Polar Ice May Show Climate Changes

By Joseph B. Verrengia Copyright 1998 Associated Press August 19, 1998

Antarctica may be an important predictor of climatic changes elsewhere on Earth thousands of years before they appear, researchers say.

Analyzing ice cores drilled from deep within glaciers, researchers found that small temperature increases in ancient Antarctica preceded, by at least a millennium, extremely rapid, substantial warming in Greenland.

The study, to be published Thursday in the journal Nature, "contradicts the hypothesis that Antarctic warmings are responses to events in the Northern Hemisphere," said Thomas Blunier of the University of Bern in Switzerland.

By deciphering these frozen traces of events that occurred more than 20,000 years ago, scientists could gain a better understanding of Earth's climate and possible global warming events today.

Blunier's findings "move us closer to the ultimate goal of predicting future climate changes," said James W.C. White, a climatologist at the University of Colorado who has drilled and studied ice cores from both polar regions.

But he cautioned that a variety of uncertainties remain. For one, findings from ice ages, when global climate was strongly affected by Northern Hemisphere ice sheets, may not be relevant to today's much balmier times.

In Blunier's study, a team of researchers from Switzerland, France, Denmark and Iceland examined slices of ice drilled from a glacier in central Greenland 650 miles north of the Arctic Circle. They then compared them with samples drilled from two locations in Antarctica.

Much like rings in a tree trunk, ice cores are thought to be a calendar of climate variations since each year's snowfall is deposited in a distinct layer. Atmospheric chemicals, dust and even bubbles trapped in the ice enable scientists to reconstruct climates of the past.

Blunier's group examined levels of methane, a heat-trapping gas, and found that that temperature fluctuations in Antarctica started 1,000 to 2,500 years earlier than in Greenland.

The fluctuations in Antarctica began about 47,000 years ago and lasted for 24,000 years. In Greenland, the temperature swings began roughly 45,000 years ago, persisting for 9,000 years.

Researchers said they are not certain why the temperature swings were not more closely synchronized, but suspect the lag is linked to how the oceans slowly absorb and redistribute heat around the globe.

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