Antarctic Peninsula now almost as warm as 12,000 years ago

Reconstructing temperature from ice

Using the ice core, Mulvaney and his colleagues were able to look far back into the temperature history of the region, and compare that with records for the collapsed ice shelves, drawn from the marine sediments deposited below them.

To reconstruct the record of temperature, they looked at the ratio of heavier to lighter versions of hydrogen in the ice core from James Ross Island. Warmer temperatures allow for the incorporation of more heavy atoms, Mulvaney explained.

Their reconstruction revealed that after the last ice age ended 12,000 years ago, the climate became slightly warmer than it is today. After being stable near modern levels for millennia, a cooling trend, which included some warming spikes, began about 2,500 years ago, ending about 600 years ago. During this time, the ice shelves along the northern peninsula re-established themselves.

Between 100 and 50 years ago, this warming trend accelerated, taking the peninsula toward temperatures last seen 12,000 years ago, Mulvaney told LiveScience.

"This means some of those ice shelves farther south are starting to look vulnerable," he said.

The loss of more ice shelves has implications for sea level. The ice shelves themselves don't cause sea level to rise when they disintegrate, but in their absence, ice from the continent flows more quickly into the ocean, contributing to rising sea levels.

"The Antarctic Peninsula is small, it's not adding a lot to sea-level rise. It's more symptomatic of the changes taking place in Antarctica,” Mulvaney said.

Observations from a number of Antarctic ice shelves elsewhere show signs of the thinning responsible for the collapse of the northernmost ice shelves as well as the Wilkins Ice Shelf on the west side of the peninsula, according to Mulvaney.  

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