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Posted at 03:17 PM ET, 07/17/2012

Ice island twice as big as Manhattan breaks off Greenland glacier


Image of new ice island recently broken off from Petermann Glacier (University of Delaware)
A chunk of ice 46 square miles in area has parted from the Petermann glacier, which feeds into Nares straight along the northwest coast of Greenland. It split off July 16 according to researchers at the University of Delaware and Canadian Ice Service.

This is the second major calving event for the Petermann glacier in the last three years. In August 2010, an ice island four times the size of Manhattan (an area of roughly 97 square miles) separated from the glacier.


Satellite image showing ice island which broke off Petermann glacier in 2010 (NASA)
Polar researcher Jason Box of Ohio State University noted the 2010 calving was “the largest in the observational record for Greenland.” He correctly predicted last summer that the piece which just broke off, about half the size, was on the brink.

While this latest piece of ice is smaller than the 2010 version, it “brings the glacier’s terminus [end point] to a location where it has not been for at least 150 years,” said Andreas Muenchow, a researcher at the University of Delaware.

“The Greenland ice sheet as a whole is shrinking, melting and reducing in size as the result of globally changing air and ocean temperatures and associated changes in circulation patterns in both the ocean and atmosphere,” he said.

Air temperatures in the region have warmed more than 2.5 degrees C (4.5 degrees F) since 1987, a rate 5 times faster than the rest of the world, Muenchow said. But he cautioned against directly linking air temperatures to the glacier’s behavior:

“[A]ir temperatures have little effect on this glacier; ocean temperatures do, and our ocean temperature time series are only five to eight years long — too short to establish a robust warming signal.”.

The New York Times presented a similar view last August, speaking to Jason Box and other scientists:

Dr. Box finds a drastic increase in sea-surface temperatures in the region, and a sharp decline in sea ice. Scientists suspect that warmer water is circulating under Greenland’s floating ice shelves and causing them to weaken. But given the dearth of measurements from beneath Petermann, they do not have hard proof that is what happened in this case.

Although not directly connected to the calving glaciers, temperatures atop the Greenland ice sheet have been unusually warm for much of the summer.


The pressure at upper levels over the last 30 days have been much above normal over Greenland. Green and yellow shades indicate these areas, and illustrate the heat dome. (NOAA)
A strong, sprawling area of high pressure at upper levels of the atmosphere - or heat dome - has covered the country (hat tip: Planet3.org).

In response to warming temperatures, measurements show the ice sheet has become darker and less reflective, absorbing more heat.

Data from NASA and Ohio State show a measure of reflectance of the ice show, known as albedo, has dipped to record low levels (since 2000, when measurements began) this summer.


Greenland ice sheet “albedo” in 2012 (black line) compared to past years since 2000. Albedo indicates how reflective the ice sheet is. (NASA/Ohio State)

What are the future implications of an ice sheet absorbing more and more heat?

Ohio State’s Box predicts unprecedented melting (relative to the modern record). He told the Hot Topic (global warming and the future of New Zealand) blog:

What I expect we will see if these low albedo conditions persist is 100% surface melting over the ice sheet. This would be a first in observations. It may not happen this year, but the trajectory the ice sheet is on, along with amplified Arctic warming, will have the ice sheet responding by melting more and more

Related links:

Ice Island Calves off Petermann Glacier (NASA, 2010)

Petermann Glacier before-after-photos 2010-2011 (Ohio State)

Documenting a Collapsing Ice Shelf (NY Times, 2011)

Glacial Change Ain’t What It Used To Be: Petermann Calves Another Huge Chunk of Greenland Ice (Think Progress, 2012)

Greenland glacier loses ice (University of Delaware, 2012)

Petermann calves again (Sea Ice Blog, 2012)

By  |  03:17 PM ET, 07/17/2012

Categories:  Latest, Climate Change

 
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