After comparing geological survey data from the 1950s to the early '70s with recent airborne laser altimetry data, scientists at the University of Alaska Fairbanks have found that Alaskan glaciers may have made the largest single glaciological contribution to rising sea level over the past 50 years. Since 1990, they have used a nadir-pointing laser rangefinder mounted in a small aircraft to monitor the volume and area changes of 67 glaciers, representing 20 percent of the glaciated areas of Alaska and neighboring Canada. Their measurements, reported in the July 19 issue of Science, indicate that the annual volume loss from Alaskan glaciers has been -96 ±35 km3 a year for the last decade, nearly twice that of the estimated amount from the Greenland Ice Sheet.