Study: Greenland Ice Shrinking Quickly
Discovery.com, Aug. 11, 2006
Aug. 11, 2006 Using a space-based system to weigh the ice loss from all of Greenland, scientists say vast amounts of glacier ice is melting into the sea, boosting sea levels and raising the specter of rapid climate change in Europe.
The new measurements show that the southeastern Greenland ice sheet has been melting five times more quickly over the last two years than it did in the year and a half before that.
The study taps data from November 2005 back to April 2002, which is as far back as the measurements go with the Gravity Recovery and Climate Experiment (GRACE), a joint NASA-German Aerospace Center mission.
Earlier this year, another air- and space-based survey led by NASA's Jet Propulsion Laboratory (JPL) used images to track the physical changes throughout Greenland. That study revealed an abrupt northward glacial retreat, spilling vast amounts of ice into the sea.
The trend in disintegrating coastal glaciers was clocked at 300 miles (480 kilometers) over the last five years. That comes to about 54 cubic miles (225 cubic kilometers) of icy water lost each year and dumped into the North Atlantic.
"We came to roughly the same conclusion," said Jianli Chen of the University of Texas in Austin. Chen was the lead author of a new report on the GRACE survey in the current issue of Science Express.
The net rise in global sea level from added glacier water comes to 0.56 millimeters per year, which is about one-fiftieth of an inch, Chen reported. Put another way, if the melting in Greenland continued at the same rate until the year 2056, it would add another inch to the already rising sea level.
For comparison, sea level rise in the 20th century was between 4 and 8 inches, without any additional water from Greenland, according to recent studies.
A Colder Europe?
Gordon Hamilton, a Greenland ice expert at the University of Maine who commented on the JPL study earlier this year, said then that all this could mean trouble not just in terms of sea level rise worldwide. There are worries that all the ice entering the North Atlantic could slow down the global heat conveyor belt known as the thermohaline circulation.
In the North Atlantic, that conveyor belt plunges down, taking with it dense, salty, cool surface waters that have ridden the Gulf Stream north. There, the current turns south and re-circulates the dense water to warmer seas.
But more buoyant, fresh, glacial water in the North Atlantic could sit atop the surface waters, blocking the sinking and halting the entire conveyor belt. If that happened, the weather would turn much colder in Europe and warmer in the tropics. It's something that could be seen in the next decade, said Hamilton.
Using a specially developed data filtering technique, Chen's team has been able to calculate the ice mass lost in Greenland.
The GRACE mass measurements show 69 percent of the recent ice loss came from eastern Greenland. Out of the 57 cubic miles (239 cubic kilometers) of water added to the sea on average per year, 39 cubic miles (164 cubic kilometers) spilled out from the eastern coast. Of that amount, more than 50 percent came from ice from glacier in southeast Greenland, the researchers reported.
GRACE measures the mass changes from ice and water movements by using twin satellites that keep a very close watch on each other to detect the slightest gravitational bumps on any portion of their subject planet.
Since water has a lot of mass, and all mass exerts gravitational force, the twin GRACE satellites have been able to provide unprecedented measurements over the past few years of not only ice changes, but even seasonal changes in water from land to seas.
The satellite studies are confirming and extending the work of ice researchers who have been seeing dramatic changes recently in Greenland's glaciers. The work has made clear that there is a glaring flaw in all the climate models used to predict climate change: they have traditionally treated Greenland and Antarctica like large blocks of ice that slowly melt, explained Hamilton.
What's happening in Greenland now shows that the glaciers can apparently hit a climate threshold and disintegrate rapidly, not at all like a giant ice cube, he said.
The new GRACE work has also underscored at least one other flaw in all the climate models used to predict climate change: They have not included sudden changes in glaciers, said Eric Rignot, leader of the JPL study.
It's also not something that modelers are going to solve very quickly, Rignot added.
"It's not like they have another model up their sleeves," said Rignot.
In order to put glaciers in the models, they need to understand exactly how glaciers work, something nobody is certain about right now, he said.