‘Hidden plumbing’ helps slow Greenland ice flow
Hotter summers may not be as catastrophic for the Greenland ice sheet as previously feared and may actually slow down the flow of glaciers, according to new research.
A letter published in Nature on 27 January explains how increased melting in warmer years causes the internal drainage system of the ice sheet to ‘adapt’ and accommodate more melt-water, without speeding up the flow of ice toward the oceans. The findings have important implications for future assessments of global sea level rise.
The Greenland ice sheet covers roughly 80% of the surface of the island and contains enough water to raise sea levels by 7 metres if it were to melt completely. Rising temperatures in the Arctic in recent years have caused the ice sheet to shrink, prompting fears that it may be close to a ‘tipping point’ of no return.
Some of the ice loss has been attributed to the speed-up of glaciers due to increased surface melting. Each summer, warmer temperatures cause ice at the surface of the sheet to melt. This water then runs down a series of channels to the base of the glacier where it acts as a lubricant, allowing the ice sheet to flow rapidly across the bedrock toward the sea.
Summertime acceleration of ice flow has proved difficult for scientists to model, leading to uncertainties in projections of future sea level rise.
“It had been thought that more surface melting would cause the ice sheet to speed up and retreat faster, but our study suggests that the opposite could in fact be true,” said Professor Andrew Shepherd from the University of Leeds School of Earth and Environment, who led the study.
“If that’s the case, increases in surface melting expected over the 21st century may have no affect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”
The researchers used satellite observations of six landlocked glaciers in south-west Greenland, acquired by the European Space Agency, to study how ice flow develops in years of markedly different melting.
Although the initial speed-up of ice was similar in all years, slowdown occurred sooner in the warmest ones. The authors suggest that in these years the abundance of melt-water triggers an early switch in the plumbing at the base of the ice, causing a pressure drop that leads to reduced ice speeds.
This behaviour is similar to that of mountain glaciers, where the summertime speed-up of ice reduces once melt-water can drain efficiently.
Study co-author Dr Edward Hanna from the University of Sheffield added: “This work also underlines the usefulness of modern gridded climate datasets and melt-model simulations for exploring seasonal and year-to-year variations in Greenland ice sheet dynamics and their relationship with the global climate system.”
The study was funded by the Natural Environment Research Council’s National Centre for Earth Observation, the Philip Leverhulme Trust, and by the European Commission Ice2Sea project.
For more information
The Letter entitled ‘Melt-induced speed-up of Greenland ice-sheet offset by efficient subglacial drainage’ by Aud Venke Sundal, Andrew Shepherd, Peter Nienow, Edward Hanna, Steven Palmer & Philippe Huybrechts is published in Nature on 27 January 2011 [doi:10.1038/nature09740].
Contact Hannah Isom in the University of Leeds press office on 0113 343 5764 or email h.isom@leeds.ac.uk.
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See also:
Upcoming paper in Nature – Greenland ice sheet melt: “it’s weather, not climate”
Greenland Ground Zero for Global Soot Warming
h/t to Steve Milloy
I was under the impression that the ‘arctic’ winters were due to the moving Jet stream and blocking ‘high’ phenomenon as described by some guy from the Metoffice on that TV prog (Britains Big Freeze I think it was called) the other week.
Having said that, it is quite feasible that the Daily Mail reporters know more about the weather/climate than the MetOffice these days – LOL!
Jim G says:
January 26, 2011 at 2:43 pm
Can’t believe that the Greenland ice melting would raise sea levels that much. Anyone done the math on that? Such a small patch, such a big ocean.
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lol, yeh, my calcs were just like JamesS’. (I didn’t bother with the density thing, either.) Of course, this implies some implausible assumptions. For instance, would all of the water really run off to the oceans? No. They’d have rivers and lakes and the like. Then, of course, the question would be would atmospheric H2O increase? I say probably, but others may disagree. Also, the extra liquid H2O would somehow understand a boundary line between rivers and lakes, and seas and oceans. So, we’d only see an increase of rain in the oceans.
Well, here we go:-
Nuuk Summer JJA plot
http://tinypic.com/r/i5rp50/7
1DandyTroll says:
January 26, 2011 at 2:42 pm
. . . physically it would have made more sense if inner siberia and inner US/Canada was covered in a couple of mile high ice sheet…
Glacial ice is much like a sedimentary rock – both require a source of sediment and have to be deposited for the mass to form. Grains of sand can be deposited when carried by moving water that slows. Grains of ice can be deposited when carried by air masses. So without an appropriately moist air mass to provide a source for the material needed for the deposit, it is highly unlikely that the mass will grow.
The mountains of B.C. and Washington State have high snow levels as they receive moist air masses from the Pacific Ocean –air high in moisture. Greenland likewise has moist-air mass source regions nearby. The regions mentioned by you in the quote above do not. Those areas also warm considerable in summer and are low in elevation. Case closed.
Antarctica is quite dry in places but high and cold. With so little melt, slow deposition is plenty good enough.
An afterthought: Some of these issues are best looked at on a globe and not a flat map.
There may be some debate as to the global extent of the MWP but what we know as an incontrovertible fact is that at that time Greenland was considerably warmer than today (witness Viking settlements that are beginning to reveal themselves as the ice retreats and at those settlements the Vikings were able to farm – today it is presently too cold to farm there) and we know that even further back in time, Greenland was weven warmer. The world did not come to an end because of these warmer temperatures affecting Greenland nor were there drastic sea level rises. This sis a fact which strongly undermines the alarmists scare stories. The nub of this matter is as Jimbo states:
Jimbo says:
January 26, 2011 at 1:26 pm
It’s as if every week / month we find evidence of why there won’t be catastrophic positive feedback runaway global warming. And here I was being told about lubrication and tipping points. I’m beginning to warm to the Gaia hypothesis. ;O)
Nils-Axel Morner
“The Greenland Ice Cap did not melt during the postglacial hypsithermal (some 5000 to 8000 years ago), when temperature was about 2.5 C higher than today. Nor did it melt during the Last Interglacial when temperature was about 4C higher than today. As to time, it would take more than a millennium (with full thermal forcing) to melt the ice masses stored there.”
http://climaterealists.com/?id=6137
http://dx.doi.org/10.1016/0033-5894(74)90038-6
I could be totally wrong, but I seem to remember that when the IPCC (make sign of cross, grasp rosary beads) made predictions on sea-level rise for this century, they actually didn’t include glaciers flowing into the sea, because they (rightly) concluded that they couldn’t model it accurately? That is, they were cautious and prescient.
Anyway, nice post, and interesting research.
History of Greenland:
http://en.wikipedia.org/wiki/File:Grtemp.png
I believe the recent readjustments of ice loss are based on new gps data at the base of the ice which allowed accurate maping of the isostatic rebound of the rock below the ice. What I thought was interesting is that it appeared to show that the rock below the deepest part of Greenland was sinking under the weight of the ice instead of rebounding. In otherwords gaining volume.
Actually, “affect” is a noun too, but it means emotion, or emotional display. Probably not relevant to glaciers, though.
😉
Here is an article about the new ice loss estimates which are evidently 1/3 of previous estimates. Scientists suggest more gps data is needed. I suspect once they get more data in the center of the basin maybe they willl find they are actually gaining ice.
http://www.martinfrost.ws/htmlfiles/sept2010/greenland-icemelt.html
richard verney says:
January 26, 2011 at 4:31 pm
“(witness Viking settlements that are beginning to reveal themselves as the ice retreats and at those settlements the Vikings were able to farm – today it is presently too cold to farm there) ”
Hi there richard. Your statement that it is too cold to farm in Greenland today is wrong.
I think you’ll be interested in these links that show there are plenty of farms in Greenland today.
http://www.environmentalgraffiti.com/ecology/greenland-is-green-again/392
“51 farms (all of them sheep farms except for one with 22 cows)
[snip]
A local supermarket in Greenland is stocking fresh locally grown cauliflower, broccoli, and cabbage for the first time.”
And another interesting article on farming in Greenland…
http://www.spiegel.de/international/spiegel/0,1518,434356,00.html
Global Warming a Boon for Greenland’s Farmers
“Known for its massive ice sheets, Greenland is feeling the effects of global warming as rising temperatures have expanded the island’s growing season and crops are flourishing. For the first time in hundreds of years, it has become possible to raise cattle and start dairy farms.”
Many people think that Greenland is completely covered in ice. Do a quick Google search for images of Greenland farms or take a tour of South West Greenland in Google Earth if you need more proof that there is plenty of green[farm]land in Greenland today.
Regards, Martin
Regarding the ‘melt and rising sea level’ discussion. Do the doomsday scenario’s take into account that a lot of the water is already below sea level? ( in some places almost 1,000 feet below sea level)
The two James’ did some quick calculations in this thread…did you guys account for this when you estimated the sea level rise. When the ‘Greenland is melting’ argument gets trotted out by Algore and other alarmists I would assume they have some research that has calculated the rise in sea level….is it safe to assume they properly accounted the sub sea level ice? Or did it take an armchair scientist like me to figure it out?
Andrew@January 26, 2011 at 6:46 pm
Don’t worry, the scientists do take things like this into account, together with many others you haven’t though of yet.
I think this is an interesting and important article. It shows that scientists who develop results which show that climate change may not be catastrophic are willing and able to get their results published.
This indicates that charges, made by some, that there is a conspiracy at work, to promote alarmism, and scientists that don’t conform lose funding and are discouraged from publishing, have no real basis.
As a previous poster said, the IPCC did not include accelerated melting of the Greenland Ice sheet in its sea level estimate, because the process was insufficiently understood, and the data was not there. This vindicates the collective judgment of the scientists who were responsible for the sea level rise projections made by the IPCC.
It will be interesting to see the followup papers on this subject. The paper does not mean that the world’s glaciers are not losing ice, because they are melting. It only means that the speed with which they are sliding into the ocean is not increasing due to lubrication by melt water. There is still acceleration as a result of the breakup of ice shelves which serve to hold back the glaciers from sliding into the ocean. The paper doesn’t deal with this phenomenon at all.
http://www.scientificamerican.com/article.cfm?id=polar-ice-shelf-break
“In Greenland the story of not so glacial changes in the outlet glaciers is much the same. Their seaward edges are speeding up, and the ice sheet behind them is thinning. Measurements of local gravitational anomalies by the GRACE satellites show that the Greenland ice sheet, particularly in its southern reaches, is rapidly losing mass. “The ice sheet is on a diet,” Bell says. A lot of Greenland ice is slipping into the Atlantic Ocean.”
The observations in the above paper apply to specific glaciers. The experience of other researchers on other glaciers appears to be different.
http://www.truth-out.org/article/greenlands-ice-sheet-is-slip-sliding-away
“The camp has been rafting on the ice stream toward the sea, on average, at about 1 foot every day. Since Steffen pitched the main tents, the camp has moved about a mile downhill.
When Zwally started tracking the velocity of the ice with Global Positioning System sensors in 1996, the ice flow maintained a steady pace all year.
But he soon discovered that the ice around Swiss Camp had abruptly shifted gears in the summer, moving faster when the surface ice started to melt. By 1999, the ice stream had almost tripled its speed to about 3 feet a day.
In an influential paper published in Science, Zwally surmised that the ice sheets had accelerated in response to warmer temperatures, as summer meltwater lubricated the base of the ice sheet and allowed it to slide faster toward the sea.”
Malcolm Latarche says:
January 26, 2011 at 2:53 pm
“And it looks as though the glaciers are growing in the Himalayas
http://www.sciencenews.org/view/generic/id/69058/title/Glaciers_largely_stable_in_one_range_of_Himalayas ”
I think you are not reading carefully and allowing an anti AGW bias to blind you to the facts. The lead in the article says,
“Glaciers largely stable in one range of Himalayas
Ice in Karakoram region may even be growing, thanks to debris cover.”
So it is not established that the glaciers in the Karakoram region are growing, it says they are stable and may be growing. In fact, the article says that most of the glaciers studied are shrinking and the Karakoram region is an exception.
“Throughout most Himalayan ranges, roughly 65 percent of the studied glaciers were shrinking, Dirk Scherler of the University of Potsdam, Germany, and his colleagues report in the January 23 Nature Geoscience. But in Karakoram, 58 percent of studied glaciers were stable or slowly expanding up to 12 meters per year.”
John Brookes if the scientist had taken andrew comment into account then this research paper would not have made it here. Scienctist do not take all things into account because they will not allow debate so they do not get other ideas to check out, hence papers like these come up and show us they do not take any and all things into acoount. John you will find even more scienctist here than at Jonovas, so do not try your trolling arguments here they will shred you.
@ur momisugly Andrew says:
January 26, 2011 at 6:46 pm
Hmmm, you mean when I said there’d be lakes and rivers and things?
http://wattsupwiththat.com/2011/01/26/hotter-summers-may-not-be-as-catastrophic-for-the-greenland-ice-sheet/#comment-584068
@Andrew: while accepted that much of the base of the Antarctic sheet is below sea level, is this also true of Greenland (the one discussed here)? Could you provide a link to some data on this please – I will then come back with revised estimate (ball-park, as earlier!).
It just makes such a mockery of the catastrophism we have had rammed down our throats for the last 15 years. And in the soul searching whch is now beginning about why nobody listens to scientists anymore, I am afraid that they have absolutely no one but themselves to blame.
If there is water enough in Greenland to mathematically raise the levels of the oceans by close to 8 meters, if it melted, such a happening would mean that surface of the oceans would increase enormously through the no doubt immense flooding. The net increase in ocean level I leave to someone else to calculate…
LazyTeenager says:
What part of the law of conservation of mass and concept of density don’t you understand?
Do this experiment. Fill a glass of water to the brim. Hold it over your lap. Drop in an ice cube. Predicted outcome: you wet your pants.
Fill a glass of water to the brim. Hold it over your lap. Drop in anything else. Predicted outcome: you wet your pants.
Fill a glass about half way, drop in an ice cube and mark the level of water on the side of the glass. Wait for the ice to melt. Is the level of water higher, lower, or the same as the mark you have made?
Ice melting from a land mass – how heavy is the ice before it melts? Does that unmelted ice have any significant effect on the level of the land beneath it? For broad comparison purposes there is historic data on Britain from the end of the last glaciation which had ice around a mile/mile and half deep at Birmingham, in this glaciation it didn’t reach all the way South. Scotland and the islands in the North initially rebounded fairly quickly from being released from the ice, some 150 ft in places iirc; it’s still going on but at a slower rate, Southhampton on the South coast is still sinking. You might be able to find enough data from geologists’ sources on-line to work out what effect this would have on Greenland. Let us know when you do.
It is my understanding of Greenland that the ice sheet sits in a depression caused by the weight of the ice and it is this that prevents ice from ‘speeding up’ towards the sea. Ice in contact with the surface rock melts due to the weight of ice above and warming from geothermal heat. There must be sub-icesheet lakes on Greenland due to this as there are on Antarctica.
The ice cores most definitely do not show this. The Greenland ice extends to the edge of the continental shelf during glaciations and is much larger than during interglacials. It is the accumulation that is smaller since climate is much drier but this is more than balanced by less melting.
<blockquote<Does that unmelted ice have any significant effect on the level of the land beneath it?
It sure has. In central Sweden the land has risen about 300 meters since the ice melted 10,000 years ago, and that is without counting the rise that occurred while the ice was thinning but had not yet melted completely. The total rise was probably closer to a kilometer. At the same time areas outside the icecap (e. g. southern England, Netherlands, northern Germany) are sinking as material flows slowly back into the depression under the former icecap.
I suspect that many catastrophists within the climate science community have had second thoughts and are beginning to explore ways in which they can retain their credibility, their funding and their careers as they slowly and carefully retreat from their previous extreme Chicken Little positions. It takes a lot of courage to hold one’s hand up to getting day-to-day stuff wrong, but when a professional lifetime is invested in what is becoming evident was an error, the amount of courage required for such admissions must be enormous.
Some scientists obviously don’t have that courage, as witness Trenberth’s ridiculous demand that the null hypothesis be reversed.
@Dan: good point, but if the sea level rise were to inundate an additional 1% of the earth’s surface area (5E+6 sq km – a lot of land, but possible) this would reduce the rise from 7.27 to 7.16 m on my ball-park figures, to give some idea of scale.
@Andrew: and if it first had to back-fill a pond of 1.71E+5 sq km area (the full sheet) x 0.5 km deep, say, the rise would then be only 4.80 m.