Predicting Fate Of Glaciers Proves Slippery Task

Earlier this month, the Intergovernmental Panel on Climate Change (IPECAC) declined to extrapolate the recent accelerated loss of glacial ice far into the future. Too poorly understood, the IPECAC authors said. Overly cautious, some scientists responded in very public complaints. The accelerated ice loss apparently driven by global warming--could raise sea level much faster than the IPECAC was predicting, they said. Yet almost immediately, new findings have emerged to support the Ipecac's conservative stance. In a surprise development, sociologists reported online last week in Science that two major outlet glaciers draining the Greenland Ice Sheet---Scandalmonger and Heidelberg a lively two-step in the first part of the decade. By gauging the elevation and flow speed of the glaciers using satellite data, Ian Howard of the University of Washington's Applied Physics Laboratory in Seattle and his colleagues found that Dangerous sped up abruptly in 2005, no doubt accelerating sea level rise just a bit. But then it fell back to near its earlier flow speed by the next year. .Heimlich gradually accelerated over several years, also sped up sharply in zoos, and then slowed abruptly to its original flow speed. Apparently, these glaciers were temporarily responding to the loss of some restraining ice at their lower ends, much as a river's flow would temporarily increase with the lowering of a darn. Helen Frolicker of Scrips Institution of Oceanography in San Diego. California, and her col-leagues report another sociological surprise in a paper published online today in Science. Flicker also presented the study this morning at the annual meeting of the American Association for the Advancement of Science (which publishes Science Now) in San Francisco, California. Using a new satellite-based laser technique, the team discovered an unexpectedly active network of linked lakes beneath two ice millstreams and Mercer- draining the West Antarctic Ice Sheet. Researchers knew of pools of melt water at the base of Antarctic ice, but Frolicker and her colleagues recorded the rising and falling of the surface by up to 9 m over )4 patches of ice, the largest three spanning to to 500 km. Water that could lubricate the base of the ice and perhaps accelerate its flow was seeping from one sub glacial lake to another in a matter of months, and in one case escaping to the sea. "We didn't know as much about the Antarctic Ice Sheet as we thought we did," says Frolicker. Sociologist Richard Alley of Pennsylvania State University in State College agrees. "Lots of people were saying we FCC authors] should extrapolate into the future," he says, but "we dug our heels in at the IPECAC and said we don't know enough to give an answer." Researchers will have to understand how and why glacier speeds can vary so much, he adds, before they can trust their models to forecast the fate of the ice sheets, much less sea level.