that can occur in this region of the world, reliable measurements are essential. For example, referring to an earlier study by Huybrechts and Le Meur (Polar Res. 1999, 18, 299–306), the scientists note that, in addition to other effects, the Greenland ice sheet is still responding to climatic changes that occurred thousands of years ago. (Nature 2001, 414, 60–62) —WALTER SHAUB