LINCOLN, Neb. (AP) - Scientists in Antarctica spent Christmas Day finishing work that may show the effects of global warming - drilling for clues about how massive ice sheets responded to past temperature changes. The project will be vital to creating a map of how the Earth may react to higher temperatures, scientists say.

One hundred scientists from four countries are working on the Antarctic Geological Drilling Program, or ANDRILL, coordinated by the University of Nebraska-Lincoln.

They gather rock core from deep below the Antarctic sea floor, then analyze it.

So far, the cores show a dynamic ice sheet that advanced and retreated more than 50 times over 5 million years.

Some of the ice shelf's disappearance was probably during times when the planet was 36 degrees Fahrenheit (2 degrees Celsius) to 37 degrees Fahrenheit (3 degrees Celsius) warmer than it is today - ''much like it will be in the next 50 to 100 years,'' said Tim Naish, a lead scientist on the project from Victoria University in New Zealand.

When drilling stopped Christmas Day, workers had bored down 4,061 feet.

''We may not understand the future, but we can understand the past,'' said David Harwood, director of the ANDRILL Science Management Office at UNL.

The drilling project took place on the Ross Ice Shelf, a floating glacier about the size of France.

The shelf is believed to be one of the most vulnerable pieces of the sprawling West Antarctic Ice Sheet, which scientists believe may have collapsed during a previous warm period. Scientists have suggested that a naturally occurring period of warmth, exacerbated by high levels of greenhouse gases, could cause an exceptionally quick contraction of ice sheets.

Researchers from the British Antarctic Survey reported last year the West Antarctic sheet may be starting to disintegrate, which could lead to rising sea levels.

With temperature change comes the acceptance that ''we're looking blindly into the future,'' Harwood said, but the ANDRILL project could at least help establish some expectations.
''We need a map,'' he said.