Antarctic Iceberg Flotilla Caused Huge Sea-Level Rise

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Antarctica's melting glaciers launched so many icebergs into the ocean 14,600 years ago that sea level rose 6.5 feet (2 meters) in just 100 years, a new study reports. The results are the first direct evidence for dramatic melting in Antarctica's past — the same as predictions for its future.

"The Antarctic Ice Sheet had been considered to be fairly stable and kind of boring in how it retreated," said study co-author Peter Clark, a climate scientist at Oregon State University. "This shows the ice sheet is much more dynamic and episodic, and contributes to rapid sea-level rise."

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Natural climate warming caused huge ice sheet collapses in Antarctica eight times in the past 20,000 years, according to the study, published today (May 28) in the journal Nature. Measurements at Antarctica's biggest glaciers, such as Thwaites and Pine Island, suggest the ice sheet is on the brink of a similar massive retreat. [Photos: Antarctica's Pine Island Glacier Cracks]

Antarctica's glaciers have been shrinking since the last great ice age ended about 22,000 years ago. This warming was triggered by wobbles in Earth's orbit, combined with warming boosts from the ocean and atmosphere, such as temperature increases from the release of carbon dioxide gas.

The last big iceberg release was 9,000 years ago, and the pace of glacial retreat slowed in Antarctica until the 20th century, when melting picked up again with man-made climate change. Current models suggest global warming has again tipped the Antarctic Ice Sheet into sudden, rapid shrinking.

But models that forecast the future of Antarctica's Ice Sheet based on its past behavior actually had little hard evidence for making comparisons until now, Clark said.