Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
Keep me logged in
New? Register here
Forgot your password?

Latest Posts

Archives

A basic overview of Antarctic ice

Posted on 29 November 2010 by robert way

Skeptic arguments that Antarctica is gaining ice frequently hinge on an error of omission, namely ignoring the difference between land ice and sea ice.

In glaciology and particularly with respect to Antarctic ice, not all things are created equal. Let us consider the following differences. Antarctic land ice is the ice which has accumulated over thousands of years on the Antarctica landmass itself through snowfall. This land ice therefore is actually stored ocean water that once fell as precipitation. Sea ice in Antarctica is quite different as it is generally considered to be ice which forms in salt water primarily during the winter months.

In Antarctica, sea ice grows quite extensively during winter but nearly completely melts away during the summer (Figure 1). That is where the important difference between antarctic and arctic sea ice exists. Arctic sea ice lasts all the year round, there are increases during the winter months and decreases during the summer months but an ice cover does in fact remain in the North which includes quite a bit of ice from previous years (Figure 1). Essentially Arctic sea ice is more important for the earth's energy balance because when it melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged.

Figure 1: Coverage of sea ice in both the Arctic (Top) and Antarctica (Bottom) for both summer minimums and winter maximums
Source: National Snow and Ice Data Center

One must also be careful how you interpret trends in Antarctic sea ice. Currently this ice is increasing and has been for years but is this the smoking gun against climate change? Not quite. Antarctic sea ice is gaining because of many different reasons but the most accepted recent explanations are listed below:

i) Ozone levels over Antarctica have dropped causing stratospheric cooling and increasing winds which lead to more areas of open water that can be frozen (Gillet 2003, Thompson 2002, Turner 2009).

and

ii) The Southern Ocean is freshening because of increased rain, glacial run-off and snowfall. This changes the composition of the different layers in the ocean there causing less mixing between warm and cold layers and thus less melted sea ice (Zhang 2007).

All the sea ice talk aside, it is quite clear that really when it comes to Antarctic ice, sea ice is not the most important thing to measure. In Antarctica, the most important ice mass is the land ice sitting on the West Antarctic Ice Sheet and the East Antarctic Ice Sheet.

Therefore, how is Antarctic Land-ice doing?

Figure 2: Estimates of Total Antarctic Land Ice Changes and approximate sea level contributions using many different measurement techniques. Adapted from The Copenhagen Diagnosis. (CH= Chen et al. 2006, WH= Wingham et al. 2006, R= Rignot et al. 2008b, CZ= Cazenave et al. 2009 and V=Velicogna 2009)

Estimates of recent changes in Antarctic land ice (Figure 2) range from losing 100 Gt/year to over 300 Gt/year. Because 360 Gt/year represents an annual sea level rise of 1 mm/year, recent estimates indicate a contribution of between 0.27 mm/year and 0.83 mm/year coming from Antarctica. There is of course uncertainty in the estimations methods but multiple different types of measurement techniques (explained here) all show the same thing, Antarctica is losing land ice as a whole, and these losses are accelerating quickly.

NOTE: This post is the Basic Version (written by Robert Way) of the skeptic argument "Antarctica is gaining ice". This post means we now have basic rebuttals for all of the top ten skeptic arguments. More impressively, the prolific Skeptical Science authors have written basic rebuttals to 65 skeptic arguments in total. Go team!

Lastly, just a reminder that Robert Way has also written a comprehensive post on the measurement of land ice loss from Antarctica which puts the recent study by Wu et al into perspective (anyone wishing to cite the Wu study is recommended to read Robert's post first).

0 0

Bookmark and Share Printable Version  |  Link to this page

Comments

1  2  3  Next

Comments 1 to 50 out of 108:

  1. The problem with Grace is evident in the earlier literature. The lack of GPS stations affect the corrections.
    On a percentage basis, the loss of land ice in Antarctica is very neglible. Because the percentage is so small, and the Grace data is subject to correction, it is virtually impossible to discern with any certainty what the land ice on Antarctica is doing.
    0 0
  2. I think it might help you to check out the following link

    http://www.skepticalscience.com/Are-ice-sheet-losses-overestimated.html

    I don't think that you are giving an honest assessment of the literature when you say that "the loss of land ice in Antarctic is very negligible" or that "it is virtually impossible to discern with any certainty what land ice is doing".

    Perhaps the following posts might be helpful.

    http://www.skepticalscience.com/Part-2-How-do-we-measure-Antarctic-ice-changes.html

    http://www.skepticalscience.com/Part-Three-Response-to-Goddard.html


    In summary there are a multitude of measurement techniques that have been employed and they all show the same consistent pattern of Antarctic ice losses. Furthermore, we do not need to correct for GIA as much with other datasets and radar interferometry does not find it at all and yet we see the same results. When you know the amount of snowfall stayed the same from last year to this year and yet you see an increase in ice velocity you know that the basin is not in balance.

    Finally, How does percentage relate to all this? It may be a small percentage of all of Antarctic ice but it still has implications for sea level rise. Lets consider that if Antarctic loses 1% of its total ice volume, it is a 0.7m sea level rise which is a lot for just from Antarctica alone.
    0 0
  3. Why is it that "skeptics" must always immediately comment on any new post here with a comment that makes it obvious that they have either not read the post and the linked sources or have not understood them?

    Camburn, please read Robert's linked references in his response to you above.

    As it stands, most of your comment is simply wrong.

    The Yooper
    0 0
  4. Yooper:
    I read his post.
    I will stand by my post.

    http://www.agu.org/pubs/crossref/2010/2010EO010001.shtml
    0 0
  5. Yooper:
    Unless you want to tell me that NCAR is not a reliable source of information.
    0 0
  6. #1: "The lack of GPS stations affect the corrections."

    Really? See Geodesy in Antarctica
    10 years of Continuous GPS measurements for geodetic tying of Antarctica and India
    Then there is GLONASS; even the Argentinians are in the act:
    0 0
  7. Re: Camburn (4, 5)

    So, please tell me how your linked study materially differs from the information contained in Robert's post?

    The Yooper
    0 0
  8. Yooper:
    The abstract on this paper was quit good. If you don't have access to the whole paper, if you live near a college, you can get access to it.
    The Geo paper is peer reviewed and shows that overall there has not been a trend established as far as land ice loss. One of the main reasons is the sheer mass of the ice field.
    0 0
  9. Camburn,

    Maybe I should have shown you this post:
    http://www.skepticalscience.com/Antarctica-absolute-temperatures-too-cold-ice-loss.htm

    If you read it carefully you would realize that melting on Antarctica is virtually irrelevant because ice losses primarily occur through glacier accelerations. So your paper on Antarctic melt trends is irrelevant to this debate.
    0 0
  10. muon@6:
    10 years is not a very long time.

    I believe the NCAR fellow. And actually, the paper about drift etc confirms the NCAR fellow in Geo.
    0 0
  11. #10: "10 years is not"
    Long enough to deflate your 'lack of GPS' objection. How long has GRACE been up?

    "I believe the NCAR fellow" That's good science, picking the study that fits your preconceived ideas? Hey Yooper, cherry-picking season came early this year!
    0 0
  12. no reason not to "believe" Monaghan. Its just that the paper doesnt say what you think it does. ie land ice loss != melt. See sealevel curve.

    What's worrying about antarctic ice loss is that models didnt predict any, though in fairness most of EAIS is behaving as expected thankfully. Getting seawater under the WAIS is the concern.
    0 0
  13. Robert:
    I understand the dynamics of glaciers quit well. Melt plays an important role in the advancement of the glacier as the melt water lubricates the base.
    And contrary to Mr. Goodard, there are melt pools on Antartica.
    The ice sheet in Antarctica seems to respond more to pressure than surface temperature.
    Western Antarctica has warmed. Yes, it is still very cold but that is not an issue in this dynamic.
    Eastern Antarctica has cooled, with a net over the continent of even temperature with regional variations.
    0 0
  14. Re: Camburn (8)

    Not having access to the full study you reference, if (as Robert points out) that the focus of the study is melt trends, then I'd have to say that using the paper to invalidate the documented losses of Antarctic ice (through observed calving and retreat of grounding lines) is an apples-to-oranges comparison.

    We can visually observe how the Antarctic is losing ice and we can document by how much. Melt as yet is a non-factor.

    The WAIS and the EAIS are both losing mass, in the multi-gigaton range yearly.

    The Yooper
    0 0
  15. Camburn,
    If you understand the "physics" of glaciers quite well then you will know that the mechanism through which antarctic glaciers have accelerated is not the same as those in many areas of greenland where the zwally effect (the melt water lubricating the base) is key. In Antarctic the key important factor is the removal of longitudinal compression forces. Warming ocean waters cause grounding line retreat which removes the compression forces and let the glaciers flow quicker. This is also well-understood "physics".

    If you really read the article's that I posted, you would see the following phrase

    "In terms of a grounding line retreat, an inland shift of the grounding line causes less backpressure through increased calving and basal melting. This process results in increased glacier velocities and subsequent inland thinning as more ice is being pulled from the accumulation zone (Bell 2008)."

    Finally,
    You seem to indicate that East Antarctica has cooled whereas Steig et al. (2009) refute your impression.
    0 0
  16. Steig et al has been put in the trash bin. The mythology of that paper was pure junk.

    Back to ice loss:
    http://www.sciencemag.org/cgi/content/full/311/5768/1754

    The WAIS has credibily lost ice. The EAIS not so credibly. NO trend discernable. The loss on the whole of Antarctica is still neglible as a percentage.
    0 0
  17. Robert:
    Yes, the warmer water that has infiltrated under the WAIS is accelerating the loss. Melt aslo plays a part further inland on that sheet. I checked my archive and foolishly didn't save that paper. The observers were quit astounded with their find.
    0 0
  18. Camburn,
    Steig et al (2009) has not been "put in the trash bin" the methods were fine. Just because Hu and them over at CA found that they forgot to correct for autocorrelation doesn't mean it was trash. They submitted their correction and the correction was published without any noticeable difference.

    "Back to ice loss"
    Yeah you are going way back. All the way to 2006. How about we stick with more recent studies shall we?

    http://www.nature.com/ngeo/journal/v2/n12/full/ngeo694.html
    http://www.nature.com/ngeo/journal/v1/n2/abs/ngeo102.html
    http://www.nature.com/ngeo/journal/v2/n12/full/ngeo694.html

    No trend discernible? What are you saying? You do realize that paper you cited was about MELT not ICE LOSS. The two ARE NOT the same. That is the whole reason I had to do the rebuttal to Goddard in the first place.

    Antarctica as a whole is not neglible. If you see the post I mentioned earlier (response to goddard) you would see that almost ALL estimates show a significant total ice loss from land ice.

    Finally, Melt plays 10% of the role, calving plays 90% of the role. Sorry but melting just isn't terribly important in Antarctic Ice Mass trends. End of story.
    0 0
  19. Robert:
    I am not talking about "melting glacier sheets". I am talking about melt ponds, just as the auther of the paper I cited did.

    Melt water DOES play a role in the WAIS.

    http://www.ingentaconnect.com/content/igsoc/jog/2003/00000049/00000164/art00013
    0 0
  20. Ok....I am done. Read this paper. Thank you.

    http://www.ingentaconnect.com/content/igsoc/jog/2003/00000049/00000164/art00013
    0 0
  21. Sorry. I meant this paper.

    http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6215004
    0 0
  22. You conflate subglacial meltwater with surface meltwater that percolates down. The two are not required to exist co-dependently you realize? Subglacial "meltwater" in Antarctica is generally caused by the warmth underneath thick ice sheets providing insulation enough that free-flowing water can exist. This is NOT the same thing as melt ponds on the surface percolating down and creating the "Zwally-effect". See no trend in melting on the surface of Antarctica tells us nothing about what is going on for ice losses in Antarctica of which 90% originates through calving. Mostly driven by the mechanisms I described from the paper by Bell 2008.

    If you want we can get more in depth about this? Meltwater percolation likely plays very little part in the accelerations of ice streams in the WAIS because these ice streams are already fastmoving ice streams which have reached their basal saturation rate as has been seen on Jacobshavn by Pelto.

    http://www.realclimate.org/index.php/archives/2008/10/what-links-the-retreat...

    Thus if you introduce more meltwater through the so called zwally effect (NOT THAT YOU COULD IN WAIS) then you wouldn't see the accelerations that have been found to be occurring due to ocean warming.

    For anyone of who might be interested here is a presentation I did on Antarctic ice changes (in 2009) Camburn, it might be of use to read it.
    http://www.skepticalscience.com/docs/Antarctic_Presentation.pdf
    0 0
    Moderator Response: Please don't use all caps. Use italics, or, if you must, bold.
  23. Robert:
    I don't have a nature sub anymore, but from the abstract of the papers you posted, it confirms what I stated.
    WAIS is loosing ice. EAIS is stable.
    Look at the error bars in the abstracts please.
    Thank you.
    And once again, the loss of ice in Antarctica on a whole is neglibable as a percentage of mass.
    0 0
  24. Actually Wu et al. 2010 (the skeptics favorite) show that ice losses are occurring in the EAIS outside of the error bars. I believe Chen et al. 2009 show it outside the error bars also (slightly) -57 plusminus 52Gtyr. I think you have to remember that Error bars go both ways but yeah EAIS is probably stable for the most part. WAIS is VERY unstable as my presentation will even attest to.

    It is not "negligible" because it represents a small portion of its mass. That's a ridiculous statement to make. If Antarctica loses 1% of its mass over the next 50 to 100 years we're in deep trouble (0.5m SLR) but according to you that is "negligible".
    0 0
  25. Er, don't mean to butt in to a robust discussion, but I also looked at the abstracts for the articles that Robert referenced.

    Camburn, you're right, the error margins are huge. But that error cuts both ways. It could be that EAIS is losing 100Gtpa or more. That's a phenomenal amount of mass loss for an area that, until recently, was thought to be *gaining* mass...

    So, we have best estimates (with a lot of uncertainty) showing WAIS losing about ~130 Gtpa, and the EAIS either stable, or losing ~50Gtpa. That's a whole lot of ice. Either way, Antarctica as a whole is losing ice. Sure, it may be a small percentage of the total ice sheet down there, but when you start talking about tens (or hundreds) of cubic kilometres of ice falling off that continent into the Southern Ocean, you don't think that's cause for concern?
    0 0
  26. In my opinion it's not the March and September ice distributions that are important. For energy balance, it's the amount and distribution of ice at the height of summer that we should focus on, rather than the extent or area at the end of the melt season. So what's happening to Antarctic ice in December?
    Also, Tamino recently had a post about sea ice in which he mentioned Antarctic sea ice, although recently increasing, was previously much less. I haven't seen this mentioned on any of the other blogs I follow. I'm looking forward to his follow up on that.
    Congrats on the progress you've made on the basic versions. Cheers.
    0 0
  27. Camburn's statement about the trashing of Steig (2009) is incorrect. It was attacked, unsuccessfully, by Steve McIntyre.

    There's a decent review, including a post by Steig, from the period - here:-

    http://www.masterresource.org/2009/01/the-buzz-about-antarctica/
    0 0
  28. It seems that Robert & Camburn are a bit like ships passing in the night.

    The papers I've read give the EAIS barely detectable losses (or even not detectable losses), whilst WAIS loss is detected with good confidence. Which is what Camburn is saying.

    Overall, Antarctica is losing mass and most of this is from the WAIS. Most papers agree that overall there is net ice loss (e.g. Camburn's Allison et al) and it is a small portion of total loss. Which is what Robert is saying and Camburn isn't disagreeing with.

    The worry is that many models don't capture ice sheet breakup and in some increased precipitation outweighs it. Now it looks like ice sheet breakup is faster than models expect and as Robert pointed out, a 1% loss of Antarctic land ice would approximately double the IPCC sea level rise projections whilst Greenland is also falling apart more quickly than models expected. This supports the results of Vermeer & Rahmstorf etc and suggests the upper bound of sea level rise is probably 3-4 times larger than IPCC, 2007.

    Of course, maybe it's natural noise and that's what we should pray for.
    0 0
  29. I just have a question about the original post. I'd just like to get a clearer understanding of the following from the beginning of Robert's article which I may have completely misunderstood.

    It says:
    "Essentially Arctic sea ice is more important for the earth's energy balance because when it melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged."

    Is the summer in Antartica in this case understood as December or June? Are you saying that most sea ice builds up during the warm months? If so, is there a simple explanation for this counter-intuitive phenomenon?
    Thanks for all the posts.
    0 0
  30. Paul Barry, it means southern hemisphere summer... so December. Nothing counter-intuitive. Ice in both hemispheres grows during the cold months and shrinks during the warm months.
    0 0
  31. So, the increase of Antarctic sea ice is also antropogenic? This looks like immunization of the AGW-theory. It does not matter which new evidence is found, it always supports the theory. When a theory reaches this stage, there is no need for further research. The billions of dollars can better be used to build dikes in Pakistan.
    0 0
  32. #31: "So, the increase of Antarctic sea ice "

    If by increase, you mean the vaguely positive trend in the red graph shown in the figure below (NSIDC):



    How do you spell 'not statistically significant'?
    0 0
  33. Thanks, CBDunkerson. That's one possible source of confusion out of the way. I have no desire to attack this article (the evidence for AGW is overwhelming, I believe) - but it is, unlike most articles I read in Skeptical Science, far from easy to follow.

    Again, this sentence is a bit of a non sequitur:"Essentially Arctic sea ice is more important for the earth's energy balance because when it melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged."

    Is more sunlight not absorbed by the oceans when Antarctic sea-ice melts? Why not - the fact that it "normally melts each summer", as the above states, tells me nothing about why it is different to the Arctic - the arctic does the same, does it not? Why does this leave energy balance unchanged? Can somebody explain to me what I need to grasp to make this logical leap (or suggest a clearer way of expressing the above)
    Thanks in advance. Great site!
    0 0
  34. Paul Barry.... I'm not an expert on Antarctic ice by any means but I believe the idea here is that summer sea ice loss in Antarctica is going to have very little net albedo change. The ice melts back pretty much to the continent as it is in the summer months. Whereas in the Arctic when sea ice melts we are left with open ocean, in the Antarctic we still have the Antarctic continent covered with ice and almost no net change in albedo.
    0 0
  35. Paul @33,

    I could be wrong. So major caveat emptor ;)

    The slight increasing trend in Antarctic ice during the austral winter is not as important or critical as the loss of summer ice up north (during the boreal summer). The reason being that changes in albedo are not really an issue, if at all, during the austral winter. In contrast, the rapid loss of ice during the boreal summer does have a large positive feedback because of the very important impacts of changes in albedo between snow/ice and ocean water.

    On another note. In recent testimony to congress, Dr. Alley said that the slow increase in Antarctic sea ice will change soon. Now Dr. Alley is a paleo scientists, so I do not know what he means by "soon"-- decades, centuries? My guess is decades.
    0 0
  36. Oh Jeez Rob, you posted that while I was typing my response. OK, we seem to be on the same page though. Good point about the impact on albedo of the Antarctic ice sheet.
    0 0
  37. #32 Muoncounter
    I have calculated trends for both extent and area of NH and SH ice. I find that the increase in SH ice extent as well as area is statistically significant at the 95% level.
    Here is a plot with trend estimates and 95% confidence limits:

    Please note that the units are given as K/year where K=millions square km's.

    Tamino finds a similar result:
    "But if one uses data for all months, the increase in Antarctic sea ice extent since 1979 is statistically significant."
    From here

    I remember having read somewhere that this is related to increased precipitation. As temperatures continue to rise this positive trend in ice area and extent will at some point reverse and become negative
    0 0
  38. Guys, the greatest Arctic sea ice trend is observed when comparing September minima across years. In fact, the greatest anomaly is occurring later in September than previously. The most important time with respect to albedo is June. The trend observed (so far) for June is quite a bit less than for September.
    Likewise, wrt albedo, the austral summer solstice is most important, and at that point the ice has not melted back to the continent. If it is slow to melt back and there is more reflective material around Antarctica in December and January, I think it should not be arm-waved away.
    There may be calculations that show the Arctic trend is much more important for planetary albedo than the Antarctic trend, and given the effect of angle of incidence, etc, those quantitative results would help greatly in supporting the intuitive argument.
    0 0
  39. RE: #33 Paul , I might try and explain too! (repetition, but with different words).


    The most important effect on heat balance is ice cover in the summer. Since 'change in heat balance' = 'change in albedo' x 'heat coming in' and 'heat coming in' is biggest in summer.

    In summer, Antarctic sea ice retreats to the edges of the continent, which is generally covered by ice too thick to melt away. So changes in summer will be a tiny change in total area.

    Meanwhile, there is still sea ice left in the Arctic in summer.

    NSIDC minimum extent for Antarctica has been pretty constantly around 3 mil sq km since satellite records began. So there has been little change in heat balance.

    Meanwhile, Arctic sea ice extent has decreased by about 2.5 million sq km and there is still another ~5 mil sq km left to go in summer. To offset the decline in Arctic ice we've already seen, you'd need a 75% or so increase in Antarctic summer sea ice.
    0 0
  40. Something else of possible interest.
    0 0
  41. Paul, yet another rewording/explanation;

    More sunlight strikes the Earth during summer than winter... especially at the poles. Ergo, a change in summer ice area is going to have a greater impact on the amount of sunlight reflected by the ice (and thus not warming the surface) than an equal change during the winter.

    Taking that into account we can then see that since the sea ice melts away almost entirely each summer in Antarctica there has not been any significant change in the amount of sunlight absorbed. Nor does the slight increase of Antarctic sea ice in winter have a major impact given the decreased sunlight during that time of year.

    So, you are correct that the amount of ice always impacts the amount of sunlight absorbed vs reflected, but the relevant bit here is that there is little sunlight at the poles in winter and Antarctic summer sea ice hasn't changed much while Arctic summer sea ice has decreased sharply.
    0 0
  42. So, the increase of Antarctic sea ice is also antropogenic? This looks like immunization of the AGW-theory. It does not matter which new evidence is found, it always supports the theory.


    When the evidence roughly fits predictions made by the theory, well, yes, of course it supports the theory. Unless you live in the denialsphere.

    Your problem is that you assume climatologists have been predicting that sea ice in Antarctica would decrease rapidly as has been predicted for the Arctic. You're wrong.
    0 0
  43. The article deals with a complex issue in an over-simplified way. Firstly, there are two quite different ice sheets the EAIS and WAIS.

    The EAIS covers the Antarctic continental land mass and, based on GRACE measurements is loosing ice at a net rate of ~57 giga-tonnes/year. The skeptic argument that this is compensated for by heavy precipitation high-up on the ice sheet is unsupported and contrary to the very low precipitation of East Antarctica.

    The WAIS is separated from EAIS by the Trans-Antarctic Mountains and is largely a marine ice sheet anchored on the seabed and rising high above the ocean surface. It is not floating. Other parts of WAIS cover the land of a scattered archipelago, the “peninsula” being the largest of the islands.

    The WAIS does not cover a land mass extending west of the Trans-Antarctic Mountains to the Peninsula as shown at Fig 1 of the article. That part of the WAIS covering land is subject to rising air and sea temperatures which are responsible for retreat of hundreds of glaciers and causing floating ice shelfs, such as Larsen B, to break away from coastal land.

    This enables glaciers previously blocked by ice shelfs to discharge ice into the ocean at a much faster rate. Relatively warm ocean water is also responsible for the retreat and speeding up of glacier flows, eg. The Pine Island and Thwaits glaciers discharging into the Amundsen Sea.

    The part of the WAIS which is a marine ice sheet is particularly vulnerable to waters of the Sothern Ocean which is being warmed by currents flowing from equatorial parts. Parts of this ice sheet, notably the massive Ross and Rönne ice shelves show signs of melting where they are in contact with the Southern Ocean.

    The Ross and Rönne ice shelves are not floating. They rest on the sea bed and are highly susceptible to seasonal surface melting and to relatively warm water melting their underside.

    Should the latter occur and should large sections of them break their connection to the seabed and the rest of the ice shelf, they would suddenly become floating ice, displacing water equivalent to their mass. This would cause a relatively sudden and significant rise in sea level.

    GRACE data shows that the WAIS is currently loosing over 132 giga-tonnes ±26 giga-tonnes of ice per annum and that the rate of loss is accelerating.

    Is this analysis wrong? Is it alarmist or merely raising issues that should be of concern and might have got a mention in the paper under discussion?
    0 0
  44. Agnostic @43,

    I agree with most of what you said, except this part,

    "The Ross and Rönne ice shelves are not floating."

    I could be wrong, but this papershows that most of the Ross shelf is floating.
    0 0
  45. Thanks for the responses to my question above (Albatross must wonder how someone could be confused by an article that already "deals with an issue in an over-simplified way"!!!).

    If this article is ever revisited, I think that there are 3 issues than ought to be teased out more clearly in its exposition: (a)the business of quantifying changes to land and sea-ice at the poles - i.e. what's happening; (b) explaining the causes of these changes (especially the differences between changes in Antarctica and the Arctic) in terms of warming/ozone etc.; (c) quantifying impacts (or feedbacks) of these changes especially in terms of albedo-loss to the planet.

    Another question comes to mind now:

    Is there a graph anywhere showing theoretical albedo changes for the Arctic, the Antarctic, the Earth generally over the past few decades (to match ice-extent in the graphs of Muoncounter and SRJ above)? Such a graph would be a very useful illustration of issue (c) which, to me, makes that other issue (about whether SH ice-extent increase is statistically significant or not), appear rather minor.
    0 0
  46. An ice shelf is by definition largely afloat. Large ice shelves are stabilized by pinning points where the ice shelf is supported, see Fleming Glacier. These can be along the margins of the ice shelf such as against an island or underneath the ice leading to an ice rise. As an ice shelf thins through basal melting or increased flow, it is less buttressed by either, which can lead to enhanced rifting, calving and flow rates.
    Each glacier is different but clearly ice melt as Robert points out is not the main issue even on the Antarctic Peninsula. Take a look at the footage from NASA's operation ice bridge . Take a look at Pine Island Glacier
    0 0
  47. I am not nearly as sophisticated in my knowledge of glaciers and climate as most of the other posters but have a decent basic science background. The question I need answered is, " If Antarctic sea ice was decreasing, would that be evidence against global warming? " Antarctic sea ice is increasing and we can find ways to explain it away, but was that what the models predicted prospectively?
    0 0
  48. Re: reluctant skeptic (47)
    "The question I need answered is, 'If Antarctic sea ice was decreasing, would that be evidence against global warming?' "
    What if it was? Do you really think it would matter?

    There has been amassed nearly two centuries of studies and evidence, along with the same physics that underlie refrigerators, microwave ovens, the internet, televisions, automobiles, heat pumps, convection ovens, pharmaceutical products, textiles, etc, that all makes climate science the robust discipline it is.

    This is not to say that uncertainty does not exist; existing uncertainties lie more in the area of rates of change and to a lesser extent, cloud effects (but that window is closing fast).

    So let's say Antarctic sea ice is decreasing and that it is evidence against global warming. It would be the equivalent of finding 2 identical snowflakes in a single snowstorm: an oddity, but certainly not something sufficient to say that there was no snow...

    To maintain that it actually could undermine AGW, by itself, would be the equivalent of saying that all of the technology I cited earlier runs on pixie dust, not on fundamental underlying physical principles.

    Would you believe that?

    The Yooper
    0 0
  49. Reluctant skeptic @47,

    "...Antarctic sea ice is increasing and we can find ways to explain it away, but was that what the models predicted prospectively?"

    I'm not sure I understand the question, maybe it was rhetorical. Model runs by Manabe et al. (1992) did in fact predict that there would be very little change in the Antarctic sea ice, at least initially.

    I do not know why the other question that Daniel addressed even warrants answering. The robustness of the Antarctic sea ice in the face of warming is not indefinite. How the Antarctic responds to further warming also depends, in part on the recovery of Antarctic ozone. So lots of uncertainty there-- I do not believe that scientists are finding ways to "explain it away". Turner and Overland (2009) provide an excellent overview of the complexities of Antarctic sea ice. This SCAR report by Turner et al. (2009) is also highly recommended.

    But we do know this, in those areas where the sea ice or ice shelves buttressing the glaciers has been lost, the glaciers have accelerated (e.g., Larsen B ice shelf). We also know that as sea levels rise grounding lines will move farther inland, making ice sheets and glaciers more unstable(e.g., recent events under the Pine Island glacier), especially as the oceans continue to warm.

    The sea ice surrounding Antarctica is important for regulating the rate of loss of ice from the WAIS and EAIS, but it is not the only player. For example, but warming oceans are also playing a role on destabilizing glaciers and ice sheets. My suggestion is to focus on these factors rather than entertaining thoughts about the onset in coming decades of decline in Antarctic sea ice might mean in terms of the theory of AGW.

    I also happened to notice that the Larsen C has been exposed to open water (i.e., wave action etc.) for several weeks now...
    0 0
  50. Agnostic @ 43 - The article deals with a complex issue in an over-simplified way

    There is only so much information one can put in a "basic" rebuttal before it ceases being a basic rebuttal. Considering the target audience are newcomers to climate science, a pretty good introduction IMO.
    0 0

1  2  3  Next

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.



The Consensus Project Website

TEXTBOOK

THE ESCALATOR

(free to republish)

THE DEBUNKING HANDBOOK

BOOK NOW AVAILABLE

The Scientific Guide to
Global Warming Skepticism

Smartphone Apps

iPhone
Android
Nokia

© Copyright 2014 John Cook
Home | Links | Translations | About Us | Contact Us