for National Geographic News
Few scientists dispute that human fossil fuel consumption is altering Earth's climate. The scope of that change, however, remains a subject of debate.
Attempting to resolve the question, research teams are braving some of the world's coldest temperatures and wickedest winds to drill ice samples from the Antarctic continent. These plugs, known as ice cores, provide a window into the past.
Two key phenomena explain why, according to John Priscu, an ecologist with the Department of Land Resources and Environmental Sciences at Montana State University in Bozeman. First is the fact that, as snow falls, it picks up whatever chemicals and particulate matter are in the atmosphere. Second, fallen snow never melts in the Antarctic.
Over time, new snow falls and older snow turns to ice, trapping tiny pockets of air in the process. "You get a chronology of the particles, chemicals, and gases," Priscu wrote in a recent e-mail from Antarctica.
Studying this chronological record allows scientists to see how the global climate responded to variations of greenhouse gases in the past.
"The past is the key to the future, because only if we know how the climate system works can we more accurately predict how it will behave in the future," said Heinz Miller, a geophysicist at the Alfred Wegner Institute for Polar and Marine Research in Bremerhaven, Germany.
Miller chairs the scientific steering committee of the European Project for Ice Coring in Antarctica, known as EPICA. The team is comprised of members from ten European countries. Earlier this year they reported on a 1.9-mile-long (3-kilometer-long) ice core containing a 740,000-year climate record.
Ice cores are cylinders of ice about six inches (ten centimeters) in diameter that are collected by drilling deep into the ice. The cores are brought to the surface in lengths of about ten feet (three meters) at a time.
The age limit of any core is determined by the thickness of the ice. While portions of Antarctica have been covered in ice for more than 20 million years, scientists don't expect to retrieve cores more than 1 million years old.
"The deepest ice moves laterally to the edge of the continent, like a ladle of pancake batter when poured on a griddle," Priscu said. "Keep pouring batter on, and it will only get so high before it spreads out and runs off the side of the griddle."
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