Where do you go to study global warming? Try the coldest, windiest, most forbidding land mass on Earth.

If you can get your sleds dug out of the snowdrifts and tolerate the occasional blinding screamer of a blizzard, and you don't mind wind chills that plummet to 60 degrees below in the summertime, Antarctica is the perfect place to hunt for clues to the complex workings of Earth's climate.

That, at least, is the conviction that has kept climate investigator Paul Mayewski and his intrepid band of meteorologists, geophysicists, atmospheric chemists, remote sensing specialists and glaciologists coming back four summers in a row to trek the continent of ice at the bottom of the world.

Because of Antarctica's remoteness, physical perils and logistical demands, its climate is the most poorly understood of any continent. Armed with the latest in modern tools of survival as well as of science, Mayewski's team of researchers from the United States, working with participants from 18 other countries in the International Trans-Antarctic Scientific Expedition, is determined to change that.

The scientists are investigating changes in Antarctic temperatures, sea levels, precipitation, atmospheric patterns and other features going back at least 200 years. They are providing "ground truth" data for comparison with satellite data. They are tracing the fallout from far-off volcanic eruptions and the wind-deposited residue of marine organisms. They are also studying how much the ice sheet may be melting, raising sea levels worldwide. Within a few years, they hope to understand how much such changes are part of a long-term natural process and what role human activity plays.

Despite its remote location, Antarctica plays a significant role in the entire global system, scientists believe. The expedition has taken the first steps, Mayewski said, to "change Antarctica from a poorly understood continent, climatically, to perhaps the best documented in the Southern Hemisphere."

In its four trips, his team has covered more than 1,500 square miles and carried out 11 lines of scientific inquiry. It has probed more than 14 miles high in the Antarctic atmosphere with research balloons and drilled nearly two miles down to the continental bedrock. On Jan. 2, Mayewski, of the University of Maine, and his team of 10 men and three women completed a trek to the South Pole, drilling and sampling all the way. It was the first U.S. overland expedition to the Pole in 41 years -- and the first devoted to science, said glaciologist Julie Palais of the National Science Foundation, which coordinates U.S. Antarctic activities.

The team flew to the Byrd Surface Camp about 800 miles from the pole and set out on Nov. 23 aboard a modern version of a wagon train, one made up of big sleds loaded with drilling, radar and other research equipment, fuel, emergency gear, snowmobiles and crates of food. They had satellite phones and navigation instruments, Internet connections and a crevasse detector to keep them from falling into an abyss.

Pulled by two 13-ton Caterpillar tractors, the two-part train included a science lab, a kitchen and, as the caboose, a portable outhouse known as the "Polar pooper." Team members dug a pit at each camp site and pulled the outhouse over it.

The presence of three women, Mayewski said, was rare and possibly unprecedented.

They didn't get far before one of their test subjects jumped up and bit them. It was the dreaded El Nino, the disruption of atmospheric patterns that, in the United States, has driven up precipitation on the Eastern Seaboard this season and triggered a series of violent Pacific storms along the West Coast. In the Antarctic, it piled soft, treacherous snow higher than anyone in the expedition had seen in their four summers on the ice.

"For the first time in four years, we were having trouble pulling the load," Mayewski said. They found themselves repeatedly mired in deep drifts, unable to move until they dug themselves out. A blizzard closed in, winds blew at a sustained 30 knots with gusts well into the 40s, and they were in a whiteout. "All we could do was sit and wait and see how deeply it would bury us," said Dan Dixon, a University of Maine graduate student.

On Nov. 28, when the weather cleared, they dug the train out and returned in temporary defeat.

"That was the worst moment," said Mayewski, a veteran of almost four decades of working in Antarctica. He described the team's adventures last week in telephone interviews from the Amundsen-Scott South Pole Station and from the main base at McMurdo.

The trekkers were witnessing a dramatic demonstration that El Nino, once thought to be a phenomenon of the tropics, has global effect, Mayewski said. It also produced warmer than usual temperatures, in the balmy range of minus 7 to minus 18 degrees Fahrenheit, compared with the typical minus 20 and lower.

On Dec. 7, equipped with more buoyant pontoon-type skis for the sleds and extra-wide tracks on both tractors, the trekkers set out again at a much faster pace -- all of 5.5 mph. The team spent most of Christmas, like every other day, doing experiments, drilling ice cores, flying ozone detection balloons and doing analysis.

The centerpiece of the effort is collecting ice cores, the most detailed natural record of climate change on the planet, Mayewski said. "Antarctica contains the largest repository, or 'library,' of ice cores anywhere." During each stop, the team drilled cores as long as 400 feet out of the two-mile-thick ice mantle, and accumulated hundreds of samples to be shipped home for analysis.

The gases and materials trapped in the layers of ice reflect atmospheric conditions at particular times in history. Scientists in Greenland have recovered ice cores covering more than 110,000 years of Earth's environmental record. Russian scientists in the Antarctic retrieved an ice record going back 420,000 years.

But ice cores are heavy, and the ITASE researchers wanted to sample many different sites. To carry the needed fuel, they limited their ice core freight to about 7,000 pounds, Mayewski said.

Even with the improved equipment, the team bogged down again as it got closer to the pole. It took both tractors pulling a single train just to get over even the gentler rises, and at another point, another heavy storm left them with four-foot drifts to shovel away.

Finally, on New Year's Day, they saw a glowing haze, directly below the sun, which they knew marked the South Pole six miles away.