Antarctic Sea Ice Re-visited

Jeff Id did an interesting post a few days ago on Antarctic sea ice in which he provided the following interesting graphic of Antarctic seaice area anomalies, which, from the texture, is daily, rather than monthly:


Figure 1. Antarctic seaice area anomaly (Jeff Id version)

Jeff’s data reference was to the following webpage at NSIDC, but, to my knowledge, this only provides gridded data in binary form and does not provide information on a daily basis. Last year, I scraped binary gridded data for the Arctic and it’s not a small job. The data has to be scraped on a day by day basis and it took me about half a day on high-speed cable. The scraping program requires a little ingenuity. Then the form of the binary data has to be figured out – which “endian” is it, the location and area of the cells has to be obtained (online in an information area), then the definitions of “area” and “extent” have to be applied. Unless Jeff found some daily data that I couldn’t find, there’s more work in this graphic than most readers realize.

Last year, I’d done this for the Arctic and felt a little out-flanked :) by another blogger managing to scrape data that I hadn’t. So I modified by scraping script, downloaded and organized the Antarctic data and produced my own version of Jeff’s graphic, which is substantially the same, but with a few interesting differences.

In producing one of these graphics, there are 5 satellites, with very short overlaps between the early satellites but a longer overlap between the two most recent – f13 and f15. I checked the overlaps for each pairing – there were noticeable differences, but in the tens of thousands of sq km, not hundreds of thousands of sq km. So I used the data as archived without attempting to make intersatellite adjustments (though that would be desirable in a lengthier exposition) and averaged the two satellites where there was an overlap.

Here’s my version of Jeff’s graphic:

Figure 2. Antarctic seaice area anomaly (Steve Mc version)

While the two graphics are reassuringly similar, as noted above, there are interesting differences. In my version, there’s a remarkable downspike in the latter part of 2008. Re-examining the underlying data, this seems to result from an error in satellite f15 in October 2008 – on October 18, 2008, f15 (improbably) showed Antarctic seaice area of over 4 million sq km less than f13. There were only a few days of huge discrepancies, but they don’t seem to have picked up this error yet. f15 was the same satellite that had problems in the Arctic in February 2009 (discussed at Watt’s Up) and results from this satellite are no longer reported.

I’ll post my scraping scripts up as CA/scripts/seaice/collation.antarctica.txt, but warn that I’ve not tried to make them fully turnkey. I’ve posted daily area and extent in tab-separated ASCII form up to May 3, 2009 at CA/data/seaice/antarctica.csv .

Update: Here is my version of the above graphic without the problematic f15 satellite. A little different than Jeff Id’s, but not enough to worry about for now.


47 Comments

  1. Posted May 6, 2009 at 9:57 AM | Permalink

    In my version, I simply removed all the NOAA15 sat files, even before the problem was detected. I did that because there was no way for me to know when the problem began and NOAA 13 data exists for most of the record. That probably accounts for the slightly higher slope in my graph.

  2. Andrew
    Posted May 6, 2009 at 10:16 AM | Permalink

    Clearly the dramatic down spike is indicative of the underlying trend and everything else is weather noise. ;)

  3. Gerald Machnee
    Posted May 6, 2009 at 11:08 AM | Permalink

    Great work Steve. Let us see what other questions result from this spike and this detail.

  4. Posted May 6, 2009 at 11:27 AM | Permalink

    Is your overall slope consistent with the recent paper by Turner et al in GRL saying 1%/decade? Yes I think it is roughly.

  5. Steve McIntyre
    Posted May 6, 2009 at 12:53 PM | Permalink

    I’ve posted my scraping scripts up as CA/scripts/seaice/collation.antarctica.txt, but warn that I’ve not tried to make them fully turnkey.

    For people interested in daily data, I’ve posted daily area and extent in tab-separated ASCII form up to May 3, 2009 at CA/data/seaice/antarctica.csv . This is a bit less than 1 MB in size. It would be nice if NSIDC provided official daily data, but in the meantime, this should be a practical alternative.

    • DeWitt Payne
      Posted May 6, 2009 at 3:42 PM | Permalink

      Re: Steve McIntyre (#5),

      I compared the last year of your area data with the data from Uni-Hamburg (AMSR-E) through 4/1/2009. The NSIDC data is somewhat noisier, probably because of the higher resolution of the AMSR-E camera. The scale is a little different as well. A regression with NSIDC as x and Uni-Hamburg as y has a slope of 1.163 and an intercept of 0.058. Out of curiosity, what was your cutoff for using a pixel?

  6. Andrew
    Posted May 6, 2009 at 12:57 PM | Permalink

    I recently had a brief email exchange with one of the curators of Cryosphere today about some odd behavior I observed in some of the plots of daily regional extent. For some reason there were sudden, unphysical jumps. They confirmed that those changes were artifacts and would look into it. There are still some jumps popping up now and then. I’d be careful of any changes in the daily data which look unnatural-they probably are glitches.

  7. Andrew
    Posted May 6, 2009 at 1:04 PM | Permalink

    A question-how is the base period for daily values calculated for determining anomalies on leap day (Feb 29)?

    • Steve McIntyre
      Posted May 6, 2009 at 1:09 PM | Permalink

      Re: Andrew (#7),

      In my anomaly calculation (and I don’t know how NSIDC does it), I allocated each day to its day of the year. Thus day 366 only occurs in leap years. In SH, it might make a little more sense to allocate days from July 1, but I can’t see that it would make enough difference to change the look of the graphic. Maybe Jeff did it that way and that’s why our results are a little different.

  8. Matthew
    Posted May 6, 2009 at 1:44 PM | Permalink

    WOW !!!!
    I didn’t realize how much work you guys had to go through to do this !!
    Thanks for doing it !1

  9. tty
    Posted May 6, 2009 at 1:58 PM | Permalink

    Andrew:

    I’ve noticed those downspikes too. Since they seem to occur mostly in spring my theory is that they are caused my meltwater pooling on the ice and being interpreted as water. When the water drains away the ice is “resurrected”.

  10. Molon Labe
    Posted May 6, 2009 at 3:44 PM | Permalink

    If sea ice is increasing, wouldn’t one expect to see a corresponding increase in Antarctic air temperature? The formation of sea ice results in the transfer of heat from ocean to atmosphere. You have the signifcant heat of formation of ice being dumped into the low specific heat atmosphere.

    I’m concerned that the warmist distraction play will be to start hyping the Antarctic air temperature increases.

  11. Posted May 6, 2009 at 4:49 PM | Permalink

    Reply to Molon Labe from an Australian observer re comment #18 on Antarctic ice:

    Molon asks how AGW proponents cope with reports of increasing Antarctic sea ice. He suggested some might seek atmospheric warming produced as a balance to the cooling process of ice formation, and misinterpret this warming as AGW. I have not seen this argument used. But I have seen two other pro-AGW arguments attempted:

    (1) Some try to attribute the ice increase to global warming causing more evaporation which can generate more ice. But most of the Antarctic has not warmed since the 1970s (see review in World Climate Report ‘Antarctica Again’ 30-1-09; the recent Steig et al. paper is also covered here).

    (2) The increasing Antarctic sea ice is now being attributed by some to the hole in the ozone layer. It is supposed to produce a cold wind which gradually works its way down to the surface, smothers AGW and increases sea ice formation. Curiously, the surface winds are supposed to be at a maximum in autumn, yet the sea ice is said by this same publication to be at a minimum in this same season, autumn. (See British Antarctic Survey Press Release 05/2009, ‘Increasing Antarctic sea ice extent linked to the ozone hole’, April 21.)

    • tetris
      Posted May 6, 2009 at 5:30 PM | Permalink

      Re: david elder (#19),
      This comment is certainly not intended to derail this thread, but there is neither a “hole in the ozone layer” in the Arctic nor are air temperatures up as per Molon Labe’s argument [they have been below the norm for the time of year]. Meanwhile, best available satellite data show that Arctic ice extent is much higher than anytime during the past decade, and well in line with the 1979-2000 average.

      • Molon Labe
        Posted May 6, 2009 at 6:23 PM | Permalink

        Re: tetris (#21), “nor are air temperatures up as per Molon Labe’s argument”

        My point is that the if the change in temperature over the course of the Antarctic winter is unusually large, the AGW crowd could seize on that as evidence of “unprecedented” warming. Their argument would be based on delta-T, not absolute temperature.

      • Molon Labe
        Posted May 7, 2009 at 3:21 AM | Permalink

        Re: tetris (#21), “nor are air temperatures up as per Molon Labe’s argument”

        I didn’t notice that you had said Arctic. In fact, Arctic air temperatures are up precisely due to the effect that I describe. Consider this excerpt from the April 6, 2009, NSIDC Arctic Sea Ice News:

        Overall, it was a fairly warm winter in the Arctic. Air temperatures over the Arctic Ocean were an average of 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) above normal, with notable regional variations. The Barents Sea region was over 4 degrees Celsius (7.2 degrees Fahrenheit) warmer than average this winter. This warmth probably stemmed from unusually low sea ice extent in the region throughout much of the winter, which allowed the ocean to pump heat into the atmosphere.

    • curious
      Posted May 6, 2009 at 5:30 PM | Permalink

      Re: david elder (#19), Anyone got a free access version of the paper this release announced yet?:

      British Antarctic Survey Press Release 05/2009, ‘Increasing Antarctic sea ice extent linked to the ozone hole’, April 21

      • Posted May 7, 2009 at 6:48 AM | Permalink

        Re: curious (#22), this was the paper I was referring to in #4.
        “Non‐annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent”, Turner et al, geophys res lett 36, L08502 (2009).
        The abstract says
        “Based on a new analysis of passive microwave satellite data, we demonstrate that the annual mean extent of Antarctic sea ice has increased at a statistically significant rate of 0.97% dec−1 since the late 1970s. The largest increase has been in autumn when there has been a dipole of significant positive and negative trends in the Ross and Amundsen‐Bellingshausen Seas respectively. The autumn increase in the Ross Sea sector is primarily a result of stronger cyclonic atmospheric flow over the Amundsen Sea. Model experiments suggest that the trend towards stronger cyclonic circulation is mainly a result of stratospheric ozone depletion, which has strengthened autumn wind speeds around the continent, deepening the Amundsen Sea Low through flow separation around the high coastal orography. However, statistics derived from a climate model control run suggest that the observed sea ice increase might still be within the range of natural climate variability.”

        The only observational result of the paper is the significant increase in ice extent. The stuff about ozone is models plus speculation. The conclusions are quite hesitant:
        “The model experiments discussed above suggest that the recent deepening of the ASL, and therefore the increase of SIE in the Ross Sea, are largely a result of the decrease of stratospheric ozone. However, the long control run of a coupled climate model does suggest that the recent increase in SIE might still be within the bounds of natural climate variability.”

        As usual, the BAS press release is misleading.

        • curious
          Posted May 7, 2009 at 6:55 AM | Permalink

          Re: PaulM (#32), Thanks Paul – I’d seen the press release when it came out and I’m interested to read the detail of what they have to say about the role of winds in temperature distribution. From the abstract it seems they may have used modelled rather than measured wind and I’d like to know more. IIRR in the full PR on the BAS site they made some fairly strong claims for the role of wind in distributing temps. which I’ve not seen discussed previously. Maybe I’ll end up stumping up for a paid copy! Any further info. appreciated.

    • Posted May 6, 2009 at 9:21 PM | Permalink

      Re: david elder (#19),

      (2) The increasing Antarctic sea ice is now being attributed by some to the hole in the ozone layer. It is supposed to produce a cold wind which gradually works its way down to the surface, smothers AGW and increases sea ice formation. Curiously, the surface winds are supposed to be at a maximum in autumn, yet the sea ice is said by this same publication to be at a minimum in this same season, autumn. (See British Antarctic Survey Press Release 05/2009, ‘Increasing Antarctic sea ice extent linked to the ozone hole’, April 21.)

      For the last two years the pattern has been a minimum about at the 79-00 average followed by a faster than normal regrowth of sea ice for about two months (starting slightly early). The growth rate then reverts to normal (last year ending up at an ~average max). So it makes sense that there could be a cold offshore air flow in March-April.

  12. Posted May 6, 2009 at 5:25 PM | Permalink

    What is interesting to me is that now that Steve has replicated basically the same Antarctic graph as I did for both the Arctic and Antarctic. The summation of the south and north ice are at about the top 97th percentile of global ice anomalies for the last 30 years. Using this same method, I found the Arctic ice is also above mean right now. This is slightly different from the results presented at the Cryosphere homepage.

    There were also questions about land mask variation the last time I did a post for WUWT. People were suspicious that the land area had changed during some point in the time series. I checked and the NSIDC data has a constant land mask for the entire time period.

    • Steve McIntyre
      Posted May 6, 2009 at 6:01 PM | Permalink

      Re: Jeff Id (#20),

      I scraped Arctic data last year. When I revisited the matter, I noticed that all the Arctic data up to Sep 30, 2008 had been replaced on Sep 30, 2008. I don’t know what the reason was or what the effect was.

    • DeWitt Payne
      Posted May 7, 2009 at 1:58 AM | Permalink

      Re: Jeff Id (#20),

      Using this same method, I found the Arctic ice is also above mean right now. This is slightly different from the results presented at the Cryosphere homepage.

      If that is the case, then I suspect the recent NSIDC data is flawed and CT is more accurate. Arctic ROOS, which compares well with JAXA, is still below the 1979-2007 average, much less the 1979-2000 average. Unfortunately, Uni-Hamburg hasn’t posted their May data yet. The Antarctic anomaly is also well below the December 2007 peak so it’s unlikely that the global anomaly is anywhere near record territory.

      • Posted May 7, 2009 at 8:16 AM | Permalink

        Re: DeWitt Payne (#28),

        I am certain that the global sea ice anomaly was near the 30 year record last month even considering the ‘slight’ difference in my calc. Last year the peak was even closer.

        Re: Steve McIntyre (#23),

        I think it was due to version change in the data set (improved intra-sat matching) I read it on NSIDC somewhere but I couldn’t find it last night.

        • DeWitt Payne
          Posted May 7, 2009 at 9:46 AM | Permalink

          Re: Jeff Id (#34),

          Is that for extent or area? Could you post the data for your peak global anomaly. I’d like to compare it to what I have and to Uni-Hamburg when they post their April data. The peak global area anomaly for CT appears to be in late 1988 and eyeballs to be about 0.5 Mm2 higher than either this year or last year. It’s really annoying that they don’t archive the data for their graphs.

        • Posted May 7, 2009 at 9:54 AM | Permalink

          Re: DeWitt Payne (#35),

          It’s area. The link above leads to my post. I also put up the Cryosphere graph for comparison.

        • DeWitt Payne
          Posted May 7, 2009 at 10:46 AM | Permalink

          Re: Jeff Id (#36),

          I’ve plotted the global area and extent anomalies using the AMSR-E data from Uni-Hamburg through 4/1/2009:

          December 2007 and April 2008 were much higher than December 2008 (and may well be 30 year records) but it doesn’t look like April 2009 will exceed the peak in December 2002.

        • Posted May 7, 2009 at 1:06 PM | Permalink

          Re: DeWitt Payne (#37),

          Your graph is different from the Cryosphere plot as well.

        • DeWitt Payne
          Posted May 7, 2009 at 1:39 PM | Permalink

          Re: Jeff Id (#38),

          That’s not surprising since it’s AMSR-E data processed by a different algorithm than Cryosphere Today uses. I can make it look just like the CT graph, though, by doing linear transforms on the Antarctic and Arctic area data separately and then summing them. When I do that, the correlation plot between the UH adjusted global area data and the CT data has a slope of 0.98 and an R2 of 0.988.

  13. David Smith
    Posted May 6, 2009 at 6:10 PM | Permalink

    Article by Eric Berger (Houston Chronicle), in case it hasn’t already been linked at CA:

    Has the Global Sea Ice Decline Stopped?

  14. Tim Channon
    Posted May 6, 2009 at 9:01 PM | Permalink

    The result I get a different processing and is a very slight decreasing on linear trend. For sensible purposes there is a flat line, no change.

    How come the different result?

    1. I chopped the tail with that anomalous problem.

    2. And this is critical: you must only include full cycles otherwise it will skew. Under that fast noise is an annual cycle. (low pass and see)

    You have presented useful new data so lets give something back.

    Not a great deal of interest in there, record is too short to show much. I wasn’t expecting the solar cycle to show but it does. Don’t take the longer period stuff too seriously, this is pushing hard on the limits.

  15. Posted May 7, 2009 at 2:02 AM | Permalink

    Re tetris #21: Molon Labe (#18, #25) and I (#19) were dealing with the Antarctic ice gain, not the Arctic ice gain. I might briefly note that recent Arctic ice recovery is consistent with this proposal that the prior ice loss was largely natural variation:

    ‘ScienceDaily 29 December 2004: Winds, Ice Motion Root Cause Of Decline In Sea Ice, Not Warmer Temperatures. — Extreme changes in the Arctic Oscillation in the early 1990s — and not warmer temperatures of recent years — are largely responsible for declines in how much sea ice covers the Arctic Ocean, with near record lows having been observed during the last three years, University of Washington researchers say.’

    Thanks to Phil (#27) for thoughts on the new ozone-hole theory for Antarctic ice gain, a subject which for us Aussies is both scientifically fascinating and a key part of our vigorous political greenhouse debate.

  16. Posted May 7, 2009 at 4:35 PM | Permalink

    Thanks to PaulM (#32) for critical analysis of the recent publication and BAS press release of a new theory linking Antarctic ice growth to the ozone hole. Pro-AGW advocates here in Australia are already hailing this theory as proof that the strong AGW position fits perfectly well with the Antarctic ice data. Others including myself would like to see more study on the matter before adopting any firm view, [snip -venting]

  17. Posted May 8, 2009 at 9:56 PM | Permalink

    I’ve expanded on the trend plot above and done a calculation of trend for each pixel of the gridded data. I don’t think I’ve ever seen the data presented this way, it revealed an increased ice level in the bering strait as the weather pushed ice out from the cap.

    http://noconsensus.wordpress.com/2009/05/08/arctic-ice-flux/

    Seeing the trend in flow show up so visibly was surprising to me.

  18. thefordprefect
    Posted May 9, 2009 at 5:56 AM | Permalink

    Just a question -don’t kow if its been brought up before.
    Why is measuring maxima amd minima the right way 6to go about this idt seems wrong!

    Arctic – Maximum extent is severely limited by land mass. Minimum is ok but start of shrinkage will be delayed by over cooling at land boundaries.

    Antarctic – Minimum extent is totally limited by landmass (once shore line is exposed it is not going to shrink further at that location!) maximum extent is better but start of growth is delayed by over heating at the boundaries.

    To me this means that global sea-ice is really only valid some time after the max/min times.

    Mike

    • David Cauthen
      Posted May 9, 2009 at 6:24 AM | Permalink

      Re: thefordprefect (#42),
      How about Arctic minimum plus Antarctic maximum? Wonder what that trend is?

      • BarryW
        Posted May 10, 2009 at 3:53 PM | Permalink

        Re: David Cauthen (#43),

        How about Arctic minimum plus Antarctic maximum? Wonder what that trend is?

        Down, at least on a monthly basis.

  19. Posted May 10, 2009 at 9:48 AM | Permalink

    I did the same plot as #41, but for the Antarctic now.

    http://noconsensus.wordpress.com/2009/05/10/antarctic-seaice-trend-by-pixel/

    Where the ice is melting is pretty interesting to me. Check out the trend around the Wilkins shelf.

  20. Posted May 11, 2009 at 8:16 PM | Permalink

    I just finished another post on the new sea ice data just released from the NSIDC. They have replaced a large gap left by the NOAA15 failure.

    http://noconsensus.wordpress.com/2009/05/11/sea-ice-data-update/

  21. Geoff
    Posted Jul 11, 2009 at 10:29 PM | Permalink

    I guess we’ll know for sure what’s going on in Antarctica very soon:

    This fall, the National Science Foundation NSF) will award a contract worth nearly $2 billion to provide logistical support for its $300-million-a-year Antarctic research program. And officials from Antarctic Research Support (ARS), a joint venture formed 4 months ago by two large systems-engineering companies for the express purpose of winning that contract, hope that the billboards demonstrate that they can be good stewards of science on the frozen continent.

    There are only a few competitors but one of them is advertising:

    Such competitions are typically very low-key, partly because the work isn’t sexy and partly because the rules governing such competitions don’t allow for much boasting. But ARS’s high-profile approach—it’s also running ads in Metro cars and on this magazine’s [Science] Web site—is part of a broader strategy to raise the visibility of its parent companies, CSC and EG&G, and tout the scientific expertise of its team, led by two scientists who held major science posts in the last Administration.

    And is the key provider of the scientific expertise?

    retired Vice Admiral Conrad Lautenbacher, the former head of the National Oceanic and Atmospheric Administration [NOAA]

    Who said climate doesn’t pay? And look at the great data we’ll be getting.

    Ref.: A Hot Competition for a Cold Contract (2009), Mervis, Science, 3 July, Vol. 325, p. 20

    • D. Patterson
      Posted Jul 11, 2009 at 10:43 PM | Permalink

      Re: Geoff (#47),

      47 July 11th, 2009 at 10:29 pm
      I guess we’ll know for sure what’s going on in Antarctica very soon:

      It might be interesting to see the results from comparing photographs of the Arctic and Antarctic contributed by passengers aboard high altitude trans-polar air flights to the satellite reports. Perhaps Anthony Watts could host the contributed photographs?

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