It’s business as usual at the Petermann glacier, doing what a glacier does, calving ice into the sea. We reported on another chunk in 2010, four Manhattans in size. Borrowing from an oft used media ploy, at this rate, it will be down to ice cube size in ten years. I wonder though, if we’d ever have noticed any of this without MODIS? Keep that in mind when reading the claims.
From the University of Delaware — An ice island twice the size of Manhattan has broken off from Greenland’s Petermann Glacier, according to researchers at the University of Delaware and the Canadian Ice Service. The Petermann Glacier is one of the two largest glaciers left in Greenland connecting the great Greenland ice sheet with the ocean via a floating ice shelf.
Andreas Muenchow, associate professor of physical ocean science and engineering in UD’s College of Earth, Ocean, and Environment, reports the calving on July 16, 2012, in his “Icy Seas” blog. Muenchow credits Trudy Wohleben of the Canadian Ice Service for first noticing the fracture.
The discovery was confirmed by reprocessing data taken by MODIS, the Moderate Resolution Imaging Spectroradiometer aboard NASA’s Terra and Aqua satellites.
At 46 square miles (120 square km), this latest ice island is about half the size of the mega-calving that occurred from the same glacier two years ago. The 2010 chunk, also reported by Muenchow, was four times the size of Manhattan.
“While the size is not as spectacular as it was in 2010, the fact that it follows so closely to the 2010 event brings the glacier’s terminus to a location where it has not been for at least 150 years,” Muenchow says.
“The Greenland ice sheet as a whole is shrinking, melting and reducing in size as the result of globally changing air and ocean temperatures and associated changes in circulation patterns in both the ocean and atmosphere,” he notes.
Muenchow points out that the air around northern Greenland and Ellesmere Island has warmed by about 0.11 +/- 0.025 degrees Celsius per year since 1987.
“Northwest Greenland and northeast Canada are warming more than five times faster than the rest of the world,” Muenchow says, “but the observed warming is not proof that the diminishing ice shelf is caused by this, because air temperatures have little effect on this glacier; ocean temperatures do, and our ocean temperature time series are only five to eight years long — too short to establish a robust warming signal.”
The ocean and sea ice observing array that Muenchow and his research team installed in 2003 with U.S. National Science Foundation support in Nares Strait, the deep channel between Greenland and Canada, has recorded data from 2003 to 2009.
The Canadian Coast Guard Ship Henry Larsen is scheduled to travel to Nares Strait and Petermann Fjord later this summer to recover moorings placed by UD in 2009. These mooring data, if recovered, will provide scientists with ocean current, temperature, salinity and ice thickness data at better than hourly intervals from 2009 through 2012. The period includes the passage of the 2010 ice island directly over the instruments.
According to Muenchow, this newest ice island will follow the path of the 2010 ice island, providing a slow-moving floating taxi for polar bears, seals and other marine life until it enters Nares Strait, the deep channel between northern Greenland and Canada, where it likely will get broken up.
“This is definitely déjà vu,” Muenchow says. “The first large pieces of the 2010 calving arrived last summer on the shores of Newfoundland, but there are still many large pieces scattered all along eastern Canada from Lancaster Sound in the high Arctic to Labrador to the south.”
Prior to 2010, the last time such a sizable ice island was born in the region was 50 years ago. In 1962, the Ward Hunt Ice Shelf, on the northern coast of Ellesmere Island in Nunavut, Canada, calved a 230-square-mile island.
Article by Tracey Bryant
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Peter Plail says:
July 18, 2012 at 1:31 am
In this Welsh view of the glacier (http://www.aber.ac.uk/greenland/Petermann.shtml) there are two adjacent pictures of the glacier taken in 2009 and 2011 which show the nature of the ice at the glacier terminus in late summer. The video points out that the ice loss is 25 times greater from the underside than the top, so changes in air temperature have a relatively minor impact (note also the snow-covered ground at either side of the channel – not a lot of melting there).
That snow-covered ground is ~3,000 feet above the surface of the glacier.
Given that the glacier is effectively anchored at the two sides to the cliffs then I would expect flexing of the central portion due to tides, the weather and the fact that the body of the glacier is pushing forward at approx 1km per year to induce stress fractures which would lead to break up, but I have seen no discussion of these effects as contributors, simply references to temperatures of air and sea. As with all alarmist outpourings, there seems to be a lot of blinkered supposition here and not a lot of fact.
Mauri Pelto was writing about these effects at least since 2008 in reference to Petermann and other glaciers.
“””””…..The Petermann Glacier is one of the two largest glaciers left in Greenland connecting the great Greenland ice sheet with the ocean via a floating ice shelf…….””””””
Golly; soon it is going to be difficult to get ice in one’s Martinus, with only two really productive glaciers left in Greenland.
This reminds me of the Telly Savalas headed gentleman writing a testimonial letter to the hair restorer company.
“Dear Sirs, before I started using your hair restorer product, I had two bald patches on my head; now I have only one !”
What we need in this world is a better class of floating ice, instead of the rotten ice we have now. Somebody should figure out how to get glaciers to make prestressed ice, like the concrete used on road bridges. Then we wouldn’t have to worry about the floating ice cracking under tensile strain, when the tide flows in underneath it and lifts it up.
Christopher Simpson says:
July 17, 2012 at 8:34 pm
Sorry, but that is false. Where did you get your arbitrary figure of ” 20 years or so” from? Unprecedented means “that which has never, ever happened before”. Period. If you want to say “unprecedented for the last x-number of years” then that’s fine. But “unprecedented” by itself means just that.
Having a bad day, David? You’re generally quicker than this. Read what I said again:
Obviously you have trouble with the meaning of words. “Unprecedented” simply means, “has never, ever happened before for at least 20 years or so.”
Seriously, though, this drives me nuts in news reports. First they say something is “unprecedented,” and in the very next sentence they’ll say that the last time it happened was such-and-such a date (generally in the ’30s or early ’40s, I notice).
We really should have an “Alarmist to Sane” dictionary.
See? That’s my point exactly — that according to the news media (and climate scientists), “unprecedented” means something that hasn’t happened in a few decades, which, of course, is not at all what it means.
I know we’re supposed to put the [Sarc] tag on things like this, but I figured it was safe to leave it off since I pretty well explained the sarcasm in the second and third sentences. I did worry that someone might not get it, but I didn’t figure it would be you.
Have a cup of tea. Things will be better.
George E. Smith; says:
July 18, 2012 at 11:54 am
But if SST is the culprit the ice would melt from the bottom up, and break off through downward stress, in which case we would expect a low tide or high pressure to trigger it. I think we should set up LASARs and mirrors between the ice and geosynchronous satellites to cue us in on when these things break. We have the technology. All we need is better windshield wipers.
–AGF
David, UK says:
July 18, 2012 at 11:54 am
Brits are supposed to able to spot sarcasm. I think you failed the test. 🙂
Cracked heads
Cracked ice
I worry more about the former
Than I worry about the later -GK
Andreas Muenchow said (July 17, 2012 at 9:32 pm)
“…We only know where Petermann Glaciers terminus was after 1875/76, because nobody was ever there to write about it before that time. The current terminus of the glacier is further back since it has ever been for the last 137 years…”
And, therefore, they have no way of knowing what the previous max/min was prior to 1875. It could be that in 1775, there was no ice there at all.
I feel the need to paraphrase the article’s first line: This is what glaciers *do*. They get thick in the middle from snowfall, then flow to the sea and pieces break off.
George E. Smith wrote:
“What we need in this world is a better class of floating ice, instead of the rotten ice we have now. Somebody should figure out how to get glaciers to make prestressed ice, like the concrete used on road bridges.”
Actually, something like this was tried during WWII. Those wacky Brits wanted to make an “unsinkable aircraft carrier”.
Pykrete
http://en.wikipedia.org/wiki/Pykrete
“””””…..Christopher Simpson says:
July 18, 2012 at 12:46 pm
Having a bad day, David? You’re generally quicker than this. Read what I said again:
Obviously you have trouble with the meaning of words. “Unprecedented” simply means, “has never, ever happened before for at least 20 years or so.”…..”””””
So which King dictated that it should be “at least 20 years” or or so for that matter. I think “unprecedented” means there is NO precedent; as in it NEVER happened before.
Okay. I know the sarcasm was quite clear enough for anyone able to read the full 75 words.of my comment. I’m just going to mosey on over to Comics Curmudgeon, where there’s a higher level of comprehension among its participants. Sorry I stepped in here.
“””””…..agfosterjr says:
July 18, 2012 at 12:41 pm
George E. Smith; says:
July 18, 2012 at 11:54 am
But if SST is the culprit the ice would melt from the bottom up, and break off through downward stress, in which case we would expect a low tide or high pressure to trigger it……”””””
Actually, I didn’t say that; must have been somebody else; obviously someone who has never heard about my “Go jump in the lake.” experiment . which usually establishes firmly in the minds of the survivors, whether floating ice is melted by the air above, or the water beneath.
In any case, the cause of the thinning is not relevent to whether the ice will break up at a high tide, or down at a low tide. The thickness (or maybe it’s the cube of the thickness) and the net pressure determine that; not which side of the ice sheet is thinner.
George E. Smith; says:
July 18, 2012 at 3:53 pm (responding to)
“””””…..agfosterjr says:
July 18, 2012 at 12:41 pm
George E. Smith; says:
July 18, 2012 at 11:54 am (and himself ?)”
But if SST is the culprit the ice would melt from the bottom up, and break off through downward stress, in which case we would expect a low tide or high pressure to trigger it……”””””
…
In any case, the cause of the thinning is not relevent to whether the ice will break up at a high tide, or down at a low tide. The thickness (or maybe it’s the cube of the thickness) and the net pressure determine that; not which side of the ice sheet is thinner.
Actually, if the ice mass were floating, then – regardless of which “side” of the ice were melting, the new mass of the ice (after melting and water runoff) would be less, the new “net mass point” of the floating ice would be balanced by the water it displaced,and proportionally equal amount of surface area would be exposed to both the sea water (below) and the air (above).
But as the original author of the paper point out above, sea water below is the driving force of ice melt. IF – and IF the ice surface is changed to a darker level or color, or a rougher color and pattern so more sunlight is absorbed, then – practically regardless of temperature – the ice will melt away from above during the hours of sunlight exposure.
=====
Assume several conditions:
1. full sunlight plus high reflectivity at +1 degree C;
2. no (or little) sunlight (as if with clouds or a daytime storm or snow covering the surface or at night) plus a high-reflectivity surface
3. full sunlight plus absolutely no reflectivity at +1 degree C;
4. full sunlight plus high reflectivity at +2 degree C;
5. full sunlight plus absolutely no reflectivity at -4 degree C;
at -4 degrees, but with all the available sunlight absorbed, the ice will disappear fastest. The disappearance will be from above if the ice shelf is fully grounded or on land. If at sea, the water below will still remove more mass than the air temperature difference between +1 degree and -4 degrees. Water below, at a 1000x greater density and a 10x larger coefficient of heat transfer across the boundary between ice and water compared to air and ice, will win out in the race to remove ice.
Responses to questions raised by others:
1. A warming trend of 1.1 +/- 0.25 degrees C per decade since 1987 does NOT imply 11 deg.-C per century. In my blog post presenting and discussing these data, I specifically point this out. The trends at Thule Air Force Base, Greenland (where records start in 1950 instead 1987) the trend is actually 0.24 +/- 0.12 deg-C per decade, or if I use Nuuk, Greenland (where records start in the 1880ies) that trend becomes 0.16 +/- 0.15 deg-C per decade. Only the last record starting well over 100 years ago can be extrapolated to 100 years, saying that Nuuk temperatures increased by 1.6 +/- 1.5 deg. -C over 100 years as the record is longer than 100 years. Note the uncertainties, they are large at 95% confidence, meaning that there is a 1 in 20 chance, that the true trend is within the +/- range. There is a 1:20 chance that Nuuk temperatures rose by more than 3.1 degrees over 100 years, but it is just as likely that the temperatures at Nuuk rose by less 0.1 degrees over 100 years. This is what confidence intervals mean and they are usually as important (I’d say more so) that the actual numbers given. There is no reason to believe that temperatures at any location should follow a linear trend, it is just an easy thing to do.
2. Nobody knows where the ice shelf was in 1770, but we know from air bubbles frozen into the ice what the atmosphere was like over Greenland at that time as well as 100,000 years back. These records show, that rapid change (anything in less than 100 years is rapid) is not only possible, but common. The associated changes have not always been kind and pleasant for living things at that time.
3. The reflectivities in the MODIS imagery I produced do NOT imply a climate change, because a different sun angle and a different angle of the satellite to the sensed location on earth will be received as a different “count” of light particles at the detectors aboard the satellite. I prefer to work with raw data (these are very raw), because fancy algorithms introduce fancy stuff that is easy to mis-interpret. The difference between ice, water, and land is a large signal where these angles do not matter. I identify features and patterns only, I make NO claims on absolute “albedo” or “corrected reflectivity” as some do who like to emphasize the drama of gloom and doom that they see even where it not as significant as they like the public to believe.
4. Petermann Glacier advances at 1 km per year, give or take a little. So, each year this glacier receives 12 km^3 of new ice that is 600-m thick where the ice, the ocean, and the bed-rock meet at what is called the hinge line. On average (NOT the last 2 or even 10 years, but the last 140 years), the glacier lost about 1 km^3 to calving (yes ice islands from Petermann have been seen in the 1880ies off Baffin Island, too), so the other 11 km^3 (if all is in balance) are lost by melting done by the ocean.
5. The ice islands that broke off are about 80-120 m thick, down from 600-m when they entered the fjord at the hinge line. I estimate that the 2010 event represented a loss of 22 km^3 (or about 2 years worth of supply) and the 2012 event represents a loss of 14 km^3. Uncertainties on these numbers are perhaps 30% because I do not know depth well enough.
6. Like it or not, but the New York Times actually discussed some the nuances on the physics rather well, e.g., http://green.blogs.nytimes.com/2012/07/18/again-a-glacier-downsizes/
7. Yes, I am vain … but we’d all off a little better, if we could chuckle at our shared vanities trying to proof or disprove global warming.
Just saw: Sea Surface Temperatures are largely irrelevant with regard to the ocean melting of Greenland’s glaciers. What matters is the local temperature at depth (below 200-m say, for Petermann), not at the surface where it is almost always near freezing with ice present which in Nares Strait is almost always. The Arctic Ocean is warmest at about 200-400 m depth (salinity stratifies it).
Dr. Muenchow,
Assuming that reduction of the Greenland ice sheet comes from four different effects :
– Increased atmospheric temperatures directly melting ice
– Melting by direct solar irradiance during summer times that certain altitudes are above 0 C during summer
– Decreased albedo enhancing the previous effect
– Increased calving and speed of glaciers, enhancing direct ice flushed into the oceans,
which of these four effects do you estimate to be most important for sea level rise, and why ?
And an additional question : how much, assuming worst case scenarios for AGW and Arctic amplification, do you estimate the rate of sea level rise to be, due to reduction of the Greenland ice sheet by these four effects combined ?
Or are there any other effects not mentioned in my list of four ?
George E. Smith; says:July 18, 2012 at 11:54 am
“””””…..The Petermann Glacier is one of the two largest glaciers left in Greenland connecting the great Greenland ice sheet with the ocean via a floating ice shelf…….””””””
Golly; soon it is going to be difficult to get ice in one’s Martinus, with only two really productive glaciers left in Greenland.
[…]
What we need in this world is a better class of floating ice, instead of the rotten ice we have now
Maybe we need a variant of Vonnegut’s ice-9…
TWO MANHATTONS
http://www.bbc.co.uk/news/world-europe-18896770
“””””…..RACookPE1978 says:
July 18, 2012 at 4:47 pm
George E. Smith; says:
July 18, 2012 at 3:53 pm (responding to)
“””””…..agfosterjr says:
July 18, 2012 at 12:41 pm
George E. Smith; says:
July 18, 2012 at 11:54 am (and himself ?)”
But if SST is the culprit the ice would melt from the bottom up, and break off through downward stress, in which case we would expect a low tide or high pressure to trigger it……”””””
…
In any case, the cause of the thinning is not relevent to whether the ice will break up at a high tide, or down at a low tide. The thickness (or maybe it’s the cube of the thickness) and the net pressure determine that; not which side of the ice sheet is thinner.
Actually, if the ice mass were floating, then – regardless of which “side” of the ice were melting, the new mass of the ice (after melting and water runoff) would be less, the new “net mass point” of the floating ice would be balanced by the water it displaced,and proportionally equal amount of surface area would be exposed to both the sea water (below) and the air (above)……”””””
Well it seems that we are talking here about a glacier; which usually is a large river of ice sitting on the ground somewhere; in this case in Greenland, apparently around 81 deg North.. This river of ice, ends up flowing out into the ocean thereby creating a tongue of ice hanging out in the ocean from the land. The land typically has some relatively fixed altitude relative to say a mean sea level datum. On the other hand, the water in the ocean does not, and tends to rise and fall typically about twice each day. Free floating ice is hence free to rise and fall along with the ocean, maintaining a typical above and below surface buoyancy balance.
The attached ice (to the glacier) has no such freedom to rise and fall along with the oceans, so it is subjected to upwards, and downward forces, due to gravity and the buoyancy pressure of the rising and falling ocean.
Thus the attached tongue of ice IS NOT floating ice; but is like a diving board in contact with the ocean and it will flex up and down as the ocean rises and falls. The mechanics of a cantilevered beam is a well understood trivial problem, including such a beam with a distributed force loading. A term bd^3 comes into play in the determination of the strain that such a beam is subjected to and of course the length of the tongue (diving board) does too. Off hand I think l^2 shows up there somewhere. I’m not going to giggle the solution to the problem since anyone who is interested can do that themselves. I lost my copy of Timoshenko 51 years ago, so I can’t readily look it up, but I can simply derive it anytime I really want to know the answer.
But I am quite sure that the answer doesn’t care whether the top of the diving board is thinner than the bottom, or which side the ice melted off; only the net thickness matters. And as I have said, anyone who doesn’t know which side sees the highest inflow or outflow of “heat”, can simply go and jump in the lake.
Now in the two photographs, the right hand one shows floating ice; the left hand one apparently doesn’t.
George E. Smith; says:
July 19, 2012 at 11:44 am
Now in the two photographs, the right hand one shows floating ice; the left hand one apparently doesn’t.
Yes George, there was an extra three weeks or so of melting and outwash in 2008 (Aug 5th). The ice island is making stately progress down the fjord as can be seen in today’s image, the sea ice is diminishing too.
http://i302.photobucket.com/albums/nn107/Sprintstar400/Petermann.jpg
Andreas, your comments are much appreciated. Thank you!
To other readers,
I’m confused; I thought the new, generally accepted unit of measure for this metric was the New Jersey. WUWT? 😉
“””””…..Phil. says:
July 20, 2012 at 9:24 am
George E. Smith; says:
July 19, 2012 at 11:44 am
Now in the two photographs, the right hand one shows floating ice; the left hand one apparently doesn’t.
Yes George, there was an extra three weeks or so of melting and outwash in 2008 (Aug 5th). The ice island is making stately progress down the fjord as can be seen in today’s image, the sea ice is diminishing too……”””””
Well I don’t know what happened to the two low altitude photos I saw before, which prompted my comment; but perhaps the MODIS images are more revealing, since they appear to show that the most recent calving is a direct result of a fracture that happened back in/before 2010, when the cantilevered tongue was about three times longer, and hence much more able to cause the fracture that was still able to hang on until now. As near as I can judge, that whole area up to the current break, is clearly ungrounded ice, and I’m quite surprised that a tongue that long and skinny is even able to hang together.
I think they are a bit loose with their description of the region as a “floating” ice shelf. The broken pieces are clearly floating, but the rest is not, since it is still attached to the land.
The broken pieces are floating and sailing away. The attached piece is still floating also, well, almost all of it, anyways. The “floating” refers to the vertical plane, there is a line upstream towards the Greenland ice sheet where all the ice is in contact with the bottom vertically. This is called the hinge line. The attached floating ice shelf is now smaller (by 4 Manhattan’s in 2010 plus 2 Manhattans in 2011 minus, for giggles, 1 Manhattan for a steady rate of new supply added). The still large floating section of the glacier is attached to land on the sides, but it is not attached to the bottom. The walls are pretty close to vertical. The friction provided by the side walls is retarding, holding back the glacier which wants to move forward more than it can because of the retarding force of lateral (not vertical) friction. I think this is what glaciologists mean by back pressure, but I am no glaciologists and call it lateral friction. Think of the cork in a wine bottle, the push or pull you apply to get it in or out is the pressure gradient (that makes your boiler explode if the pressure inside is higher than outside) force. The friction is a force balancing this, holding it back.
In a perfect balance between these two forces, the glacier keeps going at a constant rate (a body in motion without a net force applied stays in motion). Now, if you change any of these forces, acceleration or deceleration occurs. The removal of large segments that have provided frictional retardation may lead to accelerations. It is more complicated than this and there are always devils in the details, but this is good enough for now to perhaps address some of the confusion related to what is floating and what is not. The only part of this (or any) glacier that is not float is that part that is attached to bed rock (land) in the vertical, not horizontal directions.
@Decker: My statement on air temperatures was refering to the mass balance of Petermann Glacier for which air temperatures are not important. Nowhere did I say, that air temperatures were irrelevant in general. I do stand by my statement that Sea Surface Temperatures are largely irrelevant (especially if measured by satellite) to ice-ocean interactions that almost always take place below top 1 mm of the ocean which are NOT, repeat, NOT measures by MODIS channels 31 or 32 at frequencies of 11 and 12 um. I am no glaciologist, so I am teachable on glaciers, but I have learnt a few things about the oceans over the years. Show me ocean data, ocean physics, and a good argument, then I may learn more (as I always do). As it stands, I see not such thing here, but like Greenland, things do change, some for the better, some for the worse.
My point Andreas, is that truly floating ice is not too prone to break up; well not until it does a lot of melting. But any cantilevered tongue of ice, that happens to also be over open water, is subject to buoyancy forces, as the tides rise and fall twice a day; not to mention ocean storms, and since ice; like concrete is almost devoid of tensile strength, then any up and down flexure due to rising and falling ocean water, is bound to eventually crack the sheet, and with that super long tongue before the loss of the 2010 ice island, it is no wonder that it started a failure way upstream at what subsequently became the present 2012 breakoff.
With the Antarctic peninsula ice shelves that everybody seems to have apoplectic fits over, you have the whole south Atlantic, and Pacific, sloshing back and forth under those shelves twice a day; no wonder the break off at regular intervals, when they get too far extended out over the sea.
Got it. The crack or fracture or cantilever was present for for many years moving seaward with the glacier. This was the location people expected the next break, and it happened monday, a little earlier than I expected. Eric Rignot did some calculations on Petermann’s ice shelf in the 90ies as a beam that is flexed by the tides, I better read it again as I forgot his results. I think the hinge line moved vertically off the bed rock a few inches and a few 100 yards horizontally with the tides. These are not static, but dynamic environments with many moving parts that can give and take some stresses within limits. What these limits are, nobody knows, but perhaps we will find out.
We already did see what happens when the hinge line becomes unhinged as it did 20 years ago at Pine Island Glacier in Antarctica. These are the type of worries I have with regard to Petermann Glacier. In dynamcis there often are multiple stable equilibria and a transition from one steady state to another will not be a “linear” response to forcing nor will “linear trends” be of any use to describe anything useful.