Just last December findings presented at the annual gathering of the American Geophysical Union indicated that, contrary to popular belief, sea level changes owing to the thinning West Antarctic Ice Sheet (WAIS) may not pose any real threat. Exactly how sound that assertion is, however, remains unclear. According to a report published today in the journal Science, the Pine Island Glacier (PIG)the largest of the WAIS glaciersis dwindling at a rate that will set it drifting away from West Antarctica within 600 years.

Based on satellite data from 1992 through 1999, Andrew Shepherd of University College London and his colleagues estimate that the PIG is decreasing in mass by about four gigatons each year, resulting in a 0.01-millimeter rise in sea level. Although this in and of itself is relatively modest, it may provide insight into what is happening on a larger scale in the WAIS interior. The reasons why the PIG is thinning are not entirely understood, but global warming may well play a part. (The melting of the entire WAIS could cause sea levels to rise by about five meters, washing out coastal areas.) "We have monitored the change for the first time," Shepherd told Reuters. "And it is important for us now to continue to model it."