History of Arctic (and Antarctic) Sea Ice, Part 1

Nobody in his right mind disputes that since satellite observations began, the extent of sea ice in the arctic has declined dramatically; this year the summer minimum extent was the 3rd-lowest on record. There is also considerable observational evidence that arctic sea ice extent over the last few decades is much lower than it has been for at least a century prior to modern times.

A team of researchers, led by Leonid Polyak of Ohio State University’s Byrd Polar Research Center, has culled the available evidence from hundreds of studies of proxy data for sea ice extent. As reported at Science Daily, in a new paper in Quaternary Science Reviews they report their findings: that the present extent of sea ice in the arctic is at its lowest for at least several thousand years.

But we’ll address the very long-term arctic ice extent in another post. In this one, let’s look at the evidence about arctic (and antarctic) sea ice over the last century or so.

Satellite observations are not the only source of information about past sea ice. There is in fact a wealth of information, especially for the latter half of the 20th century, although the available data are extremely inhomogeneous. There’s quite a bit of information in historical charts based on in situ observations, and data from aerial reconnaissance. I’m aware of two most prominent reconstructions of arctic sea ice for the 20th century based on these data. One is the HADISST sea ice and sea surface temperature data set from the Hadley Centre (which also covers the southern hemisphere), the other is from Kinnard et al. (2008).

The HADISST data set is described in Rayner et al. 2003 (J. Geophys. Res., 108, 4407), parts of which I’ll summarize (often quoting at length). For the Northern Hemisphere, data include sea ice concentration for 1901 to 1995 assembled from hand-drawn charts, sometimes limited to ice extent, in other cases indicating concentration. These were collated by Walsh and others to give reasonably uniform estimates of sea ice extent at all longitudes. Other compilations are used to fill in areas not covered by the Walsh compilation, in particular the Great Lakes.

For the Southern Hemisphere data are more sparse but not entirely absent. In fact prior to 1973, the HADISST ice data are based primarily on climatology, i.e., on estimates of annual averages so they reflect persistent conditions but don’t include interannual variability. Climatologies for 1929-1939 were taken from Deutsches Hydrographisches Institute, and for 1947 to 1962 from Tolstikov, who summarized information from Russian expeditions. These sources indicate considerably greater southern ice extent than at present, a conclusion which is supported by other studies (de la Mare 1997, Nature, 389, 57; Jones 1990, J. Clim., 3, 1193).

For both hemispheres, quasi-weekly sea ice concentration and extent were digitized by the U.S. National Climatic Data Center (NCDC) from hand-drawn U.S. National Ice Center (NIC) analyses. These were based on U.S. Navy, Canadian and Danish aerial reconnaissance data and from retrievals from advanced very high resolution radiometer (AVHRR), passive microwave, and other satellite instruments

One of the difficulties using charts based on in situ observations is that there was very little exploration poleward of the “marginal ice zone” (the area of partial sea ice cover near the ice edge), so in older reconstructions the ice concentration was often assumed to be 100% beyond the marginal zone. By comparing in situ, aerial, and satellite observations, it’s possible to make a much better estimate of actual ice conditions throughout the polar regions.

I haven’t located the data from Kinnard et al. (perhaps someone knows a link?), but their data are graphed in Polyak et al. (2010). It shows the progression of both the summer minimum extent, and the winter maximum extent, since 1870:

I have downloaded the HADISST ice data and computed sea ice extent for both the arctic and antarctic (based on 15% concentration to be consistent with NSIDC data from the satellite era). I combined these with NSIDC satellite data since 1979 to form a continuous time series from 1870 to the present. Some of these episodes are based on climatology (i.e., averages over decadal timescales) as previously mentioned, so they don’t allow the study of interannual variability but do give strong evidence of prevailing conditions in the longer term; this is especially true of the southern hemisphere. They provide estimates of sea ice extent for the last 140 years.

Here are the Northern Hemisphere summer minimum, and winter maximum, extents (summer minimum plotted using the left-hand y-axis, winter maximum using the right-hand axis) — which are in excellent agreement with the results of Kinnard et al.:

Here are the Southern Hemisphere summer minimum and winter maximum extents:

Most of the ice reduction in the Northern Hemisphere has occurred since 1970, and the decline continues at a rapid pace. Also, the summer minimum has declined faster than the winter maximum, which is at least in part due to simple geography, i.e., the placement of land masses means that the same northward migration of ice latitude in winter as in summer corresponds to a greater reduction in area and extent during summer.

Things are different for the Southern Hemisphere. Most of the reduction has occurred since 1940, and especially since 1960, and the reduction during winter has been greater than during summer.

For both hemispheres, the decline has been strongly nonlinear. This is not just because the declines begin in the mid-to-late 20th century. For the Northern Hemisphere, the decline has accelerated even since satellite observations began, in fact it’s considerably faster post-1998 than pre-1997. For the Southern Hemisphere, the decline has retarded recently, ceasing entirely after about 1975.

In fact Southern Hemisphere sea ice extent has actually increased during the satellite era. This isn’t statistically significant if one uses only the summer minimum, or winter maximum, values, although it’s almost significant for winter maximum. But if one uses data for all months, the increase in Antarctic sea ice extent since 1979 is statistically significant.

Just as sea ice extent during the satellite era has increased in the south, it has decreased most rapidly in the north, with the northern decrease far outpacing the southern increase. For the Southern Hemisphere, summer minimum has increased at about 9,000 km^2/yr while the winter maximum has increased at about 14,000 km^2/yr. For the Northern Hemisphere, on the other hand, the decrease in winter maximum has been about 42,000 km^2/yr and the decrease in summer minimum has proceeded at about 81,000 km^2/yr — rates dramatically greater than in the south.

Despite their obvious imperfections, these are estimates based on exhaustive study of actual data — not just cherry-picked anecdotes to support some preconception or ideology. The data are clear: sea ice extent declined dramatically during the 20th century in both hemispheres. The arctic sea ice decline has accelerated to the point that it can truly be described as “alarming.” And, those who claim that in the mid-20th century the arctic was “practically ice-free” are contradicted by the data.

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87 responses to “History of Arctic (and Antarctic) Sea Ice, Part 1

  1. It doesn’t matter how “exhaustive” the study is, if the data isn’t available then its simply not available. The only data of any worth for trend analysis is that of satellite data.

    [Response: Perhaps you disparage the data because you don't like the conclusion.]

    • Do you need a satellite to tell you if your body mass is trending up or down as well?

      Rubbish criticism.

    • I think the criticism could be cast as follows: when a system exhibits an “extraordinary” behavior on a given timescale T, it means usually that the variation is well above the “normal” variability at this time scale. But to properly estimate the “normal” variability , you need a much longer period to establish a proper statistics ( such as a standard deviation). Examples of “extraordinary” behaviors are, for instance, the demographic growth on the two last centuries, which exceeds by far the “normal ” statistics on this timescale. A variation, observed on a SINGLE time period, can not be given any significance without a comparison with other comparable periods.

      What is unclear here is the period on which the “normal statistics ” is computed, since the past data are obviously much less known, with a considerable loss of variance (the “constant” ice minima are obviously wrong). So without a proper estimate of the standard deviation, what is the criterion ?

      • Of course. But Tim is saying that there is *no* information except the satellite information, which is not the case. He’s trying to throw out data–effectively a form of cherry-picking–and I don’t think there’s any doubt that Tamino has put his finger on exactly why Tim is trying to do so.

        And now, of course, there’s this:


      • When I hear this criticism of the paleoclimate record, namely that we have only indirect knowledge of it, which the “tool man” contrasts with the knowledge we gain of trends by means of satellites, I am reminded that all knowledge is from one perspective or another, indirect. There is always a means of awareness that connects yet separates us from what we are aware of, and since there is a means of awareness, it can at least potentially be influenced by other things, introducing the possibility of error. And once we become aware of this, we may choose to form theories and models of how it operates in order to put bounds on the error. This is as true of satellite measurements as anything else.

        Regarding measurements of carbon dioxide concentrations, I once wrote:

        Alternatively, if one were to assume that CO2 is “well-mixed” with a distribution estimated according to a model, one might then try to estimate temperature using lines in the CO2 spectra. This approach has actually been used before. However, AIRS is able to estimate temperature indepedently of assumptions regarding the homogeneity gas concentrations through the use of a weighting function employing eight different spectral channels. (Please see: M. Chahine (March 7-10, 2006) AIRS CO2 Retrievals Using the Method of Vanishing Partial Derivatives (VPD), AIRS Science Team Meeting, Caltch-Pasadena, CA.) Undoubtedly a good thing, because while the variation is slight, AIRS has shown that there is greater variation in CO2 concentration than one would expect simply on the basis of model calculations.


        Using the same data and the same approach of “vanishing partial derivatives” can be used to measure temperature at various altitudes. But how do we know whether or not the measurements are accurate? By means of other measurements using other methods. In the case of carbon dioxide concentrations we use flask measurements, and the two sets of data differ from one another by less than 2 parts per million.

        This principle of using more than one method of measuring the same thing in order to strengthen the justification of our conclusions is an application of a wider principle: the justification for a conclusion supported by multiple lines of evidence is often far greater than that which it would receive from any one line of evidence in isolation. Paleoclimatology makes good use of this, combining widely disparate forms of evidence that are largely independent of one-another to form its conclusions.

  2. David B. Benson


    Thank you.

  3. You say “But if one uses data for all months, the increase in Antarctic sea ice extent since 1979 is statistically significant”. I suppose have a typo there, “But if one uses data for all months, the increase in Antarctic sea ice extent since 1979 is statistically INsignificant.”

    (since this is a typo comment, it’s OK to delete it)

    [Response: No typo. If you use only the summer minima, or only the winter maxima, the estimated trend fails statistical significance, but if you use all monthly data the estimated trend passes statistical significance.]

  4. I’m amazed at the data. To my eye it looks like the ice started to melt only when we launched weather satellites. I would suggest that if you care about the sea ice we need to get the satellites back on the ground so the amount of sea ice is constant again.

    • What are you talking about? The inflection point in the Arctic sea ice (first graph above) is between 1940 and 1960, well before the start of the modern satellite record.

  5. Tamino says : ” Perhaps you disparage the data because you don’t like the conclusion.”

    There is more than one conclusion apparent in the Antarctic ice extent data. Another conclusion is that when we weren’t accurately measuring the Antarctic ice extent it was seen to be “decreasing” and when we started measuring the Antarctic ice extent accurately, it wasn’t.

    Are you suggesting this is simply a coincidence?

    [Response: Clearly you *don't* like the result, so you'll sink your teeth into any excuse to deny the data. Sounds like a textbook example of being in denial.]

  6. Yes Tim, but not so hasty.

    We mustn’t forget the very important data available from very reliable sources such as ‘Knut’s Rough Guide to the Warm Arctic’ that demonstrate grapes growing in England and mangoes growing in Greenland, proving that the MWP was warmer than now.

  7. Michael,
    Although in some places the MWP may have been warmer, globally it is warmer than any time during the last 1000 years.

  8. the SH data is remarkable in thatit may explain some of the mid 20th century cool weather. Did Antarctic circumpolar current move southwards already back in the 50s?

  9. Thank you! Very easy to understand.

  10. Tamino, any easy to understand papers that explain the ice extent theory in the Antartic? Could it be related to Dr. Curry’s latest paper about the upwelling of warmer fresher water, so it freezes easier?

    • Or maybe it’s related to ideas put forth in papers by Manabe et al almost two decades ago??

      in response to the increase of atmospheric carbon dioxide, the excess of precipitation over evaporation increases, and surface salinity is reduced in high latitudes as noted in section 8. Thus, the static stability of the near-surface water increases and the convective mixing of cold surface water with the relatively warm subsurface water is reduced, thereby contributing to the reduction of sea surface temperature in the Circumpolar Ocean. This is why sea surface temperature hardly changes and sea ice slightly increases near the Antarctic Continent in response to the increase of atmospheric carbon dioxide.

  11. Are you suggesting ice extent is an indicator of AGW? Have you considered that NAO and AO are the significant factors in ice extent?

    [Response: Look at the graphs. Do you really believe that AO/NAO caused only minor fluctuations in ice extent for over a century, then caused it to nose-dive over the last few decades? They don't behave that way, plain and simple. The idea that it's predominantly AO/NAO is a delusion.

    Wake up. Smell coffee.]

  12. Chapman, W.L. 2008 Seasonal Sea Ice Extent Time Series. University of Illinois Polar Research Group “The Cryosphere Today” http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Chapman, W.L. and J.E. Walsh 1991 Long-Range Prediction of Regional Sea Ice Anomalies in the Arctic Weather and Forecasting 6, 271-288. http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Japan Meteorological Agency 1988 Report on 30 years of Observation of Sea Ice Technical Report of the Japan Meteorological Agency (JMA) No. 109 (ISSN 0447-3868) titled “Report on 30 years of Observation of Sea Ice” by Marine Department, JMA. Published by JMA, Tokyo, February 1988. http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Kelly, P.M. 1979 An arctic sea ice data set, 1901-1956. Glaciological Data, Report GD-5: Workshop on Snow Cover and Sea Ice Data. World Data Center-A for Glaciology [Snow and Ice], 101-106. http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Walsh, J.E. 1978 A data set on Northern Hemisphere sea ice extent World Data Center-A for Glaciology (Snow and Ice), “Glaciological Data, Report GD-2″, part 1, pp. 49-51 http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Walsh, J.E. and C.M. Johnson 1978 Analysis of Arctic sea ice fluctuations 1953-77 Journal of Physical Oceanography 9, 580-591 http://arctic.atmos.uiuc.edu/SEAICE/, accessed 12/25/2009.

    Northern hemisphere mean sea ice, million sq. km

    Year Sea Ice Origin
    1870 13.37 University of Illinois Sea Ice Dataset
    1871 13.44
    1872 13.40
    1873 13.56
    1874 13.50
    1875 13.46
    1876 13.44
    1877 13.57
    1878 13.47
    1879 13.44
    1880 13.52
    1881 13.79
    1882 13.73
    1883 13.53
    1884 13.60
    1885 13.47
    1886 13.39
    1887 13.25
    1888 13.54
    1889 13.48
    1890 13.50
    1891 13.62
    1892 13.59
    1893 13.48
    1894 13.45
    1895 13.58
    1896 13.47
    1897 13.35
    1898 13.25
    1899 13.42
    1900 13.46
    1901 13.39
    1902 13.47
    1903 13.24
    1904 13.20
    1905 13.21
    1906 13.34
    1907 13.23
    1908 13.30
    1909 13.35
    1910 13.53
    1911 13.62
    1912 13.60
    1913 13.62
    1914 13.47
    1915 13.39
    1916 13.61
    1917 13.82
    1918 13.73
    1919 13.49
    1920 13.37
    1921 13.42
    1922 13.34
    1923 13.20
    1924 13.37
    1925 13.12
    1926 13.43
    1927 13.49
    1928 13.47
    1929 13.49
    1930 13.20
    1931 13.17
    1932 13.36
    1933 13.12
    1934 13.79
    1935 13.67
    1936 13.40
    1937 13.51
    1938 13.24
    1939 13.45
    1940 12.99
    1941 13.60
    1942 13.61
    1943 13.56
    1944 13.53
    1945 13.48
    1946 13.79
    1947 13.60
    1948 13.76
    1949 13.94
    1950 13.78
    1951 13.85
    1952 13.90
    1953 13.30
    1954 13.32
    1955 13.33
    1956 13.47
    1957 13.20
    1958 13.10
    1959 13.46
    1960 12.91
    1961 13.08
    1962 13.16
    1963 13.50
    1964 13.35
    1965 13.39
    1966 13.29
    1967 13.03
    1968 13.28
    1969 13.51
    1970 13.28
    1971 13.17
    1972 13.39
    1973 12.93
    1974 12.88
    1975 12.95
    1976 13.15
    1977 13.00
    1978 13.05
    1979 12.45
    1980 12.54
    1981 12.42
    1982 12.80
    1983 12.61
    1984 12.28
    1985 12.44
    1986 12.45
    1987 12.65
    1988 12.56
    1989 12.45
    1990 12.11
    1991 12.20
    1992 12.45
    1993 12.26
    1994 12.37
    1995 11.89
    1996 12.07
    1997 12.07
    1998 12.41
    1999 12.40
    2000 12.14
    2001 12.34
    2002 12.13
    2003 12.14
    2004 11.90
    2005 11.65
    2006 11.49
    2007 10.33

  13. TimTheToolMan: Winter ice extent is strongly related to latitude. If you measure the latitude of the ice margin at just one point, you can make a very reasonable estimate of the total extent.

    This is why extent is such a useful measure: it only needs observations at the ice margin, and is robust even with sparse observations.

    Concentration is a completely different problem.

    As to your “why did the trend change around 1970-80″ – that’s no coincidence at all. That’s when the global temperature trend changed. It’s not rocket science.

    Far more interesting is the question: “why did Antarctic winter ice extent decrease so much between 1940 and 1980?” That is a period that isn’t associated with any global temperature rise. Is there a link?

  14. Just trying to learn something here and I know data is not optimal, but any correlation between ozone levels and melt?

  15. It strikes me that the Arctic data also reflects the northern hemisphere accumulation of aerosols, while the Antarctic data is much less affected by aerosols, which we know affected NH temperatures from about 1940-1975. The linear trend from 1940-2010 may be more similar than the 2nd or 3rd order curves. However, the ozone and wind isues should have a current effect.
    Tim, scientists are all about using data, as long as they can identify the biases and factors affecting results – it increases our knowledge. Why some people want to throw data away because they’re not perfect always perplexes me (actually, it doesn’t – no datum is perfect, so discarding imperfect information can be a handy strategy to avoid considering unwanted evidence).

  16. Thanks tamino for correcting my mistaken typo!

    Would it make sense to examine the East and West Antarctica separately? The part of Antarctica that is prone to melting is apparently the East (one third of all Antarctica).

    • David B. Benson

      Yes, by all means separate WAIS from EAIS (land) ice. Harder to make sense of doing that for sea ice.

      WAIS is much the more seriously prone to melting; it’ll be gone in a few millennia with CO2 concentrations now those prevailing during the Miocene.

  17. WUWT fans should please consider reading the following:

    Re Arctic Sea ice:

    Re Antarctic sea ice:
    John Cook: “The bottom line is Antarctic sea ice is a complex and unique phenomenon. The simplistic interpretation that it must be cooling around Antarctica is decidedly not the case. Warming is happening – how it affects specific regions is complicated.”



    What is of concern in the Antarctica is the loss of ice from the ice sheet, and the loss from WAIS is increasing, and there are signs that even the EAIS may now be beginning to lose ice.

    • Yes..

      It is somewhat depressing, if predictable, that skeptics will relentlessly conflate ‘Antarctic Sea Ice’ and ‘All Antarctic Ice’. There are some very disturbing aspects to the WAIS – to the extent that it may have been breaking up naturally to start with – but trying to introduce such a concept to skeptic-land is tough.

      Personally, I’d not be that surprised if a large part of the WAIS became ungrounded during my lifetime, never mind the next 1000 years.

  18. Sort of pushes back the start of the Anthropocene, does it not?

    • David B. Benson

      W.F. Ruddiman makes a good case that the Anthropocene began with the first advent of wide spread agriculture; see his popular “Plows, Plagues and Petroleum”.

      But if you are referring to the decline of Antarrctic sea ice, there are other factors involved which are poorly constrained by available data.

  19. Re: “As to your “why did the trend change around 1970-80″ – that’s no coincidence at all. That’s when the global temperature trend changed. It’s not rocket science.”

    I didn’t say 1970-80, I was much more specific. We started measuring in 1979 and that is precisely the year things changed.

    As to your comment of robust accuracy from a few locations of ice extent extrapolating to an entire content of 17,000 kms coastline, do you have evidence of that? Sea ice is highly dependent on many conditions not the least of is wind so I would suggest your argument is nonsense.

    [Response: I think the phrase "a few locations of ice extent extrapolating to an entire content of 17,000 kms coastline" tells us more about your perspective than about the data. That's a false characterization.]

    • “that is precisely the year things changed”

      I know you were overly precise. I kindly modified it to a more reasonable statement, but it seems you want to cling to the silly claim. EXACTLY 1979. Ha. It’s just not true.

      And as for the robustness of latitude measurements: this paper by Eisenman deconstructs the Arctic data. The Antarctic is even more simple, being unconstrained by geography. At maximum ice extent, the icecap is basically one big circle. Yes, wind and currents play a part. But not such a large part that we can’t get good results from sparse data.

  20. Michael: “mangoes growing in Greenland” in the MWP?!? I assume you’re being ironic? Mangoes are a tropical fruit tree, and this is the first time I’ve heard that Greenland supposedly got that warm. Plus, apparently mangoes were unknown in Europe until a mention by Friar Jordanus in 1328, which is about the same time period when the Western Settlement disappears.

    And grapes are still grown in England, actually more than ever. And the decline at the end of the Middle Ages was probably partly due to the Henry VIII’s dissolution of the monasteries, which had grown most of the wine.

    • And pineapples too you warmista.

      It’s all there in “Knuts Rough Guide” (1511 edition). Available exclusively from WUWT.

    • Nah, the grapevine in my garden clearly doesn’t exist.

      Although it’s interesting, from a British perspective, that if the Arctic sea ice vanishes then – for reasons I don’t fully understand – our winters at least could prove harsher. Goog for the garden, as we say.

  21. One of the interesting things looking at sea ice from cryosphere today, is how rare it is now for ice to form in much of the Baltic (last year was the first year in a long time that it got very far south) and other peripheral areas.

  22. TimTheToolMan

    ” I think the phrase “a few locations of ice extent extrapolating to an entire content of 17,000 kms coastline” tells us more about your perspective than about the data. That’s a false characterization.”

    Not at all Tamino, I was responding to a specific statement, namely

    ” If you measure the latitude of the ice margin at just one point, you can make a very reasonable estimate of the total extent.”

    Do you also agree with this suggestion?

  23. The Antarctic data is fairly obviously near-useless prior to 1960. You only have to look at the long periods of constancy to see this – I think you should have emphasised that point rather more clearly. You have almost implied that the long constant periods are actually averages over that period. But (from memory) they aren’t: they reflect a very very few measurements from a few years in a span of decades. For the Antarctic winter data there may well be almost no data at all. Unless you’ve carefully looked at the sources, you shouldn’t even plot the data, or at the very least you should grey it out: e.g. http://en.wikipedia.org/wiki/File:Seaice-1870-part-2009.png. The same is true to a lesser extent for the NH data; the 1940-45 data is obviously just constant.

  24. Oh, but I should have said: that is only a fairly minor criticism. Otherwise, good post, and keep up the fight against Watts lies and disinformation.

  25. Great post. Thanks.

    As much as I despise Watts, I find this kind of post much more informative and useful.

    Please Tamino, save your energy and talent to things and people that deserve it.

  26. The new (to me) 1940 to 1979 data are fascinating. The winter max ice should largely be controlled by surface air temperature since the ice freezes from the top down. The antarctic ice winter max decreased by about one third during this period, and the HadCRUT temp data base for that region during that period does show a substantial surface air temperature warming trend. Conversely, the arctic ice winter max increases slightly during that period, and temperature data for that region show a cooling. So far so good.

    The summer ice minimum trend however may be largely controlled by sea surface temperatures, as almost all of the ice is submerged and in contact with water, i.e., the ice melts largely from the bottom up. The antarctic summer ice minimum extend dropped about 50% during this period, suggesting warm ocean waters. The arctic summer ice minimum extent also dropped, about 20 to 25 %, during this period when air temperatures were falling.

    The data suggests that long term trends in sea surface temperature may diverge from surface air temperatures, and may control summer ice minimum extent.

  27. Talking about Watts: he did some exciting calculations showing a divergence between IJIS and NSIDC September average extent numbers, but he seems to have some trouble with his spreadsheet. If he’s doing the calculations for his NOAA-deception-surface-stations-project, it’s no wonder it is taking so long to finish.


  28. My link is not working. You should check the last Sea Ice News (#27).

  29. steven mosher

    Thanks for reminding me about hadisst, A while back I was looking into it and then got focused on some of the sources for that data which is huge undertaking.

    looking at how they did the following would be cool:

    “The sea ice fields are made more homogeneous by compensating satellite microwave-based sea ice concentrations for the impact of surface melt effects on retrievals in the Arctic and for algorithm deficiencies in the Antarctic and by making the historical in situ concentrations consistent with the satellite data.”

    As there were no data at all for
    September – March 1901 – 1956, sea ice concentrations in
    the marginal ice zone in these months were temporally
    interpolated using available data for the summer half of
    each year, along with observed temporal intermonthly
    autocorrelations of sea ice concentration [Walsh, 1978]

    [17] Before the advent of satellite-based imagery in 1973,
    sea ice concentration data for the Antarctic are not available,
    and sea ice extent data are not readily available for indi-
    vidual months, seasons or years, although some visible and
    infrared data do exist for 1966 – 1972 [Zwally et al., 1983]
    and some undigitized charts reside in national archives (e.g.,
    V. Smolyanitsky, personal communication, 2002). Readily
    available information was limited to two historical clima-
    tologies of sea ice extent. Therefore our sea ice concentra-
    tion analysis before 1973 is derived indirectly, and does not
    include any interannual variability, though there are some
    trends resulting from the differences between climatologies
    for different period.

    Don’t get me wrong. The arctic is melting. AGW plays a role. it is alarming. action must be taken.

    • Don’t get me wrong. The arctic is melting. AGW plays a role. it is alarming. action must be taken.

      Write a book about it.

      • Philippe Chantreau

        “Write a book about it.”
        Good idea. You believed one should be written about that climategate thing. In your own words, this seems to be a much more worthy goal for action, so go ahead. It would be good to advertise it on WUWT too.

  30. David B Benson,
    The implications of Ruddiman’s analysis are scary. IF the doings of pre industrial, agricultural, man are sufficient to stop or slow down the decent into an ice age; then what will be the result of all the cr@@ we have shoved into the atmosphere?

    While the interpolation of historic data is sometimes problematic, it is a worthwhile exercise. It also tends to show global warming has been going on a little longer than generally accepted.

    • David B. Benson

      The orbital forcing which might have trigged a glacial about 2000 years ago was mighty small. So small and yet large enough that there is nothing in the Antacrtic ice core records to compare it too. So Ruddiman might be right but again, might be wrong. He has some further papers about it coming out soon which I intend to read.

      As for current and forecast conditions, CO2 concentrations are now as high as during the Miocene, with sea stands tens of meters higher than now. Other than that, I encourage reading Mark Lynas’s “Six Degrees”:

      • I actually don’t know how to take ruddiman’s argument. My understanding was that he was comparing to the wrong interglacial… That procession and tilt are antiphased which makes them unlike 400,000 years ago…

  31. Louis Hooffstetter

    I read that Anthony Watts extended an invitation to you to post an article on WUWT. You should definitely take advantage of this opportunity. Readers of both ‘Open Mind’ and ‘WUWT’ would be well served by a cordial exchange of data and opinions. I welcome your guest post and sincerely hope you accept his offer.

  32. I hate to praise Watts, since everything said about him here is pretty much true, but he does occasionally show signs of fair play. I was able to post extensively on greenhouse and GW physics for a while. He may be, like Tiberius Caesar, “Easily tempted to virtue.”

    • Actually, Watts uses the “fair play” to claim the higher moral ground: “See, *I* allow dissenting voices!”

  33. When discussing artic ice, shouldn’t ice covered lakes be included as well? This might remove some of the bias caused by artic ocean geography. For example, the Great Lakes. Although this is freshwater, there should be some sort of latitudinal trend that maybe enlightening. Does anyone have a good link to graphed data?

    [Response: The great lakes are included in most data sets.

    An article about latitudinal response is discussed here.]

  34. Fine, but the Great Lakes are far, far south of the Arctic by any definition. Obvious, perhaps, but. . .

  35. Halldór Björnsson

    There are some interesting data from the marginal ice zones that can give some perspective on this. In Iceland there is the Koch sea ice index which extends back at least two centuries, and for the GIN sea (east of Greenland) there is the Vinje index, which covers most of the 20th century. It is clear that sea ice was more persistent in Icelandic waters in the 19th century and the early 20th than subsequently. There were episodes with sea ice in the late 60s and again towards the end of the 70s, but since then there has not been any ice to speak of. In the GIN sea I think the story is similar, the current extent is anomalously low. How many hundreds of years you have to go back to find similar conditions as are observed now, I don’t know. Andrews et al (http://hol.sagepub.com/content/19/5/775.full.pdf+html) say about 800, but I’m not sure that is generally accepted.

  36. The Antarctic decline seems to cease about the same time as the ozone hole really gets serious. I do not believe the two are unrelated, with a strengthened SAO playing a big role.

    I think it would be a valuable exercise to model Antartic ice from 1950 onwards without any ozone depletion and see what the result is. Does anyone know if such a study has already been performed?

    I am trying to get my head around what an extra 8 million sq km extent looks like. It’s simple to approximate the ice as a circular area, subtract mainland Antarctia from it.

    You see that an extent of 28m sq km would have an ice front approximately 400km further north than an extent of 19m sq km, if I did the maths right. This is more than I expected and really puts the recent slight increase into perspective.

    • I’m not sure that Antarctic ice models are good enough for that yet. Or is that perception just misinformation from Judith Curry? She certainly clouds any issue she gets near.

    • Stu N,

      I’ve wondered the same thing.

      Ozone depletion cools the (lower) stratosphere over the south pole. For the north pole the Arctic Oscillation (Northern Annular Mode) changes in the NAM propogate down from the stratosphere (Mentioned in a paper – IIRC Rigor or Thomson as a personal communication). I’ve not read so much about the Antarctic but it seems not unreasonable that the Southern Annular Mode is like the NAM in that changes propogate from the stratosphere, and as the ozone hole over Antarctica cools the stratosphere it affects sea ice extent by impacting the SAM.


      Just found this on a quick google: http://www.agu.org/journals/ABS/2009/2009GL037524.shtml
      Which refers to “non-annular atmospheric circulation change” which seems to argue against what I said above. However I can’t find a paywall-free pdf to find out more.
      And this:
      Is a modelling study suggesting processes other than the SAM are responsible for the increase in Antarctic sea ice.

  37. Another two broken links to O.M. posts:

    What’s up with that (sorry), Tamino?

  38. And it looks like Greenland’s inland ice melt is accelerating.


    “New calculations show that the amount of melted inland ice in Greenland is 25-50% higher in 2010 than normally
    “It is my assessment that we have had the strongest melting since they started measuring the temperature in Greenland in 1873,” he said.”

    CP has more: http://climateprogress.org/2010/10/24/greenland-melting-noaa-2010-arctic-report-card/

  39. Leonard Weinstein

    I think you keep forgetting the carbon particles effect, which is thought to cause 1/3 or more of the recent enhanced melting.

    • Leonard Weinstein,
      No, no on is forgetting balck carbon. However, have you ever looked at dirty snow closely? The carbon causes localized heating, so, not only does it cause local melting, it also transports downward. So the effect is not cumulative. It depends on current flux of carbon. That’s why you don’t see a black surface.

      The point is that the higher temperature exacerbates the effect of the black carbon as well.

  40. Yes, Jimbo, people are aware of the WUWT site, and of the fact that people like you and Anthony take false comfort in the fact that during a significant chunk of the Holocene it was warmer than today, leading to a lot of ice melting, not just in the Arctic basin but on land, as well, causing sea levels to rise dramatically.

    Of course, the fact that sea levels rose 35m during this period of time didn’t impact New York City, therefore if it happens again, it couldn’t impact New York City, right? That’s the kind of thinking you’ve got going in your mind, eh?

  41. Leonard Weinstein

    Sorry for a late reply. Where did you get the idea that sea level rose 35 m during the warmer part of the Holocene. It rose more than that going from the glacial period to the Younger Dryas (about 120 m), and may have risen about 24 m to 36 m from the Younger Dryas to the Holocene, but has only slowly varied during the Holocene, with variation less than 1 m over the last 6,000 y. I don’t think NYC is in any danger.

  42. “I don’t think NYC is in any danger”

    I think that you will find sea-level variations around or greater than 1 meter when we have a better understanding of holocene dynamics. Grinsted et al. (2010) show that the sea-level by the end of the MWP was likely 12 to 22 cm (I think) greater than the current sea-level showing a greater sensitivity than I think you are insinuating. Before you jump the gun and call that evidence for a warmer MWP, you should not that the authors also note that we need no additional warming to nearly double that amount of rise by 2100.

    Another thing you have to consider is that the Holocene Hypsithermal did not happen synchronously throughout the planet. That is an important consideration with all of this. Ice-sheets were still present in much of the Northern NH long after they receded from their maximum extents and they initiated ice-feedback mechanisms that controlled much of the climate in the region. This is an important thing because it is essentially explaining the lack of synchronous warming throughout much of the hypsithermal despite the clear insolation trends.

    The current warming is far different. It is fast, it is synchronous, and the ice sheets are responding very quickly. NYC may not drown but depending on which ice sheet loses the most mass (for gravitational reasons) there are reasons to be worried about how much water could raise in the regions. Globally the best estimate is 0.9 to 2 meters but localized sea level rise is very dependent on which pole loses the most ice…

  43. And then the narwhals dove down and came up, with a little temperature sensory backpack. 1C underestimation in Baffin regional climate models. http://www.newscientist.com/article/dn19658-arctic-narwhals-reveal-climatemodel-errors.html

  44. Stan Yeaman

    Fascinating, but wrong. I looked over the Univ. of Svalbard’s display in 2010 at Longlearbyren, Spitsbergen which shows satellite images over the entire Arctic every four seasons for the past ten years. When you compare ‘oranges with oranges’ and not ‘oranges with apples’, ie summer minimum with summer minima over ten years, I could not see any sign of sea ice retreat. Please note that, even in mid summer, 2010, our ship had to smash through many kilometres of sea ice to get to Longyearbyren, the capital of Svalbard on the island of Spitsbergen, Norway.

    [Response: Is this an attempt at a joke?

    Even restricted only to the last 10 years, the decline of the Arctic summer minimum sea ice is both visually obvious and statistically undeniable. Unless, of course, you're in denial.

    This post begins "Nobody in his right mind disputes that since satellite observations began, the extent of sea ice in the arctic has declined dramatically." Perhaps that explains your disputing it.]

    • Please note that, even in mid summer, 2010, our ship had to smash through many kilometres of sea ice to get to Longyearbyren, the capital of Svalbard on the island of Spitsbergen, Norway.

      Stan, you’ll have to be more specific. What was the exact date? Did you come from the South?

      You see, I found a MODIS satellite image from July 6th 2011 and I don’t see any ‘kilometers of sea ice’ that you would have to smash through to get to Longyearbyen. Instead of ice I see a lot of algal blooms in Isfjorden, the fjord on the southern side of which lies Longyearbyen.

      This isn’t a surprise as Longyearbyen can usually be reached from the South already around this time of year. That this is so is shown clearly on this image I made for a recent blog post on the situation with the Arctic sea ice between Franz Josef Land and Svalbard. Sure, there might be some sea ice left in Isfjorden right now, but it’s very thin, dispersed and gone by mid-summer.

      Stan, I hope you have an explanation, or else I will have to conclude that you were lying to influence people how you see fit. They love that on WUWT, but not here.

      • Bernard J.


        You see, I found a MODIS satellite image from July 6th 2011 …

        you’re messing with Yeaman’s mind, aren’t you? ;-)

  45. Please note that, even in mid summer, 2010

    The minimum is, of course, reached in September.

    Decreasing Arctic sea ice minimums in September does not imply that a particular place in the planet must be ice free in mid-summer. Or September, for that matter.

  46. Umm, I think you meant “July 6th of 2010,” Neven.

    You are quick with Arctic news, but not that quick!

    Very interesting images, though–and it’s interesting, too, that Mr. Yeaman happened to misspell the name of the capital he visited.

    At any rate, let me fulfill one of my roles in life, which is to point out the obvious. Whatever Mr. Yeaman’s eyes may tell him, actual measurement of sea ice extent–”apples to apples” for the month of the minimum, which as dhogaza points out is September–shows an unequivocal decline over the last 10 years:


    My eyes say it could fairly be called “dramatic.”

    • Umm, I think you meant “July 6th of 2010,” Neven.

      Woops. :-B

      On the other hand, I don’t expect the image to look radically different this year, except for some more algal blooming perhaps. Mr. Yeaman could go to Longyearbyen in a kayak.

      • And the increasing Arctic algal blooming not to be understood as a good sign for the environment, should denyloose get any notion as were it. [they can find their own citations, now can they ;>]

  47. Actually, it’s ironic that Mr. Yeaman picked the last 10 years for his example. If you were to calculate the trend for that period, the decline would be way steeper than the longer term trend shown on the graph I linked, since extent in 2001 happened to be relatively high. (And of course, the last four years have been lower than any other years in the record–three of them much lower.)

    Not really significant, but definitely ironic.

    • Being a follower of the Extreme High Horizon Refraction blog http://www.eh2r.com/ , wonder if it was a mirage that created this impression of km after km of sea ice.

      EH2R has a nice item up on fragile sea ice up against Ellesmere… something not seen before up there.

      Courtesy DMI Polar NOAA AVHRR 2011-03-03 04:20 UT Amazing image for any with Arctic observation experience. Over the last 25 years this never happened. It is a sure sign of record thin ice. It very much appears like loose pack ice compared to adjoining older thicker ice. The proximity to Ellesmere of the zone where ice shatters and joins the North Atlantic was always at the North-East corner of Greenland. I dont recall seeing this kind of active ice so near to Canada by way of Northern Greenland even in the summer! The winds from multiple cyclone incursions over the Arctic Ocean also played a role.