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Greenland Ice Sheet outlet glaciers ice loss: an overview

Posted on 16 December 2010 by Daniel Bailey

The mass loss from Greenland's ice sheet has been well documented over the years.  In recent years, the rate of loss has accelerated.


Figure 1: Greenland ice mass anomaly (black). Orange line is quadratic fit (John Wahr).

To understand the causes of the acceleration we must examine how they vary in time and from glacier to glacier.  It also must be recognized that the same processes will not have the same level of impact on each glacier.  The two key mechanisms are the Zwally Effect and the Jakobshavn effect.  Let's take a closer look at those.

The Zwally Effect

This mechanism relies on meltwater reaching the glacier base via moulins and reducing the friction at the base of the glacier. This mechanism has been examined in detail and has yielded short term accelerations in the 10-20 % range (Zwally et al, 2002) (Das et al, 2008), but is of little significance to the annual flow of the large outlet glaciers.  A recent paper by Schoof et al (2010) further examines this issue.  They conclude that rapid changes in the basal water pressure is key:  long periods of sustained melt may lead to reductions in basal water pressure as the channels that drain the meltwater at the glacier base mature. 

A mature channel system would successfully remove the meltwater, instead of having the meltwater fill the channels and spread out as a lubricant over more of the glacier bed.  This is not a new concept, having been observed on Ryder Glacier during a surge after a lake outburst in 1995.  This mechanism has been observed in Iceland and Bering Glacier in Alaska as well. 

The mechanism does have limitations, however.  First of all it would be short lived, as it is only at times of rapid change in the amount of available meltwater that acceleration would occur.  The examinations of increased speeds from glacial lakes in Greenland to the base fit the pattern noted.  It is not a continuous summer long acceleration necessarily; it is often a short term rapid flow increase that is also localized.  Thus, this mechanism falls within the domain of the observed meltwater driven accelerations.  For this to be the star player, we need a glacier area where flow is slow enough for channels to develop and where basal water pressure is often limited. 

This is not the case on the rapid flowing marine terminating outlet glaciers.  The mechanism of a meltwater impulse driving short term acceleration would then be most important in regions where flow is slower and basal meltwater production not persistent.  Joughin and others, 2008 observed that seasonal drainage of meltwater to the glacier bed induces a uniform acceleration of 50–150 meters/year over a ~300 km long section of the West Greenland margin that is not drained by outlet glaciers, causing a large fractional acceleration of the interior ice sheet but a small fractional change in the speed of fast-moving outlet glaciers.  This suggests that glacial ice acceleration due to changes in seasonal meltwater flux tend to not make a significant overall change in outlet glacier ice velocities.

The Jakobshavn Effect

We are still left with the main cause of glacier acceleration in Greenland resulting from  dynamic thinning of the terminus zone of the marine terminating outlet glacier reducing the effective bed pressure, allowing acceleration – the Jakobshavn effect. The reduced resistive force at the calving front due to the thinner ice, now experiencing greater flotation, is then propagated “upglacier” (Hughes, 1986; Thomas, 2003 and 2004). This type of acceleration has a limited seasonal signal, and propagates upglacier from the terminus. 

Howat and others (2008) examined changes in terminus position, surface elevation and flow on 32 glaciers along the southeast coast of Greenland from 2000-2006. They affirmed that speedup results from loss of resistive stress at the front during retreat. Many retreats began with an increase in thinning rates near the front in the summer of 2003, a year of record high coastal-air and sea-surface temperatures.

This indicates again the importance of preconditioned thinning via melting.  The mass balance at the calving front is the sum of the ice flux from upglacier, the rate of melting above and below the waterline and the iceberg-calving rate. Mass balance transfer to the calving front is a slow process with a large lag time (centuries) and is not capable of playing a meaningful role in the recent relatively large and sudden glacier accelerations (Pfeffer, 2007).

Surface ablation and basal ice ablation are determined by the climatic and oceanographic conditions at near the glacier front. Increased ablation even in a single summer will cause thinning near the ice front.  This will reduce the effective pressure at the glacier bed, reducing friction and encouraging acceleration.  Acceleration at the calving front will then effectively pull on the ice upstream, stretching it causing further thinning and acceleration.  This is how the marine terminating outlet glaciers can respond rapidly to climate conditions.  Howat and others (2008) in observing the seasonal flow rates of 32 outlet glaciers concluded that  the presence of a seasonal oscillation in speed was ambiguous. On average, the glaciers show a difference in summer (faster) and winter (slower) speeds on the order of 10%.
 

How does this play out on various glaciers?

Petermann Glacier is a much different glacier than the large fast flowing marine terminating glaciers above. Its extensive ice tongue makes it particularly susceptible to basal melt processes, due to the area and duration of exposure of the glacier base.  Its velocity of 2-3 m/day is much lower than 10-30 m/day observed on the other marine terminating outlet glaciers.

Petermann is located on the northwest corner of Greenland and certainly experiences less melting and less snowfall. The lower 80 km (in length) and 1300 km2 (in area) of the glacier is afloat. This makes it (by area) the largest floating glacier in the Northern Hemisphere. The ice front is not impressive, unlike the faster outlet glaciers. The calving front protrudes a mere 5-10 m above sea level, reflecting the fact that the ice at the front is only 60-70 m thick.

Further upglacier, the ice at the grounding line is 600-700 m thick. The combination of velocity and thickness yield the volume of material calved each year. Petermann Glacier calves 0.6 km3 (Higgins, 1990), whereas Jakobshavn yields close to 40 km3. The thinning between the grounding line and the calving front is mainly via melting as the snowline is at 900 m. The low slope leads to very low velocities, giving the low-lying floating section plenty of time to melt, and surface melt ponds are common.  The glacier flow in the long terminus section is not susceptible to basal water pressure changes.

Left panel denotes ice velocities; the right panel shows changes in velocities
 
Figure 2. The Panel on the left shows ice velocity; the right, changes in velocity.  Areas in black are sea ice and open water.
 

 

Humboldt Glacier is much different as the lack of confining topography prevents the development of the strong ice stream flow we see on Jakobshavn Glacier or the weaker ice stream flow of Petermann Glacier and its subsequent long floating tongue.  This glacier could then be more susceptible to changes in meltwater flux.

 

Figure 3. Humboldt Glacier profile
 

 

Ryder Glacier is much different: Howat and others (2008) note that Ryder Glacier, North Greenland, accelerated by 300% over a 7 week period following drainage of a supraglacial lake in 1995.  This indicates the ability of an unusually large sudden discharge of water can increase basal water pressure dramatically and enhance basal sliding.  This glacier is in the north of Greenland and has an order of magnitude less melt than Jakobshavn and would be more susceptible to such a sudden meltwater pulses.


 

Figure 4. Horizontal velocity field of the Ryder Glacier. Contour interval is 20 m/yr (cyan) for velocity less than 200 m/yr and is 100 m/yr (blue) for values greater than 200 m/yr. Red arrows indicate flow direction and have length proportional to speed.
 

 

Essentially, several effects are at play and each glacier has its own story; but in the end they all point to a warming world, which continues apace.  The mass loss of Greenland’s outlet glaciers is not only expected to continue but to increase their acceleration as well.  Current events surrounding increased oceanic heat around ice sheet margins in Antarctic are expected to play a dynamical role in marine terminating glacial ice loss acceleration there as well.  Stay tuned...

 

Update:

Just ran across this animation over at Climate Progress:

 

The animation shows the spread of ice loss into northwest Greenland observed by NASA’s Gravity and Recovery Climate Experiment (GRACE) satellite system from 2003 through 2009 (updated to 2011; DB).

The vast majority of this blog post was contributed by glaciologist Mauri Pelto (all credit to Mauri, all errors are mine).  Examples of his work can be found at From A Glaciers Perspective and at RealClimate.

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Comments

Comments 1 to 30:

  1. I've only read the Howat 2010 paper so far but you seem to have got a few details wrong. This is what you say "Howat and others (2010) examined changes in terminus position, surface elevation and flow on 32 glaciers along the southeast coast of Greenland from 2000-2006. They affirmed that speedup results from loss of resistive stress at the front during retreat. Many retreats began with an increase in thinning rates near the front in the summer of 2003, a year of record high coastal-air and sea-surface temperatures." In fact it only studied 6 glaciers (2000-2009). Speedup is associated with reduced sea ice/melange conditions, not glacier thinning, and is correlated only with SST not with air temperature.
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    Moderator Response: [Daniel Bailey] Fixed per Mauri's comment below. Thanks for the heads-up!
  2. What's the source of Fig 1? It seems a continuation of the numbers as presented in Velicogna (2009), without accounting for the criticism of Wu et al (2010). That's not to say that Wu et al should be regarded as 'the truth and nothing but the truth', but I guess neither should Velicogna.
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    Moderator Response: [Daniel Bailey] That is just now being presented by John Wahr at AGU.
  3. #3, Bart, the Wu et al. paper has been discussed in detail here.
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  4. Daniel having quickly scanned (hence I might I have missed something) the Howat paper you link to, it looks like HR @ 2 is correct. The paper you refer to investigates 6 glaciers. Can you clarify the research you are refering to?? Are you just referencing that one paper or were there others that make up the 32 glaciers you state. Quote: "We examine data from six glaciers with ice fronts wider than 3 km."
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    Moderator Response: [Daniel Bailey] Fixed per Mauri's comment below. Thanks for the heads-up!
  5. Ian Howat of Ohio State and Ian Joughin from the U Washington have published so many fine papers it is easy to refer to the wrong one. The correct paper for the 32 glaciers is Howat et al (2008)
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    Moderator Response: [Daniel Bailey] Thanks for the update on that; fixed texts.
  6. Thank you Daniel for that excellent detailed understandable description of the state of the knowledge regarding Greenland and glacial dynamics. John Cook and his gang that could shoot straight ! - you folks are really making a difference, at least in the availability of focused science information for the layperson, I sure do appreciate it. ~ ~ ~ I have a question - Can someone address the latest thing reverberating around the AGWHoaxer's Echo-chamber: Science 23 January 2009: Vol. 323. no. 5913, p. 458 FALL MEETING OF THE AMERICAN GEOPHYSICAL UNION: Galloping Glaciers of Greenland Have Reined Themselves In Richard A. Kerr Ice loss in Greenland has had some climatologists speculating that global warming might have brought on a scary new regime of wildly heightened ice loss and an ever-faster rise in sea level. But glaciologists reported at the American Geophysical Union meeting that Greenland ice’s Armageddon has come to an end." ~ ~ ~ I cannot find any critique on Kerr's study, any information would be appreciated. peter m
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  7. #6: "Galloping Glaciers of Greenland" Here's one from this year's meeting. Not a rebuttal of Kerr, but if this was poker, his bet is called. Krabill et al 2010 Repeat airborne laser surveys of the glacier were begun in 1993 ...and continue under NASA's ongoing IceBridge program. ATM and ICESat (2003-2009) observations quantify the spreading of the region that is thinning and the volume of ice loss. Coincident acceleration of the icestream suggests a dynamic mechanism to the thinning as the icestream draws in greater quantities of ice... demonstrates thinning near the glacier snout continues at about the same rate since 1997, while further inland thinning has accelerated. -- emphasis added
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  8. #6: "Galloping Glaciers of Greenland" Actually the call was during the same meeting as Kerr's talk. Khan et al 2009: We analyze data from continuous Global Positioning System (GPS) receivers located around the edge of the Greenland Ice sheet. ... Our results show huge uplift in southeast Greenland due to mass loss from the main outlet glaciers in the region. The signal is also picked up by GRACE as a huge mass loss in the same region. Additionally, our GPS results show acceleration of uplift in northwest Greenland starting around 2006-2007. This appears to provide on-the-ground confirmation of the GRACE interpretations. So unless Kerr is ready to go all-in, he'd better fold 'em.
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  9. Could the recent sea ice deficit in Hudson Bay and in Baffin Bay be behind the current Greenland block weather pattern bringing cold weather here in the American Midwest? The past three winters have been colder and snowier than normal in the Midwest. Is it likely that warming in Greenland and the rest of the Arctic be the cause of the recent trend towards colder and snowier winters in the Midwest?
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    Moderator Response: [Daniel Bailey] The reduced sea ice is probably more of a function of warmer sea surface temperatures. The blocking patterning of which you speak is also probably helping retard the ice formation by keeping out polar air masses. RealClimate has a timely post on that very situation here. There is some evidence, gaining clarity, that some of these "different" weather events, once rare, may become more frequent in a (supposedly) warming world as atmospheric patterns reorganize to a different regime.
  10. muoncounter, I'm inferring that you are at the AGU meeting. I'm jealous! I went last year, though spent considerable time being a booth babe. Had out of town obligations this year. If you go next year, let's meet for beer!
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  11. #10: "at the AGU meeting" Nope, sitting around the house watching Congress not do anything about everything. But a beer sounds good. One correction to the prior comments - Kerr did not give a talk, he wrote about one. Selective reporting, which was picked up in watt$world with their usual cherrypicking skills. So back to citizenchallenge in #6, the game's not poker; its Go Fish!
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  12. Thanks for the information. {ps. you mean watt$ not sharing all of the story... go figure.}
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  13. #9 Karamanski, there may be a better explanation for cold midwest winters, http://nsidc.org/arcticmet/patterns/arctic_oscillation.html What is not shown in their diagram is the warmth flowing up into Greenland and (at the moment) eastern Canada. Here's a long term chart of the AO http://www.cpc.noaa.gov/products/precip/CWlink/daily_ao_index/month_ao_index.shtml and I would think that should match to cold outbreaks and lake effect snow, but the match is sporadic at best (e.g. 1977 and 2001, but not 2004)
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  14. I should end my off-topic excursion by saying I don't see a connection between the Greenland ice loss depicted above and AO (or NAO) even though the negative AO appears to sometimes pump warm air into Greenland in winter.
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  15. Arctic as a heat sink I suppose we should be looking at the heat (energy balance) of the Arctic during high pressure events in the winter to see if it is higher or lower than in the past. It's not the temperature, but the energy balance that is important. Arctic highs allow warmer air to displace the colder air southwards. But that warmer air has to lose energy as there is no solar input in winter. I wish they wouldn't give accelerations in percentages. That is almost meaningless to me. I think what is meant is a change in velocity which is what should be said. Change in velocity without a time frame is meaningless and I only noticed that information provided in one instance. Figure 1 is meaningless without a corresponding figure showing the total amount of ice on Greenland. Figure 1 is over a very short timespan almost meaningless from a climatic standpoint. A perspective of several hundred years would be helpful.
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    Moderator Response: [Daniel Bailey] Climate researchers are concerned with the change in the climate, including the change in the temperatures, hence the use of anomalies in the measurement of temperature change. In like fashion, ice researchers often measure change in ice sheet flows in percentages. Much the same thing. If you are unhappy with the wording of the post article, Mauri and I linked each reference for your easy perusal. Therein you may find the answers you seek. Lastly, Figure 1 contains incredible meaning and significance. As the very first linked reference shows, summer melt in Greenland saw a net 500 Gigatons of melt, or a bit more than the volume of Lake Erie of the US and Canada. That is a non-inconsequential amount to melt in just a few months. As such, the increasing melt signified by the curve on Figure 1 should give pause to sober minds everywhere. I invite you to visit Greenland in your several hundred years to convince yourself.
  16. @Karamanski “Is it likely that warming in Greenland and the rest of the Arctic be the cause of the recent trend towards colder and snowier winters in the Midwest?” Overland, 2010. : says that yes, that is: “While individual weather extreme events cannot be directly linked to larger scale climate changes, recent data analysis and modeling suggest a link between loss of sea ice and a shift to an increased impact from the Arctic on mid-latitude climate (Francis et al. 2009; Honda et al. 2009). Models suggest that loss of sea ice in fall favors higher geopotential heights over the Arctic. With future loss of sea ice, such conditions as winter 2009-2010 could happen more often. Thus we have a potential climate change paradox. Rather than a general warming everywhere, the loss of sea ice and a warmer Arctic can increase the impact of the Arctic on lower latitudes, bringing colder weather to southern locations.” Others have “slightly” different opinion: Are cold winters in Europe associated with low solar activity?, Lockwood et al., 2010.: “We show that cold winter excursions from the hemispheric trend occur more commonly in the UK during low solar activity, consistent with the solar influence on the occurrence of persistent blocking events in the eastern Atlantic. We stress that this is a regional and seasonal effect relating to European winters and not a global effect.” Low solar activity is blamed for winter chill over Europe, Benestad, 2010.: “The results of Lockwood et al (2010) fit in with earlier work (Barriopedro et al 2008) and provide further evidence to support the current thinking on solar-terrestrial links.” Tree rings and past climate in the Arctic, Juday 2010.: “Because many of the climate records available in this part of the world begin only in the late 1940s or early 1950s (during the one of the coldest periods of the 20th century) and continue to the present (the warmest period of the last millennium), the instrument-based record indicates a higher rate of temperature increase than the longer-term reconstructions that incorporate several cycles of temperature increases and decreases. This suggests that the strong late 20th-century warming (during the warm season) in western North America may have a considerable component of natural climate variability in the signal.”
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  17. ”The mass loss of Greenland’s outlet glaciers is not only expected to continue but to increase their acceleration as well.” ... but there are big questions, how? Greenland Ice Sheet model parameters constrained using simulations of the Eemian, Robinson, Calov, and Ganopolski, 2010.: “The most“realistic” simulations of the modern GIS (less volume and surface area) were obtained in the experiments that produced completely unrealistic simulations of the Eemian GIS (ALMOST COMPLETE MELTING [!?]).” “Finally, in spite of limitations of the model used and remaining uncertainties, our work indicates that using past and present constraints together, it is possible to rule out both too sensitive and too insensitive model versions, which enhances the credibility of modeling the stability of the GIS under global warming scenarios.” “... enhances the credibility of modeling the stability ...” - Is that enough? I recently watched the entire "scientific achievements" Edward Hanna (and citation of his papers) - an outstanding scientist, whom I really appreciate. Here are some interesting results: Observed and Modeled Greenland Ice Sheet Snow Accumulation, 1958–2003, and Links with Regional Climate Forcing, Hanna et al., 2006.: “Unusually high accumulation in southeast Greenland in 2002/03 leads the authors to study meteorological synoptic forcing patterns and comment on the prospect of enhanced climate variability leading to more such events as a result of global warming.” A spatially calibrated model of annual accumulation rate on the Greenland Ice Sheet (1958–2007), Burgess et al., 2010.: “The only statistically significant temporal change in total ice sheet accumulation in the 1958–2007 period occurred between 1960 and 1972, when a simultaneous accumulation increase and decrease occurred in west and east Greenland, respectively. No statistically significant uniform change in ice sheet-wide accumulation is evident after 1972. However, regional changes do occur, including an accumulation increase on the west coast post-1992. The high accumulation rates of 2002–2003 appear to be confined to the southeast.” Ocean regulation hypothesis for glacier dynamics in southeast Greenland and implications for ice sheet mass changes, Murray et al., 2010.: “We argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers' dynamic changes. We further suggest that the restrengthening of the EGCC resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff. We hypothesize that the main mechanism for ice sheet mass loss in SE Greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms.” Annual accumulation for Greenland updated using ice core data developed during 2000–2006 and analysis of daily coastal meteorological data, Bales et al., 2009.: “The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long-term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing ... [?!]” Hydrologic response of the Greenland ice sheet: the role of oceanographic warming, Hanna et al. 2009.: “Additional evidence from meteorological reanalysis suggests that high Greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin.” Oceanic control of the warming processes in the arctic – a different point of view for the reasons of changes in the arctic climate, Marsz, Styszyńska, 2009.: “Reaction of sea ice is the main mechanism controlling the heat content in water carried to the Arctic and influencing the SAT. Sea ice may either increase or limit the heat flow from the ocean to the atmosphere. The genesis of the ‘Great warming of the Arctic’ in the 1930s and ‘40s is the same as that of the present day.” “Dickson et al. (1996) showed that the formation of subtropical water in the Sargasso Sea on a multidecadal scale is functionally connected with convection processes in the Greenland and Labrador seas, albeit shifted in phase in relation to each other. These are elements of a general thermohaline circulation and they are dynamic elements of unquestionably natural character.” ”This means that observed in 1880-2007 climatic changes in the Arctic were promoted by the transport of variable heat content from the tropics with the oceanic circulation; they also have a natural and non-anthropo-genic genesis.” Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming, Hanna et al., 2008.: “Significantly rising runoff since 1958 was largely compensated by increased precipitation and snow accumulation. Also, as observed since 1987 in a single composite record at Summit, summer temperatures near the top of the ice sheet have declined slightly but not significantly, suggesting the overall ice sheet is experiencing a dichotomous response to the recent general warming: possible reasons include the ice sheet’s high thermal inertia, higher atmospheric cooling, or changes in regional wind, cloud, and/or radiation patterns.” Greenland’s contribution to global sea-level rise by the end of the 21st century, Graversen et al., 2010.: “Greenland contributes 0–17 cm to global sea-level rise by the end of the 21st century. This range includes the uncertainties in climate-model projections, the uncertainty associated with scenarios of greenhouse-gas emissions, as well as the uncertainties in future outlet-glacier discharge.” I especially recommend in this paper: Fig. 6 (a) Partitioning Recent Greenland Mass Loss, van den Broeke et al., 2009.: “Without the moderating effects of increased snowfall and refreezing, post-1996 Greenland ice sheet mass losses would have been 100% higher. [...]”
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    Moderator Response: [Daniel Bailey] Arkadiusz, please furnish a concluding summation to give the readers an idea of why you post the linked references with their quoted texts. Trying to guess at that hidden meaning from your post is difficult. Thank you!
  18. #17: "... but there are big questions" I'm not sure of the overall value of this small forest of linked papers towards the topic of this thread. At least Murray et al 2010 confirm a period of accelerated ice loss, as shown in this thread's Figure 1: Synchronous acceleration and thinning of southeast (SE) Greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet. We show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers, in many cases associated with a decrease in thinning rates ... Since the overall trend (again referring to Figure 1 above) is sharply down, can we not interpret the 'widespread slowdown' and 'decrease in thinning rates' as minor contributors to the trend? Some of the other papers linked in #17 refer to accumulation, which is not at all the question discussed here.
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  19. The slowdown noted in Murray et al (2010) is for the years 2006-2008 versus 2005 in southeast Greenland. The speedup in this region had a short term peak in 2005. Given the shortness of the data sets not too much can be made of this. In looking at the west coast of Greeland the same trend is not evident. The Jakobshavn was faster in 2006 than 2005. The sppedup indciated for western Greenland had a much greater extent into the ice sheet and in the number of glaciers then in southeast Greeland as noted in the nice colored images of Joughin et (2010) noted in the article above.
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  20. For the last month the temperatures over southern Greenland have been 10C above normal see this reanalysis by NOAA. The ocean temps appear to be about 5C above normal. Much of southern Greenland has been above 0C for weeks. Sea ice around southern Greenland is much reduced. How will that affect the glacier flow this year? Dr. Pelto: thank you for your very well informed comments. It is always interesting to see what professionals are thinking.
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  21. Re; michael sweet (20) Not speaking for Dr. Pelto on this one, but consider the primary mechanism for ice-loss of an outlet glacier: The Jakobshavn Effect. Increased SST's will enhance loss at the calving front due to increased melt, thinning and calving. As the loss exceeds replacement by downslope transport of ice, the calving line then retreats upslope. Most Greenland outlet glaciers are still at or relatively near their grounding lines (think terminal moraine for a terrestrial glacier). What happens as the calving front retreats upslope is the ice tongue retreats into deeper water, ungrounding the ice front. Without the resistive stress of the grounding line, more of the glacier floats and then picks up speed in the downslope direction as the loss of resistive stress is propagated upglacier. If warmer SST's persist, expect greater calving (even in the absence of warmer air temps). Air temps above 0C will drive surface melt and percolation of water from the surface through moulins, driving heat downward into the heart of the ice mass. Hope this helps, The Yooper
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  22. Keep a weather eye on SST's around the Antarctic Peninsula and the Pine Island/Thwaites Glacier areas. The Climate Progress article I linked at the end of the post shows much warmer SST's have been present around the ice shelves in those areas. Some breakup could be expected as a result. The Yooper
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  23. “... please furnish a concluding summation ...” Sorry to reply so late ... The conclusion is simple and obvious after all - the Arctic - the current changes, as a whole, the melting ice in Greenland and the Greenland Sea, severe winters in Europe, Canada, USA and central China, this is an example of a decisive influence: direct and indirect - of solar activity. The current accelerated melting of ice in NH - it is even (according to some authors, the above-mentioned papers) to 91% - just nature. Contrary to appearances, the tropics and Antarctica - SH, contain the best examples of the potential GHG RF! By the way you see - a comparison of the Eemian - Greenland ice - that physicists of atmosphere do not know what it is: "post-glacial rebound" (...). ... and paper: Overland, Wang, and Walsh, 2010.: blog news - frequently asked question: since at least 2003, and especially in 2007 - it was a record warm in Greenland - similarly, with regard ice (mass, area) - why then the winters in the temperate zone NH were warm?
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  24. #23: "an example of a decisive influence: direct and indirect - of solar activity." Please substantiate this claim. It is neither in the Arctic Report Card you linked to, nor in the Overland et al paper. However, this is: Referring to 2009, ... there were still extensive regions of open water in the Chukchi, East Siberian Laptev, and Kara Seas ... which allowed extra solar and longwave radiation to be absorbed by the ocean ... . The heat accumulated in the ocean can be released back to the atmosphere the following autumn That is clearly a reference to reradiated IR, the source for IR trapped by the greenhouse effect. So you've actually substantiated the case for greenhouse warming. Thanks!
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  25. Re: muoncounter (24) Does being done-in by one's own furnished link constitute being hoist by one's own petard? Re: Arkadiusz (23) If you're going to dig into the paleo record, by all means let us do so. You do realize, by doing so, the inevitable comp to today's warming/GHG concentrations is the PETM...(I can see a need to write up a piece on this one, too...sigh; always more work to do and never enough time in the day). The Yooper
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  26. #25: A document that turns against one's intended use is the digital petard. As for Rosencrantz and Guildenstern, "They are not near my conscience; their defeat Does by their own insinuation grow"
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  27. All right ... In a “great” nutshell : For three years I deal with problem : „thinning rates of key Greenland outlet glaciers” - what is the effect and what is the cause ? According to this work: Greenland Ice Sheet Surface Mass-Balance Modeling in a 131-Yr Perspective, 1950–2080, Mernild et al. 2010. write: “The authors simulated an 90% increase in end-of-summer surface melt extent (0.483 × 106 km2) from 1950 to 2080 and a melt index (above 2000-m elevation) increase of 138% (1.96 × 106 km2 × days).” Most researchers claim that the outlet glaciers of Greenland (including those within the land) are very sensitive to even small temperature changes ("Arctic amplification"). Cited by me first work shows the difficulties in the interpretation of old data (Eemian). Other works show the great influence of the place and size of the snowpack (SnowModel) the movement of glaciers and the "thinning outlet" (see also: The Cryosphere Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries., Fettweis et al., 2008.) . Even so. “great warming” in Greenland of the 30s (according to many of Greenland's still bigger and more violent than at present) does not give answers, how would the glaciers. Then the loss of ice - the dynamics of movement of glaciers - was (30s) faster than at present, but in the 30's was negative phase of NAO and AO (now this are positive - of course, "most frequently"), concerned mainly the warming of spring, for now - autumn, etc. Her recent works are beginning to agree on one thing - it: “... highly sensitive to ocean Conditions ..." decide on the melting and traffic of Greenland's glaciers (not just those “ending” in the sea? - Testing hypotheses of the cause of peripheral thinning of the Greenland Ice Sheet: is land-terminating ice thinning at anomalously high rates? Sole et al., 2008.). Yes: highly sensitive - the temperature - "thinning rates of Greenland Outlet Glaciers key"- a very affects the movement of glaciers across Greenland. However, with mass loss of glaciers is increasingly important that the surface of Greenland's mountainous sculpture, geothermal activity. Glaciers are to be retained in the narrow mountain valleys, narrow valleys, fjords. For this walk "... negative feedback mechanisms ... " Conclusion. The loss of ice in Greenland is not (and will) linear with respect to temperature. We do not know whether an increase in snow accumulation will be the east or west (various atmospheric circulation, different topographic features) and this will have a decisive influence on the flow of glaciers into the sea: „The greatest difference in melt extent occurred in the southern part of the GrIS, and the greatest changes in the number of melt days were seen in the eastern part of the GrIS ( 50%–70%) and were lowest in the west ( 20%–30%).[ Mernild et al. 2010.]” Mernild et al. 2010., saying: „The rate of SMB loss, largely tied to changes in ablation processes, leads to an enhanced average loss of 331 km3 from 1950 to 2080 and an average SMB level of −99 km3 for the period 2070–80.” - may be wrong. The continental glaciers 2,080 years, particularly those from the deep interior of Greenland will be stable because such accumulation of snow will stop them. These coastal (eg Jakobshavns, Helheim) BTW much farther from the sea and - in this way - lose its dynamic ... P.S. A thorough knowledge of the PETM may tell us all - and the issue about of Greenland ice ...
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  28. “direct and indirect - of solar activity.” For starters I recommend all the latest works Lockwood's (et all. of course) and especially (and “consistently”) Solar Influences on Climate (Reviews in Geophysics, 2010). If J.C. “dusting of” about this topic, I will present the latest (last 2-3 years) work - papers, showing the changes, feedback resulting from changes - in the TSI, UV, ULV, volcanic activity, magnetic, phytoplankton - ENSO - clouds - ozone, conductivity of the atmosphere, etc. ...
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  29. Arkadiusz: It certainly is a difficult problem to predict what the great ice sheets will do in the future. Past records, including paleo records, are not comparable to the present forcing: the current forcing is much bigger. Models of sea ice in the arctic have greatly underestimated current ice melt (see the IPCC report). The great ice sheets are also starting to melt long before predicted. On the other hand, if you check my reanalysis link at #20, the current anomalies over Greenland are 10C higher than historic over the ice sheet and 5 degrees higher over the ocean. Do the papers you cited refer to anomalies this high, or were they not anticipated? Most of this winter has been over 0C over the southern ice sheet. This unprecedented heat must have some affect on the ice sheet. Do you wait until the ice sheet collapses before you acknowledge there might be a problem? The ice sheet will undoubtedly have some sort of lapse time before it fully responds to the heat. How long do we have?
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  30. #27: Your linked paper "Testing hypotheses of the cause of peripheral thinning" makes a distinction between land-terminating and ocean-terminating glaciers. There was a four fold increase in mean marine-terminating outlet glacier thinning rates ... between the periods 1993 to 1998 and 1998 to 2006, while thinning rates of land terminating outlet glaciers remained statistically unchanged. This suggests that a change in a controlling mechanism specific to the thinning rates of marine-terminating outlet glaciers occurred in the late 1990s and that this change did not affect thinning rates of land-terminating outlet glaciers. This distinction argues for warmer water contributing to melting, rather than a strictly "solar influence," as you seem to suggest in #28. Would not a solar influence affect land and ocean-terminating glaciers equally? And isn't ocean warming a known symptom of the GHE?
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