Wind-driven trends in Antarctic sea-ice drift

holland-sea-ice There’s a nice paper out by Holland and Kwok, attributing much of the somewhat-hard-to-understand change in Antarctic sea ice to changes in wind forcing. The growth in Antarctic sea ice, although much smaller than the decrease in the Arctic, is still a bit embarassing; it would be much tidier if it were decreasing. The abstract says:

The sea-ice cover around Antarctica has experienced a slight expansion in area over the past decades [1,2]. This small overall increase is the sum of much larger opposing trends in different sectors that have been proposed to result from changes in atmospheric temperature or wind stress [3–5], precipitation [6,7], ocean temperature [8], and atmosphere or ocean feedbacks [9,10]. However, climate models have failed to reproduce the overall increase in sea ice [11]. Here we present a data set of satellitetracked sea ice motion for the period of 1992–2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds. We quantify dynamic and thermodynamic processes in the internal ice pack and show that wind driven changes in ice advection are the dominant driver of ice concentration trends around much of West Antarctica, whereas wind driven thermodynamic changes dominate elsewhere. The ice-drift trends also imply large changes in the surface stress that drives the Antarctic ocean gyres, and in the fluxes of heat and salt responsible for the production of Antarctic bottom and intermediate waters.

The pic I’ve nicked is Autumn (April–June) 1992–2010 ice motion and concentration trends and their relation to wind forcing. Wind-driven changes in ice motion are clearly linked to changes in ice concentration. Ice-motion trend vectors overlaid on ice-concentration trends.

So the theory is that sea ice on the edge of the pack (well, in those areas where the wind forcing is southerly) is there because its been advected north (it can’t form there thermodynamically, and is indeed melting there). And so if you increase the southerlies, you get more ice; because further south its cold enough to produce as much ice as you like, as long as you can export it. Of course all of this (assuming for the moment they are correct) just pushes the question one step further back, because they leave the changes in wind forcing unexplained. It may also help with the why-oh-why don’t GCMs produce the observed Antarctic response: because it isn’t the rather simpler to get right thermodynamics. Of course that’s probably part of why they don’t do so well in the northern hemisphere, too.

I used to share an office with Paul, BTW.

There’s also a Grauniad article. Lets take a look, and see how they do, shall we?

The mystery of the expansion of sea ice around Antarctica, at the same time as global warming is melting swaths of Arctic sea ice, has been solved using data from US military satellites.

A poor start. As I said, it hasn’t been solved, just pushed back one step to winds. And the “US military satellites” is a bit woo: they are just the satellite-derived sea-ice motion vectors, from DMSP I think.

Paul Holland at the British Antarctic Survey. “Our study of direct satellite observations shows the complexity of climate change. The Arctic is losing sea ice five times faster than the Antarctic is gaining it, so, on average, the Earth is losing sea ice very quickly. There is no inconsistency between our results and global warming.”

Accurate, and probably a good idea before the fools get overexcited. “In some areas, such as the Bellingshausen Sea, the sea ice is being lost as fast as in the Arctic,” is a useful reminder that the Antarctic trends are very regional (again, consistent with dynamics rather than thermodynamics). Overall, by newspaper-reporting-climate standards pretty good.

How about comparing the Graun to the Torygraph? Headline: Antarctic sea ice is increasing, byline The amount of ice in the Arctic may be at a record low but Antarctic sea ice is increasing, according to a new study. First two sentences rctic summer sea ice reached a minimum 3.41 million sq km this year, around 50 per cent lower than the 1979-200 average. However a study by the British Antarctic Survey (BAS) and NASA found sea ice in the Anatarctic has been increasing over the same period. Yes, they really are doing their best to mislead you. The next few sentences actually tell you something about the paper. Um, and that’s about it. A fail, I’d say.

[Update: I should have pointed out that there is a pile of existing literature about how ozone depletion has affected the surface circulation. Thanks to Eli for reminding me; I think stuff like is relevant; see comments -W]


* Nature Geoscience (2012) doi:10.1038/ngeo1627
* BAS press release

24 thoughts on “Wind-driven trends in Antarctic sea-ice drift”

  1. As Ell was saying

    Lagomorphs, and even pica everywhere ask, what does this have to do with weather (yes, yes, Eli knows) it rains in Brisbane, let alone Spain. To answer this question come Kang, Polvani, Fyfe and Sigmond in Science 332 (2011) 951 and to be honest a bunch of other people before them referenced in the “Impact of Polar Ozone Depletion on Subtropical Precipitation. They point out that there has been a strong movement of the Southern Hemisphere westerly jet towards the pole driven by the lifting of the tropopause associated with the Antarctic ozone depletion.

    Kang and friends argue, supported by modeling that this effect is seen even as far as the tropics as the Hadley cells shift poleward, an observed trend.

    Observations, cooling of the stratosphere due to the formation of the ozone hole, increased precipitation between 20 and 40 S latitude, shifting of the Southern Hemisphere westerly jet and the Hadley cell, poleward, and, oh yes, flooding in Australia can all be drawn together qualitatively as shown in the picture to the left taken from Feldstein’s appreciation in the same volume of Science, and quantitatively with GCMs.

    [Right idea but I think you have, well lets say incomplete, refs. also springs to mind (even earlier…/2001GL013376.shtml). ah, but was the one I had in mind -W]


  2. [Incivility redacted -W] Connolley said: “The growth in Antarctic sea ice, although much smaller than the decrease in the Arctic, is still a bit embarassing; it would be much tidier if it were decreasing”

    Please [Incivility redacted -W] Connolley, in all civility,

    [Given that I’ve had to redact your incivility twice already, that’s just a bit ironic, don’t you think? -W]

    can you politely explain to me, why the growth in Antarctic sea ice is “a bit embarassing” (your own words). I thought you would like the increase as it shows that in the anarctic there is no anthropogenic global warming, but a climate cooling (anthropogenic or not, who knows).

    does the fact that the southern hemisphere cools whereas the northern hemisphere maybe does not bother you somehow?

    [Your facts are wrong. The SH isn’t cooling; like the NH, its warming -W]

    please explain this to the interested audience. thank you


  3. Is the ambient polar temperature low enough to offset catabaric heating of the downslope winds off the ice dome that blow out to sea?

    The gross difference in topography seems lost on the Moranoids yawping about Antarctic ice growth .

    [The katabatic winds the flow off the continent are intensely cold. Ice formation along the edge of the continent is usally strong because of this, and because the winds push out the ice exposing the ocean -W]


  4. Dearest Mister Connolley

    you said: “The katabatic winds the flow off the continent are intensely cold. Ice formation along the edge of the continent is usally strong because of this, and because the winds push out the ice exposing the ocean”

    according to my information sources from meteorology textbooks this is totally wrong. but it is not astonishing since you are no meteorologist.

    [I think you’re just trolling. Continue in this vein, and I’ll just turn you off. Contributing here is a privilege, not a right; and keeping the signal-to-noise ratio useful here is a duty of mine.


    1. You need to cure your incivility problem; I’m not going to do it for you. You need to address me correctly, which is either “WMC” (to keep it simple) or “Dr Connolley” otherwise. False-familiarity “Dearest” is not tolerable either. Lies about my qualifications are not tolerable either.
    2. You need to stop trolling, or giving the appearance of trolling. So all this “according to my sources” but giving no sources.
    3. Most of your posts are totally content free. Don’t do it.

    If you can’t cope with those rules, then find somewhere else to talk -W]


  5. @kai

    Since you offer no alternative theory, we can only assume that those meteorology textbooks are a fiction.

    “Latent heat polynyas are maintained by persistent katabatic winds that drain off the continent. Newly formed ice is advected away by the wind, leaving the surface ice-free and open to more ice formation. In this manner latent heat polynyas can be major sources of new ice production. Coastal polynyas are primarily of this type. ”

    “Latent heat is released as water freezes and also as water evaporates into the air above the open water. Some sensible-heat exchange also occurs within latent-heat polynyas because the water in the polynya is generally warmer than the air above it even though the water is at freezing temperature.”

    There is even a picture in the second link.


  6. Dearest Weasel,

    And, as you know, Eli says that fondly, but to the subject at hand.

    Kai, a thing of no worth and deserving of less respect, asks

    “can you politely explain to me, why the growth in Antarctic sea ice is “a bit embarassing”

    Because dealing with people like Kai don’t read textbooks, when the do don’t understand them, and when they do understand them only for the purpose of twisting their intent makes it difficult to discuss complex subjects.

    Oh yes.


  7. Dear Stoat and others
    I’ve been trying to knock some sense into the readers at WUWT on this….they think it’s another ‘nail in the coffin’ of AGW of course. Makes me wonder how many nails this particular coffin can hold! Mr Richard Courtney is there trying to pretend he understands the issue.

    [Nowt I can do for you, guv, since I’m banned (all together now: if you’re not banned from WUWT, you’re doing something wrong…) -W]


  8. And so kai commits blogi-kiri, unregrettably.

    [He’s not banned, yet. But anything that isn’t useful from him, from now on, gets trashed -W]


  9. Unfortunately for both sides, still equivocal observations. If both polar areas were losing ice at somewhat the same level, the temperature driver would be obvious. But the south pole at summer is at perigee and receives 20.7 W/m2 MORE than the Arctic at summer, when the Earth is at apogee. So somehow the Antarctic shrugs off the greater sunshine energy while the Arctic falls apart.

    The Global Warming has such a strong regional character that the simplistic CO2 energy driver doesn’t make sense by itself. Are we mainly seeing an energy REDISTRIBUTION, not an energy addition?

    The energy content of the oceans and mid-troposphere tropical areas aren’t showing the energy distribution we’d expect with CO2-based warming, either. We need a negative feedback mechanism of substance or to rethink some of the global warming as energy redistribution.

    [The Arctic is a land-locked sea; Antarctica is a continent surrounded by sea. The southern ocean is a large heat sink, and warms more slowly than the Arctic. All of this the models get right, and so we understand, as I’m sure you know already. Antarctic sea ice, as this paper shows, is harder to understand, but we’re getting there. All of this understanding works; throwing it away for “something else” really doesn’t make sense -W]


  10. Doug Proctor — There are many regional differences. Ozone hole is one of those for the Antarctic.

    Not to mention it is all land while the arctic is mostly sea.


  11. I’m no scientist and probably way out of my depth here, but I’m going to be brave enough to ask questions anyway.

    Is the increase in sea ice around the Antarctic a net increase in total volume of ice for the continent and the area around it, or simply an increase of surface area of ice? I guess what I’m getting at is this: Is the ice that “blew off” the continent missing from the continent and simply relocated to the sea surface, or is it in addition to the ice that was already there?

    [The volume of ice in the sea ice is trivial, compared to the land ice on the continent itself. The area of winter ice is about the same as the area of the continent; but the continent is about 3km thick on average, whereas the ice is about 1m, so the sea ice is about 0.03% of the total. The sea ice isn’t ice that has “blown off” the continent; its ice that has formed on the sea surface. The wikipedia sea ice page should help -W]


  12. Antarctic sea ice increase due to dynamics.
    Arctic sea ice decrease due to dynamics.

    [Do you have a source for that last one or did you just make it up? -W]

    Atmosphere behaves dynamically – who’d ‘ve thunk it?


  13. I am just curious about the role of sea ice motion in dictating the new ice formation. Suppose we have a coastal region in Antarctica during winter, where the sea ice is being exported towards north. Now, this should create leads/open ocean in the coastal region, thus enhancing the ice formation process. So, is it safe to assume that a sea ice divergence should be associated with an increase in sea ice concentration? or the export would cause a reduction in the concentration? which effect will be more dominating? Thanks!!


  14. dev @23 — During winter any openings quickly freeze over (sufficiently far south); concentration remains close to 100%. Ice blown far enough north melts and in any case over summer almost all of the Antarctic sea ice melts.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s