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Reykjavik Temperature Adjustments

March 23, 2012

By Paul Homewood




Apologists for GHCN have claimed that their temperature adjustments in Iceland could perhaps be justified by station moves, changes in observational times or other non-climatic biases.

Trausti Jonsson, of the Iceland Met Office, has posted a useful article on his Iceland Weather Blog, which details the original recorded temperatures in Reykjavik, as shown in the above graph.

He makes the following comments :-

  • Relocations are marked with vertical lines. In late 1931 the station was relocated to a rooftop in the town centre and remained there until the end of 1945. The data (above and in the attachment) have not been adjusted for this change nor others. Later versions of the dataset (e.g. the one available at the IMO website) do include adjustments for the relocations.
  • In 1924 a thermograph was introduced again at the station and during 1924 to 1948 all the published temperature means in Reykjavík were calculated as the average of thermograph readings every two hours. There were daily comparisons of the thermograph and the fixed hour observations. Since 1949 the Reykjavík monthly mean is calculated as the average of observations made every three hours.
  • Some internal adjustments are needed during the early part of the series due to later changes in calculation methods. The fixed-hour means that form the basis of both the DMI average method and recent adjustments by the IMO will be made available at this website later.

To clarify, the “official” IMO dataset has already been adjusted to allow for the station moves and time of observation changes (the latter only applied before 1924). Remember that the “raw, unadjusted” figures used by GHCN are, in fact, the already adjusted official IMO ones.

There is therefore no reason for GHCN to make further adjustments.

    1. Brian H permalink
      March 23, 2012 6:05 pm

      Ah, adjusted adjustments! Where would we be without ’em?

    2. March 24, 2012 9:16 am

      There is a very good reason for GHCN to make further adjustments: To keep the process objective.

      If the algorithm is applied to every station then it’s objective. As soon as you decide to pick and choose which stations to adjust and which to exclude it becomes subjective and that could introduce a systematic bias.

      For example I notice that you have so far only highlighted warming adjustments – norway, reykjavik, cleveland, alice springs – all are warming adjustments, even though the ratio of warming to cooling adjusments in the record is pretty much 50/50. If GHCN excluded all the stations you raised as in error it would introduce a cooling bias into the overall global record if they were fixing the warming errors but leaving cooling errors in.

      What they can do is take errors you raise and use that to try and improve the algorithm (but they’d have to make sure the change doesn’t degrade the performance overall at the expense of just one stations). But they should start arbitarily excluding stations.

      • March 24, 2012 10:31 am

        Has it occurred to you that there might be valid reasons for the cooling adjustments?

        I find the argument that one set of errors is offset by another set of errors quite frankly rather a shoddy one.

        • March 25, 2012 12:20 pm

          “Has it occurred to you that there might be valid reasons for the cooling adjustments?”

          So if I can find large cooling adjustments with no obvious explanation will you report on those?

        • March 25, 2012 1:16 pm

          I would certainly be interested in what GHCN had to say about them.

          I have still not seen any evidence, though, that the adjustments “balance out” in Version 3.1.

      • Brian H permalink
        March 24, 2012 1:17 pm

        The ‘cooling adjustments’ are early in the records, the ‘warming adjustments’ are late. Spot the trend line?

        • March 25, 2012 12:21 pm

          By cooling adjustments I mean adjustments that cool the overall record. That means they either adjust the late record downward or the early record upwards.

        • Brian H permalink
          March 25, 2012 1:26 pm

          Still not-sensical. “overall” and “either-or” are not compatible.

          The point of the cool-early warm-late is to impose a warming slope. Period.

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