Danish Sea Ice Maps from Early 20th Century

February 20, 2016



I’ve had these on my hard drive for years, can’t believe I never thought to make the animation. Now someone has. Here it is.

The Danes know ice, and in the early 20th century, there was enough traffic of merchant, military, and fishing boats in the arctic to have a reasonable, first-hand observation view of ice extent in the arctic, from the Danish Meteorological Institute – which can be downloaded here.   Simple enough to compare to recent satellite measures.

Amaze your friends and neighbors!

Gerg’s Net:

The animation is drawn from the Danish Meteorological Institute’s sea ice maps for August in each year from 1920 to 1939.  The red marks show actual records of ice conditions and the white area is the inferred ice extent. The last image is the US National Snow and Ice Data Center’s satellite-derived sea ice concentration image for August 2012.

There’s also the historical sea ice extent compilation by Walsh and Chapman at the US National Center for Atmospheric Research / University of Illinois (as plotted at Cryosphere Today):

History of seasonal sea ice 1900-2010, NOAAMore Below.

Current ice from NSIDC:




18 Responses to “Danish Sea Ice Maps from Early 20th Century”

  1. Tom Bates Says:

    It looks like the ice started decreasing in 1950. What changed at that time?

  2. Tom Bates Says:

    Your image of the global mean CMIP5-all forcing has the temperature not rising from 1939 to about 1980 yet your chart in this post shows warming from 1950, The arctic seems to have been melting 10 or more years after the hiatus in warming began and 30 years before it ended. Something else than CO2 induced warming is going on.

    • MorinMoss Says:

      There was no “hiatus” in warming, only a slowing of the rise in surface temps.

      “Something else than CO2 induced warming is going on.”
      While there are still many things we don’t know precisely, what IS known is that the areas where warming happens varies over time.
      So even in otherwise warm years, you may see an increase in polar ice.

      That’s why it’s called GLOBAL warming, not warming-only-where-you-give-a-damn

    • grindupbaker Says:

      I think the bigger question from that ice extent plot at that time is not why the extent dropped precipitously by 13% 1952-1953 but why the extent rose 9% for a period of 7 years 1945-1952 before dropping back down the 9% and overshooting an additional 4%. Some weather thing, oceans & atmosphere fluctutations, for 7 years. Certainly nothing to do with GMST change over such a teensy period as 7 years. The AMOC was essentially +ve 1926-64 but it was down at ~zero 1946-51, not exactly overlaying the 7-year period but close. Maybe a few years of cooling due to AMOC change, then re-warmed back to the overall trend line. A NOAA paper by Alan L. McNab & Thomas R. Karl has “Maps of the October average height of the 700-millibar pressure surface and the anomalous height of the surface for October 1952 (fig. 3) and the June average height of the 700-millibar pressure surface and the anomalous height of the surface for June 1953 (fig. 4) are presented to show the position of atmospheric anomalies that occurred during the well-documented drought of 1952-54”. Much more exciting than NOAA and short weather things, I have a photo of my dad holding me in my blanky March 1953 in London at Fred’s wedding and I recall it was snowing the next morning, changing the dull Paddington streets at uncle Art’s place. Snow was moderately uncommon. I was very excited. Some weather thing.

      • dumboldguy Says:

        All very interesting but irrelevant, since Master Bates neither seeks truth nor understands the science of what you have outlined. He is “commenting” here only to confuse those who may not understand the science and obfuscate the truth. DNFTT.

        • Harry Twinotter Says:

          “Master Bates” 🙂

          • dumboldguy Says:

            “Master Bates” 🙂 indeed!

            Perhaps you missed the thread where some other Crocker hung that label on our boy Tom. I think it is a perfect fit for him and use it whenever appropriate, which is nearly every time he comments. Considering the WUWT-like behavior he displays when he visits here from his home over there, it is also fitting—-since WUWT is the home of the biggest climate change denial circle jerk on the planet.

    • Harry Twinotter Says:

      Tom Bates.

      You appear to be repeating the “anything but CO2” climate change denier talking point.

      The CMIP5 curve is a GLOBAL average of air temperature. The ice charts show Northern Hemisphere sea ice extent. These are two different physical processes and two completely separate data sets.

      The sea ice extent thru 1950 looks flat to me, the downward trend starts in the 1970s or 1980s. The only way to tell is to get the chart data and draw trend lines.

  3. Magma Says:

    Meanwhile, overheard at WUWT…

    Larry: “You’ve got to squint real hard to see the rebound.”

    Curly: “I’ve got it! Just turn the graphs upside down!”

    Moe: “Genius. Sheer genius.”

  4. dumboldguy Says:

    We must always remember that the deniers try to confuse the issue by using data for the EXTENT (surface area) rather than VOLUME (total quantity) of the arctic ice, and have always tried to make a big deal out of any upward year-to-year fluctuations.

    The five line plot by seasons illustrates that, yes, it gets cold in the winter in the arctic, and because of that the winter extent hasn’t declined much, as well as the fact that it has been getting progressively warmer in the summer and the summer extent has been dropping most rapidly.

    None of the graphics show that the multi-year ice is in rapid decline and that the volume of the ice sheet is therefore continuing to drop at a more rapid rate than the extent. Once we have ice-free summers, we will no longer have any multi-year ice. Ice will still form in the winter, but it will be thinner, have a smaller extent as the arctic warms even more, and not last as long—-the positive feedbacks from that are worrisome.

    • grindupbaker Says:

      Apparently the surface area of ice could be far less than the “sea ice extent” measurement (I haven’t a clue how one would find out how much less in any particular instance) because the convention is to measure how much ocean area has >15% ice by area in it and for any with >15% ice that entire piece of ocean is included as part of the “sea ice extent”. Dr. Jennifer Francis (I think, or perhaps another Dr.) has a video showing what she called “decrepit” ice (or some similar word) floating around in thousands of pieces with a fellow standing on one doing some sciency thing. She said the entire area was included as part of the “sea ice extent” (>15% ice ).

    • pendantry Says:

      Ice will still form in the winter, but it will be thinner, have a smaller extent as the arctic warms even more, and not last as long—-the positive feedbacks from that are worrisome.

      Am I wrong to believe that the word ‘worrisome’ is too gentle? As I understand it (I could be wrong), when the ice is gone, isn’t it going to be like careening down a mountainside road with failed brakes?

      • dumboldguy Says:

        I was trying not to sound like too much of a “doomer” by using “worrisome” rather than more McPherson-like language, but as redsky says, “you don’t need a crystal ball, just a little imagination” to see where things are likely headed.

        It’s one of the known unknowns that the guys with super-computers are seeking to understand, but an arctic ocean that is covered with much less ice for a much shorter part of the year can’t help but soak up more solar radiation and warm up. What impact that will have on Greenland ice sheet melt, permafrost melt, clathrate disintegration, and SLR is obvious, but it’s anyone’s guess as to the time line. IMO, we could be passing some major tipping points within 10 or 15 years (if we haven’t already done so), and that’s when we will begin “careening down a mountainside road with failed brakes”.

  5. redskylite Says:

    Brilliant illustration of how astonishingly quick the ice sheet is diminishing, l admire the skill, care and detail put into those classical maps, just picture what it will look like in another 100 years and what the effects on the climate will be. You don’t need a crystal ball for that, imagination and maybe a little help from a super-computer can work that out.

  6. This provides an excellent rebuttal to one boringly persistent denialist claim based in a 1922 press report about warm waters around Spitzbergen. Clearly not so exceptional after all. There’s quite a lot of year to year variability among those early 1920s-30s charts but there was obviously a lot more coverage back then than in recent years.

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