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GHCN Temperature Adjustments In Iceland–A Closer Look At Stykkisholmur–Part II

October 30, 2012
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By Paul Homewood


In Part I, we saw how GHCN had adjusted temperatures down at every Icelandic station for each year up to 1964, as its algorithm had spotted an abrupt shift in the temperature record in 1965 that was assumed to be due to non climatic factors.

In Part II, we will take a close look at what the scientists, who have spent years studying the regional climate, have to say. As mentioned in Part I, there are three peer reviewed papers I will refer to and links to these are at the end.


Iceland Met Office

First of all, what do the Iceland Met Office (IMO) say about Stykkisholmur during the 1960’s?

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, a very cold interval during 1979 to 1986.

The cold during the ice years was accompanied by persistent northerly winds and an associated maximum extent of the East Greenland sea ice. The air pressure during this period was generally high – the NAO was in a negative phase.


So they were in no doubt about a dramatic climatic shift at the time. And they make it clear that the shift applied to the whole island, as their graph of temperatures for Akureyri, Reykjavik and Stykkisholmur, below, shows.


Reliability of Icelandic Temperature Records

How reliable are the Icelandic temperature records? Hanna et al, in their paper “An Analysis of Icelandic Climate since the 19thC” , make the following comments:-

  • Stykkisholmur has the longest running and most uniform temperature record in Iceland.
  • Continuous observations at Stykkisholmur date to 1845. The early Reykjavık data have been used to reconstruct the Stykkisholmur series back to 1823 (Jonsson, 1989). Other long-term records are presented for Vestmannaeyjar on the south coast, Grımsey (a small island off the north coast) and Teigarhorn, in the eastern fjords. Annual averages of these series were compared over the post-1870 period to validate their homogeneity. The results indicate high correlations (r ∼ 0.9; Figure 5).

This is important. Stykkisholmur, and indeed the other stations, are well homogenised with each other, so there should not be any significant non climatic biases in any of the series, unless they all appeared at the same time at each site, which seems extremely unlikely. The IMO actually take the accuracy of their temperature records very seriously, and have already made adjustments for many years to historic “raw” data to reflect changes in location etc.


Hanna et al

So what else does the Hanna paper tell us about climatic trends in Iceland? They offer up the graph below of temperatures for Reykjavik, Stykkisholmur and Teigarhorn, which confirms the sudden drop in temperature.




They go on to make some extremely relevant comments:-

  • The warming was non-uniform in time, occurring in three distinct phases, approximately from 1880 to 1900, from 1925 to 1940, and from 1983 to 2001. Warming was most rapid in 1919–33, reaching the maximum temperatures over the entire record in 1939 and 1941. The northwestern European records surveyed do not indicate any significant trends over the 1901–30 standard period, whereas Icelandic trends are highly significant , somewhat indicating a decoupling between the Icelandic and northwestern European climates.
  • The 1990s was definitely not the warmest decade of the 20th century in Iceland, in contrast to the Northern Hemisphere land average (Houghton et al., 2001). It was cooler than the 1930s by 0.45 °C for Reykjavik, 0.41 °C for Stykkisholmur and 0.16 °C for Teigarhorn. (Contrast this statement with the current GISS graph, shown in Part I).
  • In an analysis of Greenland temperature records, Box (2002) lists 1939 and 1941 among the five warmest years and 1907 and 1983 among the five coldest years for the nearest site to Iceland, Tasiilaq, southeast Greenland. This is consistent with the results from Reykjavik (Table IV). Furthermore, this is consistent with the often-cited temperature dipole between Greenland and northwestern Europe (e.g. Van Loon and Rogers, 1978). Thus, 1941 was one of the coldest years of the 20th century in northwestern Europe, e.g. Copenhagen, Oslo, Stockholm (Table IV). 1983 was the 11th warmest year in Copenhagen, 13th warmest year in Oslo, and 18th warmest in Stockholm.
  • The Icelandic cooling from the 1940s to the 1980s is in broad agreement with a general cooling between the late 1950s and the 1990s observed in western and southern Greenland (Przybylak, 2000; Box, 2002; Hanna and Cappelen, 2003) and also agrees with the P.D. Jones/Hadley Centre data shown in Serreze et al. (2000) of a widespread cooling (or at least muted warming) over southern Greenland, Iceland and the northwestern North Atlantic. These regions experienced a prolonged and deeper mid-20th century cooling when compared with the global warming trend (e.g. Houghton et al., 2001). The contrast is attributable to variations in the intensity of the Icelandic low and is thus linked to the NAO.

So we know that :-

  1. The patterns of warming and cooling in Iceland were not always well correlated with similar changes in NW Europe, indeed often the opposite. This automatically renders any attempt to homogenise Icelandic temperature data with stations hundreds of miles away in NW Europe utterly meaningless.
  2. The sudden cooling in the late 1960’s in Iceland was part of a much wider phenomenon, and certainly applied to Greenland, where similar GHCN adjustments have been inflicted.


The Great Salinity Anomaly 1968-82

The second paper that I referred to, “One Hundred Years in the Norwegian Sea”, by Bob Dickson & Svein Osterhus, looks at events further east, towards the coast of Norway.

They discuss six major six events “that have made an impact on the physical environment of the Norwegian Sea on a timescale of decades, each seeming to involve a different mix of ocean-climate processes, and each therefore providing new insight into the varied nature of physical change and ecosystem response:

1) the Great Chill, 1900 -1920;

2) the Warming in the North, 1920 -1960;

3) the Great Salinity Anomaly, 1968 -1982;

4) the Warming of the Abyss, 1970 present day;

5) the freshening of the subarctic seas; and

6) the warming of the Arctic”


They have this to say about the great Salinity Anomaly.

During winters of the 1960s the leading mode of wintertime atmospheric pressure variability in the sector under discussion, the North Atlantic Oscillation (NAO), evolved to its extreme low index state in an instrumental atmospheric record of over a century’s duration (Hurrell 1995; Hoerling et al. 2001), and possibly much longer (e.g. Cook et al. 2002; Luterbacher et al. 2002). With anomalously high pressure persistently dominant over Greenland, a record northerly airflow swept the Norwegian Sea/Greenland Sea bringing an increasing proportion of polar water south to the seas north of Iceland in a swollen East Greenland Current. The East Icelandic Current, which had been an ice-free Arctic current in 1948-1963, became a polar current in 1965-1971, transporting drift ice and preserving it (Malmberg 1969). Aided by active ice formation in these polar conditions, the Oceanic Polar Front spread far to the south-east of normal, with sea ice extending to the north and east coasts of Iceland.

This large increase in the southward transport of ice and freshwater by the East Greenland Current, preserved by the suppression of winter convection north of Iceland, passed out to the open Atlantic through Denmark Strait in the late 1960s, and was traceable thereafter as the ‘Great Salinity Anomaly’ (GSA) around the subpolar gyre for over 14 years until its return to the Greenland Sea in 1981-1982 (Fig. 10) (Dickson et al. 1998).

[A brief explanatory note here. Rivers draining into the Arctic Ocean create a low salinity surface layer, with most of the freshwater bound in sea ice. When atmospheric conditions or ocean currents force this ice out of the Arctic, this freshwater reduces the salinity of the Norwegian and other seas.]


They go on to say.

However, the GSA is certainly one of the most dramatic events of the century in the Norwegian Sea.

Ecologically too, the GSA was a quite exceptional event. Jakobsson (1992) concluded that ‘the ‘‘Great Salinity Anomaly’’ has probably generated more variability in fisheries during the last quarter of a century than any other hydrographic event in recent years’. During its passage, Cushing (1995) found a significant reduction in recruitment in 11 out of 15 deepwater fish stocks examined. Further, as its harsh conditions closed down the ‘warming in the North’, they also established a ‘veritable desert’ for Calanus finmarchicus [that herring feed on] in waters north of Iceland (Dragesund et al. 1980; Jakobsson 1980), and set in train a change in the migration pattern of Norwegian spring spawning herring in the Nordic Seas that has taken 35 years to unfold (Vilhja´lmsson 1997; Holst et al. 2004).

So we learn again that this event affected a much wider area than Iceland itself, and that it had major consequences for the region.


Hamilton et al

Sea Changes Ashore: The Ocean and Iceland’s Herring Capital” by Lawrence Hamilton is a history of Iceland’s herring industry, and in particular the fishing village of Siglufjordur, regarded as Iceland’s “herring capital”. The years after the Second World War were a boom time for the herring industry, but then, as the paper describes:-

In the mid-1960s, large-scale physical changes took place in the seas north of Iceland. These physical changes had ecological consequences that led to the loss of the herring’s main food supply.

The authors then go on to refer to the same events as Dickson & Osterhus:-

In the mid-1960s, northwesterly winds associated with a prolonged negative NAO/AO state drove unusual volumes of polar surface water and ice through Fram Strait into the Greenland and Iceland seas.

Dickson et al. (1988:103) described this as “one of the most persistent and extreme variations in global ocean climate yet observed in this century.”

They also include a graph of temperature trends for the north of Iceland, commenting “Figure 6 illustrates the pronounced dip in salinity, sea temperature, and air temperature that marked GSA’70s and the general cooling of north Iceland climate in the second half of the 1960s. The Siglunes section (66°16′ N, 18°50′ W to 68°00′ N, 18°50′ W; see Fig. 5) is a standard oceanographic section north of Siglufjördur, often used to assess climate on the shelf (e.g., Malmberg and Jónsson, 1997). Also shown are annual air temperatures from the northeast Iceland village of Raufarhöfn. Among the available long-term air temperature records, those of Raufarhöfn best reflect climate over the ocean north of Iceland because of the village’s exposed coastal location (66°27′ N, 15°56′ W).”



They add:-

The air and water temperature records show a similar pattern. From 1920 until 1965, relatively warm conditions prevailed over the northern North Atlantic. In 1965, a sudden change occurred; drift ice and polar water covered the north Icelandic shelf during spring. The following years until 1971 were generally cold, with sea ice and polar water frequently visiting the shores. Warmer conditions subsequently returned, but climate variability also became greater and the average salinity remained below earlier levels. Since 1997 the flow of Atlantic water to the north Icelandic shelf has increased, making salinity levels almost as high as they were prior to 1965 (Jónsson and Briem, 2003). The late-1960s episode of cold air temperatures and cold, low-salinity water, marking the passage of GSA’70s, had ecological and human consequences.


The paper offers us a reminiscence of someone who lived through these times.

In the winter of ’67–’68 I remember watching the sea ice filling the fjord. I slept in a bed by the window in their bedroom, facing the sea, and every morning I would wake up, look out of the window and ask if the ice had not disappeared yet. No one liked the ice. Many had terrible experience of the ice years earlier in their lives with cold, isolation, and even starvation. The creaky sound of the blocks rubbing together and the icy, stale air that surrounded the seaside still remain a vague childhood memory in my head. (Eastfjords native recalling the last year of the herring adventure)


The effect of the GHCN adjustments can be clearly seen on the following graph, which shows the five year running average for the “GHCN adjusted” temperatures.




During the “Sea Ice Years”, the five year average bottomed out at 2.93C. In contrast, the average temperature between 1948-52 was, according to GHCN, actually lower at 2.86C. The Sea Ice Years have simply disappeared. More than that, because temperatures have been adjusted down, for every year before 1965 right back to 1881, current temperatures are far too high in comparison.

Yet there is no doubt that the ice years happened. They had a serious impact on the Icelanders themselves and they also affected a much wider area than just Iceland itself.

So what has gone wrong with the GHCN system? There is no evidence at all that the Icelandic temperature record is not robust, or, indeed, the Greenland data that correlates well to it. Even the BEST series bears this out. (See here). As the Icelandic stations are well correlated with each other, the adjustments can only have been generated by comparing with other stations hundreds of miles away in Europe, where it has already been proven that temperature trends can be totally different. But really this is an issue for GHCN to resolve, not me.

As a public body, NCDC have a duty to be accountable for all of their work, as well as to be totally transparent. They have been aware of this issue now since January, and it is surely time for them to step up to the plate and either explain how their adjustments are correct, or withdraw them. Furthermore, they must fully investigate all other significant adjustments elsewhere and withdraw them where they cannot be fully substantiated.  I would also suggest they ask themselves why these clearly incorrect adjustments were not identified and put right at the very outset. It should not be up to independent observers to be doing this for them.

I frankly find it immensely sad that, not only real events, but also the work and knowledge of serious scientists, accumulated over many years, can apparently be swept aside at the whim of an algorithm. Computer models can have their value, but we surely need to keep an eye on what’s happening in the real world.

I will leave the final words to Trausti Jonsson, who is a Senior Meteorologist, and specialises in Climatology at the Iceland Met. Trausti was also co-author in the Hanna paper.


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.



I have specifically asked the GHCN team to comment on the adjustments for Stykkisholmur. I will report back as and when I receive any reply.



1) “An Analysis of Icelandic Climate since the 19thC”  by Hanna, Jonsson & Box.

2) “One Hundred Years in the Norwegian Sea”, by Dickson & Osterhus

3) “Sea Changes Ashore: The Ocean and Iceland’s Herring Capital”  by Hamilton et al.

4) GHCN data sourced from GISS

  1. October 30, 2012 8:04 pm

    Thanks, Paul, for your efforts to unravel the global climate mystery.

    Weather and climate have always changed in abrupt and inexplicable ways, especially for those who cherry-picked data, ignored empirical data like this [1], and pretended to be able to make scientific predictions of climate change !

    That is why society is in its current mess, worldwide !

    With deep regrets,
    – Oliver K. Manuel
    Former NASA Principal
    Investigator for Apollo

    [1] “Neutron repulsion,” The Apeiron Journal 19, 123-150 (2012):

  2. October 31, 2012 2:28 am

    “This automatically renders any attempt to homogenise Icelandic temperature data with stations hundreds of miles away in NW Europe utterly meaningless. ”
    “This automatically renders any attempt to homogenise Icelandic temperature data with stations hundreds of miles away in NW Europe utterly perverse.”
    The “meaning” is there; it is that the record is being deliberately distorted. Data crime.

  3. Paul Matthews permalink
    October 31, 2012 2:21 pm

    You mentioned the 1965 cooling in an earlier thread, saying that it was established in papers of HH Lamb, in an icelandic fisheries report, and in other sources.
    The Lamb description is here.

    It’s clear that the new GHCN version V3.2 has not fixed the error you first discussed back in January (and reported to GHCN at the time).


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