Dr. Behar and his colleagues at the University of Colorado this past August released 90 yellow rubber ducks into the melt water flowing down a chasm in the largest of Greenland's 200 glaciers -- the Jakobshavn Isbrae -- which has been thinning rapidly since 1997. Each duck was imprinted with an email address and, in three languages, the offer of a reward. If all goes well, Dr. Behar hopes that one day they will emerge 30 miles or so away at the glacier's edge in the open water of Disko Bay near Ilulissat, bobbing brightly amid the icebergs north of the Arctic Circle, each one a significant clue to just how warming temperatures may speed the glacier's slide to the sea.