U.S. scientists have completed the first overland sled trek across Antarctica to the South Pole in 45 years. They embarked on the journey in search of clues to possible human effects on global climate change. They made the trip in less than one month, despite forbidding terrain and weather.

Braving a blizzard, gale force winds, and Antarctic summer temperatures down to 30 degrees Celsius below zero, a team of 13 Americans reached the South Pole by sled train on January second. They had covered the 1,250 kilometers from the Byrd Surface Camp near the West Antarctic coast in 26 days. There were flown back a few days later.

The effort was all in the name of science. Expedition leader Paul Mayewski, a climate scientist at the University of Maine, is the chief researcher for the United States component of a 19 nation program called the International Trans Antarctic Science Expedition, or ITASE for short.

"One of the things we are attempting to do with the ITASE program is to change Antarctica from the most poorly understood continent on the planet with respect to climate to the very best of any of the continents," said Mr. Mayewski.

The U.S. ITASE team completed its trek 91 years after Norwegian explorer Roald Amundsen became the first to reach the South Pole by dog sled.

But Mr. Mayewski's team faced the frigid elements with far better technology. Two big Caterpillar tractors each towed a caravan of three sleds holding tents and insulated plywood boxcar-like structures for living and working. "Certainly traveling the way we did, we're perhaps by comparison with living at home not very comfortable, but we did travel in a fair amount of comfort. When you step outside of the vehicle, you definitely get the feeling of the remoteness and the penetrating cold and how desolate one would feel if you didn't have all of the support around you," he said.

Despite the modern equipment, the haul was far from easy. The U.S. team was forced to turn back only 40 kilometers into its first attempt in late November when a deeper and softer than expected snow base caused the tractors and sleds to sink. The second outing succeeded with wider tractor treads and sled runners and pontoon-shaped sleds, which caused less drag than the previous flat sleds.

Even so, University of Maine graduate student Dan Dixon said a storm with high winds forced them to halt for a time as snow drifts built up against the sides of the train three-fourths of the way toward their goal. It was his scariest moment, helping make the sighting of the South Pole station several days later his most memorable.

"As we drove in on the last leg, it was such a great feeling to realize that we had finally reached our destination despite all our slowing up," Mr. Dixon said.

What attracts researchers to the frozen continent is its relatively unspoiled environment. All along their route, the scientists drilled hundreds of meters of ice cylinders. Paul Mayewski said the ice cores are important because frozen within them is the history of past climate as recorded in the chemical composition of eons of snowfall.

"One of the few places on Earth that you could do this would be Antarctica because there are ice cores literally anywhere you go. Our primary interest is to look at how the natural climate system operates. We are trying to look for patterns and see whether or not there is any predictability in the climate. We're also looking for human fingerprints [impact] in terms of the chemistry of the atmosphere," Mr. Mayewski said.

With such ice data and other information collected from atmospheric balloons and satellites, the U.S. scientific effort in Antarctica hopes to learn if the West Antarctic ice sheet is shrinking, how global climate affects Antarctica and vice versa, and the impact humans are having on climate.

Although this was its first trip to the South Pole, the U.S. ITASE teamed traveled about 3,500 kilometers over three previous seasons. Once Mr. Mayewski and his colleagues have a chance to analyze the data from this trek, they hope to make a similar trip in about two years starting at the South Pole.

"The U.S. has had a long history of traverse activities, but in many ways it has been reborn in the last few years and we're always trying to make traverse trains that much more efficient," he said.