Greenland ice sheet future grim, says Aberystwyth study
Dr Alun Hubbard and his team camped about 70 miles (112 km) up the ice sheet in GreenlandA glaciologist is warning that the Greenland ice sheet is "retreating and thinning extensively" after a year of record-breaking high temperatures.
by BBC, December 29, 2010
Dr Alun Hubbard of Aberystwyth University says its future is "grim" but disputes claims by other experts that it could collapse within 50 years.
He maintains it would be at least 100 to 1,000 years before it "potentially passes any point of no return leading to any widespread collapse."
Large melt lakes form on the Greenland ice sheetDr Hubbard and his team have been analysing the results of a summer-long expedition.
His team of 15 from Aberystwyth and Swansea universities spent 5 months on the ice sheet from the beginning of May.
The group camped about 70 miles (112 km) up the sheet, and measured the thickness, speed, climate, and other vital statistics using radar, seismic and geophysical equipment.
They found rising temperatures had caused extensive melting in new upper parts of the ice sheet in this "very sensitive polar region of the planet."
This has generated at least double the quantity of melt water, compared with 2009, which runs off the ice sheet into the Atlantic and Arctic oceans.
There are fears the melting of the entire sheet could raise sea levels globally by about 7m (20 ft), and a study last year found it was losing its mass faster than in previous years.
Dr Hubbard said his expedition had proved enhanced melting was more than just replenishing the oceans, it was now "directly contributing to global sea-level rise".
He said global warming -- at least local Greenland warming -- was "worse than ever."
"This year was another record-breaking year marked by very warm temperatures across Greenland and the Arctic," he said.
"This warming enhanced and extended melting into new northern and upper parts of the ice sheet generating huge quantities -- at least double that compared with the previous year -- of melt water which runs off the ice sheet into the ocean."
Dr Hubbard has spent 4 years researching the effects of climate change on the country. He has also worked on other glaciers and spent 5 years working in Antarctica before the Greenland project started.
The team of scientists and students monitored the build up and drainage of a series of large melt lakes -- up to 5 miles (8 km) across -- which form on the ice sheet surface during the summer and can drain rapidly to the bed through more than 1000m of ice.
He said the effect of this rapid drainage was to "lubricate and hydraulically lift up" the base of the ice sheet, "overcoming friction with underlying rock," thereby allowing the sheet to flow much faster.
"It's much like the ice is suddenly aquaplaning or slipping on a banana skin," he explained.
"What we observed using methods borrowed from earthquake monitoring, is that the ice sheet slides and accelerates massively when these lakes drain, but the effect is relatively short lived and that the flow does regulate as further melt water drains to the bed."
His work is part of a wider project involving researchers from Bristol, Cambridge, Edinburgh, Denmark, Sweden, the Netherlands, Germany and the United States.
Dr Hubbard and his team plan to return to the Greenland ice sheet next year to study the effect that reduced winter sea ice has on ice sheet flow and ice berg calving.
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3 comments:
"He said the effect of this rapid drainage was to "lubricate and hydraulically lift up" the base of the ice sheet, "overcoming friction with underlying rock," thereby allowing the sheet to flow much faster."
If the water is draining rapidly, there will be very little hydraulic pressure on the bottom of the ice, certainly much less pressure than the weight of the ice itself. There is no way this will overcome friction with the underlying rock. It is nonsense.
Well, first, let us not assume that the reporter quoted him correctly.
Next, of course he must be referring to only very localized areas of the ice sheet near a glacier.
Then, some of these lakes drain enormous amounts of water very rapidly, and I think there is some recent research that this water can give very short-term spurts in the speed of the glacier at some points along its stream.
So, as far as I can see, the effect of rapid drainage would depend on that individual glacier's particular characteristics.
One thing I think we can say is that there is a good chance that there will be some kind of effect, however short-term or small.
There is another thing to consider. If you observe the glacier lakes and the ice sheet melt water lakes, they grow over time and sometimes they simply all drain out at the same time over a period of just a couple of days. That is a huge amount of water.
As the temperatures increase over Greenland, the lakes are growing dramatically in number and size.
You can check out the images here (you will need to change the day number in the link -- this link is for Jan. 16, 2011):
http://rapidfire.sci.gsfc.nasa.gov/realtime/2011016/
Have a look at the images from Greenland once spring arrives.
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