‘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
It’s funny what happens when you observe instead of being a lazy git and expect Nintendo boxes to churn out the gospel. This very same method was used to find that most coral island atolls over 60 years have stood their ground or increased in size despite sea a sea level rise of 120 millimetres.
http://www.newscientist.com/article/mg20627633.700-shapeshifting-islands-defy-sealevel-rise.html
No wonder they prefer computer simulations. Reality is just toooooo stark!
David Thomasq says:
January 26, 2011 at 12:26 pm
Thank you!
So have they figured out that glaciers “retreat” when they shrink and “expand” when they are getting bigger? Or are they still on that pill about glaciers advancing into the sea is proof that they are getting smaller?
As I recall it was our good friend J. Hansen who made the claim about lubrication, but in a law suit he couldn’t name one glaciologist who agreed with him.
“Warmer Temperatures”! Are these animal, vegetable , or mineral?
vukcevic says:
January 26, 2011 at 12:45 pm
“…It is the winters that got much warmer (from -9 to -5 C) consequently less ice generated.”
I would have thought a slightly ‘warmer’ air over Greenland would hold more moisture. Even so, -5 is still below freezing. Greenland is probably the largest highest feature within the Arctic and at it’s highest point is over 3000m. You will know that with either a dry or wet lapse rate temperatures over Greenland can only be lower than what they are at sea level, and at the top that can be between -18 to -30 below the -5, or whatever the temperature is at sea level. As Greenland sticks up so much it will squeeze moisture out of whatever air that passes over it.
Anthony visited this subject back in 2009:
http://wattsupwiththat.com/2009/08/27/why-the-greenland-and-antarctic-ice-sheets-are-not-collapsing/
“In reality the Greenland and Antarctic ice sheets occupy deep basins, and cannot slide down a plane. Furthermore glacial flow depends on stress (including the important yield stress) as well as temperature, and much of the ice sheets are well below melting point.”
At least the Nature acknowledges observation instead of ignoring it.
I meant “At least the Nature article acknowledges…”
When the author (whos results we all embrace) was asked if he thought his work suggested the wider risks of global warming could be discounted, he said:
“Not at all.”
Surely a glacier’s flow depends on it’s weight, not temperature. If a glacier gains mass higher up this could increase it’s speed. So a rise in temperature could speed up a glacier as it gains mass but also shorten it as the freezing point moves up in height.
Next they will be saying that the Carbon indulgences stolen from Europe have reduced CO2 enough to explain the non-warming temps for last 12 years.
According to the mann made climate hippies Greenland has been through worse warm weather before, and the damn ice is still frakking there a t’ousand years later.
And before that there were several periods with several hundred years of warmer ‘an normal weather incapsulating that enormously thickly icy island.
Apparently, nobody seem to really know how the ice works in and for Greenland, because physically it would have made more sense if inner siberia and inner US/Canada was covered in a couple of mile high ice sheet instead of Greenland which has always be wrapped in kind of warm water.
And more ‘an a hundred t’ousand years o’ accumulated pesky soot has still to make a significant melting dent. :p
So, essentially, Greenland is in a state of abnormal flux then compared to the climate hippies standards of normal.
Besides nobody knows what the actual proper size of Greenland used to be before satellites.
Come to think of it, but what is the supposed normal size of Greenland’s ice sheet?
Well at least there is acknowledgement that a glacier is not just a big slab of ice. It has a complex internal hydraulic system that we still know very little about. We shouldn’t make assertions about what glaciers will do until we learn a lot more about them.
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.
Pardon, but this was a letter published in Nature.
I’ve taken my grain of salt.
DD More says: Since the ice has been there for 420,000 years
Well, that is true for Antarctica, but not for Greenland. The ice cores show quite clearly that there is almost no ice during the glacial maxima and a lot during the warm periods. To be clear, many mountains in Greenland were above the ice pack 30k years ago, but are currently way under the top of the ice today. As suggested above, warm weather produces more snow, cold weather produces more sublimation (less ice).
“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.”
An idiotic simplistic example that does not even begin to have real world parallels (changes in water use, coastal and water table absorption, land use changes, plate tectonics and continental drift, sea depth changes, anthropogenic and natural terraforming, precipitation changes, vegetation changes, etc).
The world is not a glass of water waiting for an ice cube to be dropped into it.
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
Isn’t this the himalayas furore all over again? A quick look at Wikipedia (yes, I know …!) gives the mean altitude of the icesheet at 2,135 metres, so its surface is about 1 mile high on average. It’s rather cooler up there than at sea level, and a slightly warmer ocean nearby will increase the hydrological cycle to give more precipitation….
The icesheet isn’t about to melt any time soon. It will take several millenia – if we are not already back in an ice age by then.
@JimG on doing the math:
Yeah, I just did a back of the envelope calculation. Using the IPCC’s figure of 2.85e6 km**3 for the ice sheet and Wikipedia’s figure of 3.6e8 km**2 for the area of the oceans, you get 2850000 km**3/360000000 km**2 = 0.00792 km, or 7.92 m sea level rise.
This doesn’t take into account a lot of other factors, but it’s ballpark figure. At least the alarmists can do their math, even if they sometime apply it strangely.
I took a look at Colorado’s Jason data – Seasonal Signal Removed, Inverse Barometer Applied
Its interesting to look at the last few years at the same point
2006.7236 26.640
2007.7280 25.493
2008.7054 23.759
2009.7370 31.748
2010.7415 28.119
A 4 year net of 1.5mm
I really wonder where this claim of dangerous sea level rise came from?
Enjoy your blog. Jaw open after finding this article today and coming here to watch you all discuss it.
But, pardon my undergraduate ignorance, are they trying to tell us that somehow we just didn’t take into account the known phenomenon of water-carved riverways under the ice?
Didn’t the Grand Canyon get carved by a river and it’s supposed to be some kind of revelation that this event, on something as soft as a little frozen water with a nice dandy island sitting under it, wouldn’t be happening? And that it might serve as a “wick” of the heat that supposedly would melt the ice sheet otherwise?
Look! A satellite photo! Newly discovered river under the ice! That doesn’t mean global warming isn’t happening though.
Thank you all.
…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.”…
Hmmm…..gridded…is that where they interpolate values where no data exists?
Modern…. does that mean, erm, adjusted, enhanced?
simulations…. what’s wrong with observation and review/documentation/research
of existing data?
Just downloaded Nuuk GISS temp data series:-
http://data.giss.nasa.gov/work/gistemp/STATIONS//tmp.431042500000.1.1/station.txt
Plotted summer June, July and August since 1881. Sorry not “web techie” young enough to be able to show the plot, but it ain’t going anywhere, plum level, maybe slightly down.
REPLY: Easy to do. Simply upload your plot to http://tinypic.com and then provide a URL for it in the comment. – Anthony
To Jim G – by the way, a ball-park calculation would go: volume of the icesheet is 2,850,000 cubic km (683,750 cu mi). When melted this gives approx 91% of its volume as water, so 2,593,500 cu km.
The earths mean radius is, say, 6,370 km so its surface area (= 4*pi*r^2) is 509,905,000 sq km. About 71% of that is ocean, which is 356,933,500 sq km.
Ocean levels will therefore rise by 2,593,500 / 356,933,500 km, which is 7.27 metres.
It’s about right.
REPLY: Easy to do. Simply upload your plot to http://tinypic.com and then provide a URL for it in the comment. – Anthony
Thanks Anthony, will have a go!