Thompson, professor of geological sciences at Ohio State University, is leading the expedition -- his 44th -- next week to a rugged and remote region of the Wrangell-St. Elias Mountain range on the U.S.-Canadian Border. There, in an ice-filled saddle between two mountain peaks, he and a team of researchers will use a solar-powered drill to pierce the ice cap and retrieve these records.

Thompson and his research team have undertaken similar missions to ice fields and glaciers to Peru, Bolivia, Antarctica, Greenland, Kurgyzstan, China, Africa and the Russian Arctic during the last quarter-century. The cores they have returned to Ohio State's Byrd Polar Research Center paint a picture of climate across the millennia, with the oldest dating back 600,000 years.

From these cores, Thompson and his wife and research partner, Ellen Mosley-Thompson, a professor of geography, have built a history of ancient climate around the world over the centuries. From this history, they should be able to determine if recent evidence of global warming is just part of a natural cycle or, as they suspect, it is evidence that human activity has altered the planet's weather system.

"The average surface temperature across the planet has risen by about .6 degrees C (1.08 degrees F) during the last century," Thompson said, "but in Alaska and in parts of Russia and Canada, researchers have seen an increase of nearly 2 degrees C (3.6 degrees F) in just the last 30 years.

"We know that some of the largest glaciers in the region have retreated more than four kilometers (2.73 miles) in just the last two decades," he said. "These large bodies of ice are remarkably sensitive to climate change."

While the retreat of glaciers is an obvious indicator that something about the climate has changed, the ice cores, with their stratigraphic layering of annual snowfall, offer the best key to understanding what those changes were, how serious they were and what caused them. That is the reason Thompson is now turning to Alaska.

Thompson's expedition should arrive in Anchorage on April 30th and from there, the team will make its way to their jumping-off point at the tiny May Creek Airport inside of the vast Wrangell-St. Elias National Park and preserve and about 30 miles east of their target destination.

From there, the expedition members will use an A-Star 350, high-altitude helicopter to cross the mountains to the Klutlan Glacier where they will establish a base camp at 10,500 feet. After a few days acclimatization, team members will be ferried up to the col, or saddle between Mount Churchill, a 15,638-foot (4,766-meter) stratovolcano, and Mount Bona, its 16,420-foot (5,005-meter) neighbor.

The six tons of equipment for the six-week expedition was trucked from Columbus to Chitna, Alaska. From there, the researchers will use a super-charged Twin Otter aircraft to carry the equipment to the drill site.

Once the drill site is established at 14,500 feet (4,300 meters), Thompson and his team will attempt to drill through the ice cap to bedrock to retrieve the entire climate record preserved there.

Unfortunately, no one knows how deep the ice is at the col so the expedition will have to use radar to gauge the depth of the ice field. They're carrying equipment that would let them drill as deep as 700 meters (2,300 feet), although Thompson thinks the distance will be much shorter.

"I believe that there is a natural limit within mountain glaciers as to how thick ice on top of a mountain range can get," he explained. "At most sites around the world, such ice fields are between 130 and 160 meters (426 to 525 feet) thick, although we have retrieved cores at one site that reached 308 meters (1,010 feet)."

The geologic history of the region will probably play an important role in this expedition. Mount Churchill experienced two major eruptions -- each more powerful than the 1980 eruption of Mount St. Helens in Washington -- in 700 A.D. and in 65 A.D. These blasts deposited thick layers of volcanic ash, or tephra, over hundreds of thousands of square kilometers in the region, including the ice on the mountain at the time. Thompson believes that those layers are perfectly preserved within the ice.

The tephra layers, however, will pose a problem for the sophisticated drill they use to core the ice so the team had to design a new drill bit assembly capable of drilling through ash that may be as much as a meter thick.

"We've prepared and tested five new drill systems on campus in anticipation of what we might face on Bona-Churchill," Thompson said. "We want to be prepared for every contingency since this expedition, aside from its importance on its own, may serve as a warm-up to future projects in areas as remote as the Antarctic Peninsula."

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