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Long Term Perspectives For Arctic Sea Ice

February 20, 2016
tags:

By Paul Homewood 

  

h/t Pethefin

 

 

Map showing maximum (April) sea ice extension in the Atlantic sector of the Arctic (Norwegian Polar Institute 2000). The map is based on a database on sea ice extension in the area shown during the past 400 years, to a high degree based on written records found in ships logbooks.

http://www.climate4you.com/SeaIce.htm#Sea

 

 

While we get excited about short term changes in Arctic sea ice extent, it is worth looking at some of the movements back and forth over the last 300 years. The above map is courtesy of

the sea ice database established at the Norwegian Polar Institute by Torgny Vinje.

Note how far sea ice expanded between 1769 and 1866. Unfortunately, nothing is shown for the warm period in the 1930s and 40s, but HH Lamb records, in Climate, History and the Modern World, how sea ice greatly expanded in what the Icelanders call the Sea Ice Years, beginning in 1965:

 

The cooling of the Arctic since 1950-60 [bear in mind the book was published in 1982] has been most marked in the very same regions which experienced the strongest warming in the earlier decades of the 20thC, namely the central Arctic and northernmost parts of the two great continents remote from the world’s oceans, but also in the Norwegian-East Greenland Sea….

A greatly increased flow of the cold East Greenland Current has in several years (especially 1968 and 1969, but also 1965, 1975 and 1979) brought more Arctic sea ice to the coasts of Iceland than for fifty years. In April-May 1968 and 1969, the island was half surrounded by ice, as had not occurred since 1888.

Such sea ice years have always been dreaded in Iceland’s history because of the depression of summer temperatures and the effects on farm production….. The 1960’s also saw the abandonment of attempts at grain growing in Iceland, which had been resumed in the warmer decades of this century after a lapse of some hundreds of years…

 

Clearly there is nothing “normal” about the period when satellite measurements of Arctic ice began.  

 

 

 

FOOTNOTE

Neven points out that there is some confusion about the 1769 line on the map. Whilst the Norwegian Polar Institute state it is for April, another paper by Isaakson et al label it as August.

 

I have just posted further clarification on this matter here.  

74 Comments leave one →
  1. February 20, 2016 2:21 pm

    Yes the Nordic Seas are key since 90% of the water entering the Arctic comes through the North Atlantic. And the Danes, Norwegians and Russians have been charting ice there for centuries. Vinje also provides this chart (included in IPCC TAR:

    • AndyG55 permalink
      February 20, 2016 7:45 pm

      There was a thing called the Little Ice Age, the coldest period in the last 10,000 years. !

      Plenty of evidence that during the first 3/4 of the Holocene the Arctic was often pretty much ICE FREE in summer. !

  2. mike fowle permalink
    February 20, 2016 3:06 pm

    My hero is H W Tilman who sailed his Bristol Channel pilot cutters into Arctic waters during the 1960s. As they were not strengthened for ice the state of the sea ice was crucial and differed widely from year to year – meaning that some years he was completely thwarted in his ambitions and at others much more successful.

  3. David Richardson permalink
    February 20, 2016 3:34 pm

    An interesting article (IMHO) at WUWT back in 2009

    http://wattsupwiththat.com/2009/06/20/historic-variation-in-arctic-ice/

    I did read a comment, perhaps at your website Ron Clutz a few weeks back, with quotes of alarm at the turn of the 20th century about disappearing Arctic sea ice then.

    We also know that the Danes got to Greenland a millennium ago and were driven out by climate change a few hundred years later. Receding glaciers in Greenland have uncovered 1000 to 2000 year old tree stumps.

    The idea that it has all being fine until 1979 is simply ridiculous.

  4. February 20, 2016 3:51 pm

    David, I am currently reading through CLIMATE CHANGE in EURASIAN ARCTIC SHELF SEAS–Centennial Ice Cover Observations, by Frolov et al. 2009.

    I came across this passage pertaining to your point above.

    “Thus, after the ((Arctic warming epoch** in the 1920s-1940s, some concern about the consequences of continued global warming was expressed (Budyko, 1969). However, the average temperature in the northern hemisphere began to decrease beginning in the middle of the twentieth century. This gave rise to concern about the possible extended continuation of this process (Gribbin and Lamb, 1978). Based on analysis of changes in ice conditions and air temperatures in the Arctic from the end of the 1960s to the mid-1970s, Volkov and Zakharov (1977) predicted further cooling and increased ice cover area in the Arctic Seas up to the 1990s. It was supposed that climatic and ice conditions by that time would approximate those that were observed in the Arctic at the beginning of the twentieth century.”

    “But, again, nature prepared a surprise: a new warming event began in the middle of the 1970s, and by the middle of the 1990s Arctic ice conditions were the mildest of the twentieth century. The scientific community again emphasized the implications of ((global warming** and predicted its catastrophic consequences. Published predictions range from the complete disappearance of Arctic Ocean ice to the onset of a new glacial epoch within a restricted time frame. All of these studies ignore natural hydrometeorological fluctuations, which, as this monograph shows, contribute to multiyear variability and can exceed by many times the anthropogenic impact on climate. This monograph is devoted to investigating the manifestations of natural fluctuations of sea ice extent and of other characteristics of climate on varying scales.”

  5. February 20, 2016 6:17 pm

    Reblogged this on Climate Collections.

  6. February 20, 2016 6:34 pm

    Hello again Paul,

    If you recall we went over all this not so very long ago:

    http://GreatWhiteCon.info/2015/04/gross-deception-measuring-arctic-sea-ice-trends/

    wherein you will find this graph, kindly provided by the NSIDC:

    • David Richardson permalink
      February 20, 2016 7:16 pm

      You seem like an expert Jim, so can you explain how the early anomalies were derived – or are you just going to insult me as you have others?

      • February 20, 2016 7:29 pm

        Who have I ever insulted David? You surely must know the drill.

        A learned paper or two, or at the very least a link to some evidence.

    • AndyG55 permalink
      February 20, 2016 7:31 pm

      Your great big CON site again , Hey Jimbo.

      Still way more Arctic sea ice than the first 3/4 of the Holocene, isn’t there Jimbo

      Still pasting those lies from the pre-satellite era I see when Its known that sea ice was far less at times.

      Still refusing to note anything about the AMO and the fact that we have just passed the peak, and that the Arctic sea ice is pretty much exactly where you would expect it to be for the phase of the AMO.

      Still one big CON from you, isn’t it Jimbo !!

      You still have to ADMIT THE THRUTH, that Arctic sea ice is still ANOMOLOUSLY HIGH compared top all but the last few hundred years of the last 10,000 years.

      ADMIT IT or STFU !!!

      • David Richardson permalink
        February 20, 2016 7:47 pm

        Jim Hunt – well I see it was to be the insult, but then I guess I expected that.

      • February 20, 2016 7:55 pm

        David,

        Why do you interpret my (virtual) words as “an insult”?

        How would you characterise Andy’s outburst?

      • AndyG55 permalink
        February 20, 2016 8:31 pm

        You are the one with the CON site. !

        Admit the truth.. sea ice is anomalously HIGH compared to the first 3/4 of the Holocene.

        You can’t admit that truth, can you. !

      • February 20, 2016 9:08 pm

        Andy,

        What “lies from the pre-satellite era” would those be? As I’ve just explained to Paul, that NSIDC graph seems to me to tie in with his narrative in the OP.

        Given that the sort of hostility you display towards me is known to be associated with fear, what is it about all this that scares you so much?

      • AndyG55 permalink
        February 20, 2016 9:13 pm

        Still too AFRAID to admit the truth about Arctic sea ice, hey Jimbo.

        So Sad..

        So PATHETIC.

      • AndyG55 permalink
        February 20, 2016 9:18 pm

        Everyone can see you slithering and sliming , trying desperately to avoid admitting that for most of the Holocene (except the LIA) Arctic sea ice was much less than now.

    • AndyG55 permalink
      February 20, 2016 7:48 pm

      I guess the IPCC were wrong yet again

      • February 20, 2016 8:04 pm

        Why do you say that Andy?

        To my ageing eyes at least, it looks like the NOAA (IPCC as you call it) and NSIDC graphs both show a dip in 1974/5.

      • AndyG55 permalink
        February 20, 2016 8:17 pm

        ipcc graph has 1976 well below 1985..

        This is changed, of course, in your fabrication.

      • AndyG55 permalink
        February 20, 2016 8:18 pm

        You still have the big TRUTH about Holocene sea ice levels which you REFUSE to admit to.

        Cowardly, to say the least.

      • Pethefin permalink
        February 21, 2016 8:30 am

        Andy, take a look at the IPCC graph from the 1996 report,
        where the 1974 is still clearly below the 1996. It was not until the 2001 report that IPCC came up with “reanalysis” with help of the sea-ice from the Great Lakes (!) and was able to make the problem go away just as they did with the MWP. Post-normal science.

    • February 20, 2016 8:31 pm

      NSIDC? Are you serious? Run by Mark Serreze?

      Do you deny that the 1970s were the coldest decade by far around most of the Arctic for the best part a century?

      Do you deny this graph?

      • AndyG55 permalink
        February 20, 2016 8:33 pm

        He refuses to admit the truth about the first 3/4 of the Holocene..

        why would he admit to any other truths. ?

      • AndyG55 permalink
        February 20, 2016 8:35 pm

        here’s unadjusted Reykjavik temps vs the AMO

      • AndyG55 permalink
        February 20, 2016 8:37 pm

        Here’s the NH sea ice extent flipped vs the AMO

      • AndyG55 permalink
        February 20, 2016 8:40 pm

        Here’s the current position on the AMO.

        Blue shading is the 1980-2010 average
        pink is an approx. of the 1sd region

        Arctic sea ice is almost exactly where it should be for the phase of the AMO.

      • AndyG55 permalink
        February 20, 2016 8:44 pm

        Gees Paul.. doesn’t the LIA stand out on that graph…

        and look… before that.. very little sea ice.

        The TRUTH will out, even if others are too scared to admit it.

      • AndyG55 permalink
        February 20, 2016 8:52 pm

        And here is the glacial progression for Mt Roosevelt glacier

        Again , that low point in 1979.

      • February 20, 2016 9:01 pm

        What have you got against Mark Serreze Paul? He struck me as very pleasant on the few occasions that I have spoken to him.

        Your quote above says “In April-May 1968 and 1969, [Iceland] was half surrounded by ice”. That period is also a peak on the NSIDC graph, so what exactly are you quibbling about?

      • February 20, 2016 11:29 pm

        Do you deny that the period from the mid 1960s to early 1980s were the coldest in Iceland & Greenland, and indeed much of the Arctic, since the early 20thC?

        And are you aware that temperatures in recent years there are no higher than the 1930s and 40s?

    • February 21, 2016 10:54 am

      Jim

      Can I just point out that neither your original graph, comment, or as far as I can see later comments have the slightest relevance to my article.

      Did you actually read it?

      • February 21, 2016 11:06 am

        Allow me to refresh your memory then Paul:

        “Sea ice greatly expanded in what the Icelanders call the Sea Ice Years, beginning in 1965”

        “Clearly there is nothing “normal” about the period when satellite measurements of Arctic ice began.”

        I take it I am correct in my assumption that you wrote those words that I read?

      • February 21, 2016 1:11 pm

        And all you have shown is a graph from 1953, which has nothing to say about the long term historical changes I have posted about, or about what Lamb says about the sea ice years.

        You have simply cluttered up the comment thread. Any more irrelevant comments will be binned.

      • Pethefin permalink
        February 21, 2016 1:36 pm

        Thank you Paul, I would recommend you to keep strict policy on trolls, personally I have grown tired of websites infected this trolls hick-jacking threads with mindless AGW-religious crap.

  7. AndyG55 permalink
    February 20, 2016 8:29 pm

    A little film that everyone should watch to get a REAL long term perspective.

  8. Ben Vorlich permalink
    February 20, 2016 8:52 pm

    There’s an interesting map of summer arctic sea ice extent during WW2. Important for the Russian convoys,

    http://omniatlas.com/maps/arctic/19421231/

    The position of PQ17 is shown in the map here with ice extent
    https://en.wikipedia.org/wiki/Convoy_PQ_17

    December 1942, convoy JW51B track and sea ice included:
    http://forum.worldofwarships.com/index.php?/topic/7353-december-31-focus-battle-of-the-barents-sea-happy-new-year/

    Convoy QP11 May 1942 track and sea ice
    http://www.qalypso.co.uk/node/357

  9. Lawrence Martin permalink
    February 21, 2016 12:41 am

    Andy
    What is with all the anger towards Jim Hunt?

    • AndyG55 permalink
      February 21, 2016 1:23 am

      He is a deliberate LIAR and CON-MAN, who over the course of 2-3 years has refused to admit the truth about Holocene Arctic sea ice.

      He just keeps pushing is deliberate mis-representation without any thought for the truth.

      .. he is a TRULY DISHONEST and slimy piece of **** !!

      • February 21, 2016 9:40 am

        For an extremely topical example of (deliberate?) mis-representation about Arctic sea ice why don’t you take a long hard look at this Andy?

        http://GreatWhiteCon.info/2016/02/gross-deception-about-dmis-missing-graph/

        Then explain to me once again who is in actual fact “a deliberate LIAR and CON-MAN”, to use your delicate turn of phrase.

      • Pethefin permalink
        February 21, 2016 9:44 am

        Andy, please stop feeding him.

      • February 21, 2016 10:57 am

        Yes Andy,

        Whatever else you may do, do not ever, ever feed the trolls:

        http://GreatWhiteCon.info/2014/09/david-roses-apocalyptic-vision-of-al-gores-nobel-lecture/

        Especially if you’re afraid that they might bite:

      • AndyG55 permalink
        February 21, 2016 9:53 am

        Your deliberate deception and mis-information is in ignoring the LIA, the dip in global temperatures in the late 1970’s, the effect of the AMO and the fact that for the first 3/4 of the Holocene there was often zero summer Arctic sea ice.

        You have yet to admit to these facts, and continue to base your scam and lies on a very short period of history.

        It is intentional DECEPTION of the worse sort.

        You are a CON-MAN and are deliberately mis-informing all that would be stupid enough to read your con web site by failing to show the REAL and full history of Arctic sea ice.

        If you did that, people would realise that Arctic Sea Ice is actually still anomalously HIGH compared to historic values, except of course as we come out of the COLDEST period of the last 10,000 years.

        Tell the WHOLE TRUTH..

        …or be forever marked as the con-artist and a liar that you are.

      • AndyG55 permalink
        February 21, 2016 9:54 am

        Pethefin.. the people feeding him are the climate troughers at Exeter Uni.

      • AndyG55 permalink
        February 21, 2016 10:00 am

        Pethefin, Are you saying we should let his mis-information stand without correction?

        I’ve said enough for people to see exactly what he refuses to admit, and to do their own homework.

        I agree.. let the scammer talk to himself.

  10. Lawrence Martin permalink
    February 21, 2016 1:41 am

    Andy
    What is it that you allege Mr Hunt is refusing to admit?
    Have you documented you assertions with peer reviewed science and has Hunt denied the validity of your interpetation of the facts?

    • AndyG55 permalink
      February 21, 2016 2:18 am

      I’ve told you what he refuses to admit..

      Read the posts if you are capable..

      Maybe do a bit of research yourself to confirm…… If capable.

  11. Lawrence Martin permalink
    February 21, 2016 3:17 am

    Andy
    I am not quite sure how you can write about the early Holocene warm period and not mention that orbital (Milankovitch) forcing gave higher summer insolation in the early Holocene. It suggests either that you don’t really understand the issues or you have a prior grudge against Hunt. Is there a long term conflict between you two that explains the hostility?

    • AndyG55 permalink
      February 21, 2016 4:21 am

      So you refuse to do the research on Arctic sea ice in the first 3/4 of the Holocene too, do you.

    • AndyG55 permalink
      February 21, 2016 4:35 am

      The latter half of last century was classed as a Grand Solar Maximum by real solar scientists, yet the Arctic sea ice is still anomalously HIGH.

      Jimbo is constantly trying to maker out it is LOW and that this is a problem.. He is a LIAR. !!

      Jimbo refuses to even admit that we are just recovering from the COLDEST period in the last 10,000 years, and that is why the current Arctic sea ice level is STILL SO HIGH.

      Do you also ignore the Little Ice Age?

      Did you notice the graph Paul posted of sea Ice around Iceland?

      You have to get a proper historical perspective, and that is what Jimbo refuses to do, by continuing to push his dishonest mis-representations of Arctic Sea Ice.

      He is acting like a low end propaganda con-man… now you may like con-men, but I don’t.

      Unfortunately, it looks like the next few decades will bring a decrease in temperatures, and Arctic sea ice will again be a major problem for those people trying to live in that area.

  12. Lawrence Martin permalink
    February 21, 2016 3:22 am

    1) The extent chart used in the First Assessment Report way back in 1990 was predicated upon 10% concentration. Therefore, all other things being equal, one would expect any anomaly swings to be greater than those seen using the current 15% threshold.

    2)
    On Fig 7.20 from the 1990 report, the peak of the smoothed anomaly gets down to about -0.35 or -0.4 million sq kms.

    Using NSIDC figures, the average annual extent (not anomaly) for the period 1979-90 works out as 12.31 million sq kms. (That period starts from the deployment of Nimbus-7, with its SMMR instrument. The end date is set coincident with the end of the chart used in the 1st assessment.)

    For the period 1991-2004, the average extent drops by a full 0.5 million sq kms to 11.81 million sq kms. (N.B. The half million drop is NOT a transient peak, but is the average across the entire period.)

    For the period 2005-15, the annual average drops to 10.92 million sq kms.

    http://bit.ly/1TsIMau

  13. Pethefin permalink
    February 21, 2016 8:13 am

    We do have scientific observations also from the period of 1893-1961, collected by the DMI:
    http://hidethedecline.eu/pages/posts/arctic-sea-ice-data-collected-by-dmi-1893-1961-259.php
    these maps were recently discussed in a scientific paper:
    http://sciencedomain.org/abstract/8837
    that was discussed by Ron Clutz:
    https://rclutz.wordpress.com/category/arctic-sea-ice/
    Unsurprisingly, just as is the case with the satellite observations 1973-1978, also these observations have been conveniently largely forgotten in order to create an alarmist illusion of lost paradise, where the extent of the Arctic sea was flat until the evils of mankind started the downfall of everything pure and good.

    • Pethefin permalink
      February 21, 2016 10:55 am

      The only really interesting scientific question concerning Arctic sea-ice seem to be the issue raised by e.g. the above mentioned scientific paper: Is there a Quasi-60 years’ Oscillation of the Arctic Sea Ice Extent? by A. Parker and C. D. Ollier: Journal of Geography, Environment and Earth Science International, ISSN: 2454-7352,Vol.: 2, Issue.: 2
      http://sciencedomain.org/abstract/8837
      Unfortunately the latest paper does not discuss the analysis by Vinje (the map in the beginning of this post) or historical accounts of Arctic sea-ice by historians.

  14. Pethefin permalink
    February 21, 2016 8:24 am

    There is a clear similarity between the 1769 sea-ice extent as depicted by Vinje and the current sea-ice extent in that both clearly show the effect of the North Atlantic Current east and west of Spitzbergen/Svalbard. The sea-ice has retreaded most in the area where the current hits the Arctic sea-ice:
    http://www.whoi.edu/main/topic/arctic-ocean-circulation
    Surely something that scientists would be interested in doing some research if there was funding for it? There must be a way to turn this into another CO2-story for funding?

  15. Pethefin permalink
    February 21, 2016 9:24 am

    The previous warming that started in 1920´s affected the Arctic sea-ice has been discussed by prof. Richard Linzen in 2009:

    starting at 17:05. Particularly the quote from the US Weather Bureau from 1922 (at 19:30) is very illuminating.
    Tony Heller has looked into several publications documenting this earlier warming period:
    http://realclimatescience.com/2015/10/more-smoking-guns-of-fraud-at-nasa/
    However, the memory of the public is very short and therefore many are gullible for a long time, some of the people all the time.

  16. Pethefin permalink
    February 21, 2016 11:25 am

    Vinje´s work, depicted in the map in the beginning of this post, initiated a 15-year scientific study into Arctic sea-ice with help of ship logbooks since 1553:
    http://wwf.panda.org/wwf_news/?14950/Ancient-logbooks-of-arctic-explorers-provide-new-insight-on-climate-change
    The results are available here:
    http://www.climate-cryosphere.org/resources/historical-ice-chart-archive
    Torgny Vinje passed away in October 2015:
    http://www.climate-cryosphere.org/news/clic-news/1507-torgnyvinje
    I hope we will have such great polar scientists in the future, unfortunately the DMI does not seem to be living up to those standards.

    • February 21, 2016 11:40 am

      I think you’ll find that in actual fact the DMI are living up to those standards. See e.g. their latest word on the subject:

      • Pethefin permalink
        February 21, 2016 12:17 pm

        Pathetic attempt to divert from the topic of this thread. There is another thread for that discussion. Learn how interact with people who do not fall for your trolling. Enough said.

      • AndyG55 permalink
        February 22, 2016 10:49 am

        And MASSIVELY ABOVE the mostly ZERO Arctic sea ice level of the first 3/4 of the Holocene.

        It is, NATURALLY, just a little bit BELOW the levels of the LIA, which was the COLDEST period of the last 10,000 years.

        But you KNOW that, don’t you Jimbo….

        you are just trying to make a FALSE PROPAGANDA MISDIRECTION.

        because that’s all you are capable of.

  17. February 21, 2016 2:09 pm

    Interesting issue! Here’s an analysis on the past of the Arctic : http://www.arctic-heats-up.com/chapter_1.html. You may find it interesting and it may help us better understand the perspectives for the Arctic.

  18. February 22, 2016 10:37 am

    Reblogged this on ajmarciniak.

  19. NevenA permalink
    February 23, 2016 4:59 am

    Unfortunately I was too busy trying to convince Paul and commenters that the old, discontinued, uncorrected DMI SIE-30% graph is in fact incorrect, and so didn’t have time to show that the green dotted line in the image at the top of this post is actually for August 1769, not April. See this paper by Isaksson et al. 2004.

    May I ask for an update to reflect this, Paul?

    • February 23, 2016 12:14 pm

      Just sorting

      Thanks

      Paul

      • Pethefin permalink
        February 23, 2016 12:33 pm

        As with everything Neven writes, one should proceed with precaution. The Isaksson et. al. paper states that the map they use is an updated version of Vinje 1999, whereas http://www.climate4you.com/
        where the map is from, states the map is from 2000. Unless Neven can come up with a newer publication by Vinje, I would assume the Norwegians behind climate4you know better.

    • February 23, 2016 12:38 pm

      Neven

      Have you got a link to the original Vinje 1999 paper?

      Vinje, T. 1999. Barents Sea ice edge variation over the past 400 years. Extended Abstracts, Workshop on Sea-Ice Charts of the Arctic, Seattle, WA, USA. World Meteorological Organization, WMO/TD No. 949, pp. 4-6.

      I’ve searched everywhere, it may be that it was a WMO workshop job, and never put online

      Thanks

      Paul

      • Pethefin permalink
        February 23, 2016 12:57 pm

        And here’s the publication from 2000 that climate4you is referring to as a source of the map:
        http://brage.bibsys.no/xmlui/bitstream/handle/11250/172727/melding1999.pdf?sequence=1

      • Pethefin permalink
        February 23, 2016 1:33 pm

        The map is found on page 7. The only part of text dealing with the map is attached to the map and has been written in English (and in Norwegian).

      • NevenA permalink
        February 23, 2016 3:11 pm


        Have you got a link to the original Vinje 1999 paper?

        No, Paul, unfortunately not. I looked for it too everywhere a few years go. I did find an extended abstract however for the paper in this Proceedings of the workshop on Sea-ice charts of the Arctic 1998 (under download, right-click the PDF and save as). The paper appears to be explicitly and exclusively about the ‘August ice edge’.

        The figure at the top of your post isn’t in there, but there is a time series that shows how far north the ice edge was during August. Eyeballing the timeseries I’d say it’s about 79-80° N, which is just north of Svalbard (see the daily Uni Bremen SIC map) and corresponds perfectly to the green dotted line in the image at the top of your post.

        Again, Isaksson et al. (2004) have the same line for 1769 and explicitly state it’s for August, accompanied by the text “Years with extreme April ice-edge locations were 1866 (maximum) and 1995 (minimum).” Now, the line for 1769 would be an even more extreme minimum for August, but the following sentence reads: “The sea-ice edge for August 1769 is shows as an example of a year when Whalers Bay north of Svalbard was open.”

        The 2001 Vinje paper has the same figure but without the green dotted ice edge for 1769. Why not include it if it’s for April? Below the figure it says ‘courtesy S. Østerhus’.

        The publication from 2000 that climate4you is referring to as a source of the map, indeed contains the map with the green dotted 1769 ice edge on it, and although it says Ysterhüs 98/10 in the image (which I assume is the same Svein Østerhus) I couldn’t find any mention to a paper in the reference list, and I couldn’t find a paper on Google Scholar by the author either that contained anything.

        It looks highly likely that the green dotted line in the image at the top of the post, derived from the 1999 Norwegian Polar Institute Year Report Pethefin linked to, either erroneously made it into the map, or was erroneously described as representing the ice edge in April 1769 (the other lines are for April). I don’t know how the error was made or by whom.

      • Pethefin permalink
        February 23, 2016 3:18 pm

        It is indeed a puzzle where the 1769 line in the map came from. The Vinje 2001 has this in its list of references:
        Østerhus, S., and T. Gammelsrød, 1999: The abyss of the Nordic Seas
        is warming. J. Climate, 12, 3297–3304.

        An error? Maybe, maybe not and in which publication?

      • NevenA permalink
        February 23, 2016 3:33 pm

        My guess is that the error was made in that 1999 Norwegian Polar Institute Year Report – published in 2000 – that contains the image in question (at the top of this blog post). I can’t prove it, of course. It wasn’t made in Vinje 1999 because the extended abstract I linked to is explicitly about the August sea ice edge.

        There’s nothing preceding it that we can find from Svein Østerhus, and afterwards the 1769 ice edge is either explicitly referred to as August ice edge (Isaksson 2004) or it isn’t there in a similar image showing the three other April ice edges (Vinje 2001).

      • Pethefin permalink
        February 23, 2016 3:30 pm

        There’s also this Vinje 2003 but I haven’t been able to get access to it:
        http://academic.research.microsoft.com/Publication/5604955/ice-extent-variations-during-last-centuries

      • NevenA permalink
        February 23, 2016 5:10 pm

        I found it here, Pethefin, but it doesn’t contain any reference to the image, I believe.

      • February 23, 2016 5:33 pm

        Thanks.

        I’ve just posted anyway, and will add a footnote to the original post

      • Pethefin permalink
        February 23, 2016 5:58 pm

        Thanks, Neven, nothing there as you said.

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