Guest Commentary by Mauri Pelto
The net loss in volume and hence sea level contribution of the Greenland Ice Sheet (GIS) has doubled in recent years from 90 to 220 cubic kilometers/year has been noted recently (Rignot and Kanagaratnam, 2007). The main cause of this increase is the acceleration of several large outlet glaciers. There has also been an alarming increase in the number of photographs of meltwater draining into a moulin somewhere on the GIS, often near Swiss Camp (35 km inland from the calving front). The story goes—warmer temperatures, more surface melting, more meltwater draining through moulins to glacier base, lubricating glacier bed, reducing friction, increasing velocity, and finally raising sea level. Examining this issue two years RealClimate suggested this was likely the correct story. A number of recent results suggest that we need to take another look at this story.
The Acceleration:
Jakobshavn Glacier, West Greenland, retreated 30 km from 1850-1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining an estimated 6% of the GIS. The glacier terminus region also had a consistent velocity of 19 meters/day (maximum of 26 m in glacier center), from season to season and year to year, the glacier seemed to be in balance, as I noted in a 1989paper. This is the fastest glacier in the world, no steroids needed. After 1997 it began to accelerate and thin rapidly, reaching an average velocity of 34 m/day in the terminus region. The glacier thinned at a rate of up to 15 m/year and retreated 5 km in six years. Jakobshavn has since slowed to near its pre-1997 speed, the terminus retreat is still occurring, but likewise is.
Helheim Glacier, East Greenland had a stable terminus from the 1970’s-2000. In 2001-2005 the glacier retreated 7 km and accelerated from 20 m/day to 33 m/day, while thinning up to 130 meters in the terminus region. Kangerdlugssuaq Glacier, East Greenland had a stable terminus history from 1960-2002. The glacier velocity was 13 m/day in the 1990’s. In 2004-2005 it accelerated to 36 m/day and thinned by up to 100 m in the lower reach of the glacier. Helheim and Kangerdlugssuaq combined drain 8 % of GIS. Hence, they are more than canaries in the coal mine. In 2006, the velocity of Helheim and Kangerdlugssuaq decreased to near the 2000 level, the terminus of Helheim advanced a bit (Howat et al., 2007).
The first mechanism for explaining the change in velocity is the “Zwally effect”, which relies on meltwater reaching the glacier base and reducing the friction through a higher basal water pressure. A moulin is the conduit for the additional meltwater to reach the glacier base. This idea, proposed by Jay Zwally, was observed to be the cause of a brief seasonal acceleration of up to 20 % on the Jakobshavns Glacier in 1998 and 1999 at Swiss Camp (Zwally et al., 2002). The acceleration lasted two-three months and was less than 10% in 1996 and 1997 for example. They offered a conclusion that the “coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming”. The acceleration of the three glaciers had not occurred at the time of this study and they were not concluding or implying that the meltwater increase was the cause of the aforementioned acceleration. However, many others have made this assertion and are investigating (Stearns and Hamilton, 2007). Examination of recent rapid supra-glacial lake drainage documented short term velocity changes due to such events, but they had little significance to the annual flow of the large glaciers outlet glaciers (Das et.al, 2008).
The second mechanism is a “Jakobshavn effect”, coined by Terry Hughes, (1986), where a force small imbalance of forces caused by some perturbation can cause a substantial non-linear response. In this case an imbalance of forces at the calving front propagates up-glacier. Thinning causes the glacier to be more buoyant, even becoming afloat at the calving front, and is responsive to tidal changes. The reduced friction due to greater buoyancy allows for an increase in velocity. This is akin to letting off the emergency brake a bit. The reduced resistive force at the calving front is then propagated up glacier via longitudinal extension in what R. Thomas calls a backforce reduction (Thomas, 2003 and 2004). For ice streaming sections of large outlet glaciers (in Antarctica as well) there is always water at the base of the glacier that helps lubricate the flow. This water is, however, generally from basal processes, not surface melting.
If the Zwally effect is the key than since meltwater is a seasonal input, velocity would have a seasonal signal. If the Jakobshavn effect is the key the velocity will propagate up-glacier, the terminus velocity will be impacted by tides, and there will be no seasonal cycle.
On Jakobshavn the acceleration began at the calving front and spread up-glacier 20 km in 1997 and up to 55 km inland by 2003 (Joughin et al., 2004). On Helheim the thinning and velocity propagated up-glacier from the calving front. Each of the glaciers fronts did respond to tidal variations indicating they had become afloat, detached from their bed (Hamilton et al, 2006). This had been the case at Jakobshavn for the last 50 years, but not for Helheim or Kangerdlussuaq. In each case the major outlet glaciers accelerated by at least 50%, much larger than the impact noted due to summer meltwater increase. On Jakobshavn the acceleration was not restricted to the summer, persisting through the winter when surface meltwater is absent.
As a result of the above Luckman et al. ( 2006) concluded:
“The most plausible sequence of events is that the thinning eventually reached a threshold, ungrounded the glacier tongues and subsequently allowed acceleration, retreat and further thinning. It is reasonable to believe that the 1998 Jakobshavn speed-up, also following a long period of stability, was triggered by the same processes of thinning but occurred earlier and after a shorter period of thinning because the tongue was already afloat.”
Examination of the acceleration of other glaciers such as the Petermann Glacier indicate a much smaller acceleration than that observed on three glaciers we have focused, and indeed it is in the summer and of a magnitude that the Zwally effect could explain (Rignot, 2005). Other large outlet glaciers such as the Rinks and Daugaard-Jensen have been stable since 1960 (Stearns et al, 2005). Many other lesser outlet glaciers have accelerated substantially.
That each of the three glaciers has a reduced velocity in 2006 and 2007 despite some exceptional melt conditions in 2007 further suggests that meltwater is not the dominant driver of the acceleration of the main outlet glaciers. Temporarily, there appears to be a force imbalance at the glacier fronts. This will reduce the annual contribution to rising sea level from glacier dynamic changes. The bad news is that the degree of acceleration that can occur via the Jakobshavn effect is greater in these cases than that from the Zwally effect. The Zwally effect is nonetheless real and also implies a direct sea level impact of greater melt.
The Jakobshavn is of particular importance as it has a bed below sea level for at least 80 km inland from the terminus. In this reach there are no significant pinning points, or abrupt changes in slope or width (Clarke and Echelmeyer, 1996) that would help stabilize the glacier during retreat. It is the only outlet glacier of GIS to lack these, and can then (via backforce reductions) tap into the heart of GIS. We know that surface melting is a slow process for raising sea level. but as Greenland’s major outlet glaciers have recently shown, rapid acceleration can quickly deliver large volume of ice to the ocean. The pace of change is not glacial.
Clarke, T.S. & Echelmeyer, K. 1996: Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland. Journal of Glaciology 42(141), 219–232.
Hughes, T. (1986), The Jakobshavn effect. Geophysical Research Letters, 13, 46-48.
Pelto, M.S., Hughes, T.J. & Brecher, H.H. 1989: Equilibrium state of
Jakobshavns Isbræ, West Greenland. Annals of Glaciology 12, 127–131.,
Thomas, R. H. Abdalati W, Frederick E, Krabill WB, Manizade S, Steffen K, (2003) Investigation of surface melting and dynamic thinning on Jakobshavn Isbrae, Greenland. Journal of Glaciology 49, 231-239.
Thomas RH (2004), Force-perturbation analysis of recent thinning and acceleration of Jakobshavn Isbrae, Greenland, Journal of Glaciology 50 (168): 57-66.
Another contributing factor here appears to be the Arctic Spring Haze of airborne pollutants –
http://www.sciencedaily.com/releases/2008/04/080407132120.htm
Warming air melts the ice faster, thin ice is blown apart by the winds and currents in the Arctic Ocean, leading to large areas where the ocean can freely exchange heat with the atmosphere (the rate being dependent on wind and other factors – for more see http://eesc.columbia.edu/courses/ees/climate/lectures/o_atm.html ).
The actual effect of all that is not intuitive, but has to be analyzed using computers for data collection, data analysis and modeling. A lot of “skeptics” don’t seem to understand the basic process of model design and refinement – make a model, see what it misses, refine the model, see what it misses, and keep iterating. It is not a “curve-fitting process” – real data is used to initialize the model, but then no comparison is made to the real data until afterwards. So, the question is, has anyone made a model, which, when initialized with say, 1980 conditions, predicts the rapid loss of sea ice in the Arctic? Such a model might have a difficult time predicting the amount of Arctic spring haze pollution each year – so that might be an external variable, set by the researcher.
It’s also worth looking at some glaciers that are not going with the overall melting trend:
http://www.springerlink.com/content/a3581383141m4126/
Howat et. al 2006: A precipitation-dominated, mid-latitude glacier system: Mount Shasta, California
So, that’s a very useful number – 1C rise in temp must be countered by a 20% increase in precipitation. Is it widely applicable, or limited to mountain glaciers, or to Shasta in particular?
Re 91
Greenland has the potential to make its own weather. It rises to produce orogenic precipitation, whchever way the wind blows. Its ice provides a temperature diferential to steer winds from either the North Atlantic or the newly ice free Arctic Ocean.
These days, I think of Greenland less as a pile of ice accumulating snow, and more as a water shed with a summer (March to November) rainy season – with no plants to retard runoff. Where does that water go? How much energy does water flowing through a moulin release?
Re #101
Regarding the comments about arctic haze, our ‘Johnny on the spot’, Wayne Davidson has been observing very clear skies for the last couple of years and associates that with the warming and melting.
http://www.eh2r.com/
Regarding the 1º/20% increase number I would expect that to be site dependent although there must be a link everywhere.
Mauri Pelto,
Thanks for the article and your active involvement in this thread.
#87 Gary,
Didn’t you think to check around for the uncertainty involved in the 3.05mm/yr you quote? Or do you really think it’s 3.05 exactly with no uncertainty?
From IPCC AR4 Chapter 5
http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
“Numerous papers on the altimetry results (see Cazenave and Nerem, 2004, for a review) show a current rate of sea level rise of 3.1 ± 0.7 mm yr–1 over 1993 to 2003 (Cazenave and Nerem, 2004; Leuliette et al., 2004)”
So that’s 2.4 to 2.8mm per year. If you’re worried about supposed IPCC bias you may want to try reading the references from which those AR4 statements are drawn.
The second item you link to merely shows that a lot of work is being done by the experts, so it is pointless to draw conclusions at this stage with respect to Argo, deployed in 2003. However it should hhave been apparent to you from your first link that the altimeters show a sea level rise from 2003 to 2007 at the same rate as previously. And the previous rise was in part due to thermal expansion. So if the oceans have really cooled…
Well it’s discussed in the article, which is an interesting lay person’s read through to the final paragraph(hint).
Sorry but the Investor’s Business Daily page at the end of your final link is a complete joke (It’s your use of it that suggests to me you’re in denial. Getting suckered by such carp is almost on the same level as believing a schoolkid can undermine a whole branch of science.)
You state “the U.N. admits there has been no atmospheric increase in temperature since 1998” The Investor’s Business Daily(IBD) article you link to implicitly supports this contention. Yet it is only the article itself that makes this incorrect assertion, not the UN!
Have a look at the CRU global average temperature: http://www.cru.uea.ac.uk/cru/data/temperature/nhshgl.gif Have a look at that graph, it’s telling the true sceptic something crucial. (scientists should be sceptical, denialists cling to their precious beliefs in the face of evidence)
By any of the 3 main datasets it is clear that 1998 was an outlier, this is accepted, it is only those in denial (like the author that article) who make a straw man of 1998. i.e.
From the IBD article:
“If that’s the case, then why can’t the Pacific’s El Nino current, which played a large part in the warm reading for 1998, simply been seen as a “variability” and not part of a greater warming trend? Because it doesn’t fit the agenda?”
To which I answer:
“El Nino IS seem as natural variability, you dolt.”
It would be correct to say “global average temperature remains below the 1998 peak in the CRU dataset”. But it is clearly wrong to say “There has been no increase in global average temperature since 1998.” Both of those statements are factual and as Mark Twain once said (paraphrased); a person is entitled to their own opinion, but they are not entitled to their own facts.
Click on this link http://data.giss.nasa.gov/gistemp/maps/
Select “Hadley/Reyn_v2” as ocean data source. Then select year/month or year and annual/seasonal averages. You will find that the cooling is predominantly in the southern hemisphere’s oceans, mainly the Pacific – that’s the La Nina.
This supported by considering the GISS 3 latitude banded plot: http://data.giss.nasa.gov/gistemp/graphs/Fig.B.lrg.gif
And is the detail I suggested is also available to a sceptic looking at the CRU plot. The northern hemisphere continues to warm on a multi-year timescale. Tamino also covers this here: http://tamino.wordpress.com/2008/01/24/giss-ncdc-hadcru/ NB the last graph and text around it.
In short there is NO evidence that Global Warming has stopped.
To underline the errors you’ll get (either way – alarmist or denialist) in fussing over blips, in the IBD article they also state:
“Of course the IPCC spins the news.
You should look at trends over a pretty long period,” said WMO Secretary-General Michel Jarraud, “and the trend of temperature globally is still very much indicative of warming.”
Jarraud is of course not spinning, in both the reference to La Nina and the need to look at the relevant timescales is a warming to view data in it’s relevant context. The weakness of focussing on year to year fluctuation is demonstrated by playing “time machine” with one of the temperature datasets. Pretend we’re in 1991 on the CRU dataset, after that you have 3 cooler years cooling, then the temperature rises again. 2007 was only the 4th year below the previous peak. Without a La Nina it may have been higher, as for 2008, we’ll see. You could also try “Time Machine” with your altimeter SLR graphs.
In the IBD article they refer vaguely to a ‘bombshell’ paper that shows “”the weight of the current evidence . . . supports the conclusion” there is no agreement between the models and the observation temperatures.”
I can only presume this is a reference to Douglass et al which was done by RC last year https://www.realclimate.org/index.php/archives/2007/12/tropical-troposphere-trends/ The headline results of Douglass are (IMHO) not worth the paper they’re written on.
Anyway, at least the last sentence gave me a giggle:
“The global warming debate is not over. Indeed, the debate is beginning to favor the skeptics.”
Yes that’s it old bean, if you keep on repeating it, it’ll come true.
Soon the denialists will be clicking the heels of their shoes together as they wish with closed eyes. Unfortunately for them a physical system like the Earth’s climate is not amenable to sleight of hand and “Wormtongue” council.
Re#99
“Pete, the remnants of the older sea ice have all already broken up and appear ready to weaken substantially.”
Just look here for evidence of that (particularly the Beaufort sea):
Today http://manati.orbit.nesdis.noaa.gov/ice_image21/D08112.NHEAVEH.GIF
Last year http://manati.orbit.nesdis.noaa.gov/ice_image21/2007/D07100.NHEAVEH.GIF
The white sea areas are perennial ice, the grey ice formed this winter
Phil, I don’t find any discussion of aerosols or spring haze in the Wayne Davidson reports – mostly he is talking about the effects of warm Arctic air. For a better discussion of that, try this news report:
http://www.nunatsiaq.com/archives/41217/news/nunavut/41217_05.html
So, he hasn’t been observing “very clear skies” – just a warm air mass. In fact, there’s no way he could get comprehensive data on aerosols from his weather station.
From the NOAA people:
NOAA’s “State of the Arctic” reports of the past few years make for interesting reading in light of recent events – and now they may be wondering why they got it so wrong. (Quote: “There are indications that some components of the physical system may be recovering and returning to the recent climatological norms observed from 1950 to 1980.” – Oct 2006, NOAA State of the Arctic Report)
Re 96
If water falls a kilometer down a moulin, where does its kinetic energy go? Not to the basal ice? If the Melt water is 0C and the basal ice is -10C, why can’t the falling water warm the colder ice below? Suppose the basal ice is near the maximum temperature at which it has the mechanical strength to support the ice above it. (This would be some temperature below its pressure melting point.) Then, additional heat is advected to the basal ice. The additional heat weakens the ice. It is not necessary to melt the ice in-situ, only warm to it the point where it loses the required structural strength to support its overburden. The situation at the base of the GIS where ice is under significant pressure is somewhat different from a glacier. (The ice in a glacier is more likely to relive stress by creep. Except see http://query.nytimes.com/gst/abstract.html?res=980CE1D81F39E233A25757C1A9619C94639ED7CF)
What is the mechanical process of ice failing? Is that process different when ice is near its pressure melting point? What are the molecular physics of ice in structural failure under high pressure? By and large, the engineering community has only looked at the smaller loads found in the near surface environment. (My calculation is that under very high pressures, ice failure releases heat. This is not inconsistent with http://www.luth.se/depts/lib/coldtech/ct91-1.html and http://www.bjerkas.info/Papers/2004-JSC-454-Bjerkas.pdf.
When I look at (http://nsidc.org/data/virtual_globes/ ), I see increasing areas of melt and increasing days of melt across the GIS, melt season by melt season. Since melt drains off ice, or down through moulins in the ice very rapidly, area and depth of supraglacial lakes is not proportional to total surface melt. Moreover, colder ice tends to hold water on its surface better than warmer, weaker ice. Thus, as a percentage of total melt, I would expect less water on the surface of the Greenland Ice Sheet now, than in the past. On the other hand, now and in the near future, I would expect a larger volume of melt water advecting heat to the base of the ice.
Re: #105
Phil, thanks for the images. Yikes!
OK, I am going to go out on a limb here and say that, in my opinion, due to lack of funds, personnel, equipment, rapidity of the changes, etc., research so far on Greenland has largely been limited to the tail of the elephant. We need more indepth surveys of the ice streams and what their dynamics are.
The amount of meltwater generated has increased, the amount draining through moulins has increased. The amount of increase is not known, but it has not increased by anything close to 50%. In the rapidly moving outlet glaciers the base of the glacier is at the pressure melting temperature not -10 C. The cold water cannot provide that much heat to the ice via advection. The amount of water is also not that much greater. Focus on what is happening at the glacial front, that is where the critical changes have been occurring. The point of this point was to clear up the misconception that increased meltwater delivered to the bottom of the GIS is driving the acceleration of the large outlet glacier. It is not, for all of the reasons noted.
Despite all our speculation, this seems conclusive (I hadn’t seen this when I posted immediately after it):
mauri pelto Says:
22 April 2008 at 9:40 AM
“… it is not the surface melting that has driven the acceleration. End of story. It is not what is happening upglacier that has been the key. …..”
and goes into detail about why.
“Phil, I don’t find any discussion of aerosols or spring haze in the Wayne Davidson reports – mostly he is talking about the effects of warm Arctic air. For a better discussion of that, try this news report:
http://www.nunatsiaq.com/archives/41217/news/nunavut/41217_05.html
So, he hasn’t been observing “very clear skies” – just a warm air mass. In fact, there’s no way he could get comprehensive data on aerosols from his weather station.”
So I was dreaming when I read this:
“Now in very warm Resolute April, again with clear skies,”
“especially clear Arctic skies”
“its hard for me to understand what LaNina has to do with Arctic clear air.”
“Extraordinary persistence of the cold temperature North Pole since last March 07 has its roots in clear air over Ellesmere North Baffin Islands area,”
et cetera?
It’s clear from reading his reports that Wayne thinks the Arctic air is currently unusually clear and that this is related to the melting. No what instrumentation he has I’m sure that he would notice ‘haze’.
Perhaps I’ve missed this, but someone upthread asked how we know this melting isn’t a return to equilibrium from an earlier cool period.
I looked at the terrain near the glacier’s outflow area and saw a significant number of marks from where a much larger glacier had been there, presumably millenia ago.
Obviously, the glacier is melting, my question is — how much and for how long? Because I’m starting to get concerned by the rhetoric about “We have to do even more, because it might be even worse!” and the prospects in that another century or two there’s a “Little Ice Age” and entire world has shifted into “It’s getting warmer! It’s getting warmer!” The worst possible scenario is often not the one that isn’t planned for — it’s the one that was intentionally ruled out. Knowing how much and for how long would be a good thing in terms of understanding how much this might be a response to emerging from the early 1800’s.
#111 Phil and Ike. There is definitely warming Up Here, along with remarkably clear air, an astronomer friend calls it: “molecular air” . First there seems to be a small misunderstanding of the Arctic . There are no highways, no factories, nothing but Antarctic like wilderness without all the ice. A single station observing an increase in air quality has a range much greater than a simple dot on a map. The atmosphere moves, not the station, so a continuous stream of observations of clear air is very significant. There are two basic ways of seeing clear air, by colour and also by brightness during the long night. Over the last few years, both colour, so crisp “molecular colours” were noted along with brighter twilights ( really startling High Arctic dwellers) at the horizon (thickest air possible), indicating a reduction in air turbidity amongst other refraction effects.
http://www.eh2r.com/comparepages/compare_main.html
using a photometer one can observe various brightness depending on Aerosols, Ice crystals ,clouds and refraction effect as well. Clear cloudless air has been a dominant player here
since March 07. Not only at one station, but as reported during the great melt of 07.
I would also like to thank Mr Pelto for his helpful presentation and feedback, I still wonder if there are there are deep inside the core temperature measurements within Ice sheets…
Mauri,
(#96) I think this puts a finger on where I am not understanding the argument. I don’t see why a seasonal signal 35 km upstream would be preserved as seasonal and not just show up as a general acceleration.
The thinning at the outlet is not due to melting, correct? Thus, I am picturing it as owing to acceleration through mass conservation. Is this a problem?
After this portion, I think I follow: the thinner ice floats closer to the shore and thus the calving front retreats. This then can provide a feedback for more acceleration, more thinning and further retreat of the front.
But, what was the origin of the original acceleration and the initial thinning? If it is merely chaotic, then the vissitudes at the outlet have no importance. The calving front will advance and retreat with no particular effect on average flow. If it is driven by an upstream requirement for greater outlet capacity then, again, it would seem that the upstream effects, where more material is being supplied by the effects of AGW is the thing to watch. If, contrary to the idea that enhanced local melting has little to do with the behavior of the outlet, warming is the cause of the thinning, then we see two potentially independent behaviors that could both contribute to sea level rise: A clearing of the plug and a larger supply of material to bubble on out.
Further thoughts would be appreciated.
Thanks.
Regarding the ongoing changes in the Arctic:
http://download.current-biology.com/pdfs/0960-9822/PIIS0960982207013255.pdf
Hoye et. al. Rapid advancement of spring in the High Arctic (2007)
http://www.axcessnews.com/index.php/articles/show/id/14475
U.S. scientists to study Arctic smog
So, has spring sprung across the northern Arctic? Probably around now – see the satellite view at http://www.opentopia.com/sunlightmaphemi.html
One aspect of this is the poleward atmospheric transport of organic pollutants. It’s the reason that so many organochlorine compounds are found in Inuit peoples and mammals in the region. They might actually have a minimal aerosol effect themselves – but they do condense out in the cold. See for example:
http://www.sciencemag.org/cgi/content/abstract/269/5221/240
Kidd et al “High Concentrations of Toxaphene in Fishes from a Subarctic Lake(1995), Science
As a result of this phenomenon, polar bears have among the highest levels of persistent organochlorine pollutants of any species:
http://www.ec.gc.ca/science/sandemay00/article4_e.html
The mechanism is also understood:
http://www.nature.com/nature/journal/v395/n6702/full/395585a0.html
Blais et al 1998 “Accumulation of persistent organochlorine compounds in mountains of western Canada”, Nature
Organochlorines are only one part of what gets transported north: http://www.physorg.com/news125121864.html
So, it’s easy to see how it could have a contributing influence. Indeed, it seems to be having a large influence in Alaska right now:
http://www.adn.com/news/alaska/story/383984.html
#105, 108:
Sea ice images shrunk and animated here.
There is of course no lack of energy in water at 0C. Because that’s actually water at 273Absolute running past ice at say only 243A. There’s no shortage of dT there, and the transfer will happen. Interesting, when you think of it in those terms; liquid water – the bete noir of the cryosphere – is perforce always at or above 273A while precious ice is always colder. Where water flows the energy goes, absolutely.
There is mention above and elsewhere that parts of interior Greenland (and Antarctica) beneath the glacial ice sheets are below sea level. Are there topographic maps which show this? And are the below-sea-level interior basins potential seas like the Aral or Caspian or are they potentially joined to the ocean like Hudson Bay or the Mediterranean? If the latter is there a below-present sea level connection (blocked by glacial ice) or is some amount of sea level rise required?
George, have a look at:
http://cegis.usgs.gov/sea_level_rise.html
http://cegis.usgs.gov/video/sealevel_world.avi
Check out the centre of Australia at around +70m, and google-fly over Ukraine through the Caspian then north to the Artic ocean looking for land levels above/below 80m Florida and Amazonia long gone. Nice places to sail, but you wouldnt want to live there.
It has been understood for sometime based on Investigations by the University of Alaska and ETH Zurich that the majority of the fast flow of Jakobshavns Isbrae is from deformation of the basal ice not sliding (Luthi et al, 2002) Borehole measurements revealed the existence of a substantial temperate layer, at the pressure melting point near 0oC at the base of the ice stream. The thickness of the temperate basal layer is between 40 and 50 m at the drill site, with a very high temperature gradient (0.11 K/m) in the ice above it.
Continued thinning of the terminus reach of outlet glaciers has been observed by Pfeffer (2007) to explain rapid retreat and acceleration of tidewater glaciers such as Columbia Glacier, Alaska.
The comparatively short duration of speed-up on Jakobshavns, Kangerdlugssuaq and
Helheim Glacier along with the speed up beginning at the calving front and working up glacier suggest this as the cause (Thomas , 2004; Howat and others, 2007). Howat and others (2005) proposed that the observed speed-up resulted from two effects, increased effective stress over the glacier’s main trunk following retreat of the calving front, with subsequent thinning propagating upglacier resulting in steeper surface slopes and velocity increase. Retreat of the calving front terminated where the bed slope reversed, allowing the glacier to re-equilibrate (Howat and others,2007). The reversed bed slope would inhibit steeper surface slopes from propagating upglacier.
Csatho et.al, (2007) note that the periodic thinning near the terminus of Jakobshavn has led to accelerated retreat in the past as well. Thinning can and does occur via increased ablation, which can then lead to greater flotation and acceleration.
Csatho, B., A.F. Schenk, C.J. van der Veen, and W. Krabill (2007), Intermittent
thinning of Jakobshavn Isbræ, west Greenland, since the Little Ice Age. Journal
of Glaciology
Howat, I.M., I. Joughin, S. Tulaczyk, and S. Gogineni (2005), Rapid retreat and
acceleration of Helheim Glacier, east Greenland. Geophysical Research Letters
32, L22502, doi:10.1029/2005GL024737.
Howat, I.M., I. Joughin, and T.A. Scambos (2007), Rapid changes in ice discharge
from Greenland outlet glaciers. Science 315, 1559-1561.
Joughin, I., W. Abdalati, and M. Fahnestock (2004a), Large fluctuations in speed on
Greenland’s Jakobshavn Isbræ glacier. Nature 432, 608-610.
LÜTHI, M. et al, 2002; Mechanisms of fast flow in Jakobshavn Isbræ, West Greenland: Part III. Measurements of ice deformation, temperature and cross-borehole conductivity in boreholes to the bedrock Journal of Glaciology, 48,162, 369-385
Pfeffer, W.T. (2007), A simple mechanism for irreversible tidewater glacier retreat.
Journal of Geophysical Research 112, F03S25, doi: 10.1029/2006JF000590.
Thomas, R.H. (2004), Force-perturbation analysis of recent thinning and
acceleration of Jakobshavn Isbræ, Greenland. Journal of Glaciology 50, 57-66.
Dr. Pelto, do you think there is anything that can be said about changes in behavior of meltwater on the surface of the ice (Greenland and Antarctic)? Is there a change in the amount or is it just being noticed and reported? If there’s a change on the surface, is there more meltwater going down into the ice? Is water in a crack able to make cracks larger? and if so, is anything known about what’s going on deeper?
I get the impression that “no data” is the answer about this, and wonder if I’m missing something — is it being talked about, even if nothing’s yet being published?
Re: #90 Phil. Fenton, #93 Nick Barnes, #105 Phil, #116 GlenFergus
The National Snow and Ice Data Center continue to update their graph in strange and miraculous ways. The graph of April 23 is now nearly identical to the graph of April 20, and now, once again, shows a very precipitous drop in Arctic sea ice relative to 2007.
At this point, it seems illogical to assume that processing errors and missing signals are at the root of these modifications.
All three graphs can be viewed here:
http://climatechangepsychology.blogspot.com/2008/04/national-snow-and-ice-data-center-graph.html
Thank you to Leon in Holland for giving me the heads up, again.
A few months ago there was a discussion about Greenland, and somebody post a link to graphics they had made of Greenland’s bedrock topography and a rendition of what Greenland would look like if ice free. The center of the island was open ocean, and there was a ring of mountainous islands around it. I’ve tried to find that link for george, but have had no luck.
Re: #123 JCH
See the link in comment #18
Using a value of 3m SLR for BAU-induced structural and dynamical suppression of the world economy (estimated by mapping deep into characteristic supply chains through specific plants and linking these up through the building blocks of the current global economy, and assessing capex, operational integrity, and safety margins etc as a function of SLR) and taking a value for world GDP as US$ 54,000,000,000,000, and equating 3 m SLR to 1.2 million km3 of ice (from the data in post 47), one can estimate the economic value of each km of ice. The value is about 44 million US $ per km3 of ice. That’s a lot of money being melted away.
mg (125) — A current estimate of the world’s GDP is $76 trillion per year, not 54 any more…
>National Snow and Ice Data Center charts
page says: “temporary spurious results may occur.”
http://nsidc.org/arcticseaicenews/
“The satellite data sources for these products, while generally providing complete coverage, are subject to gaps (shown in dark grey) in coverage because of satellite operations. In the daily extent timeseries, gaps are replaced with values interpolated from surrounding days, but temporary spurious results may occur. The current satellite source is aging and showing more frequent data gaps. NSIDC is investigating a reliable replacement data source. —Credit: National Snow and Ice Data Center”
Ike, #115, I find no contradictions with all your info, Arctic Haze is simply not as strong as it use to be, at least here, there are still toxins falling mixed with ice crystals, the recent air clarity may be attributed in part to a dominant wind change from Northwesterlies to Easterlies. A warmer atmosphere everywhere and in Russia especially may have reduced heating pollution a great deal, also abating haze. Over all, its been better “smog” wise for a few years now.
#125 mg,
Sorry, but in view of the uncertainties involved, I (and many others) find all such attempts to “value” the “fixtures and fittings” of this planet utterly unconvincing.
In light of our continued inadvertent “terraforming” of the Earth, it’s worth remembering that when one says of a person that they “know the cost of everything and the value of nothing.” It is not meant as a compliment.
;)
Thanks, Tenney, for the link at #18 to the ice-free Greenland simulation. I was hoping for something more like a topo map, but even from the link it appears that the interior below sea level basin(s) of Greenland are connected to the ocean by below sea level channels. If this is the case, is it only the weight and strength of the ice which currently fills the channels that prevents the ocean from reaching into the interior basins? And are there conditions of glacial deterioration under which the North Atlantic will be able to force its way below the ice?
126. it doesn’t really matter which value for world gdp value one takes although care should be taken not to use estimates too close to the point of global economy phase transition. the point of post 125 is to highlight that economic/financial connection can be made between phase transformation of ice sheets and BAU suppression of circuit configurations underpinning the current form of the world economy. more complex analysis of this looks at autocatalysis mechanisms during the time-lagged damage cascades and potential opportunities for recovery & reconstruction from BAU-derived economic residue. Better to mitigate.
George, try this:
http://stephenschneider.stanford.edu/Publications/PDF_Papers/ToniazzoEtAl2004.pdf
George, this is another one for you:
http://stephenschneider.stanford.edu/Publications/PDF_Papers/ToniazzoEtAl2004.pdf
129. there is no attempt whatsover to attempt to suggest that anyone knows the cost of everything or even the cost of a lot of things or even the cost of a few things. the issue to be addressed is to find ways of creating dialogue between those who are observing the disastrous events unfolding in nature and those whose world view is driven by financial and economic matters, irrespective of the planetary implications. if the communications disconnect cannot be addressed urgently and if people driving the massive engines of GHG emissions cannot be woken up then that is very sad, for many will suffer. at the end of the day, each of us in our own way trys to do something to give others a way of looking at this situation and using tools & techniques to create common forms of understanding of this perilous situation. It is through common forms of understanding that hopefully the greatest and fastest and most effective forms of mitigatory actions can be achieved. the planet is in great peril and everything living on the planet is in great peril; no-one in their right mind would want any compliments. these are the days when all of us should be feeling shame for what is happening and for what is being done to the earth.
Dear George,
First there is the sheer enormity of Greenland and the amount and thickness of the ice sheet on top of it. Its weight depresses the land, but it is estimated that if the ice were to disappear, it would take 10,000 to 20,000 years for the land to spring back, which is not on a scale that is of relevance to our current problem.
Next there is the fact that we are only just beginning to get enough data to even talk about what the glaciers, ice streams, ice shelves, and ice sheets are going to do. It is all still pretty vague. Some new satellites are supposed to help with this lack of data.
And we can also see that in the last 15 years, things have changed much more rapidly than expected and in ways that were not predicted. So, pretty much no one knows with any certainty what is going on (in my opinion).
But in answer to your question, I will just make an educated guess as I am not a scientist. I would imagine that the ice sheet will remain so large and heavy that there is little chance of the surrounding ocean penetrating and lifting up the ice sheet, at least not on a time scale that would be of interest to us now.
Phil. Felton, JCH, Tenney Naumer ,mg and Edward Greisch, thank you for the info on the bedrock topography of Greenland as I had also wondered about the frequent claim that it is x% underwater.
There would seem to be quite a discrepancy between the 2 sources linked too (18, 132) however (even when you leave out the rebound)…
> discrepancy
Maybe; I think most of that comes from deep ice penetrating radar work, of which there’s not a lot available. What are you looking at?
Seems to me the pictures are illustrations, and you’d want to see numbers for topography in the original data set (and know the accuracy) — looks like much vertical exaggeration in the former’s color graphic (#18); in the latter, Schneider (#132), “at the horizontal resolution of the atmospheric grid, the coastal mountain ranges are represented with a reduced altitude, as illustrated by Fig. 2.”
Both show a good bit of the area’s under ice.
I wonder if the ring of land around an almost landlocked body of water accelerates freezing — isn’t that true for the Arctic generally, that it’s protected to some extent so easier for it to cool off? Same for the area we call Greenland?
Mauri (#120),
Thanks again. Ablation (melting at this altitude) may have been the spur for the initial thinning that then propogates itself through floatation further and further in the inland direction.
I think though that one does want to watch smaller accelerations in the larger masses of ice which are available at higher altitude. The depth of ice is more than a km, and apparently all of it is accelerating.
Chris
Those who are interested in Greenland bedrock, look at the maps in this paper:
http://www.cpom.org/research/jlb-ag.pdf
JCH@139: thanks. So the submarine grounding is only in the interior: although the ice streams have worn channels in the bedrock, and of course the outlet glaciers have submarine grounding, this erosion is not sufficient to link the sea to the inland basin.
Nick, I’m completely unqualified to comment. I lack the background to understand scientific papers, so I just look at the pictures.
There are some more pictures in this one; in fact, Googling Bamber in scholar yields a lot of visual goodies of Greenland:
http://nsidc.org/data/docs/daac/nsidc0092_greenland_ice_thickness/parca_paper1.pdf
I do wonder if they’re incorporated SLR into those maps. Is it?
131. An example which illustrates very clearly the connection between plant location and meltwaters from the ice sheets is illustrated by the map on this page http://www.nea.fr/html/general/profiles/japan.html
By accumulating maps of critical nodes across different sectors (refineries, power plants, etc) one can build up a variety of indices (eg economic disengagement probabilities) for physical nodes as a function of sea level rise. Since SLR is a global attribute, engulfment of nodes on the industrial staircase is global. CBRN release profiles are global. Damage cascades through what are currently considered as “value adding chains” are near-enough spontaneous with physical node take-outs. There isn’t enough money in the global economy to shift ensembles of coastal industrial plant simultaneously to higher grounds.
The observations being made of ice sheet dynamics and meltwater rates are critical for a proper assessment of the risks involved and the necessity to engage industrial leaders in full dialogue about the potential impacts.
JCH@141: that’s a great paper, thank you, and I find it very reassuring about GIS collapse.
There is indeed a submarine basin in central Greenland, but (a) it’s not very deep (a few hundred metres at most) and (b) it is not connected to the sea by any channel below sea level.
The outlet glaciers are mostly grounded above sea-level, even hundreds of metres above sea-level, within a few dozen kilometres of the sea. The main exception is the NEGIS, which flows down its own basin, much of which is submarine, to the sea. The paper asserts that the basin causes the ice-stream rather than vice versa.
The paper includes a look at the “excess thickness” (above flotation thickness) of submarine-grounded outlet glaciers (Humboldt, Petermann, NEGIS), and finds it above 500m within 25km of the sea. This is all good news, because it bounds the possible magnitude of Jakobshavn-effect mass loss (the Jakobshavn effect can’t operate if an outlet glacier’s terminus isn’t floating or nearly floating). And if the current paper is right and the Jakobshavn effect is much greater than the Zwally effect, then this is all very reassuring for GIS.
Another paper, this one specific to the NEGIS: http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/28280/1/CSD1-41.pdf
To answer your question, SLR would be almost invisible on these maps. The contour lines are 200m apart, and even total ice loss at both poles adds up to less than 100m.
My mistake: the paper I linked to in my last comment is not NEGIS-specific. I do highly recommend it, though.
Thanks JCH (#141)!
Has anyone mentioned the very recent Joughin, Das, et al. stuff that shows meltwater acceleration on one glacier taken over the year had a much smaller effect on the glacier outlet? This claims that the meltwater speeds up flow by silly amounts (50-100%)inland but only ~15% near the outflow
From an article in the 4/18 issue of Science by Richard Kerr Richard Alley of Penn State is quoted:
Mauri,
Great post. But looking at these 3D images of Greenland:
http://membrane.com/sidd/greenland.html
http://stephenschneider.stanford.edu/Publications/PDF_Papers/ToniazzoEtAl2004.pdf
I technically conclude (I’m not a scientist): Greenland’s a great big bathtub with great big holes in its sides!
That signals to me intuitively, that calving, while dominant so far, is destined to play a very minor role. I’d describe the calving as like splashing a bit of water over the tub’s edge.
Seems to me that ice melt, internal reservoirs and internal collapse, while minor thus far, will soon dominate. We could very much face a situation of non-linear dumping into the oceans and resulting catastrophic sea rise.
Dear Eli,
That depends on how you define “ridiculously.”
Did you see the NewScientist article on the possibility of the North Pole being ice free this year?
http://environment.newscientist.com/article/dn13779-north-pole-could-be-ice-free-in-2008.html
> internal reservoirs and internal collapse
How would we tell?
Is there any GRACE information showing loss of mass, but without a corresponding decrease in elevation of the surface?
Anyone doing ice-penetrating radar that would detect voids in the ice below the surface?
Tracing those moulin lake waterfalls to find out where that amount of water could go without increasing the outfall or lifting the ice surface?
Other ideas?
Anyone who has whacked a solid-looking piece of wood and found it had been riddled by termites — or walked out on a sheet of ice and found that it had a big void under it — has had this kind of surprise.
But how can we look for the problem if it’s there?
Send your contributions to:
The Society for Connecting all of Greenland’s Mountains with Dikes
General Delivery
New Orleans, LA
We’re going to make that sucker into a great big bowl of ice water.