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Climate Hustle

Greenland's ice mass loss has spread to the northwest

Posted on 30 March 2010 by John Cook

Past studies have found most of Greenland's ice mass loss had occured in the south. However, new research has been published (Khan 2010) examining the pattern of mass loss over the entire Greenland ice sheet (H/T to Riccardo). Satellite gravity data and Global Positioning System (GPS) measurements both find that mass loss has been spreading up along the northwest coast of Greenland, starting in late 2005. This increase in mass loss is shown most dramatically in this animation created by co-author John Wahr:

Ice mass loss from Greenland

GPS data is obtained by placing GPS receivers on bedrock adjacent to the ice sheet. As the massive Greenland ice sheet loses mass, the bedrock undergoes vertical crustal uplift. Bedrock near the Thule Air Base on Greenland's northwest coast rose by about 4 centimeters from October 2005 to August 2009. As accelerating ice mass loss causes accelerated crustal uplift, the observed uplift show strong agreement with the loss of ice mass measured by satellite gravity data. These observations indicate that the accelerated mass loss is dominated by the increasing velocity of outlet glaciers. Large glaciers in the north-west region are sliding downhill faster and dumping more ice in the ocean.

The GPS data provides yet another line of evidence that the Greenland ice sheet has been losing mass at a significant rate. Satellite radar altimetry and airborne laser altimetry have observed thinning near ice sheet margins. Radar interferometric surveys find that glaciers are sliding faster in the ocean. And the overall picture given by the satellite gravity data shows that mass loss of the entire ice sheet is still accelerating (Velicogna 2009).

What will happen to Greenland in the future? Various independent studies predict global sea level rise of around 1 to 2 metres by 2100, with Greenland being a significant contributor (Vermeer 2009, Pfeffer 2008). Models predict that at the rate we're emitting CO2, collapse of the Greenland ice sheet is likely within the next few centuries (Stone 2010). This is backed up by studies of earth's past history which find ice sheets are highly sensitive to warmer temperatures. Global temperatures just 1 to 2°C warmer than now saw sea levels over 6 metres higher than current levels (Kopp 2009).

Science is about piecing together the full body of evidence to improve our understanding. As more data comes in, we're now seeing many lines of evidence painting the same picture. The Greenland ice sheet is highly sensitive to warming temperatures and is likely to contribute sea level rise in the order of metres.

UPDATE 2 Apr 2010: Many thanks to Robert Simmon at NASA who pointed me in the direction of another instructive animation of ice mass loss from Greenland as measured by the GRACE gravity satellites:

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Comments 1 to 50 out of 69:

  1. Good post. It is interesting to see these rapid changes in the ice sheet. What will this look like when it is all linked together in the next IPCC report?

    Last paragraph typo: pointing painting (delete pointing)
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    Response: "What will this look like when it is all linked together in the next IPCC report?"

    We'll have to wait till 2013 to find out.

    Thanks for the typo alert.
  2. So, it seems the bedrock in coastal Greenland is isostatically rebounding faster than global sea level is rising. Based on recent headlines in the popular misrepresenting climate science, can we expect to see this reported as; "Relative sea level falling at an accelerating rate in Greenland due to climate change"?

    You read it here first ;)
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  3. Nicely written. Yet another integration of independent data sources pointing to the same thing. GPS, gravity and altimetry would be enough to convince a literate person that the northern hemisphere is in deep trouble -- and that's without using any of the so-called controversial temperature data! (Of course, temperatures also say the same thing).

    And here's another connection from a recent study of caves in the southwestern US.
    "Both research teams found that climate in the Southwest oscillated rapidly between wet and dry as the North Atlantic cooled and warmed between 50,000 and 10,000 years ago. Their findings reinforce computer model predictions of similarly abrupt climate change during the coming century, as emissions of greenhouse gases, such as carbon dioxide, heat the atmosphere."
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  4. If you extrapolate the current ice loss trends from the Arctic and Antarctic for about 30 years, which are accelerating, what kind of sea level rise would that generate and how would that compare to the current maximum projections for 2040? I have a nagging feeling that they might be above the current maximum predictions that would lead to a 2 meter sea level rise.

    Other questions, what would constitute a collapse of one of the ice sheets? And do you think there is a failing mechanism for an ice sheet that would lead to collapse? If so, what kind of thing are we looking for.

    Because of my job in coastal engineering, I'm very interested in sea level rise. Even a one meter rise would lead to a mind boggling amount of problems to current coastal structures. Let alone if we are confronted with a 2 or more meter rise.
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    Response: "If you extrapolate the current ice loss trends from the Arctic and Antarctic for about 30 years, which are accelerating, what kind of sea level rise would that generate and how would that compare to the current maximum projections for 2040?"

    I'm wary of statistical extrapolations of the current accelerating trend of ice mass loss. The reason is there are physical constraints on how fast the glaciers can move so one imagines (hopes) eventually the rate of ice mass loss might stabilise. Note - that's the rate of ice mass loss that might level out - I'm not saying mass balance will stabilise. Therefore papers like Pfeffer 2008 are useful in that they look at the physical constraints of Greenland's glaciers, leading to an estimated sea level rise of 1 to 2 metres by 2100.
  5. I understand that you are wary of the extrapolation. I am too, that is why I "only" limited it to 30 years, which is stretching it, even in my standards.

    I will not discredit any paper, simply because I do have not the necessary background to do so in any constructive sense. I do however doubt the overall accuracy of the predicted sea level rise, because in so far I was able to follow it, it has mostly been on the conservative side. Since the current ice loss in in both the Arctic and Antarctic is going faster than almost all of the projections, that would lead to the conclusion that maybe our long term prediction might be off as well.

    An other factor is, in so far as I have read and am aware of, is that our current understanding of ice sheet dynamics and glacier flows is not that well know as we would like and problematic in some aspects. Coupling that to the astonishing rate that the glaciers are retreating and that some mayor glaciers might not be so protected or constrained as we thought they were, to me gives enough reason to do a re-evaluation of current projections or at least do a major worst case scenario exercise.
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  6. #5 Arjen, you might want to check out this post at RealClimate by Stefan Rahmstorf, which involves one way to extrapolate accelerating sea level rise. Your idea to extrapolate is interesting, but I agree with John that it is dangerous to extrapolate too far. Nevertheless, here it is, based on Velicogna (2009). After 30 years, the rate of sea level rise would be faster than the present by 5.1 ± 1.5 mm/yr if the present acceleration in mass loss from Greenland and Antarctica continues. If we take the present rate of sea level rise as 3 mm/yr (approx altimetry rate), then after 30 years the total rise would be 16.5 cm instead of 9 cm (linear extrapolation). If you are even more bold and extrapolate out to 100 years, you would get 1.15 meters of sea level rise. Take that with a very large grain of (sea) salt, but that number lies within the range of what Vermeer and Rahmstorf (2009) and others have gotten from fitting an empirical relationship between past temperature and past sea level.

    Here are the conclusions from Velicogna (2009):

    "We showed that a detailed analysis of the GRACE time series over the time period 2002–2009 unambiguously reveals an increase in mass loss from both ice sheets. The combined contribution of Greenland and Antarctica to global sea level rise is accelerating at a rate of 56 ± 17 Gt/yr2 during April 2002–February 2009, which corresponds to an equivalent acceleration in sea level rise of 0.17 ± 0.05 mm/yr2 during this time. This large acceleration explains a large share of the different GRACE estimates of ice sheet mass loss published in recent years. It also illustrates that the two ice sheets play an important role in the total contribution to sea level at present, and that contribution is continuously and rapidly growing."
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  7. Well done again, John. I came across this paper over the weekend and thought of alerting you to it, but got involved in other things.

    Readers might be interested to know that over the last 3 summers, an extensive GPS network has been established all over Greenland, the new GNET GPS network. Quite a few new sites have been built in Antarctica as well. Over the next few years, the change in ice mass will be weighed very effectively by GPS.
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  8. These are worrying signs, especially if you live in the Netherlands...

    However, I do wonder if this (acceleration) will be a continuing trend, or that it has been caused by weather or one of the many oscillations (which I hope, but wouldn't count on it). The measurement time series are still rather short. I find it somewhat surprising that these great ice masses have such a rapid response on climate, because usually such large bodies of ice have considerable inertia (e.g. the Antarctic ice sheet is still responding to the current Holocene (?)). I'm not sure though, and I should maybe talk about this with some of the experts at our research institute (IMAU).
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  9. #4 Arjen at 14:10 PM on 30 March, 2010
    "Response: [...] "an estimated sea level rise of 1 to 2 metres by 2100"

    Get real. Current mass of Greenland ice sheet is somewhere around 2.4 × 1018 kg. Average loss between April 2002 and February 2009 is estimated to be 2 × 1014 kg/year. That is 0.0083%.

    On the other hand, global ocean surface area is some 3.6 × 1014 m2. A one meter increase by Greenland ice melt would require 3.6 × 1017 kg, which is 15% of the entire ice sheet mass.

    If that much ice is supposed to melt in nine decades and acceleration of melting is uniform, in the final year (2100) the annual melt should be 1.2 × 1016 kg, sixty times more than the 2002-2009 average.

    The bulk temperature of Greenland ice sheet is around -30 °C. To warm it up to 0 °C and melt requires about 4 × 105 J kg-1. So to melt that much ice in a single year takes 4.8 × 1021 J, that is 1.5 × 1014 W. As the surface area of the ice sheet is 2 × 1012 m2, the average heat flux required is 75 W m-2. That's much. The average annual insolation at TOA (Top of Atmosphere) over Greenland is 193 W m-2, most of it reflected back to space by clouds and the ice surface itself. And even at -30 °C, outgoing heat radiation of ice surface is 198 W m-2 (it is 315 W m-2 at 0 °C).
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    Response: As discussed in the article above, the predominant contributor to sea level rise from the Greenland ice sheet is not ice melt but speeding up of the glaciers, dumping more ice into the ocean.

    The source for sea level rise of 1 to 2 metres by 2100 are two peer-reviewed papers, Vermeer 2009 and Pfeffer 2008. These papers use two independent methods to come to the same answer. Pfeffer in particular looks at the physics of glacier discharge and finds accelerating discharge of glaciers into the ocean the main reason why sea level rise is so large.

    Accelerating glacier discharge has already been observed by radar interferometric surveys. This is corroborated by GPS observations in Khan 2010.
  10. Arjan,
    unfortunately no one still came out with a reliable ice sheet dynamics model. The IPCC AR4 did not include the ice sheet melting contribution to sea level rise because a reliable prediction was not possible.
    From then, scientists made a few step forward, but more than this it is the new data that rise concern. Although still not conclusive for accurate projections, the new data show acceleration of melting in Greenland, in West Antarctica and possibly even in East Antarctica. And we know from paleo reconstructions that rates of the order of meters per century are indeed possible.
    Although no one can say conclusively that the current acceleration trend will continue, all the signs point in this direction.

    As for The Netherlands, already in 2008 your Delta Commitee projected 0.65-1.3 meters by 2100. They included the caveat of the unknown response of Greenland and Antarctica ice sheets and concludes "that this level may be higher than has been assumed up till now.". But, according to the Delta Committee, the impact will vary in different part of the coast. The engineer point of view is not general and needs an expert and specific advice.
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  11. There is no reason to extrapolate the current Greenland ice loss for many decades into the future. The current ice loss has only little to do with general global warming. Persistent patterns of wind have caused an abnormal warming in the Arctic region. That pattern can change again, and probably will, as it has often done. That would reverse the current alarmist predictions.
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  12. # Berényi Péter,
    Thank you for giving us the correct numbers, and a more realistic view on the Greenland ice, than the ones coming from makers of the usual panic reports!

    In Wikipedia (''Greenland ice sheet'') I just read that 'the warmest decades were the 1930s and 1940s'. Not now. Why was nobody alarmed 70 years ago?

    Also, (Wikipedia) mean annual temperatures on the ice sheet domes are -31°C (on the north-central part of the north dome), and -20°C (at the crest of the south dome). How is ice going to melt with those kind of temperatures?
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  13. Berényi Péter , you need to read more carefully.

    John Cook wrote Various independent studies predict global sea level rise of around 1 to 2 metres by 2100, with Greenland being a significant contributor (Vermeer 2009, Pfeffer 2008).

    That does not mean that Greenland's contribution alone would be 1-2 m of SLR.

    Read the two papers that John linked. Pfeffer et al. 2008 derive total SLR of 0.8 to 2.0 m by 2100, with 0.2 to 0.5 m of that coming from Greenland and the remainder from Antarctica, other glaciers & ice caps, and thermal expansion. Vermeer and Rahmstorf 2009 give a range of 0.8 to 1.8 m by 2100, again including a mix of contributions from all the above sources.

    From the Velicogna paper that BP cites, ice mass lost from Greenland in 2007-2009 averaged 286 Gt/yr. The 21st century average would only have to be a factor of about 4-5 greater than this to yield +0.3 m SLR from Greenland and +1 m SLR total. Considering that the rate of loss of mass from Greenland doubled over the 2002-2009 period, this doesn't seem especially farfetched.
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  14. Argus writes: Also, (Wikipedia) mean annual temperatures on the ice sheet domes are -31°C (on the north-central part of the north dome), and -20°C (at the crest of the south dome). How is ice going to melt with those kind of temperatures?

    Ice melts below the equilibrium line, and ice is discharged into the sea by marine terminating glaciers. Ice in the center of the sheet then flows outward.
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  15. To clarify my comment above, over the past decade the rate of ice loss from Greenland accelerated by about 11% per year. This is highly unlikely to continue (there would be no ice left by ~2075 or so).

    If that acceleration dropped to 3% per year tomorrow and continued for the rest of the century, you'd end up with 0.3 to 0.4 m SLR from Greenland, 1.0 m SLR total. Greenland would still have 93% of its ice. The ablation rate in 2100 would be around 4000 GT/year, compared to 286 GT/year in 2009.

    That's still a big increase in ablation over the next 90 years, but much more reasonable than Berényi Péter's calculations above.
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  16. The spread of the mass loss to the northwest over this time period represents the shifting of the maximum ice melt anomalies from southern Greenland beginning in 2002-2007
    Tedesco et al., 2008 . Whereas northern Greenland began a series of substantial melt anomalies in 2005, with 2008 being the record.
    Box et al. 2009
    This has had implications for the Petermann Glacier in northern Greenland which has the longest floating glacier tongue in the Northern Hemisphere.
    Petermann Glacier Retreat
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  17. One thing that caught my eye just a few minutes ago was this snippet from an interview with James Lovelock, talking about what it would take to make us take action on climate change:

    There has been a lot of speculation that a very large glacier [Pine Island glacier] in Antarctica is unstable. If there's much more melting, it may break off and slip into the ocean. It would be enough to produce an immediate sea-level rise of two metres, something huge, and tsunamis.

    Two meters? Is the PIG really that big? This is the first time I've seen someone provide a number for such an event. Even assuming a fairly large fudge factor, 2 meters of "immediate" SLR is an astounding number.

    Source for the above quote:
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  18. Nope, the PIG isn't that big, though PIG is huge for a glacier. The entire drainage area for PIG is about 10% of the West Antarctic Ice Sheet, so even if all of that ice went into the ocean it would be less than 1 m SLR. Either Lovelock was being misquoted or his imagination was running away with him.
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  19. Also Lou (#17), what I've read on the PIG leans towards the collapse becoming more of a prolonged calving event rather than an abrupt, tsunami-inducing slip. That makes sense to me since the underlying topography slopes upward toward the sea, up to the outlet, which is the current grounding line. It would be similar in nature, though larger, than what is happening with the Columbia glacier.

    RealClimate post

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  20. I think this post characterizes what Alarmists tend to say. The ice is disappearing hence increased CO2 is to blame. Nothing could be further from what is truly happening.

    For starters, ice can disappear by evaporation and sublimation resulting from wind blowing over its surface. Of course the predictions of massive sea level rises don't factor in this.

    John Daly, who has written a number of books arguing against the alarmist view, has posted temperature data that he obtained from GISS and CRU. He subdivided the data into regions, including the Arctic, and has data from a number of stations located in Greenland.

    What is interesting is the temperature plots from 1930 onwards from stations located on Greenland show consistent temperatures and no rising temperatures - especially the the heights needed to melt glacial ice.

    Here are a few examples:

    On another note regarding isostatic recovery, it should be noted that the norther part of North America is still rising. Canadian scientists have noted that while sea levels elsewhere in the world have risen marginally, they have found no signs of similar rising in the Canadian artic. They have concluded that this phenomenon is the result of isostatic recovery. What climate scientists need to take into account is the amount of water being displaced by this isostatic recovery - said water of course flowing into the other oceans and contributing to their rise. In other words, not all of the rise in ocean levels can be attributed to glacial melting.

    Finally you have to understand that when glaciers move, they are not melting but are growing. Glacial ice disappears from melting AND evaporation and sublimation.

    Since historical Greenland temperatures appear to be somewhat static since the 1930's, and keeping in mid that even if they are warmer than in the past, temperatures still remain sub-zero for most of the year, it is unlikely that any melting of Greenland ice is attributed to higher temperatures brought on by increased levels of atmospheric CO2. Scientists should look elsewhere for the cause if they are serious in trying to determine what is happening there.
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  21. There's also Pritchard et al 2009 that finds significant thinning of glaciers on Greenland. Thinner glaciers means less mass, although how much less mass is more difficult to quantify. Here's an image from the paper (click for a larger version)

    Notice how the thinning matches up with the GRACE and GPS data from Kahn paper. So that's three independent datasets (four, if you include prior radar altimetry data).

    Thanks for pointing this one out, John. Now to get a copy of that paper for my own post at S&R.
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  22. This is of interest:

    The ice below the melt line does melt in the boreal summer:

    The area experience summer melt is also increasing:
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    Response: Fixed your broken image and yes, a preview feature is coming.
  23. Geo Guy, you've got that backwards. There are multiple independent lines of evidence showing that Greenland is losing mass both by melting and by discharge from accelerating marine-terminating outlet glaciers. These independent lines of evidence include:

    (1) gravity data from GRACE, which yields the total mass balance of the ice sheet;
    (2) laser and radar altimetry measurements of ice sheet elevations;
    (3) interferometric radar measurements of increases in the velocity of outlet glaciers; and
    (4) high-precision geodetic GPS measurements of bedrock and ice elevations.

    I'm going to ignore the suggestion that Greenland is losing 300 GT/year of mass (and accelerating) due to "sublimation," since I assume that wasn't serious.

    Re: temperature, John Daly is not a reliable source, his graphs don't show data for most of the past decade, and Jan Mayen is not in Greenland.
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  24. Ok, I give up, here is the link for the melt season anomaly in 2005:

    Melt season anomaly in 2006

    And the melt anomaly in 2007:

    And in 2008:

    This is also quite striking, melting ice reveals new island off coast of Greenland:
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  25. This article might answer people's questions as to the mechanisms responsible for the acceleration of ice loss (i.e., acceleration of outlet glaciers) from Greenland:
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  26. #20 GeoGuy, like Ned #24 I have to assume your suggestion of sublimation was not serious. Please re-read John's post. The mass loss is not all caused by melt and runoff -- much of it comes from glaciers dumping large amounts of ice into the ocean, where it then melts. We know this from direct observation, time-lapse photography, repeat satellite imaging, estimation of glacier velocities from radar interferometry and direct measurement, etc.

    The isostatic uplift doesn't have to be inferred from relative sea level, it has been measured directly. See Sella et al. (2007) in GRL, or free ftp access (according to Google) at the author's ftp site.

    As far as accounting for the effect of isostasy in sea level rise, you need to acquaint yourself with the work of Jerry Mitrovica and colleagues, who have done that (and more).
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  27. Looking at Albatross' last link, I found this to be quite interesting:

    "Based on the differences he saw between his map and his new observations, he concluded that the surrounding ice had retreated at least 10 kilometers (6 miles) in the previous five years."
    An average of 2 km/year. Some should instruct these glaciers to stop being so alarmist, it's starting to look bad.
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  28. Geo Guy,

    John L. Daly died in 2004 & the charts you reference have not been updated since 2003, most of them end in 1999 or 2000. Daly's site has been maintained by a colleague, but even that is quite outdated:
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  29. Thanks John, sorry to make work for you. You must feel like you are a school teacher at times, making sure everyone is behaving and also having to help out :)

    NewScientist (13 January 2010) has an article on the potential impact on global SL if the PIG were to slide into the ocean-- they reckon that would increase global SL by about 24 cm.

    And yes, scientists think PIG exceeded its tipping point in 1996.....
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  30. Thanks for the pointer to that article, Albatross.

    The exact quote from New Scientist:

    The model suggests that within 100 years, PIG's grounding line could have retreated over 200 kilometres. "Before the retreating grounding line comes to a rest at some unknown point on the inner slope, PIG will have lost 50 per cent of its ice, contributing 24 centimetres to global sea levels," says Richard Hindmarsh of the British Antarctic Survey, who did not participate in the study.


    I wish people would push Lovelock (and everyone else) harder to back up such pronouncements.
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  31. When will arrive the MELTING ANOMALY MAP FOR 2009?

    GRACE show it will probably be a record-breaking one!
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  32. GeoGuy #20: "temperature plots from 1930 onwards from stations located on Greenland show consistent temperatures and no rising temperatures - especially the the heights needed to melt glacial ice."

    Perhaps we should listen to the local population:
    "A Greenlandic supermarket is stocking locally grown cauliflower, broccoli and cabbage this year for the first time. Eight sheep farmers are growing potatoes commercially. Five more are experimenting with vegetables. And Kenneth Hoeg, the region’s chief agriculture adviser, says he does not see why southern Greenland cannot eventually be full of vegetable farms and viable forests."

    " ... Cod, which prefer warmer waters, have started appearing off the coast again. Ewes are having fatter lambs, and more of them every season. The growing season, such as it is, now lasts roughly from mid-May through mid-September, about three weeks longer than a decade ago."
    Again, evidence of warming that isn't dependent on temperature data.

    Wonder if there's any beachfront property available in Narsarsuaq.
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  33. In response to Ned 23 and Jeff 26 (and others who find it difficult to believe that sublimation does not play a role in the disappearance of glaciers), when air temperatures fail to move above melting (even in the summer) plus when you factor in the thermodynamics of the amount of heat needed to melt ice, and given the polar regions are sub zero for half the year, the melting of glaciers at the rates indicated in the loss of mass just are not possible from an increase in atmospheric temperatures.

    For anyone who has worked in the far north in the winter, the sublimation of snow cover is quite observable as is the reduction in ice on the lakes.

    Geologists Andrew Fountain, Karen Lweis and Peter Doran authored an article in Global Planetary hange (Vol 22 Issues 1-4) from which I took the following quote:

    "In polar regions, where melting is typically absent, sublimation is the only significant process by which glaciers lose mass and its rate largely depends on wind speed rather than temperature."

    The reduction in glaciers located in high elevations in Chile and Mount Kilimanjaro etc are attributed to sublimation and not melting.

    Observations being made about Greenland and interpretations as to the cause of the change in Mass blaance that are posted here simply have no scientific basis attached to them.
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  34. Geo Guy, just to be clear are you in doubt about the GRACE results indicating loss of ice mass on Greenland, observed acceleration of ice loss at the margins of Greenland?

    Also, you probably did not notice that the paper you cite refers to closed drainages and has no particular relevance to Greenland or other locations where glaciers or ice sheets are connected to outflows. Sublimation or melting is the only available means of attaining mass balance for glaciers in closed drainages. The Greenland ice sheet and associated glaciers are of course not confined to closed drainages.
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  35. By the way, here is the paper Geo Guy cites, and here is a full text article fully disclosing the context of the situation Geo Guy believes overturns ice mass loss in a completely different situation.
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  36. And even beyond that, let's consider an imaginary ice sheet somewhere undergoing significant annual mass loss via sublimation. Um, where does the ice go? Into the air as water vapor. And then? It rains out ... and winds up in the ocean.

    Simple fact - any loss from any ice sheet winds up in the ocean. Yes, humans have created some extra lakes with dams, and a warming atmosphere will almost certainly retain more water vapor, but the former is a relatively small (though measured!) effect while the latter is obviously something that an AGW denier isn't going to want to talk about.
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  37. #33 Geo Guy, yes, but 300 gigatons per year by sublimation due to changes in winds? Please. Not credible.

    You are going to have to do better than a blanket claim that all of the observations being made about Greenland have no scientific basis. On what basis do you make that sweeping claim?
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  38. For a historical perspective:

    Was there a 1930s Meltdown of Greenland Glaciers? by Adam Herrington

    True, it is an undergraduate rersearch paper at the Ohio State University, still, it says something. It also provides plenty of literature on the subject.
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  39. 2009 melt anomaly in Greenland was not that large. For the Bulletin American Meteorological Society 2009 State of the Climate (in press), I write the Glacier and Ice Sheets section. Here is the line on the melt anomaly..."On the Greenland ice sheet SSM/I brightness temperature daily variations (Tedesco, 2008) identifies melt extent and number of melting days compared to the 1979-2008 average. Negative anomalies occurred in 2009 along Southern and West Greenland, positive anomalies along Northern and East Greenland. The melt extent was 670, 000 km2, slightly lower than in 2008. Surveys of Greenland marine terminating outlet glaciers from MODIS imagery (J.Box, Ohio State U. Byrd Polar Research Center) indicate that the 34 widest glaciers collectively lost 106.4 km2 of ice between late summer 2008 and late summer 2009. "
    So melt anomalies were above normal in the northern section of the ice sheet, but not a record.
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  40. # 37 - Jeff Its not the observations that are wrong, its the interpretation to those observations that are off base. With regards to sublimation, if that is not the driving force for ice loss in sub zero weather, perhaps you can tell us what is. Please don't say a 1 degree increase in atmospheric temperatures brought on by man made CO2 - that just does not make any sense. Even if the temperatures went from minus 20 to minus 10, that still will not result in melting of polar glaciers etc.

    With regards to GFW - your view assumes a constant level of water vapor in the atmosphere but in face the water content has increased on average at a rate of 1% per year since 1980 - hence the water resulting from the sublimation of ice fields does not all end up in the ocean.

    Everyone seems to assume when glaciers reduce in size it is because they are melting. What I am trying to point out is that in the polar regions and higher elevations, a small increase in average global temperatures will not and cannot melt those glaciers by itself. Something else is at work and we need to look at the other driving forces that affect glaciers to determine just that. Also the disappearance of glaciers at their margins is a normal observation - they disappear in the areas of ablation. Also glaciers move as a result of the build-up of ice in their centers which pushes the underlying ice outwards. When glaciers are retreating, you don't see that movement.

    Simply posting maps here showing larger areas of ice loss over a given period of time is meaningless. It certainly is no way near being "Quad Erata Demonstratum".

    As for Doug, # 34, my point is the ice loss identified by GRACE is not due to melting. There are other factors at work there - similarly to what is going on in the arctic. Those observations reported do NOT support the theory that man-made CO2 is causing warmer temperatures that are resulting in the disappearance of the Greenland ice.

    Also the glaciers in South America and in Africa that have disappeared are not closed systems and their disappearance has been attributed to sublimation and not warmer temperatures.

    As I mentioned in a previous post, the thermodynamics required to melt that ice simply from a rise in temperature just are not there. For instance, the energy needed to melt a volume of ice is the same temperature needed to raise the temperature of the resulting water to a 140 F level. With a global temp average increase of under 1 degree over 100 years, you do not need a science degree to figure out that polar ice is not disappearing from that marginal increase in temperature.

    One last word on the subject, the IPCC identified in one of its reports that glacial melting has been noticeable since 1970. In fact, geological literature identified glacier melting in the 1930's - well before the recorded increase in CO2 levels as measured in Mauna Loa. In addition, the rising temperatures in the arctic oceans were identified in the 1930's so what were are seeing today started well before 1970.

    Just as I find it difficult to accept that climate is being affected by only one factor - the rise in atmospheric CO2, (simply because there are multiple factors at play when it comes to climate), I also find it difficult to accept that the polar ice cap and glaciers are reducing simply due to one factor when there are so many others at play.

    Sometimes in science we have to step back and ask ourselves "Does it make sense?" In this case it doesn't make sense to me.
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  41. #40 Geo Guy, the mechanism for much of or most of the ice loss is glaciers flowing and dumping ice into the ocean. John said this in the original post. The ice does not have to melt in place. If the lower part of a glacier accelerates due to, for example, its interactions with warmer water at its terminus, or increased lubrication due to melting on its lower part, accelerated ice flow will propagate up glacier and into the ice fields/ice sheet that feed the glacier. The ice thickness changes as a result of this flow, and these changes have been observed directly in addition to the indirect observation of Khan et al. (the earth is responding like a scale to the ice, and the GPS is measuring the upward displacement of the scale as the weight on it is removed).

    This is not my idea -- it is based on direct observations (visual, time-lapse photos), glacier velocity observations, basic glacier physics, and even seismic recordings.

    And nobody here is saying that the ice loss is all due to melting in place, except perhaps those who suggest they don't believe any of this because the ice can't be melting in place.
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  42. Geo Guy, perhaps I'm misunderstanding you, or maybe you need to add just a jot of qualification to your writing. When you say " point is the ice loss identified by GRACE is not due to melting. There are other factors at work there - similarly to what is going on in the arctic. " I take it you do not discount the loss of ice mass, but you are pointing out that no single process is accountable for all of the loss of mass, the movement of water in space and state? I'm sure you're right about that.

    Of course, nobody here or elsewhere (well, the sane, anyway) has said that every last gram of ice seen to vanish in the past few decades is down to a single factor, so you won't find anybody worthwhile to argue that point with you. What we can say (and I imagine you could model this if you cared to take the time) is that sublimation alone cannot account for the entire loss of mass on the Greenland ice sheet.

    As to your speculation about the available amount of extra energy required to produce a phase change of a given mass of water from solid to liquid (melt ice), as an exercise take a look at the summer Arctic sea ice anomaly for any of the past few years and then compute for yourself the additional energy being absorbed by the ocean due to the loss of albedo. In case you don't want to do that work, I'll cut to the denouement, plot spoil and say that where energy arrives counts for a lot; using global temperature change to predict the behavior of ice in a given region is a futile approach.
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  43. Geo Guy,
    you might be interested in digging a little deeper. Following van den Broeke et al. 2009, they calculated the overall mass balance (surfaces mass balance SMB minus discharge D) and compared it with GRACE results. The former (SMB-D) compares well with the latter (r=0.99, fig. 1 in the paper). Next they show that from somewhere in the '90s SMB has been increasingly negative and D also increased (fig. 2a). The two mechanisms turn out to be comparable in magnitude.
    In fig. 2b you'll find the components of SMB, namely precipitation, runoff and sublimation. Sublimation had almost no part in the balance.
    Also very interesting is fig.3 where they quote SMB and D separately for various regions of the ice sheet.
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    Response: The paper van den Broeke et al 2009 is expounded upon in some detail in an earlier blog post Why is Greenland's ice loss accelerating?
  44. This discussion has gotten very strange.

    The mainstream scientific view of climate change impacts on the mass balance of the Greenland ice sheet is a model of clarity and consistency (both internal consistency and model-observation consistency).

    1. We know CO2 and other greenhouse gases are increasing, and physical models suggest that should lead to warming overall and particularly in the northern hemisphere high latitudes (polar amplification). Observed warming from multiple sources matches this.

    2. Physical models of glaciers and ice sheets suggest that this warming should lead to a negative mass balance and loss of ice via both melting (primarily in summer below the equilibrium line) and the accelerated discharge from marine terminating outlet glaciers. Remote sensing data specifically confirm (a) an increase in melting, and (b) an increase in glacier velocity.

    3. Other techniques (GRACE, high-precision GPS) confirm the overall negative mass balance that would be expected from the mechanisms in (2) above.

    That's a very clear, coherent picture. I'm a bit mystified as to why Geo Guy would write Sometimes in science we have to step back and ask ourselves "Does it make sense?" In this case it doesn't make sense to me. Whereas to me, this topic (Greenland ice sheet) seems quite sensible and straightforward, and trying to introduce other explanations for the observed loss of mass raises more problems:

    What mechanism would produce a large and rapidly increasing rate of sublimation in Greenland? What evidence is there for this increase in sublimation? Why would all the remote sensing data on melting and velocity be wrong?

    Occam's Razor suggests that the straightforward explanation is preferable to the convoluted and mysterious one.
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  45. @Geo Guy, you're wrong on so many levels. Others have so thoroughly hammered on the "ice flow and berg calving" vs "melt in place" issue that I haven't felt it necessary to mention it until now. But again, that's the dominant means of mass loss from Greenland. And yes, the increase in ice flow and calving is driven by the "marginal" increase in global temperature (which is both predicted and observed to be greater at high latitudes - see "polar amplification").

    I'm going to pick on something else. Your ludicrous assertion that "water content [of the entire atmosphere] has increased on average at a rate of 1% per year since 1980" Wrong. Water content of the stratosphere may have done that (see Wikipedia), but not the whole atmosphere. Such an increase in the stratosphere would deprive the ocean of ... wait for it ... less than 0.0025 mm/y. That is of course negligible compared to the 3mm/y rise we currently see, and the glacial contribution to same. There probably has been a small increase in tropospheric water vapor too, but on a similar absolute scale (not % scale). And of course that increase in tropospheric water vapor is predicted as a positive feedback in global warming.

    Finally, we know CO2 isn't the only factor, so fighting that position is a complete straw man argument. However CO2 is the "biggest control knob".
    Carbon black (aka soot) is known to be an important player in reducing ice albedo, thus contributing to the warming/melting of ice. But even if there was some way to eliminate soot emissions without changing our fossil fuel economy, that would only slow down the warming. (And indeed, there are people working very hard to reduce soot emissions.)
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  46. Geo Guy, it's good that you "find it difficult to accept that climate is being affected by only one factor - the rise in atmospheric CO2, (simply because there are multiple factors at play when it comes to climate)," because nobody else accepts that, either. It's a straw man. See CO2 is not the only driver of climate.
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  47. #40, Geo Guy, I just noticed this in your comment: "Also glaciers move as a result of the build-up of ice in their centers which pushes the underlying ice outwards. When glaciers are retreating, you don't see that movement."

    This is wrong. Glaciers retreat when the melting/ablation/calving at their terminus causes more mass loss than is made up by flow. But glaciers are always flowing. If more mass flows out of a section of a glacier than is replaced by new accumulated snow->firn-ice and flow from even higher up, the glacier loses mass in that section. Some glaciers flow very slowly, but given gravity and a slope, any large mass of ice flows downhill.
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  48. That's probably enough about Geo Guy.

    Does anyone have any insight into what the heck is going on with arctic sea ice extent? Is this just a short term weather phenomenon? It's pretty weird to see this kind of growth in late March. As significant as the mass loss from Greenland has been, I don't think freshwater bergs are contributing that much to sea ice.
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  49. GFW, sheer speculation on my part but since we earlier had a powerful positive temperature anomaly over much of the Arctic ocean this winter, perhaps things were "primed" for a rapid growth of ice once air temperature slid back into a more normal regime?

    Easy come, easy go, maybe. For my part I'm going to reserve any judgment about the health of Arctic ice until much later, August or September. Extent is has been dethroned, seems to me, with volume being the real story now.

    But again, I'm speculating.
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  50. The record of ice cover in the Arctic is full of rapid growths and rapid collapses. I don't think it makes much sense to discuss the trend over a month or over a year, it looks too random in the short perspective. The long term decreasing trend is clear though : look for instance at the tale of the tape from "cryosphere today".
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