CorrectionsMay 1, 2013
A recent article on the GRACE project ("GRACE Satellite Data Delineates Changing Earth Surface," by James Case, SIAM News, March 2013) asserted that, during the last Ice Age, "much of the northern hemisphere was covered with snow and ice to a depth of perhaps 200 miles." The correct figure is 2 miles. The article also states that "the Greenland ice sheet is roughly as massive as a puddle 4 cm deep covering an area the size of Colorado." It ought to have said that the annual decrease in volume of the Greenland ice sheet would cover an area the size of Colorado with melt-water to a depth of 3 to 4 feet, not centimeters. SIAM News regrets the errors.