221 Responses to "Sifones, frentes glaciares y la aceleración de los glaciares exteriores de Groenlandia"
Hank Robertssays
> a reality TV show about glaciers?
That’s a scary thought. I’m old enough to remember when “watching glaciers melt” was a simile for something very slow and very boring, like “watching the grass grow.” Now, you’re right, people would tune in to watch. Good grief.
Several named effects have been discussed in this thread, although there is a further named effect concerning the ice sheets which may be worthy of note. The following is an extract from an as yet unwritten draft of the sea level rise section of the IPCC’s 10th report on climate change, expected to be published some time around 2060. There was a bit of a delay because the authors couldn’t agree on the wording. An extract from the technical section on sea level rise reads:
“Each of the ice caps sat on a pole
…
…
All the world’s governments and all the world’s industrialists couldn’t put the icecaps together again.”
After a lot of deliberation they did agree on a name for the effect, but for the moment it is being kept secret, although one suspects it might get leaked.
As the icesheets slip off their perch and crash into lots of little pieces (just like an egg that falls – or is pushed? – onto the ground), it is about time some the world’s top industrialists had the courage to convene through a globally broadcast internet conference and tell the world’s public what they are going to do specifically about the icesheets.
Mikesays
#194 “My guesstimate is that the perennial sea ice has dropped by ~half this winter.”
http://www.agu.org/pubs/crossref/2008/2007JC004257.shtml
Josefino C. Comiso
Cryospheric Sciences Branch, NASA Goddard Space Flight Center
Journal of Geophysical Research
22 February, 2008.
“Arguably, the most remarkable manifestation of change in the polar regions is the rapid decline in the Arctic perennial ice cover. Changes in the global sea ice cover, however, have been more modest, being only slightly negative in the Northern Hemisphere and even slightly positive in the Southern Hemisphere”
This paper confirms that there is at least some thickening ice in the Antarctic : http://www.agu.org/pubs/crossref/2008/2007JC004284.shtml
H. Jay Zwally
Cryospheric Sciences Branch, Goddard Space Flight Center
Journal of Geophysical Research
19 February, 2008.
Ron Taylorsays
If you want to so something “chilling,” watch this Japanese video of polar satellite images, showing the disintegration of multi-year ice during last winter.
The image is a low-resolution reproduction of a sequence of satellite images of Arctic ice this past fall and winter. The sequence runs in a continuous loop from October 01, 2007, to March 15, 2008. A link to the high-resolution video file is also provided.
Note the stream of multi-year ice flowing out of the Arctic basin down the east coast of Greenland at one o’clock in the image. As of the middle of March, most of the basin, including the pole itself, appears to be covered only by seasonal ice.
Hank Robertssays
> This paper confirms that there is … some thickening … Zwally
“May–June (fall) and October–November (late winter) of 2004 and 2005” and “0.28 m in 2004 and 0.29 m in 2005” — but are you claiming a trend based on these numbers? The paper’s not about that.
Phil. Feltonsays
Re #205
Nice video similar to the Quikscat one I showed in #194 (interesting that the Japanese look at it upsidedown ;) ) The shots of the ice breaking up and squeezing through the Nares strait are really good.
Mikesays
The paper referred to sea level contribution, and post #194 speculated on the loss of sea ice. I posted a link to a paper that indicated that net loss of global sea ice was slight. That paper made the, perhaps surprising to some, that Antarctic sea ice had increased, so I looked for and found a confirming paper.
No I’m not claiming a trend.
It is interesting, though, that the Arctic and Antarctic often seem to go in different directions.
Keep looking into things and you will rapidly find information that will tell you that it is not at all surprising that the Arctic and the Antarctic would tend to go in different directions with regard to sea ice extent (at the present time, but perhaps not so much in the future when the ozone hole over the Antarctic is repaired).
mgsays
some interesting data on bursts of seismic waves in an ice stream (60 miles wide and one-half mile thick)
” … combined seismological and global positioning system (GPS) analyses to reveal two bursts of seismic waves from an ice stream in Antarctica every day, each one equivalent to a magnitude seven earthquake”
An interesting title for the article “Something’s shaking in Antarctica”
I recall reading somewhere that ice quakes don’t occur in Antarctica. Well that’s another tick in the nonlinearity box.
Arch Stantonsays
>”…Well that’s another tick in the nonlinearity box.”
Doubtful, the article implies that the quakes were previously undetected, not that they are new.
Stevesays
I propose another mechanism which needs to be considered regarding ice flows. Glacier ice is under extreme pressure, and it is also just slightly below freezing. It should not be considered solid like a diamond, but rather solid like a candle. Waxy. When an individual molecule of water happens to have enough energy to jump to a neighboring location it may do so. Remember, the ice is not a rigid crystaline structure, but an amorphous solid. It is possible for a molecule to ‘wiggle around’ in this solid. When the headend pressure is relieved, the pressure differential (head to tail) is increased, this will accelerate the flow rate and increase the thinning. One must consider the pressure, temperature, viscosity, and perhaps chemical composition of the particular ice to properly model this.
Ray Ladburysays
Steve, the physical properties of ice are known over a broad range of properties that encompasses all conditions occurring terrestrially. Were the ice homogeneous (and yes, amorphous solids can be homogeneous) and the terrain it advances over even moderately smooth, modeling would be a tractable problem. As it is, you have a variety of processes going on, and which are most important is still moot.
Excerpt follows, click link for full article from New Scientist.
Cite to Science magazine is at end of excerpt.
——
Van de Waal believes that the channels that carry the meltwater out to sea freeze up during the winter months. In summer, pulses of water rushing down the moulins to the bedrock overwhelm the narrowed channels, and the increased pressure lifts the ice sheet off the rock, enabling it to move faster.
However, after a few days the channels are forced open by the water, and it drains away from the glacier. As a result, the ice grinds back down against the bedrock and the lubricant effect is lost.
No lubrication
Van De Waal says this indicates that, overall, meltwater has a negligible effect on the rate at which the ice sheet moves.
Not all scientists agree. Jay Zwally of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US, says that averaging data over the last 17 years does not make sense because the most rapid melting at the edges of the ice sheet did not start until recently.
“It’s only in the last five years or so that the warming signal has really been visible,” he says.
Zwally told New Scientist that unpublished data from the eastern edge of the ice sheet suggests between 3% and 5% more ice is being lost because of lubrication than would otherwise happen. That is less than the 25% that was previously calculated, but still significant, he says.
Journal reference: Science, vol 321 p 111
——–
[Response: Mauri Pelto discussed this exact issue here in one of his guest posts a couple of months back. – gavin]
Does anyone know what is going on at Jakobshavn? Between the 28th and 29th of July, the satellite images appear to show that something massive occurred (large white mass representing ice) in the waters at the outlet point.
Oh, and the images from the 28th and the 29th are no longer available, but if anyone wants them, I saved them and can e-mail them. In any case, today’s image shows that the bay is full.
OK, I know I can be a complete dummy — in any case, I cropped the images from the 28th and the 30th and posted them on my blog so anybody can see what I am going on about:
> a reality TV show about glaciers?
That’s a scary thought. I’m old enough to remember when “watching glaciers melt” was a simile for something very slow and very boring, like “watching the grass grow.” Now, you’re right, people would tune in to watch. Good grief.
Here’s one for the paleo-Arctic:
http://www.agu.org/pubs/crossref/2008/2008GL033263.shtml
Megatides in the Arctic Ocean under glacial conditions
Several named effects have been discussed in this thread, although there is a further named effect concerning the ice sheets which may be worthy of note. The following is an extract from an as yet unwritten draft of the sea level rise section of the IPCC’s 10th report on climate change, expected to be published some time around 2060. There was a bit of a delay because the authors couldn’t agree on the wording. An extract from the technical section on sea level rise reads:
“Each of the ice caps sat on a pole
…
…
All the world’s governments and all the world’s industrialists couldn’t put the icecaps together again.”
After a lot of deliberation they did agree on a name for the effect, but for the moment it is being kept secret, although one suspects it might get leaked.
As the icesheets slip off their perch and crash into lots of little pieces (just like an egg that falls – or is pushed? – onto the ground), it is about time some the world’s top industrialists had the courage to convene through a globally broadcast internet conference and tell the world’s public what they are going to do specifically about the icesheets.
#194 “My guesstimate is that the perennial sea ice has dropped by ~half this winter.”
http://www.agu.org/pubs/crossref/2008/2007JC004257.shtml
Josefino C. Comiso
Cryospheric Sciences Branch, NASA Goddard Space Flight Center
Journal of Geophysical Research
22 February, 2008.
“Arguably, the most remarkable manifestation of change in the polar regions is the rapid decline in the Arctic perennial ice cover. Changes in the global sea ice cover, however, have been more modest, being only slightly negative in the Northern Hemisphere and even slightly positive in the Southern Hemisphere”
This paper confirms that there is at least some thickening ice in the Antarctic :
http://www.agu.org/pubs/crossref/2008/2007JC004284.shtml
H. Jay Zwally
Cryospheric Sciences Branch, Goddard Space Flight Center
Journal of Geophysical Research
19 February, 2008.
If you want to so something “chilling,” watch this Japanese video of polar satellite images, showing the disintegration of multi-year ice during last winter.
http://www.homerdixon.com/download/arctic_flushing.html
From the video:
The image is a low-resolution reproduction of a sequence of satellite images of Arctic ice this past fall and winter. The sequence runs in a continuous loop from October 01, 2007, to March 15, 2008. A link to the high-resolution video file is also provided.
Note the stream of multi-year ice flowing out of the Arctic basin down the east coast of Greenland at one o’clock in the image. As of the middle of March, most of the basin, including the pole itself, appears to be covered only by seasonal ice.
> This paper confirms that there is … some thickening … Zwally
“May–June (fall) and October–November (late winter) of 2004 and 2005” and “0.28 m in 2004 and 0.29 m in 2005” — but are you claiming a trend based on these numbers? The paper’s not about that.
Re #205
Nice video similar to the Quikscat one I showed in #194 (interesting that the Japanese look at it upsidedown ;) ) The shots of the ice breaking up and squeezing through the Nares strait are really good.
The paper referred to sea level contribution, and post #194 speculated on the loss of sea ice. I posted a link to a paper that indicated that net loss of global sea ice was slight. That paper made the, perhaps surprising to some, that Antarctic sea ice had increased, so I looked for and found a confirming paper.
No I’m not claiming a trend.
It is interesting, though, that the Arctic and Antarctic often seem to go in different directions.
On Antarctica:
http://www.newswise.com/articles/view/540496/
links for sea surface temperature anomaly plots to go with the satellite images linked in post 204 can be found here
http://weather.unisys.com/surface/sst_anom.html
http://sharaku.eorc.jaxa.jp/cgi-bin/amsr/polar_sst/polar_sst.cgi?lang=e
Re: #207
Dear Mike,
Keep looking into things and you will rapidly find information that will tell you that it is not at all surprising that the Arctic and the Antarctic would tend to go in different directions with regard to sea ice extent (at the present time, but perhaps not so much in the future when the ozone hole over the Antarctic is repaired).
some interesting data on bursts of seismic waves in an ice stream (60 miles wide and one-half mile thick)
http://www.eurekalert.org/pub_releases/2008-06/wuis-dsa060208.php
” … combined seismological and global positioning system (GPS) analyses to reveal two bursts of seismic waves from an ice stream in Antarctica every day, each one equivalent to a magnitude seven earthquake”
http://sciencenow.sciencemag.org/cgi/content/full/2008/604/3
An interesting title for the article “Something’s shaking in Antarctica”
I recall reading somewhere that ice quakes don’t occur in Antarctica. Well that’s another tick in the nonlinearity box.
>”…Well that’s another tick in the nonlinearity box.”
Doubtful, the article implies that the quakes were previously undetected, not that they are new.
I propose another mechanism which needs to be considered regarding ice flows. Glacier ice is under extreme pressure, and it is also just slightly below freezing. It should not be considered solid like a diamond, but rather solid like a candle. Waxy. When an individual molecule of water happens to have enough energy to jump to a neighboring location it may do so. Remember, the ice is not a rigid crystaline structure, but an amorphous solid. It is possible for a molecule to ‘wiggle around’ in this solid. When the headend pressure is relieved, the pressure differential (head to tail) is increased, this will accelerate the flow rate and increase the thinning. One must consider the pressure, temperature, viscosity, and perhaps chemical composition of the particular ice to properly model this.
Steve, the physical properties of ice are known over a broad range of properties that encompasses all conditions occurring terrestrially. Were the ice homogeneous (and yes, amorphous solids can be homogeneous) and the terrain it advances over even moderately smooth, modeling would be a tractable problem. As it is, you have a variety of processes going on, and which are most important is still moot.
http://environment.newscientist.com/article/dn14251-greenland-ice-sheet-slams-the-brakes-on.html?DCMP=ILC-hmts&nsref=news4_head_dn14251
Excerpt follows, click link for full article from New Scientist.
Cite to Science magazine is at end of excerpt.
——
Van de Waal believes that the channels that carry the meltwater out to sea freeze up during the winter months. In summer, pulses of water rushing down the moulins to the bedrock overwhelm the narrowed channels, and the increased pressure lifts the ice sheet off the rock, enabling it to move faster.
However, after a few days the channels are forced open by the water, and it drains away from the glacier. As a result, the ice grinds back down against the bedrock and the lubricant effect is lost.
No lubrication
Van De Waal says this indicates that, overall, meltwater has a negligible effect on the rate at which the ice sheet moves.
Not all scientists agree. Jay Zwally of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US, says that averaging data over the last 17 years does not make sense because the most rapid melting at the edges of the ice sheet did not start until recently.
“It’s only in the last five years or so that the warming signal has really been visible,” he says.
Zwally told New Scientist that unpublished data from the eastern edge of the ice sheet suggests between 3% and 5% more ice is being lost because of lubrication than would otherwise happen. That is less than the 25% that was previously calculated, but still significant, he says.
Journal reference: Science, vol 321 p 111
——–
[Response: Mauri Pelto discussed this exact issue here in one of his guest posts a couple of months back. – gavin]
Does anyone know what is going on at Jakobshavn? Between the 28th and 29th of July, the satellite images appear to show that something massive occurred (large white mass representing ice) in the waters at the outlet point.
See: http://www.seaice.dk/iwicos/latest/envisat.GMM3d.n.20080731.gif
Sometimes, you have to start at this link to get to the composite satellite images:
http://www.seaice.dk/latest-ice.html
On the 28th the waters were clear, on the 29th the little bay is full. Anyone know anything about this? Thanks
Click on the farthest left image, which will take you to the pages of the latest satellite photos.
Oh, and the images from the 28th and the 29th are no longer available, but if anyone wants them, I saved them and can e-mail them. In any case, today’s image shows that the bay is full.
Well, obviously my knowledge of the geography of Greenland is pitiful. In fact, the area I am talking about is to the east of Qeqetarsuag. Sorry.
OK, I finally figured it out — it is the outlet for the Ilulissat glacier. Anybody know what is going on there?
OK, I know I can be a complete dummy — in any case, I cropped the images from the 28th and the 30th and posted them on my blog so anybody can see what I am going on about:
http://climatechangepsychology.blogspot.com/2008/07/western-greenland-28-and-30-july-2008.html