Reykjavik Temperature Adjustments
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.