Antarctic Sea Ice Gain

We’ve looked at Arctic sea ice data, noting not only its overall decrease but changes in the annual cycle as well. As one reader suggested, let’s take a similar look at sea ice in the southern hemisphere.

Unfortunately I don’t know where to get data for Antarctic sea ice volume. But extent and area data are available, and I’ll use the monthly averages from NSIDC. This enables us to compute two derived quantities, the “spread” (extent divided by area) and “split” (extent minus area).

First of all, here are the time series for both (extent in black, area in red):


There’s no visually obvious change, but we shouldn’t expect to see it in the raw data. We can, however, transform to anomaly values (values minus the long-term average for the same month) to remove the influence of the seasonal cycle:



Both have shown increase over time which is statistically significant. The smoothed values for extent have increased by about 0.57 million km^2, area by about 0.51 million km^2. The reason for its increase is uncertain, but two possibilities which have been suggested are: 1, increased precipitation (snowfall) due to warming near the tropics; 2, intensification of the “polar vortex” perhaps due to changes in stratospheric ozone concentration.

Despite the fact that the southern ice pack is larger overall than the northern, its increases are much smaller than the decreases noted for the northern hemisphere, 1.96 million km^2 in extent and 1.92 million km^2 of area. This puts the lie to claims (oft repeated) that southern gain even “almost” balances northern loss — the northern extent loss is 3.4 times as great as the southern extent gain while northern area loss is 3.8 times as great as southern area gain. When one is nearly 4 times as big as another, they are certainly not “balanced” and anyone who claims so is either a fool or an outright liar.

Here’s the average annual cycle for extent and area:


Again, extent is in black and area in red, while the vertical bars show the difference between the two (which we’ve called “split”). Both quantities reach their annual minima in February and maxima in September.

If we look at the rate of increase (as estimated by linear regression) for each month separately, we find no real evidence of any seasonal pattern, just the kind of fluctuations which could be random:


Windowed Fourier analysis enables us to look for changes in the size, shape, and timing of the annual cycles. Although all those parameters fluctuate, there’s no sign of any trend in them. The annual cycles of southern hemisphere sea ice extent and area have not shown the dramatic changes which have been observed in the northern hemisphere.

I also looked at “spread” and “split” for the southern ice pack. Here are the raw data series:



Transforming to anomaly values, we see that spread has slightly declined:


However, this seems to be a reflection of the fact that overall ice cover has increased, since the split has shown no trend at all:


In fact, split has shown no real trend for any time of year — the one significant value (June) is actually within random fluctuation, given that we’re computing trends for 12 separate months of the year:


The average annual cycles show how these parameters vary throughout the year (again I’ve plotted the individual monthly values in time order so these are 12 monthly “time series” compressed onto a single plot):



One interesting observation is how skewed the split cycle is, rising steadily from February through November, only to take a nose-dive from December to January.

There’s very little meaningful change, if any, in the annual cycles of southern hemisphere sea ice split. There is some evidence, for instance, of a small decrease in the phase of maximum:


However, when looking for trend in many variables you should expect to find something that crosses the 95% confidence level just by chance. This may or may not be a real trend, it’s possible that the split cycle hasn’t really changed over time other than random fluctuations.

In summary, the southern hemisphere shows significant sea ice gain over the last 34 years, but it is dwarfed by the sea ice loss in the northern hemisphere (which is more than 3 times as great). The annual cycles of extent, area, and split, have shown little if any change. Spread has shown a declining trend, which seems to be due to the fact that split is stable but the overall area is increasing. All in all, other than the increase in extent and area, the southern ice pack has shown surprising stability during the satellite era.

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38 responses to “Antarctic Sea Ice Gain

  1. > Unfortunately I don’t know where to get data for Antarctic sea ice volume

    I’d be surprised if there are any. Thickness measurements are far sparser than the Arctic.

    > intensification of the “polar vertex”

    Vortex :-)

    [Response: Doh!]

    > The reason for its increase is uncertain

    Holland and Kwok say its changes in wind forcing (e.g. but they don’t say what changes the wind forcing :-)

  2. Antarctic sea ice is almost all seasonal—that is, thin, single-year ice—which means that its annual cycle of loss and recovery has very little significance for the study of climate change, when compared to Arctic sea ice variation.

    The fake sceptics of course always like to bring up the fact it’s largely ignored as somehow indicating evidence for a conspiracy.

  3. There are analyses that suggest that southern ice extent was considerably greater in the decades before satellite observation. I don’t know how good the data is though.

    It’s unfortunate there is no volume analysis for southern sea ice. Presumably the gravity satellites (i.e. GRACE) are useless for this, but shouldn’t Cryosat-2 be just as effective in the south as it is in the north?

    • GFW | March 16, 2013 at 8:47 pm | Reply
      There are analyses that suggest that southern ice extent was considerably greater in the decades before satellite observation. I don’t know how good the data is though.

      Try here.

      • I always wonder why the data back to Nimbus5 isn’t tacked on to the standard post 11/78 NSIDC Antarctic data. There’s even Nimbus1 data from 1964 showing the Antarctic maximum (& Arctic minimum) that year although there too the 1973-79 data fails to make a showing.
        It’s a shame as it would put a lid on all the noise about “new maximum Antarctic Sea Ice records.”

        BTW. Did anybody notice that in 2012 Arctic minimum SIA = Antarctic minimum SIA. Probably the first time that happened for a while.

    • We published some ice core proxy evidence suggesting a 20% decrease in sea ice off the East Antarctic coast over the mid- to late- 20th century (Curran et al., 2003, This is corroborated by whaling records (de la Mare ref in the Curran paper).

  4. Congratulations. You have verified the findings of SCAR. See Bulletin 184 (2009)
    “Increased growth in Antarctic sea ice during the past three decades is a
    result of the strengthening of surface winds around Antarctica caused by
    development of the ozone hole; these winds have limited the impact of
    global warming on Antarctic climate. When ozone levels recover, towards
    2070, sea ice is likely to retreat considerably.”
    Any comments on the Whitehouse Report?

    [Response: I consider him to be not just incorrect, but generally unreliable.]

  5. David B. Benson

    The circumpolar vortex, aided by the coriolis effect, tends to move the sea ice northwards, increasing (what I think is) extent. The circumpolar vortex has been changing due to some mysterious effect of the so-called ozone hole.

  6. Henry Herbert

    Interesting, educational posts.
    I am reaaly just asking how much your ‘reasonable rates’ are.

    [Response: The rate depends on the client and the project. Standard rate for profit-making corporations is $150/hr. It's considerably less for non-profit endeavors, even more so for those I regard as especially interesting or worthwhile. In such cases I often negotiate a price for the project rather than an hourly rate.]

    I live in New Zealand, our data is gathered and stored by NIWA, and it is possible to look at a variety of temperature / rainfall data. But I don’t really know how to begin.
    I live in Palmerston North at the moment. What I am asking for is for an analysis of the temperature / rain data relating to PN. Probably hoping for a slight increase in he severity of rain recently, with no great trend in amount likely, maybe more / longer dry spells, probably higher minimum temps in winter esp (less frosts), with a trend to max temps minimally up.

    NZ has never featured on your blog of course – we are a tiny country (same area as UK) in the middle of the Pacific. Probably among the most favoured nations on earth, climate change wise, as we are expected to be able to grow grass longer, with our eastern / northern areas drier (2 – 4 x frequency I think). So – farming might have to move areas, but as a whole the country will probably produce more… We are in the middle / end of a drought – the whole of the Norht Island is a drought zone now (declared for finacial assistance reasons by the government). It might provide you with an interesting topic, although the Arctic, Europe and indeed your own country no doubt provide lots of intrest for me.

    I was hoping that if I saw how you got the data, and measured some simple things about it, that I could replicate that myself for other sites in the NIWA database. Any site would do of course (if one is apparently easier than another from your point of view). I think that one merely has to register on the NIWA site to get access to the data (free for me I think). I don’t know how that is applied to someone coming from a US address.

    Once again – I do applaud your articles (except that you do appear modestly rude at times).

    [Response: Only "modestly"?]

    If you were thinking of other topics that might not have occurred to you – then the statistical approach of people like ?Lucia (The Blackboard I think) is of interest. Not the outcomes per se, but why they are so wrong (at times you dismiss the site, and fo course for mathematically competent people, there may be no difficulty in seeing her errors)

    [Response: Lucia's "statistical approach" is to do whatever she can to "falsify" her fake portrayal of what the IPCC projects. We are not impressed.]

    A separate point is medical statistics. I don’t think that I have ever seen auto-correlation mentioned in such articles (I am a hospital doctor). SHould they be? Have you ever looked at some medical data – perhaps relevant for one of your future books if not your climate change related website !! But – again of potential interest. Not to mention that there is oodles of data produced, and perhaps there is equal public benefit in much of it being freely available.

    [Response: Autocorrelation is most common in time series data. Is there much of that in medical research? It could also be present in other data under some circumstances. Generally, the data will tell you whether autocorrelation is present, and if it is then it should be accounted for.]

    Anyway, thank you for your advice.

    Henry Herbert

    • Henry, you get the temperature and precipitation data for Palmy from
      You have to register but its free for 2M lines of data. After that is case of selecting datatype (you probably want “statistics calculated from observations” and then monthly statistics, mean temperature and rainfall). However, when you go to select station, you will find the first major problem for amateurs playing with this data – there isn’t a continuous station record for PN. The high school goes back to 1902 but finishes at 1958. The modern stations only go back 1991. How do you compare and splice? 3238 is probably a good bet though. I’m not so sure I’d expect a trend in precipitation for PN.

    • Horatio Algeranon

      fake poortrayal of what the IPCC projects

      – by Horatio Algeranon

      The IPCC has been strawsified
      That really cannot be denied
      They failed to claim
      What strawmen proved wrong
      And Lord* knows straw
      Is very strawng

      (*Mocktman, of course)

      • Hmm, why am I reminded of Blake’s couplet?

        “I MOCK thee not, though I by thee am mockèd;
        Thou call’st me madman, but I call thee blockhead.”

        Or maybe fractured Shakespeare:

        “Mortals, what fools these Lords can be!”

  7. FYI — 2012 September’s Oceanography is dedicated to Antarctica and includes an IMO pretty good primer on Antarctic sea ice by Maksym et al..

  8. With a H/T to Rabett Run, increased Antarctic sea ice with increasing CO2 and warming was predicted over 20 years ago by Manabe et al 1991,, page 795.

    This discussion was in context of some of J. Curry’s statements regarding her claims and papers regarding increasing sea ice, that did not properly credit Manabe et al (,

    Mechanism: an increased supply of fresh surface water from both land-bound ice melt and increased precipitation increases the halocline gradient, reducing upwelling of warmer bottom waters with the air-cooled surface (reducing the effective thermal mass exposed to the air), decreasing sea surface temperature, and thus leading to more sea ice.

    This effect is primarily on Antarctic winter ice (little if any affect on global albedo, incidentally, as it melts away almost completely in the summer), and is an effect likely to fade with additional warming. While this is based on a modeling study, it’s very interesting to note that these rather counter-intuitive predictions match observations a few decades later.

  9. Fresh water is lighter than sea water and has a higher freezing point. Are there Antarctic seas with poor mixing and thus quick freezing due to melt water off the continent?

    • I believe that, according the Manabe paper I referred to above, although higher run-off is a factor the primary influence is increased precipitation around the Antarctic. And that due to GHG caused warmer air, and associated higher absolute humidity.

      And thus fresher surface waters, a higher haolcline gradient, less mixing, cooler surface temps, and more sea ice with rising CO2 and temperatures.

      There are of course other influences, such as changing wind patterns around Antarctica – this is but one possible influence. And while sea ice shows a slight increase around Antarctica, land-based ice according to GRACE data is definitely in decline (NASA –

      I have in fact pointed noted the Manabe paper on WUWT ( as a possible and predicted mechanism behind increased Antarctic sea ice – with (ahem) rather unsurprising responses.

  10. Last September I heard from someone at the University of Washington that Jinlun Zhang (PIOMAS) is working on a model to produce Antarctic sea ice volume, but that it would be “some time” before the kinks were worked out and it was made public.

    “We have a good handle of the extent of the Antarctic sea ice, but the thickness has been the missing piece to monitor the sea ice mass balance,” said Thorsten Markus, one of the authors of the study and Project Scientist for ICESat-2, a satellite mission designed to replace the now defunct ICESat. ICESat-2 is scheduled to launch in 2016. “The extent can be greater, but if the sea ice gets thinner, the volume could stay the same.”

  12. > Steve L … mixing ….
    Interesting question that’s being looked at in much detail, as the global ocean circulation is driven by salinity changes:
    4th May 2012
    “New research by teams of Australian and US scientists has found there has been a massive reduction in the amount of Antarctic Bottom Water found off the coast of Antarctica.

    “Comparing detailed measurements taken during the Australian Antarctic program’s 2012 Southern Ocean marine science voyage to historical data dating back to 1970, scientists estimate there has been as much as a 60% reduction in the volume of Antarctic Bottom Water, the cold dense water that drives global ocean currents….”

  13. Tamino, this might be little off-topic, but really, why bother to even discuss climate change when your read THIS from Obama:

    “Let’s keep moving forward on an all-of-the-above energy strategy. A strategy where we produce more oil and gas here at home, but also more biofuels and fuel-efficient vehicles; more solar power and wind power. A strategy where we put more people to work building cars, homes and businesses that waste less energy. We can do this. We’re Americans. And when we commit ourselves to something, there’s no telling how far we’ll go.” – cited at CP. Ok, now I think we are really fuc*ed… Alexander

    • That’s why the education effort must continue–this is where the middle of the roaders are right now: concerned about climate change, but not yet understanding that it’s not a far-off problem.

      Yeah, we are in a situation evocative of sexual encounters of the most unpleasant sort, but there’s still a big difference between bad and worse.

    • The best the Taminos of the world can do as individuals right now is to promulgate good info and to counter propaganda. That is not an unimportant thing. The rest is going to be political action which against entrenched well monied interests takes a lot of time.

      This is going to go on for decades. We are not even up to the Surgeon-General’s Report of 1964 in the analogical tobacco timeline yet where an authoritative, incontrovertible review that pointed to direct, casual harm. I doubt that IPCC5 will do so either but will rather be couched in “highly probables” as did prior tobacco reports.

      If we are in the 40s or 50s of the same sort of analogical timeline, there is basically a lifetime of work left to do to even mitigate a large portion of the harm.

      MADD is just over 30 years old and only in the past 10 or so have made really significant gains politically that have led to some reduction.

    • Horatio Algeranon

      – by Horatio Algeranon

      To cut emissions
      Just increase.
      Might sound odd
      But “War is Peace”
      “Black is White”
      And “Tar is Good”
      “Tarry Pipe
      Oirlwell rules
      In times like these
      To cut emissions
      Just increase.

  14. I think one of the main points missed (deliberately in my opinion) by those who attempt to compare sea ice in Antarctica and the arctic is that sea ice is far far less relevant in Antarctica as the sea ice is surrounding a land continent. Arctic sea ice goes right over the pole. Antarctic sea ice is a fair distance from the pole because of the continent there. What would be interesting would be to look at the trends in arctic sea ice (no land ice there) and Antarctic sea and land ice.
    From what I have read one explanation for increasing antarctic sea ice is increased precipitation which is climate change related.

  15. Thanks for the analysis, Tamino.

  16. Satellite detection of sea ice thickness depends on observing how high above sea level the ice ‘surface’ is (the freeboard). Then assuming an ice density, you can estimate ice thickness. The problems in this are that snow cover interferes with the observation, and that small errors in freeboard estimates make for relatively large errors in thickness for thinner ice. Effectively, current practice suggests that altimetric estimates of ice thickness below about 1 meter are not really usable. The canonical winter maximum average ice thickness in Antarctica is 0.6 meters. Oops. And the Antarctic ice tends to have substantial snow cover. A double challenge, compared to the thicker and less snowy Arctic (ice surrounded by land doesn’t get as much snow as ice surrounded by ocean).

    I think I’m the original source for noting Manabe’s prediction of increased Antarctic ice cover (in the blogosphere, that is) —

    A reader here also asked about the pre-1979 satellite data over at my place The fuller answer is there, but for brief here: the previous satellites are not as good for sea ice measurement as the 1979 and following instruments. They’re certainly not directly comparable to the later instruments, and whether they can be used at all is a question. The IPCC 3AR figure shown is ignoring the giant Weddell Polynya that ESMR (NIMBUS 5 instrument) detected. I tend to think that one should not ignore it.

    Steve L:
    The continental melt water comes largely from the base of the ice shelves, rather than runoff from the continent. So it is fresh, but supercooled (with respect to the surface melting point, thanks to the pressure-induced depression of the freezing point) and mixes with the surrounding waters on its way out to the open ocean. By the time it gets out there, it’s no longer a fresh water. To the extent that you get a meltwater lid in the Antarctic, it is in the summer melt season. This does make a stable layer, and is a major contributor to the biological blooms in the Antarctic.

    Hank Roberts:
    Antarctic Bottom Water formation ws the topic of my thesis. Much fun, and this reduction is what my now-ancient model would have predicted. (Grumbine, 1991).

    Questions welcome over at my question place (link above). I’ll try to pay attention here, too.

  17. Steve L., Robert Grumbine – melt water effects:

    So the fresh water – low salinity layer looks like a good candidate for the rising Antarctic winter ice maximum? An ugly writing on the wall if it is.

    • One recent paper attributes the trends in Antarctic sea ice to divergence due to changes in atmospheric circulation (if I remember correctly based upon earlier literature, I believe partly as the strengthening of the Antarctic Polar Vortex) and freshening due to melt resulting in ocean stratification.

      Please see:

      Holland, Paul R., and Ron Kwok. “Wind-driven trends in Antarctic sea-ice drift.” Nature Geoscience (2012).

  18. The ice maximum has more to do with snow -> insulating layer, per Manabe’s 20 year old prediction.

    • waynedavidson

      It can also be snow (from snow showers) almost floating on the surface misinterpreted as sea ice, as I have filmed and documented on my website. There is also lack of ice analysis data, like the extent of Glacier ice which may have some influence over the formation of sea ice. A massive iceberg reduces the wind around it and favors sea ice formation.

  19. Rather off-topic; please feel free to move to a more appropriate thread, and edit out the bits about typos and suggestion for the next edition as you see fit.

    I’ve just finished reading “understanding Statistics”, and would strongly recommend it to anyone wanting to learn basic statistical methods, with a minimum of maths, but without sacrificing understanding. I’d say the book lives up very well to its intended purpose, I’m sure the climate debate in the blogsphere would improve immensely if everybody bought a copy and read it!


    page 195 section 13.6, line 3 “exptected”

    page 338 eqn 23.7, Ithink it should be 0 if beta1 = 0 rather than 1 on the last line.

    Suggestion for next edition:

    The book does a good job of warning against over-interpreting tests of statistical significance (reject or do not reject the null hypothesis), but the discussion of confidence intervals could do with making it more clear that the true value will lie in 95% confidence intervals constructed according to some method, but that doesn’t mean there is a 95% probability that the true value lies within the particular confidence interval we have calculated from a particular sample (as discussed a little polemically in Jaynes article on “Confidence Intervals vs Bayesian Intervals”). This is a pretty important point in really understanding what a confidence interval actually is, but people tend to treat them as if they were credible intervals, and it would be worth discussing that point in more detail. There is nothing wrong with either kind of interval as long as they are interpreted as what they actually are!

  20. I think that I can explain the increase in Antarctic sea ice, it is due to declining Arctic sea ice. The albedo effect in the Arctic is of course greatly accelerating the warming there, both due to sharp declines in sea ice and snow cover (snow cover is actually declining even more than sea ice, and the curves would make a very good future blog for you, see Rutgers data). Thus the Arctic is warming from the higher solar absorption (shortwave). Thus, less heat is traveling northward from atmospheric and ocean circulation patterns. Thus, more heat goes into the southern hemisphere (as Oz is finding out). This increases the delta-temperature gradient with the south pole and strengthens the AAO (Antarctica Oscillation, also known as the SAM (Southern Annular Mode). Thus cooling the region and generating more sea ice. Underneath the ice there is still warming from the ocean, as indicated by the GRACE satellite data showing declining Antarctic glacial ice volume.
    Regards, Paul

  21. Sorry, it’s not about Arctic not Antarctic, but the Arctic thread seems to be already closed for commenting. There’s a thing I can’t understand about Arctic sea ice – how come according to NSIDC the maximum sea ice extent in 2013 was the 6th lowest in satellite history while Jaxa is showing it to be higher than the 2000′s (not even 2010′s) average?