ANTARCTIC: ice shelves breaking up due to decades of higher temperatures

Two ice shelves on the Antarctic Peninsula known as the Larsen B and Wilkins are in "full retreat" and have lost nearly 3,000 square kilometres of their total area in the last year, say scientists in Colorado and the United Kingdom.

Researchers at the University of Colorado at Boulder’s National Snow and Ice Data Centre and the British Antarctic Survey attribute the retreats to a regional warming trend. The trend has caused the annual melt season to increase by two to three weeks over the last 20 years, they said.

Satellite photos monitored by NSIDC show that the Larsen B ice shelf has continued to crumble after an initial small retreat in spring 1998. In a series of events that began in November 1998, an additional 1,714 square kilometres of shelf area caved away, said Research Associate Ted Scambos of CU-Boulder’s NSIDC.

On the opposite side of the peninsula, the Wilkins Ice Shelf retreated nearly 1,100 square kilometres in early March of last year, said Scambos.

Scientists looking at weather satellite imagery at that time suspected a break-up was underway and had their suspicions confirmed by radar satellite images.

“The radar images showed a large area of completely shattered ice, indicating an ice front 35 kilometres back from its previous extent,” said Scambos. “The sudden appearance of thousands of small icebergs suggests that the shelves are essentially broken up in place and then flushed out by storms or currents afterward.”

The British Antarctic Survey scientists had predicted one of these retreats, using computer models to demonstrate that the Larsen B was nearing its stability limit. With the small break-up observed last spring, the shelf had already retreated too far to continue to be supported by adjacent islands and shorelines.

Scientists at both institutes expected the two shelves to fail soon, but the current disintegration is occurring at an even faster rate than earlier break-ups gave reason to anticipate.

“We have evidence that the shelves in this area have been in retreat for 50 years, but those losses amounted to only about 7,000 square kilometres,” said David Vaughan, a researcher with the Ice and Climate Division of the British Antarctic Survey. “To have retreats totalling 3,000 square kilometres in a single year is clearly an escalation. Within a few years, much of the Wilkins ice shelf will likely be gone.”

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