Redefining ‘Glacial Pace': Greenland’s Fastest-Moving Glacier Sets New Speed Record Of 150 Feet A Day
"Redefining ‘Glacial Pace': Greenland’s Fastest-Moving Glacier Sets New Speed Record Of 150 Feet A Day"
CREDIT: NASA/Tim Williams
Climate change is remaking our vocabulary. The permafrost ain’t perma thanks to global warming. The Everglades ain’t forever thanks to sea level rise.
“Glacial pace” used to mean “suggesting the extreme slowness of a glacier.” But one can hardly use that term when scientists who track warming-induced glacial movement have found that the world’s fastest glacier is speeding up to record levels — and may more than triple its speed again in coming decades:
“The latest observations of Jakobshavn Glacier show that Greenland’s largest glacier is moving ice from land into the ocean at a speed that appears to be the fastest ever recorded … in summer of 2012 … more than 10.5 miles (17 kilometers) per year, or more than 150 feet (46 meters) per day. These appear to be the fastest flow rates recorded for any glacier or ice stream in Greenland or Antarctica.”
Why is this happening? “The calving front of the glacier is now located in a deeper area of the fjord, where the underlying rock bed is about 0.8 miles (1.3 km) below sea level, which the scientists say explains the record speeds.” But as fast as Jakobshavn is moving now, the study in The Cryosphere predicts it could well speed up even more:
While the current increase in annual discharge flux remains less than a factor of three, the increase plausibly could reach or exceed a factor of 10 within decades. This is a consequence of the fact that retreat into deeper water increases both speed and thickness of the terminus.
Coincidentally Jakobshavn “is widely believed to be the glacier that produced the large iceberg that sank the Titanic in 1912.”
Also coincidentally, a new study in the journal Nature explains why “Over the past two decades, ice loss from the Greenland Ice Sheet increased four-fold contributing to one-quarter of global sea level rise”:
The Greenland Ice Sheet is a 1.7 million-square-kilometer, 2-mile thick layer of ice that covers Greenland. At its edge, glaciers that drain the ice sheet plunge into coastal fjords that are over 600 meters deep -– thus exposing the ice sheet edges to contact with the ocean. The waters of the North Atlantic Ocean, which surround southern Greenland, are presently the warmest they have been in the past 100 years. This warming is due to natural climate variability and human induced climate change, and climate models project that it will keep getting warmer.
The warming water leads to “submarine melting,” whereby the ice sheet melts faster wherever the glaciers extend into the ocean. But there is much more going on than a warming ocean, as explained in the review paper by physical oceanographers Fiamma Straneo at Woods Hole Oceanographic Institution and Patrick Heimbach at MIT:
A warmer atmosphere is resulting in increased surface melting above the ice sheet, and this runoff too enhances submarine melting. Surface melt water falls through cracks in the glacier creating a freshwater river that rushes out into the ocean at the base of the glacier, sometimes 600 meters (1,800 feet) below sea level. This river mixes rapidly with the dense, salty seawater, contributing to the heat transfer from the ocean to the ice, resulting in even more submarine melting beneath the sea surface.
The lead author helpfully provides a metaphor to help explain what is going on:
Straneo describes it as follows: “If you put an ice cube in a glass of water and don’t touch it, it will take a few minutes to melt. But if you stir it, you are making it easier for the warmer water to reach the ice surface, which makes the ice melt faster.”
In a warming climate when both the ocean and atmosphere are warming, Straneo says, “it’s like a double hit on submarine melting. It increases because the ocean is warming, but also because there’s increased surface melt that flows to the ice-ocean boundary and increases submarine melting even more.”
Imagine how fast Greenland will be melting if we stay near our current path of carbon pollution emissions and the Arctic warms some 20°F. With the warming we’ve had so far, glaciers are vanishing everywhere right before our eyes. Glacier National Park is projected to go glacier-free within a decade or two and Himalayan glaciers are being “decapitated.” Bolivia’s 18,000 year-old Chacaltaya glacier is gone.
The whole idea of “glacial” change as a metaphor for change too slow to see will vanish in a world where glaciers are shrinking so fast that you can actually watch them retreat and then disappear. Greenland’s glaciers are moving faster than America’s climate policy, which, I suppose, isn’t saying that much….