Last Remnant of North American Ice Sheet Likely To Disappear In 300 Years

Credit: Jeff Schmaltz/NASA Earth Observatory.

Melting at a not-so-glacial pace

The Laurentide Ice Sheet covered millions of square miles of North America episodically since the start of the Quaternary Period roughly 2.5 million years ago. The ice sheet grew and shrank over time as Earth went through various climate cycles, but started retreating around 14,000 years ago when Earth’s climate warmed considerably. The receding ice stabilized about 2,000 years ago as the Barnes Ice Cap, a Delaware-sized chunk of ice on Baffin Island in the Canadian Arctic.

The Barnes Ice Cap remained the same size for the past 2,000 years until the effects of recent warming caught up with it.

Miller was doing research on Baffin Island in 2009 when he realized the ice cap had noticeably shrunk compared to images of it from a few decades ago. He then recruited Adrien Gilbert and Gwenn Flowers from Simon Fraser University to develop a model for determining how the ice cap might behave in the future.

Glaciologist Roger Hooke drilled a hole into the Barnes Ice Cap in 1978 and cased it with pipes to measure internal strain in the ice cap. When he finished, the pipes stuck out above the ice by about 0.5 m (1.5 feet). When Miller visited the ice cap in July 2010, at least 32 m (100 feet) of pipe lay on the ground (broken, as shown here). That would equate to an average of about 1 meter (3 feet) of ice lost per year.

In the new study, the researchers used the model to estimate when the ice cap would disappear under different greenhouse gas emissions scenarios. They found the ice cap is melting at all elevations and they project it to be gone within 200-500 years under all future emissions scenarios.

The researchers also collected rock samples around the ice cap to determine whether it had shrunk to a similar size at other times during its history.

They found it to be extremely rare for the Barnes Ice Cap to completely disappear, even during warm interglacial periods. The rock samples showed the ice cap shrunk to its current size only three times and disappeared no more than twice in the past 2.5 million years.

What’s most unusual about the ice cap’s situation is that it is now melting when the summer sun is weakest: Earth is currently as far from the sun as it can get during the Northern Hemisphere’s summer, Miller said.

This image shows Sagar Camp, the very summit of the Barnes Ice Cap and the remains of a glaciological camp occupied in 1963 that was hurriedly abandoned. The camp has been buried by snow ever since and never seen before now. That it has just melted out is confirmed by the poles still vertically in place in the ice.

“The geological data is pretty clear that [the Barnes Ice Cap] almost never disappears in the interglacial times,” he said. “The fact that it’s disappearing now says we’re really outside of what we’ve experienced in a two-and-a-half million-year interval and we’re entering a new climate state.”

The new study is yet another demonstration that humans are pushing the Earth system outside of conditions that have existed over the last million years, said Richard Alley, a glaciologist and climate scientist at Pennsylvania State University in State College, Pennsylvania, who was not connected to the study.

“We have very high scientific confidence that almost all the glaciers on Earth are shrinking, because of warming that is primarily being caused by our greenhouse gases,” he said.

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