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Greenland ice cores show clues to climate change

22.06.2008
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Greenland ice cores show clues to climate change
By Michael Kahn

LONDON (Reuters) - An analysis of Greenland ice cores shows how atmospheric changes during the last ice age probably spurred wild temperature swings, a finding researchers said on Thursday could help predict future climate change.

The northern hemisphere emerged from the last ice age 14,700 years ago with about a 12 degree Celsius (22 Fahrenheit) spike in just 50 years before plunging back into icy conditions, then suddenly warming again 3,000 years later, the researchers said.

Rapid changes in atmospheric circulation -- such as where storms occurred or where the jet stream was -- coincided with each temperature shift, pointing to a potential trigger for severe climate change, the researchers said.

"We know abrupt climate change happens," said Jim White, a paleoclimatologist at the University of Colorado at Boulder in the United States, who worked on the study.

"We don't know why it happens and we don't know what to look for as a first early warning."

The researchers did not deal with current climate change, which may be rapid for humans but is actually slower than the abrupt changes they were looking into.

They did however say that the findings could give scientists clues to what may trigger sudden severe changes in the future.

The U.N. Climate Panel last year blamed human activities, led by burning of fossil fuels that release heat-trapping gases into the air, for global warming that may disrupt water and food supplies with ever-more droughts, floods and heatwaves.

Knowing more about past changes can help scientists and policymakers better prepare for future temperature rises that the U.N. panel predicts will range from 1.8 to 4 degrees C (3.2 to 7.2 degrees F) this century, the researchers said.

"It tells us that there are some tipping points in our climate system and that it can change very quickly," said Dorthe Dahl-Jensen of Denmark's University of Copenhagen, who led the study. "We should be aware that these abrupt climate changes can happen."

The team, which published its findings in the journal Science, analyzed ice cores drilled between 1998 and 2004 from a two-mile stretch in Greenland to chart past temperature and precipitation swings.

They found different amounts of dust blown across Greenland from around the world as evidence of changing atmospheric conditions right before the abrupt temperature changes, White said.

"We are beginning to tease apart the sequence of abrupt climate change," he said. "Since such rapid climate change would challenge even the most modern societies to successfully adapt, knowing how these massive events start and evolve is one of the most pressing climate questions we need to answer."

(Reporting by Michael Kahn; Editing by Will Dunham and Richard Meares)

source: REUTERS

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