One of the world's most rapidly flowing glaciers may have just set another record, and it's not one not that bodes well for low-lying coastal cities and nations around the world, which are vulnerable to sea level rise.
During the past month, a NASA satellite as well as European satellites captured images showing a sudden loss of ice, also known as a calving event (or in this case, possibly multiple events) from Greenland's Jakobshavn Isbrae Glacier between July 31 and August 19, 2015.
Images posted on the Arctic sea ice blog, which closely tracks developments in the Arctic, narrowed the timeline of the ice loss to between August 14 and 16. This is backed up by observations from satellites operated by the European Space Agency, or ESA.
NASA satellite images on July 31, 2015 (first) and then on August 16, 2015 (second), showing the movement of the calving front further inland, or to the right.
It's unclear if this sudden ice loss set a record, according to NASA.
"Some observers have speculated that the area of ice lost could be the largest on record. However, these estimates are preliminary, and satellite images from before and after an event cannot show whether the ice was lost all at once, or in a series of smaller events," NASA stated on its Earth Observatory website.
Nevertheless, the event was significant because it once again signaled the rapidly changing ice conditions in Greenland as air and ocean temperatures increase.
According to the ESA, the calving front now appears to be located at its most easterly location since monitoring began in the mid-1880s. Data from two ESA satellites, known as Sentinel 1A and 2A, show that the glacier lost a total area of 12.5 square kilometers, or about 4.8 square miles, in this calving event.
"Assuming the ice is about 1400 meters deep, this equates a volume of 17.5 cubic km — which could cover the whole of Manhattan Island by a layer of ice about 300 m thick," the agency stated on its website.
In other words, the ESA data shows that the ice that broke off in the latest calving event would be sufficient to cover Manhattan in nearly 1,000 feet of ice.
Faster ice loss
“The calving events of Jakobshavn are becoming more spectacular with time, and I am in awe with the calving speed and retreat rate of this glacier,” said Eric Rignot, a glaciologist at NASA's Jet Propulsion Laboratory, in a statement.
Studies have shown that Jakobshavn's summer flow speeds have sped up dramatically during the past few decades, and this one glacier was responsible for raising global average sea level by about 1 millimeter, or .04 inches, between 2000 and 2010, a figure that is likely to increase as global warming continues.
Jakobshavn retreated more than 25 miles between 1850 and 2010, and since 2010, the retreat has sped up dramatically.
In fact, a 2014 study published in the open access journal Cryosphere found that the glacier was moving at average speeds of about half-a-mile per year, or more than 150 feet per day, during the summers of 2012 and 2013.
“We are now seeing summer speeds more than four times what they were in the 1990s, on a glacier which at that time was believed to be one of the fastest, if not the fastest, glacier in Greenland,” said study author Ian Joughin, a glaciologist at the University of Washington, in a press release when that study was published.
Jakobshavn is not just any old glacier. It's important because it helps drain a large portion of the Greenland Ice Sheet. As it moves faster, it transports more ice at a faster rate into the sea, adding to sea level rise.
"This glacier alone could contribute more to sea level rise than any other single feature in the Northern Hemisphere," NASA stated on its website.
According to the ESA, this glacier drains 6.5% of the Greenland ice sheet, producing around 10% its icebergs. The agency said in a statement that this totals about 35 billion tonnes of ice calved off each year.
Given its rapid movement, Jakobshavn has been the scene of several famous large calving events, including one in July 2010, when the glacier shed a 2.7 square-mile chunk of ice in the span of 24 hours, pushing the calving front one mile further inland.
Major calving event at Jakobshavn isbrae, Greenland on Aug 14, 2015. The glacier retreat is galoping inland. http://t.co/Eb28J79f6v
— Eric Rignot (@erignot) August 18, 2015
Scientists think the ice loss has sped up so much because of a combination of warmer air temperatures during the short Greenland summers, as well as warmer ocean temperatures, which are undermining the glacier's ice tongue — the part that sticks out into the ocean and serves as a brake to all the ice behind it — speeding up the ice's movement into the sea.
Climate scientists have raised alarms about such outlet glaciers in recent years, both in Greenland and Antarctica, because when they become unstable and move more swiftly into the sea, the ice they hold back begins to move as well, endangering low-lying coastal cities and countries around the world.
Massive calving event seen on the Ilulissat Glacier in western Greenland in 2008, as shown in the film "Chasing Ice."
In the case of Jakobshavn, as the ice has retreated, the calving front has reached a deeper area of the fjord, and this has further sped up the melting.
The calving front is now located in an area where the base of solid rock that it rests upon is more than 1,000 feet below sea level, making the glacier especially vulnerable to intrusions from relatively mild water as ocean currents in the regions change in response to global warming and other factors.
“What is important is that the ice front, or calving front, keeps retreating inland at galloping speeds,” said NASA's Rignot, in a statement.
Worries about Greenland's stability
Greenland is the world's largest island, extending more than 1,200 miles from its southern to northernmost points, and if all of its ice were to melt — which would likely take many centuries — the oceans would rise by more than 20 feet.
Already, the melting of the Greenland ice sheet is one of the largest contributors to global sea level rise, accounting for about .02 inches of the .13 inches per year global average sea level rise (local rates of sea level rise vary significantly).
A study published last year found that glaciers long thought to be stable and resistant to rapid melting in northeastern Greenland, which tends to be colder than the area where Jakobshavn is, may nonetheless share the latter glacier's fate.
The study, published in the journal Nature Climate Change, found that three glaciers holding back a vast ice stream in northeast Greenland, are now thinning and moving more rapidly into the sea.
The most recent report from the U.N. Intergovernmental Panel on Climate Change (IPCC) found that global average sea level is likely to increase by 10.2 to 32 inches by the year 2100, with a highest emissions scenario showing a sea level rise of between 21 and 38 inches by the end of the century if greenhouse gas emissions continue to rise unabated.
The recent observations from Jakobshavn and the glaciers in northeast Greenland, plus data showing the West Antarctic Ice Sheet may be increasingly unstable, suggest that sea level rise is likely to be at the higher end of the predicted range, if not significantly higher than that.
average Greenland ice reflectivity rockets back to normal after dark July pic.twitter.com/uSGAkB4an6
— Jason Box (@climate_ice) August 17, 2015
As for this calving event, it's not yet clear where it falls in the recent history of Jakobshavn.
“Overall, I don’t think that they really can nail the ‘largest’ [calving event] or not,” wrote Richard Alley, a glaciologist at Pennsylvania State University, in an email to the Washington Post.
Alley told the Post that the calving event may have occurred in several smaller installments, keeping it from setting a record for the single largest observed calving event.
“I wouldn’t get too excited on this, even though it is not good news,” he wrote.