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Greenland Glaciers — not so fast!

Filed under: — eric @ 15 May 2012

There have been several recent papers on ice sheets and sea level that have gotten a bit of press of the journalistic whiplash variety (“The ice is melting faster than we thought!” “No, its not!”). As usual the papers themselves are much better than the press about them, and the results less confusing. They add rich detail to our understanding of the ice sheets; they do not change estimates of the magnitude of future sea level rise.

One of these recent papers, by Hellmer et al., discusses possible mechanisms by which loss of ice from the great ice sheets may occur in the future. Hellmer et al.’s results suggest that retreat of the Ronne-Filchner ice shelf in the Weddell Sea (Antarctica) — an area that until recently has not received all that much attention from glaciologists — might correspond to an additional rise in global sea level of about 40 cm. That’s a lot, and it’s in addition to, the “worst case scenarios” often referred to — notably, that of Pfeffer et al., (2008), who did not consider the Ronne-Filchner. However, it’s also entirely model based (as such projections must be) and doesn’t really provide any information on likelihood — just on mechanisms.

Among the most important recent papers, in our view, is the one by Moon et al. in Science earlier this May (2012). The paper, with co-authors Ian Joughin (who won the Agassiz Medal at EGU this year), Ben Smith, and Ian Howat, provides a wonderful new set of data on Greenland’s glaciers. This is the first paper to provide data on *all* the outlet glaciers that drain the Greenland ice sheet into the sea.

The bottom line is that Greenland’s glaciers are still speeding up. But the results put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest, an idea that some had raised after a doubling over a few years was reported in 2004 for Jakobshavn Isbræ (Greenland’s largest outlet glacier). Let it not be said that journals such as Science and Nature are only willing to publish papers that find that thing are “worse than we thought”! But neither does this new work contradict any of the previous estimates of future sea level rise, such as that of Vermeer and Rahmstorf. The reality is that the record is very short (just 10 years) and shows a complex time-dependent glacier response, from which one cannot deduce how the ice sheet will react in the long run to a major climatic warming, say over the next 50 or 100 years.

These new data provide an important baseline and they will remain important for many years to come. We asked Moon and Joughin to write a summary of their paper for us, which is reproduced below.

Guest Post by By Twila Moon and Ian Joughin, University of Washington

The sheer scale of the Greenland and Antarctic ice sheets pose significant difficulties for collecting data on the ground. Fortunately, satellites have brought in a new era of ice sheet research, allowing us to begin answering basic questions – how fast does the ice move? how quickly is it changing? where and how much melting and thinning is occurring? – on a comprehensive spatial scale. Our recent paper, “21st-century evolution of Greenland outlet glacier velocities”, published May 4th in Science, presented observations of velocity on all Greenland outlet glaciers – more than 200 glaciers – wider than 1.5km [Moon et al., 2012]. There are two primary conclusions in our study:
1) Glaciers in the northwest and southeast regions of the Greenland ice sheet, where ~80% of discharge occurs, sped up by ~30% from 2000 to 2010 (34% for the southeast, 28% for the northwest).
2) On a local scale, there is notable variability in glacier speeds, with even neighboring glaciers exhibiting different annual velocity patterns.

There are a few points on our research that may be easy to misinterpret, so we’re taking this opportunity to provide some additional details and explanation.

Melt and Velocity

The Greenland ice sheet changes mass through two primary methods: 1) loss or gain of ice through melt or precipitation (surface mass balance) and 2) loss of ice through calving of icebergs (discharge) (Figure 1) [van den Broeke et al., 2009]. It is not uncommon for people to confuse discharge and melting. Our measurements from Greenland, which are often referred to in the context of “melt”, are actually observations of velocity, and thus relate to discharge, not in situ melting.


Figure 1. Components of surface mass balance and discharge. Most components can change in both negative (e.g., thinning) and positive directions (e.g., thickening).

When glaciologists refer to “increased melt” they are usually referring to melt that occurs on the ice sheet’s top surface (i.e., surface mass balance). Surface melt largely is confined to the lower-elevation edge of the ice sheet, where air temperature and solar radiation can melt up to several meters of ice each year during summer. Melt extent depends on air temperatures which tend to be greatest at more southerly latitudes. Meltwater pools in lakes and crevasses, often finding a path to drain through and under the ice sheet to the ocean. Glaciologists and oceanographers have found evidence for notable melt where the ice contacts ocean water [Straneo et al., 2010]. So, when you hear about ice sheet “melt”, think surface lakes and streams and melting at the ends of the glaciers where they meet the ocean.

So, why focus on velocity instead of melt? Velocity is more closely related to the discharge of ice to the ocean in the process of which icebergs break off, which float away to melt somewhere else potentially far removed from the ice sheet. You can picture outlet glaciers as large conveyor belts of ice, moving ice from the interior of the ice sheet out to the ocean. Our velocity measurements help indicate how quickly these conveyor belts are moving ice toward the ocean. Given climate change projections of continued warming for the Greenland ice sheet [IPCC, 2007], it’s important to understand at what speeds Greenland glaciers flow and how they change. On the whole, the measurements thus far indicate overall speedup. It turns out that on any individual glacier, however, the flow may undergo large changes on an annual basis, including both speeding up and slowing down. With these detailed measurements of glacier velocity, we can continue to work toward a better understanding of what primary factors control glacier velocity. Answers to this latter question will ultimately help us predict the ice sheet’s future behavior in a changing climate.

Sea Level Rise

Translating velocity change into changes in sea level rise is not a straightforward task. Sea level change reflects the total mass of ice lost (or gained) from the ice sheet. Determining this quantity requires measurements of velocity, thickness, width, advance/retreat (i.e., terminus position), and density – or, in some cases, an entirely different approach, such as measuring gravity changes.

Our study does not include many of the measurements that are a part of determining total mass balance, and thus total sea level rise. In another paper that we highlight in our study, Pfeffer et al. [2008] used a specifically prescribed velocity scaling to examine potential worst-case values for sea level rise. The Pfeffer et al. paper did not produce “projections” of sea level rise so much as a look at the limits that ice sheet dynamics might place on sea level rise. It is reasonable to comment on how our observations compare to the prescribed velocity values that Pfeffer et al. used. They lay out two scenarios for Greenland dynamics. The first scenario was a thought experiment to consider sea level rise by 2100 if all glaciers double their speed between 2000 and 2010, which is plausible given the observed doubling of speed by some glacier. The second experiment laid out a worst-case scenario in which all glacier speeds increased by an order of magnitude from 2000 to 2010, based on the assumption that greater than tenfold increases were implausible. The first scenario results in 9.3 cm sea level rise from Greenland dynamics (this does not include surface mass balance) by 2100 and the second scenario produces 46.7 cm sea level rise by 2100. The observational data now in hand for 2000-2010 show speedup during this period was ~30% for fast-flowing glaciers. While velocities did not double during the decade, a continued speedup might push average velocities over the doubling mark well before 2100, suggesting that the lower number for sea level rise from Greenland dynamics is well within reason. Our results also show wide variability and individual glaciers with marked speedup and slowdown. In our survey of more than 200 glaciers, some glaciers do double in speed but they do not approach a tenfold increase. Considering these results, our data suggest that sea level rise by 2100 from Greenland dynamics is likely to remain below the worst-case laid out by Pfeffer et al.

By adding our observational data to the theoretical results laid out by Pfeffer et al., we are ignoring uncertainties of the other assumptions of their experiment, but refining their velocity estimates. The result is not a new estimate of sea level rise but, rather, an improved detail for increasing accuracy. Indeed, a primary value of our study is not in providing an estimate of sea level rise, but in offering the sort of spatial and temporal details that will be needed to improve others’ modeling and statistical extrapolation studies. With just ten years of observations, our work is the tip of the iceberg for developing an understanding of long-term ice sheet behavior. Fortunately, our study provides a wide range of spatial and temporal coverage that is important for continued efforts aimed at understanding the processes controlling fast glacier flow. The record is still relatively short, however, so continued observation to extend the record is of critical importance.

In the same Science issue as our study, two perspective pieces comment on the challenges of ice sheet modeling [Alley and Joughin, 2012] and improving predictions of regional sea level rise [Willis and Church, 2012]. Clearly, all three of the papers are connected, as much as in pointing out where we need to learn more as in indicating where we have already made important strides.

Alley, R. B., and I. Joughin (2012), Modeling Ice-Sheet Flow, Science, 336(6081), 551-552.
IPCC (2007), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, S. Solomon et al., Eds., Cambridge University Press, ppp 996.
Moon, T., I. Joughin, B. Smith, and I. Howat (2012), 21st-Century Evolution of Greenland Outlet Glacier Velocities, Science, 336(6081), 576-578.
Pfeffer, W. T., J. T. Harper, and S. O’Neel (2008), Kinematic constraints on glacier contributions to 21st-century sea-level rise, Science, 321(000258914300046), 1340-1343.
Straneo, F., G. S. Hamilton, D. A. Sutherland, L. A. Stearns, F. Davidson, M. O. Hammill, G. B. Stenson, and A. Rosing-Asvid (2010), Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland, Nature Geoscience, 3(3), 1-5.
van den Broeke, M., J. Bamber, J. Ettema, E. Rignot, E. Schrama, W. Van De Berg, E. Van Meijgaard, I. Velicogna, and B. Wouters (2009), Partitioning Recent Greenland Mass Loss, Science, 326(5955), 984-986.
Willis, J. K., and J. A. Church (2012), Regional Sea-Level Projection, Science, 336(6081), 550-551.


269 Responses to “Greenland Glaciers — not so fast!”

  1. 51
    TimD says:

    Seems pretty clear that a bunch of folks have a beef against Dan H. Don’t get the history, but it seems like the most reasonable thing to do is to refute his positions with real data and peer reviewed papers. Like this…

    Dan H., I think I read the paper more carefully than you. We were talking about ice mass loss in Greenland and YOUR ref clearly stated that ice mass loss in Greenland continued to accelerate in ’11, and it is clear by looking at normal sources of the data. The Bergmann paper is a clear outlier. “Area and extent” refers to surface melting, which is probably small compared to warm seawater infiltration eating away at the ice from the base, but it was still large. In general, both the Greenland and Antarctic ice mass loss from normal analysis of GRACE data fits nicely with an exponential curve that has a doubling time of less than ten years

    The big questions we have left here, in my opinion, is how long will Greenland and Antarctica mass loss continue to fit exponential curves and if most of this phenomenon is due to seawater infiltration from below (which I think is the likely case) what does this mean when most of the continental ice sheets are grounded below sea level? In this regard, I don’t think Eric’s statement that ” the results put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest, an idea that some had raised after a doubling over a few years was reported in 2004 for Jakobshavn Isbræ (Greenland’s largest outlet glacier)” was useful or anywhere near true. It is well known that all glaciers individually move in fits and starts, but the overall Greenland ice mass loss is consistently accelerating, nicely fitting an exponential curve. Ice discharge directly by calving of outlet glaciers may be the smaller effect relative to seawater infiltration or non-linear behavior as basal ice is warmed by infiltration of surface melt water. Over the period of the GRACE data measurements, ice mass loss was clearly both increasing monotonically (ignoring seasonal effects) and exponentially, right up to 2011. Gee, I hope Eric reads this…

  2. 52
    Susan Anderson says:

    What Tamino said @~48

    As a lowly hanger-on, I have the luck to know a bit about how these people operate, but with only a little less history with scientists and scientific integrity and a lot less hard work in the mid-oughts following these intruders to their sources, I might have been taken in.

  3. 53
    Susan Anderson says:

    Simon Abingdon, clever but not good. They are not true skeptics, as they treat most science as suspicious to a fault, and the very small minority, some of whom are either funded or supplied by wealthy interests, and their hangers-on, as gospel bearers.

    I’m for the skeptics who started this blog to answer real questions, and not for those who wish to cause doubt and delay regardless of the validity of the issues they raise and the answers provided – often hundreds of times.

  4. 54
    Steve Fish says:

    Re- Comment by tamino — 18 May 2012 @ 11:01 AM, currently at #49:

    I strongly support Tamino in that I agree that obvious troll posts, such as those by Dan H, should go to the Bore Hole. I also caution that this is different than new posters who ask naive questions, regardless of the perceived motivation (e.g. talking points). I am seeing some recent questions/challenges in the Bore Hole that would provide excellent teaching moments. The emphasis should be to reduce distraction and improve education, especially for those just beginning to learn about climate. Steve

  5. 55
    wili says:

    Thanks for reinforcing my point, tamino.

    Only slightly off topic–I highly recommend tamino’s recent post on GW and denialists:

    http://tamino.wordpress.com/2012/05/16/why-i-must-speak-out-about-climate-change/

    “Why I Must Speak Out about Climate Change”

    “Over thirty years ago, James Hansen was lead author of a scientific paper titled Climate Impact of Increasing Atmospheric Carbon Dioxide. They estimated that doubling the amount of CO2 in the air would raise global temperature about 2.8 degrees (C, equal to about 5 degrees F). They projected that from 1980 to 2010, earth would warm a little more than 0.4 degrees C. High northern latitudes, however, would warm at a much faster rate. We would likely see the start of melting of the great ice sheets in Antarctica and Greenland. They further suggested that we could start to lose much of the sea ice in the Arctic, which might even open the Northwest and Northeast passages.

    That was over thirty years ago. What has happened since then?

    From 1980 to 2010, earth warmed about 0.5 degrees C. High northern latitudes, however, warmed at a much faster rate. We’ve seen rapid melting of the great ice sheets in Antarctica and Greenland. We’ve already lost much of the sea ice in the Arctic, which has opened the Northwest and Northeast passages.

    The science is clear…

    Yet there’s a powerful movement to deny it. Some stems from political ideology, some from mistrust of government, and yes, a heckuva lot of it is spread by the fossil fuel industry — because it’s their product that is the cause of the problem. They make immense profits, and they see any interference or accountability — any at all — as a threat to their already bloated wealth. So, rather than accept that something has to change, rather than adapt to the situation, they deny reality and fight tooth-and-nail to preserve the status quo.

    Wake up! We can’t afford to let them build their wealth on our misery. The science really is clear. Stop letting PR pundits and politicians in denial send our future down the toilet. Stop letting them sucker you.”

    It is long past time for all of us with half a heart and half a brain to stand with Tamino, Hansen and the many other brave and intelligent voices calling for a responsible approach to the globe’s future, and to stand against the forces of ignorance, greed and destruction–the Koch’s, Heartland, and denialists of all stripes.

  6. 56
    Hank Roberts says:

    > excellent teaching moments
    Depends on who’s offering to do the teaching; once people have noticed the Start Here button, and clicked it, the quality of their questions gets either much clearer, or else much more suspicious and political.

    That’s really the first teaching moment, right there.

    Those who can find and follow the Start Here link on the main and every other page — have already taught themselves something, and the teaching moments available can be more useful.

    Those who never find the Start Here button and persist asking the Frequently Answered Questions already answered for them in the Start Here section — are less teachable, probably.

    It’s a lot easier to mislead people who haven’t read the stuff in the Start Here section at least once.

    That’s why the misleading posters get commented on. It’s unfair tactics to mislead those who can’t even find the Start Here button to begin with.

    Or that’s what I think today, anyhow.

  7. 57
    Steve Fish says:

    Hank, you are getting too jaded. Naive posters who get rebuffed will never learn anything because they will be pissed off. I agree that RTFM is a truism, but in reality most folks don’t. I say, give them a few chances with direction before giving up. Steve

  8. 58
    Jim Larsen says:

    Dan H says, “I have been around long enough to know that we scientists”

    OMG!! Dan H probably has a high school diploma (they give ‘em out for attendance mostly), but I can’t fathom much more. (feel free to correct my unsubstantiated estimate Dan H)

    Dan H does add to the mix – BUT ONLY IN SMALL DOSES. Perhaps RC would profit from a “limited commenter” policy. Let Dan H and other prolific but barely useful folks (oops, does that include me?) post maybe 3 comments to each thread, or perhaps five comments per week for all threads combined, then the rest go to borehole regardless of value. He’d learn efficiency and provide some value without smearing “stuff” all over each and every thread.

    I think the moderators would be wise to pay attention to the dismal hit count RC gets as compared to sites like WUWT. If we subtract the hits from regular users, then RC’s hit count probably goes down to irrelevant. The moderators can either accept irrelevance or improve the experience for the typical user. Previously I suggested a type of ranking of commenters. Nobody even bothered to comment on the idea, good or bad.

    RC could use fewer but better and more responded to comments, and RC’s moderators could save themselves time and effort while improving the site by working on issues such as Dan H with the thrust being to allow Dan H et al to contribute to the RC experience without soiling the nest. After all, Dan H is nearly the perfect example of the person who needs to be debated to carry the day. Simply banning or boreholing him would just make RC more irrelevant. Perhaps the moderators could place “lines in the sand”, where a commenter could be asked to substantiate an outrageous claim or publicly retract it, with their commenting privileges suspended until they do so. “Put up or shut up permanently” so to speak.

    Perhaps there should be two levels of comments for each thread. Extremely constructive comments could be placed first, and often responded to, while those which aren’t so constructive could be placed at the end. Then, visitors could read the posts and the constructive comments and get a good, efficient conversation, yet everyone is treated fairly by being posted on the thread. The truly dismal could still go to the borehole. (Note: boreholed comments should probably have a note placed in the original less-constructive comment thread pointing to the boreholed comment, similar to but more informative than the way edited out text is noted by [edited]. Then, folks who want to read what Dan H said could click the link and see the boreholed comment.)

    In any case, I think a discussion amongst the moderators and the regulars should take place on how to improve the effectiveness of RC, as currently WUWT et al are eating RC’s lunch. There are a lot of talented folks who spend a lot of time on RC. Their time and talents could probably be utilized far more efficiently. For example, a cadre of vetted regulars could moderate and respond to most comments, leaving the principals to do higher level work, including their day jobs. Another possibility is that comments which raise interesting and important questions could be flagged, inviting further discussion. Most important, the whole experience needs to be streamlined. 300 comments later, a thread is useless other than as pseudo-entertainment for regulars. Not a single “normal” user will ever read down a 300 comment thread. Much better would be 30 highly productive comments in a discussion format, with 270 also-rans listed afterwards. Bandwidth gets ever cheaper, but human reading time will always remain expensive. And if I knew my comment had to compete to get in the “top 30″, I’d put a lot more care and consideration into it than I do now.

    Another improvement would be to get rid of the Start Here button. Instead, a Start Here thread should remain at the top of the threads list. First thread seen, first thread clicked. Solves the problem and everyone who has already seen it just clicks on the subsequent threads instead.

    One last thing while I’m on my soapbox. Some of the regulars have been getting rather abusive. I see the same couple of folks (one especially) ridiculing new and old commenters and their thoughts. I’m sure that behaviour has reduced RC’s hit count. The behaviour is poisonous and catching. I’ve even seen it cropping up amongst the moderators. The wide-open 300+ comment format surely has at least partially led to this unfortunate situation.

  9. 59
    Brian Dodge says:

    “Greenland glacial history, borehole constraints, and Eemian extent.”, L. Tarasov and W. Richard Peltier atmosp.physics.utoronto.ca/people/lev/g6jgrpub.pdf shows graphs of temperature versus depth of the GIS(Figs 7 & 8.) There is a positive gradient below ~ 1.5 km to the base, and Figure 10 of the following article shows that large basal areas of the northern GIS are at the pressure corrected melting point.

    “The effect of the north-east ice stream on the Greenland ice sheet in changing climates” eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/28280/1/CSD1-41.pdf – “Simulations into the future showed clearly a strong susceptibility of the Greenland ice sheet to global warming on time-scales of centuries. However, the enhanced basal sliding in the NEGIS area calibrated by the paleoclimatic simulations does not speed up the decay of the ice sheet significantly. By contrast, surface-meltwater-induced acceleration of basal sliding for the entire ice sheet can lead to a dynamic speed-up of its disintegration if the surface meltwater coecient is an order of magnitude larger than the estimate of Appendix A. While this process was found to be enhanced moderately in the NEGIS area, the presence of the NEGIS is not crucial for it. So we finally conclude that the NEGIS, unless it behaves in an unexpected way[e.g. like the Larsen Ice shelf - BD] by dramatically increasing its area or speeding up beyond our reasoning, can increase the decay of the Greenland ice sheet to a limited extent, but does not have the potential to dynamically destabilize the ice sheet as a whole.”

    I note that the surface slope of the GIS is low (0.01 – Parizek and Alley 2004), and the basal slope is negative(much of the base is below sea level due to isostatic depression) except at the edges. An X km increase in snow line/surface melt elevation moves the line inland 100X km; at some point, this will result in moulins draining toward the middle of the ice sheet, and accumulation of subGIS lakes – which have very low basal friction – instead of drainage to the sea. I wonder if this would cause exponential, or catastrophic changes in ice export versus temperature, e.g., if the km3(i)/T curve would be analogous to the i/v curve of a junction diode or an SCR.

    See “Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods”, STEARNS et al http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/Stearns.pdf “Our findings provide direct evidence that an active lake drainage system can cause large and rapid changes in glacier dynamics. The causes of rapid changes in outlet glacier flow speed are not fully understood.”

    Some no doubt will say that since we don’t fully understand the GIS dynamics and associated risks, we shouldn’t disturb our highly profitable BAU.

  10. 60

    Recent baseline date for glacial melt-rate is problematic in that we’ll get the “really bad news when its too late.

  11. 61
    Dan H. says:

    Tim,

    This paper presents a nice synopsis of the GRACE analyses, partially explaining some of the many differences in results:

    http://www.springerlink.com/content/kh05734436864k62/fulltext.pdf

    The authors state that this study is “in agreement with other recent GRACE studies,” and shows 2007 as having the highest net ice loss. The authors also decided to represent the GRACE observations by a linear trend, and “cannot observe a significant acceleration term over whole data series.” Adding the 2010 and 2011 values to their time series does not change this conclusion.

  12. 62
    Hank Roberts says:

    > Dan H.

    That’s a link to a paywalled site, not to the paper.
    There’s not even a summary there.

    Have you read it?
    If so, where?

  13. 63
    Dan H. says:

    Hank,

    Sorry, I did not realize that when I accessed the paper. The paper is entitles, “Mass loss of the Greenland ice sheet from GRACE time-variable gravity measurements,” by Joodaki and Nahavandchi. I will see if it is available elsewhere.

  14. 64
    dbostrom says:

    Depriving the locally famous annoyance of the positive feedback derived from constantly reading its own name as repeated by other people might help as well as prove intriguing.

    Reply, even quote, but don’t repeat the annoyance’s name, don’t attribute. The annoyance’s behavior in the face of failure to successfully manipulate will be information in itself, even if there’s no obviously perceptible response at all.

    Volunteer anonymous experimental subject is at hand, so why not turn the knobs and see what happens?

  15. 65
    Hank Roberts says:

    How did you “access” the paper?
    First hand at the paid site?
    Second hand from someone else?

  16. 66
    Ric Merritt says:

    Walter Pearce, #50: Dan H “makes me yearn for the Rod B. era”.

    Hey, has anyone seen Rod and Dan in the same room?

  17. 67
    Dan H. says:

    Hank,

    Cannot find a freebie. The best I can do is link to the most relevant graphic here (results from JPL):

    http://engenheiro.blogspot.com/2012/04/mais-um-belo-desservico-que-o-jornal.html

    While these numbers cannot be directly compared to the noaa values, if one assumes that the most recent melt was also 70% higher than the 2003-2009 average, then the value would be ~-135. This correlates well with the noaa statement where 2005 had almost as much mass loss as 2010.

  18. 68
    Aaron Lewis says:

    Re: 38
    What scares me is loss of albedo across the Arctic and transport of heat via water vapor to the GIS. It does not matter if the heat comes from the ice free Arctic Ocean, the North Atlantic, or direct light on the GIS.

    Water flow rates during draining of surface lakes from GIS exceed water flow rates over Niagara Falls. However, since the fall through the GIS is greater than the head at Niagara Falls, more energy is released – all inside the ice. The problem is that large volumes of ice do not have to melt, only warm enough that they have less structural strength. And, not all the ice must warm, only small volumes that create structural weaknesses.

    While it certainly takes super computers to get all the detail correct, one can do engineering estimates with a slide rule in the back of your day planner. You will not like the results, but you will not like the results of a super computer program any better. And there lies the rub. Nobody in the organization will like those results, so everybody will fudge them down a bit and the final output of the super computer will be a fairy tail where everybody lives happily every after.

  19. 69

    “…shows 2007 as having the highest net ice loss…”

    Again, the location of the highest outlier in a series by itself says little about the trend, its acceleration–or really, much of anything.

    As always when I encounter this line of rhetoric, I’m driven to wish that 1998 and 2007 records would be firmly obliterated, just to eliminate those particular ‘cherries’–for a moment.

    Then I recall that it’ll just be “Warming stopped in 201-/Sea ice has been recovering since 201-.”

  20. 70
    dhogaza says:

    TimD:

    Seems pretty clear that a bunch of folks have a beef against Dan H. Don’t get the history, but it seems like the most reasonable thing to do is to refute his positions with real data and peer reviewed papers. Like this…

    The history is that many people, as you suggest, have treated DanH seriously, only to find that after correcting his misreading of papers, etc, he just waits a bit then reposts the same mistaken conclusion, as though he was never corrected.

    Over and over again, with a persistent pattern spanning many sources that do not say what he claims they say.

    I shall sit back and see if you’re as patient with his modus operandi a few months from now as you are today …

  21. 71
    Hank Roberts says:

    How did you “access” the paper?
    First hand at the paid site?
    Second hand from someone else?

  22. 72
    TimD says:

    Dhogaza, please don’t worry much about me getting excessively cozy with Dan H. I don’t think I in any way cut him any breaks in our interactions, other than being polite that he referred to some papers. I just don’t have any emotional investment in this guy, as so many of you seem to. Why that should be is clear to me – I just haven’t beat my head against the wall with this guy as long as you have. But when he said the opposite of what the paper he referred to actually said, I just corrected him. But you folks were going “Here he goes again!” I am sorry you good people have been afflicted with the nonsense that comes with someone clinging desperately to untruths that the deluded person finds painfully challenging his/her deeply held beliefs. You have to imagine just how difficult for a free-market, small government conservative to consider the existence of a huge, global problem that can only be effectively addressed by some form of global enforcement of rules. Everyone deserves some sympathy, even Dan H. I recall a Rolling Stones song about that.

    [Response: Can everyone please not clutter up threads with comments about other commenters? It is extremely tedious. This is a post about glaciers in Greenland. - gavin]

  23. 73
    Susan Anderson says:

    Very interesting material from those sticking to the topic. I’m especially grateful to Aaron Lewis and Brian Dodge. I hope more will do so (stick to topic, that is).

  24. 74
    TimD says:

    Well, gavin, since your remark was clearly directed at my remark, I feel it reasonable to respond. A plethora of posts containing nothing but attacks on a commenter occurred from #28. Where were your oh-so-wise, peacemaking comments at that time? Or do you only comment about certain “other commenters”? I was doing my best to return the discussion to the topic of Greenland Ice sheets when this chorus of attacks sprang up, and that is a problem on a site like this. These things should be nipped in the bud and when they aren’t it becomes a reasonable topic of discussion, although I would rather discuss climate change. This is a moderation problem.

    [Response:I agree it is a moderation problem - but we have day jobs and this task is not always our highest priority. My comment was not really directed at you, rather you were a trigger for a general comment. Discussion of the character of other commenters, their motives, moderation, tone etc. are boring, and we try and discourage it (albeit imperfectly). And on this thread, this comment is the last word on that. - gavin]

  25. 75
    TimD says:

    Bravo, and thanks Gavin. I also have a day job but happen to believe that rapid climate change is perhaps the most significant threat to humans in modern history. The issue of exponential growth of ice mass loss is a critically important sub topic and that is clearly related to the topic at hand. In #51 I directly challenged a key assertion in the main article by Eric that the study he cited ”put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest”. I strongly suggested he respond, but in the entire thread he has only had time to do a little misguided sniping about the mention of volcanoes. The question of exponential ice loss is probably more important than whatever else Eric might be doing at the moment, I would think.

    [Response:One thing I know is LESS important than what I am doing at the moment: responding to people that tell me what I AM doing is not as important as what they think I'm doing. But to respond to your criticism: I am not saying exponential change cannot happen. I was saying that speculation on the basis of a few years of data (which was done) has not (yet) been borne out by the facts.--eric]

  26. 76
    Mauri Pelto says:

    The recent Moon et al (2012) paper is an excellent paper. Having reviewed at least six papers this year on this topic area, the conclusions fit the results of the other more regional based papers. A 25-30% acceleration in marine terminating outlet glaciers is nothing to ignore. More importantly is that this mean increase lumps all of the marine terminating glaciers into one pool. I suggest that going forward we will need to separate the marine terminating glaciers into two categories. Those that end in deeper water and those ending in shallow water. This was the focus of the categorization of Greenland glaciers in Skeptical Science. There are two key reasons. 1)If enhanced basal melting from seawater is key, this mechanism is typically not a shallow water mechanism. Secondly thinning of a glacier tongue that is at least partially afloat, more likely in deep water, reduces backforces and enhances velocity and calving. This is a mechanism that is more pronounced in deeper water terminating glaciers. In a recent paper, final draft due out soon by Mernild et al (2012), the fastest five glaciers are the largest, and these have experienced the most losses too. Epiq Sermia is an example of a glacier where detailed data provides much food for thought.

  27. 77
    Dan H. says:

    Tim,
    To reinforce Eric’s statements, see the following article about regional variations in Greenland.

    http://www.agu.org/pubs/crossref/2011/2010JB007789.shtml

    The estimated ice mass loss from NW Greenland glaciers increased from 30 to 130 Gt/yr, while SE glaciers decreased from 110 to 0 Gt/yr over the periods 2002-05 to 2007-09.

    All told, we have less than 10 years of GRACE measurements, such that making long term predictions based on these estimates are still precarious. None of these studies precludes the idea that ice mass loss could accelerate exponentially. However, there is no evidence that it has been recently.

    Another study found large variations in the changes in the three largest Greenland glaciers.

    http://www.agu.org/pubs/crossref/2011/2011GL047565.shtml

    An attempt has been made to compare recent satellite data with other, earlier calculations.

    http://www.staff.science.uu.nl/~broek112/home_files/MB_pubs_pdf/2011_Hanna_JGR.pdf

  28. 78
    TimD says:

    Eric, if the work you are doing is less important than the question of exponential ice sheet mass loss, you still could be doing Nobel Prize level work, so it isn’t much of a dig, if you think about it. For the record, I haven’t checked your CV and I have no idea what you are doing. I would love to hear about your work. But you did say ”put speculation of monotonic or exponential increases in Greenland’s ice discharge to rest”, which sounds like plain English for “negated that possibility”. Clearly that is not the case, and in general, extrapolating trends is a lot of what scientific prediction is about. Hansen’s work, which I cited, pointed out that answering the question of how long that trend of rapid acceleration in mass loss persists (we all appreciate that exponential growth is a temporary condition) is critically important. Your suggestion that the exponential growth has stopped is certainly not supported by the latest and highest quality data (Grace) and in human terms, the title of your little review was misleading and, in effect, fuel for the skeptics. Whatever you believe to be true, I think that in this environment, you need to take better care with your use of language. In any case, the paper you cited only considered mass loss from ice stream discharge, which many believe is small compared to the effect of basal melting in response to rapid warming of arctic sea water. An exponential function plus a linear function is still an exponential function.

  29. 79
    Mauri Pelto says:

    Tim: Ice stream discharge is not small compared to melting in Greenland. There just is a very small area of the ice sheet available to be melted by seawater unlike Antarctica. It is true the increase in surface melting is not considered in the paper, nor it should it be. This is a dynamics paper. Petermann Glacier is one of the few with a large floating ice tongue available for melting. Nearby Humboldt Glacier even though larger does not.

  30. 80
    wili says:

    Two topics I would like to see discussed further–effect of isostatic rebound (if that’s the right term), and methane and CO2 release from soils newly emerging from the icesheet as it melts.

  31. 81
    TimD says:

    Mauri, I think there may be some semantic problems here. I took Eric’s use of ice discharge to mean total ice mass loss. I used the more specific “ice stream discharge”. But I definitely didn’t mean “surface melting”. I was talking about basal melting. I think that there is considerable uncertainty as to how efficient the salinity/density convection mechanism is at melting basal ice, but if you are looking for energy sources to melt Greenland ice, the very rapid increase in SST is a reasonable place to look. I suspect that the advent of the recent phenomenon of large moulin floods could have opened paths through the ice to the ocean that then reversed and began to rapidly melt ice at the base of the ice. But whatever the mechanism of exponential ice mass loss seen by Grace measurements, we need to understand it pretty soon.

  32. 82
    David B. Benson says:

    wili @80 — I’m unsure what about isostatic rebound puzzles you. However, under the ice in Greenland and Antarctica is surely nothing but bedrock.

  33. 83
    Hank Roberts says:

    > how efficient the salinity/density convection mechanism is …

    One indicator I know the biologists are looking at that probably correlates (somehow) with both basal melt (pure fresh water) and surface melt (nice fix of heavy metals, nitrates, etc. deposited by the wind over the winter) — which probably give different kinds of plankton a boost at the ice edge.

  34. 84
    wili says:

    Thanks, David. But even bedrock rebounds when millions of tons of overlaying weight starts to be removed from above it. My understanding is that the center of the island is slightly below sea level now because of all the pressure from above. As the ice starts to melt, presumably that will start to bow upward, going from concave to flattish to convex. I would think that this change would accelerate the rate at which ice slips into the sea. I know that this is a long-term thing. But is there anything basically wrong with that basic picture that anyone cans see? Is this rebound figured into the major models for what is going to happen with the Greenland icesheet at what rate?

    And by bedrock, do you mean that there is probably no or not much methane under the ice? Wasn’t there vegetation there before it was covered with ice? Did that all just disappear over the ages?

  35. 85
    wili says:

    Hank posted this over at the open thread (#135) and it seemed to me to be relevant here:

    http://www.bbc.co.uk/news/science-environment-18120093

    http://news.bbcimg.co.uk/media/images/60347000/jpg/_60347194_60347193.jpg

    —excerpt follows—
    researchers on the new Arctic project, led by Katey Walter Anthony from the University of Alaska at Fairbanks (UAF), were able to identify long-stored gas by the ratio of different isotopes of carbon in the methane molecules.

    Using aerial and ground-based surveys, the team identified about 150,000 methane seeps in Alaska and Greenland in lakes along the margins of ice cover.

    Local sampling showed that some of these are releasing the ancient methane, perhaps from natural gas or coal deposits underneath the lakes, whereas others are emitting much younger gas, presumably formed through decay of plant material in the lakes.

    “We observed most of these cryosphere-cap seeps in lakes along the boundaries of permafrost thaw and in moraines and fjords of retreating glaciers,” they write, emphasising the point that warming in the Arctic is releasing this long-stored carbon.

    “If this relationship holds true for other regions where sedimentary basins are at present capped by permafrost, glaciers and ice sheets, such as northern West Siberia, rich in natural gas and partially underlain by thin permafrost predicted to degrade substantially by 2100, a very strong increase in methane carbon cycling will result, with potential implications for climate warming feedbacks.”

    The story is also covered nicely in the NYT:

    http://green.blogs.nytimes.com/2012/05/21/popping-the-cap-on-arctic-methane/

    (Sorry, Hank–It may be that I’m just a bit desperate to get this thread back to something at least marginally connected to its stated topic :-/)

  36. 86
    Hank Roberts says:

    Wili, maybe you know different — I think that the glaciers pretty much rest on bedrock — they grind everything down to the bedrock! — so it doesn’t seem likely that any moving glacier is going to have permafrost melting under it. Now in the central parts of Greenland (and Antarctica) it might be different –would the weight of the ice push all the softer stuff out to the edges over geological time? Or would there be masses of organic material under the icecaps?

  37. 87
    David B. Benson says:

    wili @84 & Hank Roberts @86 — All the ice eventually moves to the sea over geologic time and so has surely removed every trace of organic matter. Recall that the longest ice cores go back ‘only’ less than 800,000 years and Antarctica has be covered with ice for far longer than that

    wilw @84 — Yes, rebound will occur over a long enough time. In my amateur opinion it is a minor effect with regard to the ice melting.

  38. 88
    TimD says:

    Wili, I think that isostatic rebound is relevant to the current topic, not so sure about methane emissions from permafrost melting. The methane issue is very important in terms of it being a huge potential positive feedback mechanism, since it is a very potent GHG and there is lots of organic matter locked in permafrost that is doomed to thaw. Also, there is lots of methane stored as methane ice (clathrate) in shallow offshore sediments that could be catastrophically released as the sea surface temps increase rapidly. In general,there are lots of positive climate feedbacks in the arctic and very few negative feedbacks, which tend to only kick in after the climate has been hugely altered.

    But post-glacial isostatic rebound is a concept near and dear to geophysicists since it opens a window to learn about the rheology of the upper mantle, a key issue in plate tectonics. You can read a decent review of it at http://en.wikipedia.org/wiki/Post-glacial_rebound. Because mantle mass is moving around, there is an easily measurable effect on a sequence of gravity measurements, so it is quite relevant to the analysis of the Grace data. But at the same time, because the mantle viscosity is so high, the mantle flow patterns are very stable and not that hard to separate from changes in ice mass when looking at gravity data. The extremely accurate gravity field information from the Grace satellites is very important to ice mass change in places like Greenland since it sees the entire picture, seeing changes through the entire crust and into the mantle. It is so sensitive that it can see the change in mass from a single big rain storm and in the case of Greenland, the Grace data can see ice mass changes at the base of the ice sheet that is very difficult to measure in other ways. That is a critical issue given that it appears that rapidly warming SST is providing a mechanism to melt perhaps the majority of the ice lost from below. (Full disclosure; I am a geophysicist with a long-standing interest in climate issues).

  39. 89
    wili says:

    Thanks Hank and David. I, also, had always assumed it was pretty much bed rock under the ice, but that line from Hank’s article gave me pause:

    “Using aerial and ground-based surveys, the team identified about 150,000 methane seeps in Alaska and Greenland in lakes along the margins of ice cover.”

    Why would there be so much methane coming out of lakes at the margin of ice cover if it’s just bedrock? Since the Greenland sheet has started to shrink (not radically yet, and mostly at its southern end so far), I would assume that many of these ‘lakes’ are in areas that had been covered with the ice sheet up to fairly recently.

    But perhaps I’m jumping to conclusions. Perhaps it’s time to see if I can get to the original study. Has anyone found an accessible copy?

  40. 90
    wili says:

    OK, I tracked it down. Here is the relevant section from the abstract of the article:

    “Here, we document the release of 14C-depleted methane to the atmosphere from abundant gas seeps concentrated along boundaries of permafrost thaw and receding glaciers in Alaska and Greenland, using aerial and ground surface survey data and in situ measurements of methane isotopes and flux. We mapped over 150,000 seeps, which we identified as bubble-induced open holes in lake ice. These seeps were characterized by anomalously high methane fluxes, and in Alaska by ancient radiocarbon ages and stable isotope values that matched those of coal bed and thermogenic methane accumulations. Younger seeps in Greenland were associated with zones of ice-sheet retreat since the Little Ice Age. Our findings imply that in a warming climate, disintegration of permafrost, glaciers and parts of the polar ice sheets could facilitate the transient expulsion of 14C-depleted methane trapped by the cryosphere cap.”

    http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1480.html

    So it is specifically from the boundary of “receding glaciers” in Greenland where they found these methane leakages.

    How much of the “1,200 Pg” (=~ a trillion tons?) of methane they mention are under which of these formations? How fast a feedback should we expect from this source? When we add it to the other carbon feedbacks, and consider that all of these will be feeding back on each other…shouldn’t we be starting to get a bit…worried?

    (reCaptcha: tibugee unusual)

  41. 91
    Hank Roberts says:

    Thanks David, that fits my recollection — both for Greenland and for Antarctica; I do recall some imagery from deep ice drilling in Antarctica that reached the bottom of the ice and found only a meter or so of water then rock, and mention that the pressure was enough to make water and rock flour flow uphill from the low spots and squeeze out toward the edges.

  42. 92
    Jim Larsen says:

    wili, rebound in Greenland is 1.4-10mm/yr, depending on location. It’s expected to double by 2025 for exactly the reasons you proposed.
    http://www.skepticalscience.com/greenland-rising-faster-as-ice-loss-accelerates.html

    Compare that rate to the thinning of the ice sheet. Page 2 shows thinning at the margins of ~50cm/yr over much of the island. They conclude, “Even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years.”
    http://www.cesm.ucar.edu/working_groups/Land+Ice/presentations/2012/wang.pdf

  43. 93
    MARodger says:

    Re:- old vegetation under ice caps.
    The Baffin Island ice caps are sat on old vegetation (& so presumably frozen soils). This is possibly because the ice is not thick enough to ‘unstick’ itself & start flowing.
    http://www.sciencedaily.com/releases/2008/01/080128113831.htm
    Antarctic & Greenland ice is thick.

  44. 94

    “Or would there be masses of organic material under the icecaps?”

    Interesting question–I’ll opine that if there were, you’d find extremophile bacteria munching happily away at it.

  45. 95
    wili says:

    Thanks, Jim. So up to 2 cm/year by 2025.

    That might seem slight. But consider that a marble on a level table top will stay in place for ever. But tip the table even a mm, and it is likely to start rolling toward the edge of the table. So ice that might not otherwise moved toward the sea, may start doing so with even a slight shift in the tilt of the land.

    Interesting point about Baffin Island. It sounds like they may be talking about deep methane associated with coal seams in this article, so it may be beneath bedrock, but still be able to be liberated through cracks in the rock once the overlying ice is gone.

    In any case, this paper seems to present another very large quantity of free, gaseous methane (1,200 Pt vs 5 Pt in all the atmosphere now), ready to go directly into the atmosphere once the ice keeping it capped in is gone or weakened–another potentially enormous feedback that can drive a runaway GW scenario. It sounds as though it is a very small source right now, but once that camel’s nose gets under the tent, the whole thing is likely to come down, especially when this is added to all the other sea and terrestrial feedback ready to kick in (if not started already).

  46. 96
    MS says:

    Re organic material in ice cores:
    It seems the NGRIP project in Greenland (2003) found a little organic material in a deep ice core.
    Ref North Greenland Ice Core Project

  47. 97
    Hank Roberts says:

    > a little organic material

    Very tiny fragment, photographed: http://www.gfy.ku.dk/~www-glac/ngrip/index_eng.htm
    They said in 2003 they might be able to confirm what it was.
    did they?

  48. 98
    Hank Roberts says:

    > a little organic material

    Very tiny fragment, photographed: http://www.gfy.ku.dk/~www-glac/ngrip/index_eng.htm
    Their press release is promising; has anyone seen a conclusion about their speculation from 2004 when they’d just recovered this material?

    http://www.gfy.ku.dk/~www-glac/ngrip/presse_070804_eng.html

    It does suggest there’s organic material and dissolved gas — but that’s a press release and we know about those being consistently wrong.

  49. 99
    TimD says:

    I’m new to this insular little group, so I don’t know your customs. Clearly welcoming new people isn’t one of them. But since there is interest in methane releases, even if marginally related to the topic at hand, it is an interest of mine and I think I can contribute usefully to the discussion.

    Methane ice occur at shallow levels in sediments all around the world and they are particularly easy to see on reflection seismic sections. Methane ice is stable in the deep waters of the Gulf of Mexico and played a part in the BP disaster. A professor/friend from SMU who works on methane ice sent me this link about Russian scientists discovering rapid increases in methane release http://www.independent.co.uk/news/science/vast-methane-plumes-seen-in-arctic-ocean-as-sea-ice-retreats-6276278.html Since, in the arctic, methane ice is stable at the surface, it can be rapidly warmed beyond its stability zone and disassociate to methane gas and water. It is pretty clear that this is what is going on in arctic oceans. It is not at all unreasonable to suspect that we are seeing the beginning of an exponential increase in clathrate gas releases as losses of sea ice, huge changes of albedo and resultant SST increases hit this very fast feedback mechanism. I proposed to my friend that once the gas disassociation gets started in permeable sediments, the rising bubble column will reduce the hydrostatic pressure and effectively pump warm water from the surface through the sediments, leading to rapid heat transfer through the sediments by mass transfer rather than conduction. If that is what is going on here, very rapid and very large increases in methane release from the arctic seems pretty likely. Clearly, this could be a huge wild card in terms of climate change modeling. Just another example of arctic fast feedback surprises that leave vaunted arctic scientists with mouths agape.

  50. 100
    dbostrom says:

    Hubris along the lines of “just another example of arctic fast feedback surprises that leave vaunted arctic scientists with mouths agape” tends to find a chilly reception no matter where it’s found.

    Social calibration is key; before assuming that mouths will be left gaping by a “new” thought, raise the periscope out of the cranium and scan the horizon. There are 7 billion thinking people on the planet; the risk of conceptual aliasing due to imaginary originality is fairly large.


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