I n March, 2002, NASA and the Deutsches Zentrum für Luftund Raumfahrt, the German aerospace agency, launched a pair of satellites from the Plesetsk Cosmodrome, a former intercontinental-ballistic-missile site in northern Russia, to map changes in the earth’s surface. The satellites, nicknamed Tom and Jerry, have been chasing each other around the globe ever since. Separated by a gap of approximately a hundred and thirty-seven miles, they sometimes pull apart, only to draw closer again. By monitoring their relative positions to the fantastic exactitude of one micron—less than one-fiftieth the width of a human hair—scientists can detect tiny variations in the earth’s gravitational field.
Now, almost four years to the day after they were launched, Tom and Jerry have yielded a scarily significant result: Antarctica is losing ice. The rate of loss, according to researchers at the University of Colorado, in Boulder, who analyzed changes in the continent’s gravitational pull, is around thirty-six cubic miles per year. (For comparison’s sake, the city of Los Angeles uses about one-fifth of a cubic mile of water annually.) The finding, which was reported two weeks ago in the online version of Science, is particularly ominous, because climatologists had expected that even as the ice sheet lost mass at its edges, its over-all mass would increase, since rising temperatures would lead to more snowfall over the continent’s midsection. If the loss continues, it will mean that predictions for the rise in the sea level for the coming century are seriously understated.