Posted on 12/21/2005 8:39:29 AM PST by cogitator
In the first direct, comprehensive mass survey of the entire Greenland ice sheet, scientists using data from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (Grace) have measured a significant decrease in the mass of the Greenland ice cap. Grace is a satellite mission that measures movement in Earth's mass.
In an update to findings published in the journal Geophysical Research Letters, a team led by Dr. Isabella Velicogna of the University of Colorado, Boulder, found that Greenland's ice sheet decreased by 162 (plus or minus 22) cubic kilometers a year between 2002 and 2005. This is higher than all previously published estimates, and it represents a change of about 0.4 millimeters (.016 inches) per year to global sea level rise.
"Greenland hosts the largest reservoir of freshwater in the northern hemisphere, and any substantial changes in the mass of its ice sheet will affect global sea level, ocean circulation and climate," said Velicogna. "These results demonstrate Grace's ability to measure monthly mass changes for an entire ice sheet – a breakthrough in our ability to monitor such changes."
This figure shows the ice mass loss in Greenland as observed by GRACE over the period 2002-2005 measured in cubic kilometers per year. The ice mass loss observed by GRACE contributes about 0.4 mm/yr to global sea level rise. GRACE is continuing to observe Greenland and other polar ice caps to better understand these phenomena.
Other recent Grace-related research includes measurements of seasonal changes in the Antarctic Circumpolar Current, Earth's strongest ocean current system and a very significant force in global climate change. The Grace science team borrowed techniques from meteorologists who use atmospheric pressure to estimate winds. The team used Grace to estimate seasonal differences in ocean bottom pressure in order to estimate the intensity of the deep currents that move dense, cold water away from the Antarctic. This is the first study of seasonal variability along the full length of the Antarctic Circumpolar Current, which links the Atlantic, Pacific and Indian Oceans.
Dr. Victor Zlotnicki, an oceanographer at NASA's Jet Propulsion Laboratory in Pasadena, Calif., called the technique a first step in global satellite monitoring of deep ocean circulation, which moves heat and salt between ocean basins. This exchange of heat and salt links sea ice, sea surface temperature and other polar ocean properties with weather and climate-related phenomena such as El Ninos. Some scientific studies indicate that deep ocean circulation plays a significant role in global climate change.
The identical twin Grace satellites track minute changes in Earth's gravity field resulting from regional changes in Earth's mass. Masses of ice, air, water and solid Earth can be moved by weather patterns, seasonal change, climate change and even tectonic events, such as this past December's Sumatra earthquake. To track these changes, Grace measures micron-scale changes in the 220-kilometer (137-mile) separation between the two satellites, which fly in formation. To limit degradation of Grace's satellite antennas due to atomic oxygen exposure and thereby preserve mission life, a series of maneuvers was performed earlier this month to swap the satellites' relative positions in orbit.
In a demonstration of the satellites' sensitivity to minute changes in Earth's mass, the Grace science team reported that the satellites were able to measure the deformation of the Earth's crust caused by the December 2004 Sumatra earthquake. That quake changed Earth's gravity by one part in a billion.
This figure shows the effect of the December 2004 great Sumatra earthquake on the Earth's gravity field as observed by GRACE. The signal is expressed in terms of the relative acceleration of the two GRACE satellites, in this case a few nanometers per second squared, or about 1 billionth of the acceleration we experience everyday at the Earth's surface.
Dr. Byron Tapley, Grace principal investigator at the University of Texas at Austin, said that the detection of the Sumatra earthquake gravity signal illustrates Grace's ability to measure changes on and within Earth's surface. "Grace's measurements will add a global perspective to studies of large earthquakes and their impacts," said Tapley.
Grace is managed for NASA by JPL. The University of Texas Center for Space Research has overall mission responsibility. GeoForschungsZentrum Potsdam, or GFZ, Potsdam, Germany, is responsible for German mission elements. Science data processing, distribution, archiving and product verification are managed jointly by JPL, the University of Texas and GFZ.
Imagery related to these latest Grace findings may be viewed at: http://www.nasa.gov/vision/earth/lookingatearth/grace-images-20051220.html
Here's the Web site:
and an image of what the satellites look like (though they aren't this close):
Tell me it ain't so !
http://tinyurl.com/8q4up
Looks like Greenland will live up to its name.
And Vikings everywhere will rejoice that a thousand years of freezing will end.
Have Californians started snatching up exposed Greenland real estate yet?
Eric the Red returns !
"Greenland hosts the largest reservoir of freshwater in the northern hemisphere, and any substantial changes in the mass of its ice sheet will affect global sea level, ocean circulation and climate," said Velicogna."
Ummmm. Greenland didn't start out with a 'mass of ice' so even if the ice does melt, it will just revert back to where it came from (Water) without any appreciable rise in ocean levels. Just like there wasn't any appreciable 'decline' in Ocean levels when the ice formed.
I guess these 'scientists' forgot why it was named 'Greenland'.
The oceans have been higher in the past. Ask Florida (all of those phosphate deposits in the central part of the state formed underwater, for example). Colder global temperatures mean more deposition of precipitation as ice and snow on land, with the water derived from the oceans, lowering sea level.
So if ice and snow are accumulating eleswhere would they even bother to report it?
Only ten bucks away from saving the cute and snuggly polar bears!
We'll always have polar bears, thanks to the magic of cgi! ;)
It would have to happen to allow an answer for your question to be possible. And the ice mass would have to be pretty substantial; though it's big, I doubt Vatnajokull has enough (and Iceland's tectonic instability probably dominates gravity measurements over it, anyway).
"Greenland ice, like Antarctic ice, is above sea level (not floating in the oceans) so melting of the ice cap contributes to sea level rise."
That's why I used the term 'appreciable' in my statement.
The effect of the ice melting in Greenland wouldn't 'add' to the levels of the oceans, but more likely return them to their original levels before Greenland developed ice caps.
I agree, very cool!
"So if ice and snow are accumulating eleswhere would they even bother to report it?"
I actually did read somewhere a while back that they have detected increases in the artic ice pack in other areas where they had expected deceases.
This would not be a welcome outcome for coastal residents.
Um ... the Vikings named Greenland what they did, because it was an Ice Mass, and they called Iceland what they did, because it was actually livable ... they wanted anyone who heard about the islands to visit Greenland first, and in so doing, be scared to death of what they would find on Iceland, thereby leaving Iceland solely for Vikings.
The naming of both Greenland and Iceland was a plot completely based on Xenophobia - and Greenland has not been Green at any time when viewed by humans.
To add to that...
-1st year sees an increase
-2nd year is flat
-3rd year would be an increase except for the drop from 2004.6 to 2004.9 (a warm autumn)
My question is: where's the missing data? Notice that certain time intervals are tighter than others...
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