Arctic Ice

[J10]

Please continue your comments here.

[Gray-Wolf]

So ,where do we go from here?

Is the second lowest figure recorded a sign of recovery or is it a positive indicator of more of the same? Will the re-consolidation of sea ice progress as normal or does the lack of perennial ice mean we now must accept a 'differing' kind of re-freeze?

Though an 'average' kind of year this year we saw (IMO) an incredible amount of melt including the loss of a fair percentage of the ice shelves to the north of Ellesmere Island and a very worrying 'crack' in the middle of Greenlands largest glacier develop.

We have 'eye witness reports' (from the continental shelf off Siberia) of methane bubbling up from the cathrites below and new reports telling us that the permafrost holds twice as much CO2 as previously thought, permafrosts that appear to be melting.

We have, for the second year running, an increase in atmospheric methane concentrations and the Arctic seems to be the most likely culprit for the increases.

So, let's sit back and observe our futures in the making!

Edited September 24, 2008 by Gray-Wolf

[SnowBear]

Not sure we can draw any real conclusions for another few years as yet GW. We might be in a continued ice break up phase, we might be in a recovery phase or we might be at a plateaux. I guess any ice that has stayed since the ice creation through last winter would now become perennial ice and thus a small recovery has been seen this year. At least in regard to last year. This winter will be interesting.

Edited September 24, 2008 by SnowBear

[Mondy]

Relatively thin first-year ice is more prone to melting out completely than older, thicker ice. However, more of this year’s first-year ice survived the melt season than is typical. Sea ice age maps from Sheldon Drobot, our colleague at the University of Colorado at Boulder, show that much more first-year ice survived in 2008 than in 2007. This is one of the reasons that 2008 did not break last year's record-low minimum.

One cause of the high first-year ice survival rate was that this summer was cooler than in 2007. Lower temperatures slowed the melt rate in the early part of the season. While conditions in August favored rapid ice loss, they were not enough to make up for this early-season "cushion." Furthermore, much of this year's first-year ice was located at higher latitudes than in 2007, covering even the geographic North Pole. Regions that are far north have lower melt rates because they receive less solar energy than more southerly regions.

Pretty natural to me. Colder 2008 than 2007.

This year, the wind patterns were different, leading to a less compacted ice cover.

Which explains why 2007 was so "alarmingly scary" to some. The wind patterns hammered the ice last year, not all things agw.

http://www.nsidc.com/arcticseaicenews/

[Gray-Wolf]

Which explains why 2007 was so "alarmingly scary" to some. The wind patterns hammered the ice last year, not all things agw.

Unless , of course, our tinkerings have now started to augment existing global weather patterns or create novel global climatic 'expressions'............... :lol:

[Gray-Wolf]

http://www.sciencedaily.com/releases/2008/...80926194613.htm

so we saw quite a fantastic rate of melt through Aug, much faster than last years melt rates in fact.

[Gray-Wolf]

Polar ice loss heralds a change in the weather

By Tim De Chant | Published: September 17, 2008 - 09:44AM CT

With the autumnal equinox less than a week away, a months-long night is about to descend on the North Pole. As the sun sweeps lower across the arctic skies, ice sheets that cap the northern ocean are beginning to expand. While this summer's minimum polar ice extent failed to surpass last year's retreat, scientists are not greeting the news with a sigh of relief.

The record minimum set in 2007 caught many by surprise, but this year's observations are equally disconcerting. Experts expected the winter of 2007-2008 to bolster the sea ice and hold the 2008 minimum well above the record low. Instead, the 4.52 million square kilometers of ice recorded on September 12, 2008 was just 10 percent shy of the record minimum. These numbers make for good press, experts say, but the real focus should be on the overall trend towards ice-free summers in the Arctic.

Arctic sea ice minimum extent for 2008.

Average minimum extent for 1979-2000: orange line "The key thing is the long-term changes," said Walt Meier, research scientist at the US National Snow and Ice Data Center. "No summer sea ice would be a dramatic change," he told Ars. "We're heading towards a new state in the Arctic."

The National Snow and Ice Data Center is hesitant to point an official finger at the exact cause of this year's decline, but early evidence suggests ice pulling away from the mainland is to blame. As the polar cap retreats northward, ice shelves that are otherwise sheltered from wave action and warmer sea water are exposed. Massive tracts then tear loose and drift to sea—like the part of the Markham Ice Shelf that broke off earlier this summer. This year's pattern of ice retreat is not a new phenomenon, but it popped up in more locations than experts had expected.

In 2007, scientists were stunned by the Arctic sea ice's rapid retreat. "Last year was kind of mouth dropping in terms of how far it fell," Meier said. "To get that kind of response, you need a real kick in the pants," he said, adding that high temperatures, favorable winds, and particularly clear skies around the summer solstice all worked in concert to reduce the ice to its lowest extent on record.

"In a lot of ways, this year is more remarkable than last year," Meier said. Cooler temperatures and cloudier skies kept the ice from reaching another record, but scientists were looking for those factors to help the ice to regain some of the area it lost last year. This summer's extent, he said, was not the significant rebound he and his colleagues were expecting.

"It’s going to take more than a year to turn this around," Meier said. In fact, it would take four to five consecutively cool summers to regain what has been lost in the past two years, he said. "It doesn’t seem like that’s realistic under current conditions."

Only seven years ago, climate scientists on the Intergovernmental Panel on Climate Change (IPCC) were certain that the Arctic would retain some amount of sea ice until 2100. In the most recent report released in early 2007, the panel revised the estimate down to a range from 2070 to 2100. Now, most sea ice experts agree that summer ice may vanish from the North Pole in 2030—some even posit 2012 as the landmark date. Such an extreme prediction would have been mocked only five years ago but today, many scientists acknowledge its possibility.

Two summers of sea ice surprises and constant revision of expectations highlight one glaring trend: the North Pole will soon be free of ice during its sunny summer months. A watery pole will be more than simply evidence of climate change—it will turn into a contributing factor. Gleaming white ice at the pole reflects the continuous summer sun, increasing the Earth's albedo. Without the ice to reduce the sun's heating power, the Arctic Ocean's temperatures will shoot up in the summer, disrupting ocean circulation patterns around world over. And, as ocean currents shift, weather may fall into unpredictable patterns.

"The fact that you have cold water at the pole and warm water closer to the equator, that is a major factor in what your weather patterns are," Meier said. "if you’re changing the temperature at one end, it’s going to change your circulation patterns. And that's going to affect weather patterns throughout the northern hemisphere."

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I think we'll find more and more predictions regarding the impacts of a low ice arctic as the next couple of years roll by. As the aticle points out we have rapidly altered predictions as we witness the rapidly collapsing Arctic.

Edited September 30, 2008 by Gray-Wolf

[BLAST FROM THE PAST]

Experts expected the winter of 2007-2008 to bolster the sea ice and hold the 2008 minimum well above the record low.

Where are these expert expectations then. I read nothing of the sort anywhere so would be interesting to read them.

BFTP

[Gray-Wolf]

Where are these expert expectations then. I read nothing of the sort anywhere so would be interesting to read them.

BFTP

Could name a number of 'armchair experts' that were, and are, predicting a global cooldown currently :lol:

[laserguy]

Could name a number of 'armchair experts' that were, and are, predicting a global cooldown currently

And I'm one of the blighters.... absolutely :lol: !

[BLAST FROM THE PAST]

Could name a number of 'armchair experts' that were, and are, predicting a global cooldown currently :lol:

At least you can find the quotes and currently that's exactly what we are getting . Is this being said now because a record minima wasn't reached and so they are trying to sensationalise it a bit more? Let's see these experts quotes so we can satisfy ourselves that they were 'expecting' much greater ice extent so we can then dismiss spin.

BFTP

Edited September 30, 2008 by BLAST FROM THE PAST

[If Wishes made Weather]

Sorry about this (I know I'm going to get :lol: cked for this), but is there anything in the idea that once/if the Arctic ice is gone, the gulf stream will go galloping past our shores without so much as a hello, and we will be plunged into eternal winter/compulsory wearing of ex army stockings etc ... ?

Tim

[Gray-Wolf]

I do think that most all folk, experts or just interested folk, expected more ice than we ended up with. When you take into account both the cold back end of winter and the 'average' summer conditions it seemed quite likely (to some) that we'd hang onto more than we did.

No spin, just genuine concern that as the ice pack looses it's perennial then it is less able to keep the ice shelfs and glacier snouts from the types of collapse we saw this year, even when 'average conditions' prevail.

Personally I think we are beyond the 'tipping point' and so can hold out no hopes for recovery. As the article plainly shows we'd need many years of ice build just to rebuild what we have lost over two years and that is just not going to happen even if nature conspires to pull out all of the 'cold' stops.

And let us not forget 'Antarctica' that was always predicted to 'lag behind' in the effects of warming. We are now seeing the warming able to breach mid-winter cold in it's efforts to destroy the ice shelfs down there.

Game over really. :lol:

[Roger J Smith]

After the results of 2007 and 2008, it will be of interest to monitor whether a sort of polar oscillation will now become a feature of ice melt. I'm referring to the largest melt anomalies being around 160 E in 2007, and 40 E in 2008. Given the range of vulnerable outer edges of the ice pack, these represent almost opposite cases, so an oscillation may be linked to some kind of QBO signal in high latitudes (warming greater near the Bering Strait in 2007, and north of Norway in 2008).

The other possible trend to monitor is a 3-5 year cooling and return to larger ice extent over the near term. I've already said that a more extensive melt could develop in a future warming episode that I expect around 2018-23, and that's when we could see the first seasonal melt of the whole mass of sea ice. Before that comes, I do think there is some chance of a return to levels more similar to the 1980s if not the 1970s. That trend should peak around 2012 to perhaps 2015.

I think the southern hemisphere is probably about as cold as it can get in this epoch and so some reduction of peak ice can be expected there, after recent record seasons.

[Gray-Wolf]

From those who predict the course of climate change we are told to 'expect' a slowdown in warming in the short term. If we fail to see this (in significant terms) then we can be assured that our predictions are currently underestimating the scale of the problem by quite a wide margin. If we do see a slowdown in the rate of change (which would truely surprise me) then we must not be fooled by those who will claim the problem is 'sorted'.

The paper I posted above is the first to detail possible impacts upon our current climate systems for the northern hemisphere and this would alter much in the way we currently predict our multidecadal climate patterns and the impacts they impart to the weather we would expect to occur in the various stages of these multidecadal climate patterns. We have been in our 'cold phase' here in the northern hemisphere for a number of years now and yet have managed the 3 most extreme melt seasons since satellite records began.Not seeming to run it's normal course is it?

[Mondy]

the 3 most extreme melt seasons since satellite records began.Not seeming to run it's normal course is it?

You said it..(in bold)

Shame all this data wasn't available many thousands of years ago. The internet is a wealth of info, whichever way you look at it.

[Gray-Wolf]

All of the paleo-dating of the ice shelfs we lost this year show that they have been in place for many thousands of years. Some of the sea floor data showing continuous ice cover would also support that this is an event unprecedented during Homo Sapien Sapien's time in the northern hemisphere.

As you say Col, 'tinternet is a wondrous thing :o

Moving away from past why not explore what the future holds for the region that has not been experienced before. As we know shipping is on of the most polluting forms of transport on the planet (the report over summer had it being 3 times dirtier than previous estimates) and now ,since Russian expanded it's 'Arctic Borders' and started on the worlds lagest ever nuclear powered ice breaker, we have the prospect of not only shipping but heavy industy up there exploiting the mineral wealth (and all the pollution that encompasses). With year round 'ice free' shipping lanes to service the industry what of the soot on the high arctic ice pack? will lowering it's albedo be a nothing?, will breaking up the contiguous pack have no impact on its mobility in the arctic Gyre?

I tire of looking back when our problem is in front of us and far removed from past experience.

What say you??

[Roger J Smith]

GW, you are making a more valid point about the albedo changes and sooty deposition problem than the IPCC, and in my view this should have been front and centre in the campaign to change global air quality. If this had been the case, we would not have had the contentious Kyoto approach asking the developed world to cut back on carbon emissions while the larger soot producers in eastern Asia were not tackled at least with equal vigour. We all saw with the Summer Olympics how gross the industrial pollution potential is from eastern China, they had to cut back their normal economic activity by two thirds to get through the period with tolerable air quality. On a much larger scale, all this soot is probably making more of a difference than most realize, whether they are "warmers" or "skeptics" -- and I have been saying this from the outset, because it dawned on me in the 1990s that if ice was gradually being depleted in the Beaufort Sea despite only a modest rise in temperatures, the cause and effect might have more to do with albedo considerations than ocean currents or ambient temperatures. Of course all are related too, once you get open water then the air can sustain higher temperatures.

If in fact the atmosphere is trying to return to a colder configuration but the ice pack is signalling resistance due to the albedo reduction, then we would get into a very unstable set of changes where the large open water zones started to act like Great Lakes in producing large downwind snow belts in Siberia and northern Canada. This could only lead to colder source air masses in the long run for more temperate zones further south.

This effect seems to have set in on a modest scale in northern Canada during September, the snow cover charts are showing a fairly widespread 15-30 cms on the northern mainland between 64 N and the islands of the Arctic archipelago, and this looks a bit early in its more southerly range. The snowfall climatology of the arctic islands is not what some might expect, these islands are often covered in September and October by meagre amounts of snow that then drifts extensively so that higher rocky areas are swept clear and lower protected areas might accumulate 30-40 cms, and this climatology extends into what we call the Barrens formerly Keewatin territory and now the western part of Nunavut, to about Great Bear Lake in the west and the northeast arm of Great Slave Lake in the south. Further south from that, the terrain becomes forested (lakes are abundant throughout both zones) and winter snowfall is generally heavier, taking longer to accumulate before the mid-winter dry spell develops under arctic high pressure. The heaviest snow outside of lake effect zones in central Ontario would probably run from east of Lake Winnipeg across northern Ontario into western Quebec and then towards Labrador. Those areas get snow cover of about 50-75 cms in a typical winter, and it lasts from about mid-December to mid-March at those levels before slowly reducing.

This is one reason why the whole question of climate change is so complicated, whether the changes are natural or partly man-made being somewhat irrelevant to the outcome. A zone of much heavier snowfall could easily shift north in a gradually warming climate while the increased sea effect added snow from north to south, so the net result could be a local doubling of snowfall in critical areas that have been known to spawn continental glaciation in the past, like Keewatin and Ungava. In fact, before the global warming orthodoxy began, it was common to read in the Ice Age textbooks of the 1970s that a warmer climate usually set in over these regions in winter as glaciation began. Once a large mass of land ice developed and self-reinforced over successive years, it drastically altered the circulation and air mass characteristics over large regions, so then cooling set in, and as more recent scholars of this subject have been pointing out, there is a tendency for glaciation only to relinquish its hold near the peak of externally forced warming -- for example, the Younger Dryas period when the last large chunks of the recent glacial period let loose torrents of freshwater from lakes dammed up behind them, was only a few thousand years before the Climatic Optimum where the Milankovitch factors peaked (already) and the temperate zone climates were generally warmer than even now.

Bottom line is this -- nobody should be too sure that arctic ice melt, for whatever reason, is the first stage of a hemispheric warming and rising sea levels. It could be the event that unbalances the delicate equilibrium that has been in place during the relatively warm 20th century (to present) climate with its range of conditions, and there would be no particular reason to rule out a rapid return to at least Little Ice Age conditions if not something more drastic. It only takes one successful year of over-summer snow retention in critical areas to get this process started. In June 1816, various reports show how far down that road the climate was able to get in a cold period possibly assisted by volcanic dust, for example, ice remained in lakes around James Bay well into July, there was snow in New England in early June, and frosts that killed crops in July and August in southern Ontario and western New York. A year just slightly colder than that could sustain permanent snow cover over parts of the glacial formation zone around Hudson Bay, then you start into the next season presumably with Hudson Bay only half melted, the circulation already stuck in a late autumn pattern, and from there you could have the critical 3-5 year period of progressive snow accumulation. Once you get snow cover to 100 cms in regions of north-central Canada, the radiation budget is not really sufficient to melt it all and it rapidly accumulates. That's apparently how these glacial periods get started, with the same general process in northern Sweden and advancing out from higher elevations of various mountain chains. In the last several Ice Ages, most of the time at least, eastern Siberia did not become glaciated. This to me suggests another possible factor to watch out for, drift of the North Magnetic Pole into the area of the New Siberian Islands, which would replace the current slack circulation favouring arctic high pressure to a mean southerly drawing mild air from China and central Asia. In other words, the Icelandic low would try to form over the region, and this would surely increase snowfall further west which is probably why the glaciation usually extends as far northeast as the Urals and the Ob valley of west Siberia.

[Gray-Wolf]

Very interesting post Roger. We have already had our 'Green snow' to the north of industrialised Asia and recent Co2 measure have moved the highest areas of production from the old west to the new Indo-chinese region.

The fact that through our 'industrialisation' we had only 'low tech' methods of extraction of coal probably led to a higher quality of coal being extracted (only recently did we return to the 'slag heaps' to re-use the quality of coal that was once 'waste') and so the pollution produced was not on the scale of the current chinese problem. I think I'm right that it was only the Silesia's coal fields, and their low quality 'brown coal' (lignite) that was utilised in NW Europe. It would seem that by utilising modern methods China burns nothing but 'brown coal'.

If you look at the recent 'heavy snow' events around the Northern hemisphere (how many stadias had there roofs collapse in Eastern Europe over the past 3 years?) there does seem to be a change occurring in the intensity of some of our current weather events.

[stewfox]

"The fact that you have cold water at the pole and warm water closer to the equator, that is a major factor in what your weather patterns are," Meier said. "if you're changing the temperature at one end, it's going to change your circulation patterns. And that's going to affect weather patterns throughout the northern hemisphere."

I think we'll find more and more predictions regarding the impacts of a low ice arctic as the next couple of years roll by. As the aticle points out we have rapidly altered predictions as we witness the rapidly collapsing Arctic.

If we assumed a worse case scenario and all the ice went in the summer by 2012

Has any research been done with regard to the impact on global currents re melting of all that ice

I assume it wouldn't effect the Gulf Stream etc ??

How many cubic miles of ice up there end of last summer and how thick was it ?

In a nut shell could we get a colder winter if there was massive influx of cold water released in the summer ??

[Roger J Smith]

Stewfox, this is exactly the paradox of total meltdown, it then requires many decades to warm up the arctic atmosphere to the point where this open Arctic Ocean can be seen as an extension of a global ocean, what's more likely to happen as soon as the total meltdown occurs is a rapid re-freeze from the cold pole around 85N 160W outwards, a sort of mega-rebound potential that could restart a colder climatic phase. This would all happen within a decade of the total melt, I would speculate, far too quickly for Greenland to start melting down substantially, and too quickly to leave any signal in the mid-latitude ocean temperatures. Intuitively, when the arctic ice all melts in some future summer season, the northward currents in various locations would increase due to reduced resistance. However, a thin skin of fresh water would be likely to form over the polar region and with the land masses snow-covered and getting rapidly colder in the autumn of that year, ice would rapidly re-appear. I think there would be a number of these episodes before a more sustained melt episode, and every fifty years that goes by in that oscillating mode, the atmosphere would be progressively cleaner due to technological advance, the Milankovitch drivers would be more conducive to cooling, and the odds of a natural cold cycle would be increasing as well as the odds of a volcanic dust veil event.

It is for all those reasons that the IPCC scenario of a progressively melting arctic and a permanent shift to an ice-free northern hemisphere seem unrealistic to many. The arctic ice has many different ways of reappearing even if it melts for a while, as the Ice Age cycle proves, there is nothing permanent about northern hemisphere climate in the general conditions of the present geological era. And I don't think human activity is a factor large enough to throw off that cyclical process.

[Mondy]

STUCK IN THE ARCTIC FOR THREE WEEKS...AND COUNTING

Btw, check the 2008 growth already

Onwards and upwards ;-)

Edited October 2, 2008 by Delta X-Ray

[Gray-Wolf]

http://nsidc.org/news/press/20081002_seaic...essrelease.html

I thought I had to be correct about ice volume, now we have it from the horses mouth (NSIDC release above)

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Melting of Arctic ice 'fascinating ... alarming'

Remaining ice is in precarious shape, scientists say

Margaret Munro, Canwest News Service

Published: Thursday, October 02, 2008For scientists, this year's ice season was like the NHL playoffs.

They placed bets, pored over satellite images, and speculated endlessly on how much Arctic ice would survive the summer.

"Everyone was following it," said Louis Fortier, scientific director of the Arcticnet, which funds and co-ordinates much of Canada's polar research. "It was like the hockey final"

At one point, it looked like 2008 might shatter last year's retreat of ice.

So much ice had melted by the end of August it was possible for the first time in human history to circumnavigate the North Pole, prompting one prominent U.S. scientist to say the ice cap has entered a "death spiral."

In the end, the ice cap survived for at least another year. The U.S. National Ice and Snow Data Center is expected to issue its wrap-up report Thursday, which will confirm 2008's Arctic retreat as the second worst on record after 2007's stunning loss.

But the ice that survived is in precarious shape heading into the winter.

Most of it is first-year ice less than a metre thick, says Walt Meier, a research scientist at the U.S.-based centre, which tracks the ice by satellite as it waxes and wanes through the year.

Thick, multi-year ice used to cover much of the Arctic Ocean year-round. All that is left of that cement-like ice is now jammed up in a strip against Canada's Arctic islands and northern Greenland.

The rest of the old, hard ice either melted this summer or was flushed down into the Atlantic Ocean, where it disintegrated.

"We're left with much less multi-year ice compared to the same time last year," said Meier.

"So even though there is more ice total, most of it is the first-year variety that is pretty thin."

In many ways, 2008 was "as remarkable or even more remarkable" than 2007, he says, because the ice did not bounce back despite summer conditions that were much cooler than the 2007 Arctic heat wave.

Now that the 2008 numbers are in, researchers are revising their estimates on how much longer the Arctic summer ice can survive.

Fortier says it is a bit of game and "exciting" for scientists to see their predictions about climate change coming true much faster than expected.

However, "what is so fascinating from a scientific point of view is also very alarming," he said.

The rapid pace of change in the North suggests the scientific community and the United Nations Intergovernmental Panel on Climate Change have likely also underestimated the pace of other climate changes coming down the pipe.

"The Arctic is a bellwether for change that is coming globally and is coming much faster than any of the models suggested it should," said David Barber, an ice specialist at the University of Manitoba.

Or, as Fortier at Laval University puts it: "I think we are in for a few surprises."

The iconic ice cap has topped the planet for eons. But in the last two years the sea ice retreated by summer's end by more than half, to well below five million square kilometres.

Both years it retreated to more than 30 per cent below the average minimum seen between 1979 to 2000.

Remaining ice is in precarious shape, scientists say

Margaret Munro, Canwest News Service

Published: Thursday, October 02, 2008Many polar watchers believe the ice has passed a "tipping point" and will soon give way to open water in late summer.

Barber says sediments from the sea floor indicate the Arctic has had ice continuously for 1.1 million years.

Fortier says it may be even longer, pointing to studies that indicate multi-year ice pack has been carrying driftwood from Siberia across to Greenland for close to 14 million years. Meier says there is a possibility the ice melted back during warm spells 8,000 and 130,000 years ago.

But he stresses this is the first time humans have played the lead role in driving the retreat.

There is widespread scientific consensus that rising atmospheric temperatures caused by greenhouse gas emissions are largely responsible for the big melt.

As the ice retreats more solar energy is being absorbed by the dark Arctic waters, raising the temperature of the ocean surface, which then slows formation of new ice as the winter chill sets in.

There is also evidence more water is flowing into the Arctic from the Pacific and Atlantic, carrying heat with it.

"It's like the ice is between two fires -- the atmospheric heat and the ocean heat," says Fortier.

<H6 class=copyright>© The Vancouver Sun 2008</H6>

Edited October 3, 2008 by Gray-Wolf

[Gray-Wolf]

Thinning Greenland Glacier Due To Ocean Warming And Atmospheric Changes

The retreating ice of Jakobshavn Isbrae.by Staff Writers

New York NY (SPX) Oct 03, 2008

The sudden thinning in 1997 of Jakobshavn Isbrae, one of Greenland's largest glaciers, was caused by subsurface ocean warming, according to research published in the journal Nature Geoscience. The research team traces these oceanic shifts back to changes in the atmospheric circulation in the North Atlantic region.

The study, whose lead author was David Holland, director of the Center for Atmosphere Ocean Science, part of New York University's Courant Institute of Mathematical Sciences, suggests that ocean temperatures may be more important for glacier flow than previously thought.

The project also included scientists from the Wallops Flight Facility, Canada's Memorial University, the Danish Meteorological Institute, and the Greenland Institute of Natural Resources.

Jakobshavn Isbrae, a large outlet glacier feeding a deep-ocean fjord on Greenland's west coast, went from slow thickening to rapid thinning beginning in 1997. Several explanations have been put forward to explain this development. The scientists in the Nature Geoscience study sought to address the matter comprehensively by tracing changes in ocean temperatures and the factors driving these changes.

In doing this, they relied on previous results published by others that used NASA's Airborne Topographic Mapper, which has made airborne surveys along a 120-kilometer stretch in the Jakobshavn ice-drainage basin nearly every year since 1991.

While many other glaciers were thinning around Greenland, these surveys revealed that Jakobshavn Isbrae thickened substantially from 1991 to 1997. But, after 1997, Jakobshavn Isbrae began thinning rapidly. Between 1997 and 2001, Airborne Topographic Mapper surveys showed an approximately 35-meter reduction in surface elevations on the glacier's 15-kilomater floating ice tongue.

This is far higher than thinning rates of grounded ice immediately upstream.

The researchers reported that these changes coincided with jumps in subsurface ocean temperatures. These temperatures were recorded by the Greenland Institute of Natural Resources from 1991 to 2006 over nearly the entire western Greenland continental shelf.

These data indicate a striking, substantial jump in bottom temperature in all parts in the survey area during the second half of the 1990s. In particular, they show that a warm water pulse arrived suddenly on the continental shelf on Disko Bay, which is in close proximity Jakobshavn Isbrae, in 1997.

The arrival coincided precisely with the rapid thinning and subsequent retreat of Jakobshavn Isbrae. The warm water mass remains today, and Jakobshavn Isbrae is still in a state of rapid retreat.

The remaining question, then, is what caused the rise in water temperatures during this period.

The researchers traced these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. The warm, subsurface waters off the west Greenland coast are fed from the east by the subpolar gyre-or swirling water-of the North Atlantic, by way of the Irminger current.

The current flows westward along the south coast of Iceland. Since the mid-1990s, observations show a warming of the subpolar gyre and the northern Irminger Basin, which lies south of Greenland. The researchers attributed this warming to changes in the North Atlantic Oscillation (NAO), which is a large-scale fluctuation in the atmospheric pressure system situated in the region.

The surface pressure drives surface winds and wintertime storms from west to east across the North Atlantic affecting climate from New England to western Europe.

Specifically, they noted a major change in the behavior of the NAO during the winter of 1995?, which weakened the subpolar gyre, allowing warm subpolar waters to spread westward, beneath colder surface polar waters, and consequently on and over the west Greenland continental shelf. "The melting of the ice sheets is the wild card of future sea level," Holland explained, "and our results hint that modest changes in atmospheric circulation, possibly driven by anthropogenic influences, could also cause future rapid retreat of the Antarctic Ice Sheet, which holds a far greater potential for sea level rise."

[jethro]

To be fair though, Jakobshavn has been in retreat since at least the 1850's; it's retreat was faster during the 30's&40's than it has been in recent times.

http://www.ferdinand-engelbeen.be/klimaat/...nd_glacier.html