NOT-SO-GLACIAL RETREAT: New findings show how Greenland's meltdown has proceeded in fits and starts, the latest burst coming between 2005 and 2010.
Image: Anders A. Bjork, Natural History Museum of Denmark
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Future sea levels depend on how much and how quickly the massive ice sheet covering Greenland melts. Satellite-based measurements have revealed that Greenland's glaciers are melting and on the move—and the ice sheet has lost some 36 billion metric tons of ice each year in recent years from its northwestern flank. Thanks to weird weather, nearly the entire ice-covered surface of the world's largest island melted for a period this year.
View a slide show of Greenland's meltdown.
Now aerial photographs reveal that this loss of ice is driven more by the accelerated breakdown of ice sheets where they reach the sea (and a subsequent speed up in outflowing ice) than the difference between snowfall and such surface melt. Danish scientists identified two periods of ice loss—1985 to 1993 and 2005 to 2010—that have been responsible for the bulk of Greenland's meltdown. The research appears in Science on August 3.
In fact, outlet glaciers have receded by more than 100 meters across the northwestern edge of the ice sheet. For example, the Sverdrup Glacier retreated by 1,000 meters between 2005 and 2010, also losing 80 meters in height. Roughly 80 percent of the ice loss seems to be attributable to this kind of loss at glacier outlets rather than the glacier as a whole. The cause may be warmer ocean temperatures, although sea-surface temperature measurements are lacking to definitely prove that hypothesis.
Aerial maps that extend the record back as far as the 1930s may help further refine scientists' understanding of this meltdown in the north—and its implications for how much the seas will rise in coming decades.
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12 Comments
Add Comment"Roughly 80 percent of the ice loss seems to be attributable to this kind of loss at glacier outlets rather than the glacier as a whole. The cause may be warmer ocean temperatures, although sea-surface temperature measurements are lacking to definitely prove that hypothesis."
Reply | Report Abuse | Link to thisAs the ice wrinkles and cracks the albedo changes too. Less sunlight is reflected. Melt water reduces the insulation factor of fresh snow on the surface and transports surface heat throughout the glacier by peculation. Friction creates heat in the faster moving ice. Warmer ocean water infiltrates the melt water under the ice. It's a cumulative effect.
What many skeptics don't understand about global warming is that the difference in temperature between frozen water and liquid water is less then one degree. Once it melts, water transports heat much faster then the frozen ice did.
An increase of just one degree can melt thousands of square miles of arctic and glacial ice. Imagine what a 10 degree change in the arctic regions can do.
People barely notice a difference of a few degrees, but mother nature is much more sensitive. If the changes take place over millenniums, nature can adapt, but if it happens in a matter of centuries or worse yet decades, the effects can be catastrophic.
"peculation" ? Pretty funky spell checker. Oh well, it took nearly four years to get Obama in the spell check database.
Reply | Report Abuse | Link to thisFlea:
Reply | Report Abuse | Link to thisFrom a thermodynamics standpoint, water that has just gone through the transformation of a solid to a liquid (given that just enough energy was introduced it to cause it to melt) is the same temperature that it was just prior to the change of state; 32 deg. F/ 0 deg. C. Both ice and liquid water can be exactly the same temp.
And the heat created by friction of "faster moving ice" would be immeasurable. The point that is made regarding more liquid water in a glacial "system" (for lack of a better word) is that the glacier would move more quickly downhill to the ocean, because of the lubricative effect of increased liquid H2O.
sorry, "to it"
Reply | Report Abuse | Link to thisOnly a F00L would read politics into pure science. I am sure you are not that kind of person?
Reply | Report Abuse | Link to this"Both ice and liquid water can be exactly the same temp."
Reply | Report Abuse | Link to thisLet's not get nit picky. You know exactly what I was saying. When the ice melts the water temperature continues to rise whether you think so or not.
As for friction creating heat, I never said it was not negligible, however that may not be altogether true either.
I still say the melting is due to a cumulative effect of all the factors I mentioned and perhaps a few others I did not.
"Only a F00L would read politics into pure science. I am sure you are not that kind of person?"
Reply | Report Abuse | Link to thisAt least a fool like me knows the difference between an "o" and a zero.
Anyway, pure science and politics have been jousting for as long as man has formed governments. I won't even get into the follies created by religion.
Re: "Thanks to weird weather, nearly the entire ice-covered surface of the world's largest island melted for a period this year."
Reply | Report Abuse | Link to thisThe statement prompts to me to ask:
How long was the period of melt?
What is the current status of the melt?
That's a good question Bill. Being the middle of summer and considering it has happened before it is likely not going to stay like that for long.
Reply | Report Abuse | Link to thisThe issue is why it happened this time, and in the past. There is no proof that even if it happens every 150 years or so, as some scientist have hypothesized, the cause is the same each time and unless we study all the data not just ice core samples, perhaps there is something more to be learned.
If however it begins to happen more regularly then it would definitely point to a trend caused by man this time.
I would be interested to know the duration of past events like this and the correlation to other natural phenomena like extreme volcanic activity or massive solar storms.
It is apparently not due to the Milankovitch cycles as they do not correspond to any 150 year cycle. I suspect that the 150 year cycle is more likely a coincidence that has not yet been fully verified at any rate.
singing flea,
Reply | Report Abuse | Link to thisPerhaps the adage, “Time will tell,” applies in this case.
Most glacier meltwater disapears into crevasses and ends up in deep underground rivers where it is difficult to quantify since the resurgences are well below sea level.
Reply | Report Abuse | Link to thisAttempts to descend into even quite modest sinks have failed as the air is irrespirable because of ice dust. These rivers are kilometers down and hundreds of miles long and must represent considerable quantities of meltwater. So far research into them has been inadequate.
If you recall, the time the melting was announced was about a week after the summer heat wave broke over the Midwest. I presume that that heat dome found its way over Greenland. I believe that such an event is more a product of unusual weather that occurs occasionally. Its not really a direct product of GW.
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