From the University of Colorado at Boulder, worry over something that is a natural process that has happened for thousands of years. You gotta love this one: ” Catastrophic lake drainages were 3.5 times more likely to occur during the warmest years than the coldest years.”. Gee, ya think? Or how about this one: “Once the water reaches the ice sheet’s belly that abuts underlying rock, it may turn the ice-bed surface into a Slip ‘N Slide, lubricating the ice sheet’s glide into the ocean.”. Hmm well, the “may” weasel word says that they really don’t know. The Greenland ice sheet is up to 1.8 miles (3 kilometers.) thick in the middle, and that huge weight depresses the underlying crust, which assumes the concave shape of a saucer. So I guess I’m not too worried about it slip-sliding away. And as WUWT has covered before, the warming in Greenland has some issues.
CU-Boulder study shows Greenland may be slip-sliding away due to surface lake melt
Like snow sliding off a roof on a sunny day, the Greenland Ice Sheet may be sliding faster into the ocean due to massive releases of meltwater from surface lakes, according to a new study by the University of Colorado Boulder-based Cooperative Institute for Research in Environmental Sciences.
Such lake drainages may affect sea-level rise, with implications for coastal communities, according to the researchers. “This is the first evidence that Greenland’s ‘supraglacial’ lakes have responded to recent increases in surface meltwater production by draining more frequently, as opposed to growing in size,” says CIRES research associate William Colgan, who co-led the new study with CU-Boulder computer science doctoral student Yu-Li Liang.
During summer, meltwater pools into lakes on the ice sheet’s surface. When the water pressure gets high enough, the ice fractures beneath the lake, forming a vertical drainpipe, and “a huge burst of water quickly pulses through to the bed of the ice sheet,” Colgan said.
The study is being published online today by the journal Remote Sensing of the Environment. The study was funded by the Arctic Sciences Program of the National Science Foundation.
The researchers used satellite images along with innovative feature-recognition software to monitor nearly 1,000 lakes on a Connecticut-sized portion of the ice sheet over a 10-year period. They discovered that as the climate warms, such catastrophic lake drainages are increasing in frequency. Catastrophic lake drainages were 3.5 times more likely to occur during the warmest years than the coldest years.
During a typical catastrophic lake drainage, about 1 million cubic meters of meltwater — which is equivalent to the volume of about 4,000 Olympic swimming pools — funnels to the ice sheet’s underside within a day or two. Once the water reaches the ice sheet’s belly that abuts underlying rock, it may turn the ice-bed surface into a Slip ‘N Slide, lubricating the ice sheet’s glide into the ocean. This would accelerate the sea-level rise associated with climate change.
Alternatively, however, the lake drainages may carve out sub-glacial “sewers” to efficiently route water to the ocean. “This would drain the ice sheet’s water, making less water available for ice-sheet sliding,” Colgan said. That would slow the ice sheet’s migration into the ocean and decelerate sea-level rise.
“Lake drainages are a wild card in terms of whether they enhance or decrease the ice sheet’s slide,” Colgan said. Finding out which scenario is correct is a pressing question for climate models and for communities preparing for sea-level change, he said.
For the study, the researchers developed new feature-recognition software capable of identifying supraglacial lakes in satellite images and determining their size and when they appear and disappear. “Previously, much of this had to be double-checked manually,” Colgan said. “Now we feed the images into the code, and the program can recognize whether a feature is a lake or not, with high confidence and no manual intervention.”
Automating the process was vital since the study looked at more than 9,000 images. The researchers verified the program’s accuracy by manually looking at about 30 percent of the images over 30 percent of the study area. They found that the algorithm — a step-by-step procedure for calculations — correctly detected and tracked 99 percent of supraglacial lakes.
The program could be useful in future studies to determine how lake drainages affect sea-level rise, according to the researchers. CIRES co-authors on the team include Konrad Steffen, Waleed Abdalati, Julienne Stroeve and Nicolas Bayou.
###
kbray;
since all such “errors” are in the direction of hyping and exaggerating AGW “trends”, no apologies are warranted. There is prima facie evidence of manipulation and fudging from stem to stern in climastrology.
Miss Grundy:
At April 17, 2012 at 4:57 pm you present a common misunderstanding when you say;
“I believe that’s the principle behind ice skating. The weight of the skater on thin blades exerts a momentary strong pressure on the ice, which melts and allows the skater to glide forward. The momentarily-melted water re-freezes once the skater has moved on.”
Sorry, but No!
All solid ice is coated with a liquid phase at all temperatures down to less than -40 deg.C.
This surprising fact was first discovered by Michael Faraday (of electricity fame) and has been subject to much study since. It is important for several reasons which include the fallacious arguments of the study reported in the above article. (And an amusing ‘home experiment’ demonstrates this strange property of ice surface; see below).
Firstly, the effect occurs because the bonds which link ice molecules exist in the ice but not outside the ice’s surface. Hence, normal vibration of the ice molecules induces a transition between solid and liquid properties in a surface layer.
Hence, ice is slippery because its surface is wet, and skaters slide on the liquid phase which coats the surface of the ice.
Similarly, if introduction of liquid water beneath a glacier is to reduce friction between the glacier and the underlying ground then the introduced water must lift the glacier above the surface roughness of the ground. Introduction of a thin layer of water makes no difference because the bottom of the glacier (i.e. ice) is always coated with a very thin layer of water.
Also, the liquid phase occurs between molecules of liquid ice. This must affect compositions of gas samples ‘trapped’ in ice. Gases dissolve in water and different gases have different solubilities. Ionic diffusion of gases through the liquid phase between molecules can be expected to alter relative concentrations of gases in parts of the ice over time.
The ‘home experiment’ is as follows.
1.
Place an ice cube on top an empty wine bottle.
2.
Attach a heavy weight to each end of a length of thread.
3.
Place the thread across the ice cube such that the weights hang down the sides of the bottle.
4.
Wait (and occasionally watch) for some hours.
5.
The thread travels down through the ice cube until the thread rests on top the bottle. The ice cube then shows no visible indication that the thread has passed through it.
This happens because the weights pull the thread through the liquid phase on the ice surface. This creates new ice surface below the thread, but this new surface also has a coating of liquid so the thread is pulled through that. The solid reforms above the ice (with no distortion) because the liquid phase is only a surface effect. If the thread were to ‘cut’ the ice by a pressure effect (as you suggest) then the ice cube would exhibit visible evidence that the thread had ‘cut’ it.
Richard
Aaargh!
In my above post I wrote;
“Also, the liquid phase occurs between molecules of liquid ice. This must affect compositions of gas samples ‘trapped’ in ice. Gases dissolve in water and different gases have different solubilities. Ionic diffusion of gases through the liquid phase between molecules can be expected to alter relative concentrations of gases in parts of the ice over time.”
That is nonsense. I intended to write.
“Also, the liquid phase occurs between crystals of ice. This must affect compositions of gas samples ‘trapped’ in ice. Gases dissolve in water and different gases have different solubilities. Ionic diffusion of gases through the liquid phase between crystals can be expected to alter relative concentrations of gases in parts of the ice over time.”
Sorry.
Richard