Will sea levels rise sharply? Drilling could tell

Scientists don't expect definitive answers from their work for several years. But a preliminary analysis of the sediment shows that the Ross Ice Shelf retreated and expanded at least 60 times over the past 13 million years, rapid swings according to Naish.

"So that should ring alarm bells," he says. "It was quite dynamic."

Moreover, those swings occurred when levels of carbon dioxide, the key greenhouse gas tied to warming, were 30 percent lower than today.

It's not just rising sea levels that worry scientists. A rush of fresh water into the ocean from a  melting ice sheet could destabilize ocean currents, altering the marine ecosystem and possibly even the weather.

"If you very abruptly put a lot of melt water into the ocean you change the salinity of the ocean, you affect the whole productivity of the Southern Ocean, which is key to the whole global food chain," says Naish.

Salt water is denser than fresh water and sinks in a motion that creates currents. Melt water, however, dissipates instead of sinking and a huge amount could slow currents and reduce the amount of heat transported toward Europe, says Lionel Carter, another project scientist and a marine geologist at the University of Wellington in New Zealand.

With so much at stake, the scientists are treading carefully. In fact, they plan to drill several more holes to get a better history of the vast Ross Ice Shelf. The next drilling, set for 2008 at a nearby location, will extract sediment that goes back an additional 4 million to 5 million years.

After that, the drilling project could expand to other ice shelves around the white continent.

For Naish, Antarctica's ice shelves are "the early warning systems" of climate change that can alert mankind to potential disaster.

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