One study found that warming temperatures are causing glaciers the size of Manhattan to trigger quakes, and computer models of climate and ice indicate that by about 2100, average temperatures could be 2.3 degrees Celsius warmer than today and that over the coming centuries, the world's oceans could rise 3.9 to 6 meters -- conditions last seen 129,000 years ago, between the last two ice ages.

    The findings, published in the latest edition of the journal Science, are consistent with other recent studies of melting and erosion at the poles. Many experts say there are still uncertainties about timing, extent and causes.

    But Jonathan T. Overpeck of the University of Arizona, a lead author of one of the studies, said the new findings made a strong case for the danger of failing to curb emissions of carbon dioxide and other heat-trapping greenhouse gases.

    According to the computer simulations, the global warming caused by greenhouse gases could amplify the melting around Antarctica beyond that of the last warm period, which was driven mainly by extra sunlight reaching the northern hemisphere.

    The researchers also said that stains from dark soot drifting from power plants and vehicles could hasten melting in the Arctic by increasing the amount of solar energy absorbed by ice.

    The future rise in sea levels, driven by melting of ice from both Greenland and West Antarctica, would occur over many centuries and be largely irreversible, but could be delayed by curbing emissions of the greenhouse gases, the researchers said.

    In another article in Science, researchers say they have detected a rising frequency of earthquake-like rumblings in the bedrock beneath Greenland's ice cap in late summer since 1993.

    The jostling of the giant ice-cloaked island is five times more frequent in summer than in winter, and has greatly intensified since 2002, the researchers found. The data mesh with recent satellite readings showing that the ice can lurch toward the sea during the melting season.

    H. Jay Zwally, a NASA scientist studying the polar ice sheets with satellites, said the seismic signals from ice movement were consistent with his discovery in 2002 that summer melting on the surface of Greenland's ice sheets can almost immediately spur them to shift measurably, according to the New York Times.

    "Models are important, but measurements tell the real story," Dr. Zwally said. "During the last 10 years, we have seen only about 10 percent of the greenhouse warming expected during the next 100 years, but already the polar ice sheets are responding in ways we didn't even know about only a few years ago."

    In both Antarctica and Greenland, it appears that warming waters are also at work, melting the protruding tongues of ice where glaciers flow into the sea or intruding beneath ice sheets, like those in western Antarctica, that lie mostly below sea level.

    Many experts on climate and the poles, citing evidence from past natural warm periods, agreed with the general notion that a world much warmer than today's, regardless of the cause of warming, will have higher sea levels.

    But significant disagreements remain over whether recent changes in sea level and ice conditions cited in the new studies could be attributed to rising concentrations of the greenhouse gases and temperatures linked by most experts to human activities. Enditem

    (Agencies)