Why The GHCN Adjustments In The Arctic Are Wrong

By Paul Homewood

GHCN are quite clear on why they adjust temperatures. This is what their Technical Report says:

The nature of the homogeneity adjustments made to remove non – climatic influences that can bias the GHCN – M temperature record are described in Lawrimore et al. 2011 for version 3.0.0. In brief, adjustments are necessary because surface weather stations are frequently subject to minor relocations throughout their history of operation and may also undergo changes in instrumentation as measurement technology evolves. Furthermore, observing practices may vary through time, and the land use/land cover in the vicinity of an observing site can be altered by either natural or man-made causes. Any such modifications to the circumstances behind temperature measurements have the potential to alter a thermometer’s microclimate exposure characteristics or otherwise change the bias of measurements relative to those taken under previous circumstances. The manifestation of such changes is often an abrupt shift in the mean level of temperature readings that is unrelated to true climate variations and trends.

To identify and correct these biases, GHCN use their “Pairwise Homogenisation Algorithm” (PHA). Essentially, this compares temperature trends between nearby stations, so as to highlight the outlier.

So, if we apply this principle to the Arctic temperature adjustments, there are three key issues to address.

1) Has there been an abrupt shift in temperatures?

Yes, emphatically so, as the raw temperature record below for Akureyri in Iceland shows. There was a sharp decline in temperatures between 1964 and 1966, when annual means fell from 4.7C to 2.18C.

http://data.giss.nasa.gov/cgi-bin/gistemp/show_station.cgi?id=620040630003&dt=1&ds=1

And it was precisely that time when the GHCN algorithm kicked in , and decided to cool the years preceding this decline, and adjust upwards the years after.

ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/products/stnplots/6/62004063000.gif

2) Was the shift real?

Was this abrupt drop in temperature a real, climatic event, or simply a reflection of changing observation practices?

The overwhelming evidence is that it was genuine, and there will follow a detailed post on this.

Indeed, it was so remarkable a change that it has been described as certainly one of the most dramatic events of the century in the Norwegian Sea.

3) What other stations have been used for homogenisation?

The PHA has concluded that this sudden drop in temperature was not real, based on trends at “nearby” stations. Yet, this is not a case of a solitary station in Iceland being adjusted to bring it into line with other Icelandic stations. Indeed, all Icelandic stations have been adjusted in the same fashion.

It is not even a case of the Icelandic stations being brought into line with other nearby Arctic sites in, say, Greenland, as they have also been adjusted in the same way.

Nick Stokes has a useful little App on his website, which maps which sites have been adjusted up (pink), down (blue) and no change (yellow). This shows the preponderance of the pinks.

(One little note – there are a few blues in the area I have covered, but each stopped recording many years ago or, in the case of Egedesminde, were not operational in 1940. The only exception to this is Angmagssalik, which most definitely has received a warming adjustment: [this may be due to Nick’s data not being up to date])

http://moyhu.blogspot.com.au/2015/02/google-maps-app-showing-ghcn-adjustments.html

The only conclusion can be that GHCN stations hundreds of miles away, and outside of the Arctic region, have been used for homogenisation. And here lies the problem – is there any reason why we would expect climate in, for instance, Britain to follow the same pattern as Iceland or Greenland?

Certainly not according to the experts, as this paper “AN ANALYSIS OF ICELANDIC CLIMATE SINCE THE NINETEENTH CENTURY” by Hanna, Jonsson & Box, published in 2004 showed.

They had this to say:

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.

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.

In short, there exists a temperature dipole, with cold years in Iceland and Greenland associated with warm years in NW Europe, and vice versa. Any climatologist worth his salt would not attempt to homogenise the two regions.

Of course, all of these scientists might have got it totally wrong, and it might be Nick Stokes and his algorithm who have got it right. Who said pigs could not fly!