NASA eyeballs glacial melt in Greenland

By Andrew Freedman

* Several rain chances this week: Full Forecast *



Satellite images from DigitalGlobe, via NASA, showing the recent breakup of part of the Jakobsahvn Isbrae glacier.

The Jakobshavn Isbrae glacier, one of the largest glaciers in Greenland, swiftly lost a 2.7-square mile chunk of ice between July 6 and 7, NASA announced late last week. The ice loss pushed the point where the glacier meets the ocean, known as the "calving front," nearly one mile farther inland in a single day. According to the space agency, the new calving front location is the farthest inland on record.

Events such as this one are not unusual, but rarely do scientists see them unfold in near real-time. Researchers working with the space agency spotted the rapid ice loss using high-resolution satellite imagery. Two such images tell the story. In the first image (above), a rift, which looks like a narrow horizontal line indicated by the red arrow, can be seen developing in the glacier. In the next image, taken a day later, the ice below the rift has collapsed into the sea and the location of the calving front has retreated.

Why does this glacier matter to me, you ask?

The short answer: sea level, although this particular event won't raise the level of the Potomac or any other U.S. river anytime soon. Unlike the loss of sea ice, glacial melting causes sea level to increase, and the fate of glaciers like this one will play a key role in determining by how much sea level increases.

The Jakobshavn Isbrae is what is known as an outlet glacier, which the National Snow and Ice Data Center defines as "a valley glacier which drains an inland ice sheet or ice cap and flows through a gap in peripheral mountains." In other words, it serves as a drainage pipe from the land ice into the ocean. According to NASA, the Jakobshavn Isbrae, which is located in western Greenland at about 69 degrees north latitude, is the largest outlet glacier in Greenland, draining 6.5 percent of Greenland's ice sheet area.

Scientists at NASA, NOAA and other agencies are keeping close tabs on Greenland's ice due to its significant ramifications for global sea level rise. If the entire Greenland ice sheet were to melt (a process that would likely take several centuries to play out, even with more global warming than we've already seen), sea level would rise by as much as an estimated 23 feet globally. NASA reports that "as much as 10 percent of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere."

Interestingly, this particular glacier has been retreating especially rapidly in recent years. As the below image shows, the ice front receded more 27 miles in 160 years, but in recent years the ice loss rate has increased, with six miles of retreat observed in just the past decade.



Location of the successive calving fronts of the Jakobshavn Isbrae glacier between 1851 and 2009. Credit: NASA. Enlarge image.

Recent studies have found that warming ocean temperatures may be responsible for much of the increased melting of Greenland's outlet glaciers, and this may be accelerating the melting of the larger Greenland ice sheet. For example, one study published in Nature Geoscience in February concluded that glaciers in west Greenland are melting 100 times faster at their undersea end points than on the surface.

This event would support the ocean-driven melt theory, according to a NASA ice specialist.

"While there have been ice breakouts of this magnitude from Jakonbshavn and other glaciers in the past, this event is unusual because it occurs on the heels of a warm winter that saw no sea ice form in the surrounding bay," said Thomas Wagner, cryospheric program scientist at NASA Headquarters, in a press release. "While the exact relationship between these events is being determined, it lends credence to the theory that warming of the oceans is responsible for the ice loss observed throughout Greenland and Antarctica."