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Tuesday, November 20, 2007

Going, going, gone? Greenland's ice sheet is no longer in balance.

"Inland ice as seen from a helicopter, near Ilulissat in Greenland."

Do you see the black spots in the photograph that are pockmarking the landscape? A few short years ago, they were not there. They are called "moulins," and they are holes in the ice sheet where the melt water disappears deep underground. Scientists have found that, via these channels, the melt water is travelling some 2 km to the bottom of the ice sheet to the bedrock where it collects. For example, a lake of water 500 meters deep was discovered under the Ilulissat Glacier. This immense amount of water is acting as a lubricant, causing the glacier to flow faster to the ocean. (The Ilulissat is possibly the fastest moving glacier in the world, discharging icebergs at a rate of some 2 meters per hour or 17,500 kilometers per year. However, this summer, an extraordinary event occurred -- in an hour and a half, 5 km surged out, proving that glaciers need not move along at a snail's pace.) The ice sheets and the glaciers are moving so fast now that annual snowfall cannot replace the amount of ice being lost, as it had been doing up until recent years.

Now, the old logic was this: The Greenland Ice Sheet is so thick that it will just melt on the top, and so this will take thousands of years. Sounds reasonable to me. No one could have guessed that the melt water would find its way to the bottom of the ice. Then, the moulins began to appear. Initially, there were not so many of them. Just tens of them. Then hundreds. Now, there are thousands of them. This all occurred within a decade, which on the geological timescale, is about a microsecond or less.

And, would you believe that Greenland is not the most serious problem in this regard? No, no, the more serious problem is down there in Antarctica. That thing can't melt, can it? Too cold down there, isn't it? And it is snowing a lot more down there, too, isn't it, so, in fact, the ice sheet down there is increasing, not decreasing, isn't it?

Ah, but did you know that the bedrock on which Antarctica's western ice shelf is resting just happens to be way the hell under sea level (see image)? Hmm, so what? Well, we know that the temperature of the ocean water that moves past it is rising. Not only this, but the speed of the waves is increasing, as is the speed of the winds. But, you might say, this ice is already underwater, and ice takes up more space than water, so if it melts, the sea level will go down, not up, won't it? Good thinking -- if not for that fact that if the ice shelf breaks off and floats away, there will be nothing left to buttress the ice sheet behind it, and it will be highly likely to move at a greatly accelerated pace to the ocean -- just like pulling the cork out of a champagne bottle (perhaps that is exaggerating a bit, but I think you get the picture).

Below, from JPL: "NASA's QuikScat satellite detected extensive areas of snowmelt, shown in yellow and red, in west Antarctica in January 2005." Click on the image to enlarge it.

Left: a graphic rendition of the layers of Antarctica, by JPL. Click on the graphic to enlarge it.

YouTube videos of NASA's Dr. James Hansen explaining the problems:

Below is a badly written article about the recent findings on the melting of the Greenland ice sheet.

Greenland ice cap melting faster than expected

COPENHAGEN (AFP) — The ice cap in the northern hemisphere is melting a lot more rapidly that scientists thought, according to new research published Thursday by the Danish National Space Center.

"Until 2004, the glacier mass in the southeastern part of the island lost about 50 to 100 cubic kilometres (12 to 24 cubic miles) per year. After this date, the melting rate accelerated to 300 cubic kilometres per year. It's a jump of 400 percent, which is very worrying," National Space Center head researcher and project chief Abbas Khan told AFP.

The ice cap, located in Greenland, is melting four times more rapidly than at the beginning of the decade according to the study. Glaciers in southeastern Greenland release icebergs into the sea, corresponding to a giant ice cube measuring 6.5 kilometres (4 miles) per side. (BLOGGER'S NOTE: the author of this news article neglected to mention that this 6.5 cubic kilometers is the total volume of the glaciers' outflow per year, and the melting figures are for the ice sheet itself -- what the glaciers output is in addition to this melting of the ice sheet.)

"It's an alarming development," Khan said. "We do not know if it is due to global warming or other factors."

The results of the study were made in conjunction with US-based University of Colorado and published Thursday on an online edition of Geophysical Research Letters magazine. (BLOGGER'S NOTE: Geophysical Research Letters is not a "magazine." It is an academic journal containing peer-reviewed, scientific research articles.)

The researchers measured ice melt with ultra-sensitive Global Positioning Systems (GPS) stations located in the mountains and along the ice cap.

The measurements indicated that the mountains hugging glaciers in the southeastern part of Greenland rose four to five centimetres (1.5 to two inches) per year, and that the banks of the glaciers thinned 100 metres per year. (BLOGGER'S NOTE: It would have been nice if the author had mentioned the banks' surface area. The mountains are "rising" because they had been "depressed" by the weight of the ice. So much ice is melting that the bedrock underneath the ice sheet is "springing" back up.)

The Greenland ice cap measures 1.7 million square kilometres (656,000 square miles) and is 3.2 kilometres (two miles) thick.

I found the proposed declaration, below, on a website of a global climate change skeptic. He attributed its authorship to Dr. James Hansen. He accuses Dr. Hansen of being an advocate and not a scientist. Excuse me, but where is it written that scientists cannot be advocates. Jeez! If they cannot be advocates for the Earth, then who can?

Declaration for our presidential candidates to sign:

"Whereas, the climate system is nearing tipping points with likely devastating consequences for much of creation;

Whereas, the responsibility of the United States for excess CO2 in the air exceeds that of any other nation by more than a factor of three;

Whereas, the rest of the world cannot be expected to take needed actions until the United States exercises responsibility and leadership;

Whereas, some lawmakers and executives in the United States appear to be unduly swayed by special interests;

It therefore becomes important for citizens to be keenly aware of the position regarding global warming of all candidates for election."

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