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Iceland’s “Sea Ice Years” Disappear In GHCN Adjustments

January 28, 2012
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By Paul Homewood




There was a very sudden climatic shift in Iceland in 1965, with temperatures falling dramatically. The following six years were known there as the “Sea ice years” and saw major economic upheaval as a result.

This event is well known in meteorological circles, for instance H H Lamb reported that sea temperatures around the Faroe Islands fell by 1.0C and were as cold as at any time in the previous 100 years. ( This series of sea temperatures is one of the longest in the world, dating back to 1867).

The Icelandic Ministry of Fisheries report that “After a generally warm period in the northern North Atlantic from 1920 to 1964, the period from 1965 to 1971 was characterized by very low temperatures and salinity typical of polar water. This was often accompanied by sea ice over the northern shelf. In some of those years, the sea ice covered the whole north and east coasts of Iceland. Temperature differences in the waters north of Iceland between these two periods were up to 3°C. “


Not just sea temperatures, but land ones too. The Iceland Met Office tell us “The 20th century warm period that started in the 1920s ended very abruptly in 1965. It can be divided into three sub-periods, a very warm one to 1942, a colder interval during 1943 to 1952, but it was decisively warm during 1953 to 1964.The cold period 1965 to 1995 also included a few sub-periods. The so called “sea ice years” 1965 to 1971, a slightly warmer period 1972 till 1978 and a very cold interval from 1979 to 1986”.

The effects on fishing and agriculture were immense, for instance “In a single year, 1967, yields of hay per hectare were 870 kg lower than the average over the previous 25 years. Over 1000,000 ha there was a decrease in production of 87,000 tonnes, at that time worth 260 million krónur, reducing the basic productivity of Icelandic agriculture by 20 per cent (Grove 1988). The year 1967 was not the only one with severe icing; 1970 and 1975 were similar in many respects.”

Unsurprisingly these times are indelibly printed in the minds of Icelanders who lived through them. It therefore must come as a bit of a shock to them when they learn that the experts at GHCN seem to have decided these events never happened. Their statistical programmes are designed to weed out sudden changes that could be due to factors such as station location changes. Their latest Version 3.1, issued last November, appears to have decided that the warming from 1920 – 1964 never really took place, and, consequently, it could not have become colder again in the following years. The GISS graphs below, which use GHCN temperatures, makes this abundantly clear. The first is the new version introduced in December, the second the original version.




So what do the local experts have to say?

Ole Humlum , Professor of Physical Geography at the University of Oslo, is an expert on Arctic Climate and includes the following comment in his 2011 Update :-

Please note that as the GHCN v2 database is no longer being updated, and since late November 2011 the GISS surface temperature analysis is based on the adjusted GHCN version 3 data. Graphs comparing results of the GISS analysis using GHCN v2 and v3 are available on the GISS homepage for comparison. Apparently this change also resulted in some surprising effects for several individual station data series available from the GISS database, which raises a number of concerns.

I’ll leave the final words to Trausti Jonsson, one of the most experienced and respected scientists at the Iceland Met Office :-

In 1965 there was a real and very sudden climatic change in Iceland (deterioration). It was larger in the north than in the south and affected both the agriculture and fishing – and therefore also the whole of society with soaring unemployment rates and a 50% devaluation of the local currency.  It is very sad if this significant climatic change is being interpreted as an observation error and adjusted out of existence.

I have been working for more than 25 years in the field of historical climatology and have been guilty of eager overadjustments in the past as well as other data handling crimes. But as I have lived through these sudden large climatic shifts I know that they are very real.

  1. Robin permalink
    January 28, 2012 8:27 pm

    Paul, I have the Iceland data and have now looked at some of it. Will email some script and plots. Basically, what I find is just the same as in analyses I made some years ago, principally that a major upward shift occurred in mid 1920s, with another sharp downward change at 1965 (or close to then – see my plots, later), The low temperatures prevailed (and indeed declined further in the late 1970s). with a major rise during the period about 1983 to about 2000, since when there has been a steady (warmish) regime.

    I may modify this stuff as I look further, but in essence it sums up my interpretation of the /real/ Iceland data.

  2. lolwot permalink
    January 29, 2012 8:33 pm

    “Their latest Version 3.1, issued last November, appears to have decided that the warming from 1920 – 1964 never really took place”

    Are you sure that the warming was there in Version 3.0?

    I mean on December 14th 2011 GISTEMP switched from using GHCN v2 unadjusted to GHCN v3 adjusted. Isn’t that alone enough to explain why the warming disappeared from GISTEMP Reykjavik?

    In other words is this removal of warming issue a fundamental side effect of GHCN3 homogenization that has existed all along rather than something that has only happened since November 2011?

    • January 29, 2012 10:53 pm

      Could have been either. Still waiting for GHCN to comment. Version 3.0 was only introduced in May 2011 and as you say, GISS went straight from V2.0 to V3.1.

      Either way the adjustment suddenly appeared last year.

    • Paul Matthews permalink
      January 30, 2012 9:24 am

      You can download the data for v3.0 and v3.1 from the GHCN ftp site.
      In version 3.0, Nov 5th 2011, the adjusted and unadjusted data sets are the same – both look like the second graph.
      In version 3.1, same date, the large adjustments reducing the 1940s warmth and eliminating the 1960s cooling suddenly appear, giving the first graph.
      So Paul’s original post is correct.


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