GHCN Temperature Adjustments Affect 40% Of The Arctic

By Paul Homewood

Before After

There has been much discussion recently about temperature adjustments made by GHCN in Iceland and Greenland, which have had the effect of reducing historic temperature levels, thereby creating an artificial warming trend. These can easily be checked at the GISS website, where both the old and new datasets can be viewed as graph and table data, here and here.

It has now been identified that similar adjustments have been made at nearly every station close to the Arctic Circle, between Greenland and, going East,via Norway to Siberia, i.e 56 Degrees West to 86 Degrees East, about 40% of the circumference.

So it is perhaps time to recap where we are now.

Background

The NCDC has produced the Global Historical Climatology Network (GHCN), a dataset of monthly mean temperatures, since the 1990’s. Version 2 was introduced in 1997 and included “Methods for removing inhomogeneities from the data record associated with non-climatic influences such as changes in instrumentation, station environment, and observing practices that occur over time “. The GHCN datasets are used by both GISS and HADCRUT for calculation of global temperatures, as well as NCDC themselves.

In May 2011, NCDC brought out Version 3, which “enhanced the overall quality of the dataset”, but made little difference in overall terms. However, only two months later in July, a Google Summer Student, a graduate called Daniel Rothenberg, was brought in to convert some of the GHCN software and make modifications to “correct software coding errors”. The result was Version 3.1, which went live in November 2011. (The full technical report is here).

It is this latest version that has thrown up the Arctic adjustments we are now seeing.

Until December, GISS used Version 2 unadjusted temperatures. Since then, they have changed to using Version 3.1 adjusted temperatures.

Basis of Homogeneity Adjustments

It is worth taking time to be clear why temperature adjustments are made (or should be). As far as GHCN are concerned, they explain their logic thus :-

Surface weather stations are frequently subject to minor relocations throughout their history of operation. Observing stations 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. Ultimately, these artifacts (also known as inhomogeneities) confound attempts to quantify climate variability and change because the magnitude of the artifact can be as large as or larger than the true background climate signal. The process of removing the impact of non-climatic changes in climate series is called homogenization, an essential but sometimes overlooked component of climate analysis.

It is quite clear. Their algorithms should look for abrupt changes that are not reflected at nearby stations. It has nothing to do with “averaging out regional temperatures” as is sometimes claimed.

GISS also make homogeneity adjustments, but for totally different reasons. In their case, it is to make an allowance for the Urban Heat Island Effect (which is not spotted by GHCN because it is a slow change).

Effect of The Adjustments

Appendix A lists every current GHCN station with records back to 1940,that lie between Greenland, at a latitude of 56 W, around to a point about midway across Siberia at 86 E and which are situated close to the Arctic Circle. The table shows the adjustment made by GHCN for 1940 data. Out of 26 stations, the adjustment has reduced actual temperatures in 23 cases, many substantially. In contrast, 2 remain unchanged and only one has a positive adjustment (and this is insignificant). As a crude average, the adjustment works out at a reduction of 0.70 C.

These adjustments typically extend back to the beginning of the station records (though Reykjavik is an exception) and most continue at the same level till about 1970. ( Some of the Russian stations last longer – e.g. Ostrov Dikson’s disappears in 2009).

By 2011, however, the adjustments disappear at ALL of these sites. In other words, an artificial warming trend has been manufactured.

It is worth spelling out two points :-

1) Within this arc of longitude, there are no other stations within the Arctic Circle.

2) With the exception of Lerwick and Vestmanneyja, I can find no stations, in the region, below a latitude of 64 North with similar adjustments. Why is 64 North significant? GISS produce zonal temperature data, and their “Arctic” zone goes from 64 North to the Pole. Coincidence?

Is there any justification for adjusting?

Trausti Jonsson, a senior climatologist at the Iceland Met Office, has already confirmed that he sees no reason for the adjustments in Iceland and that they themselves have already made any adjustments necessary due to station moves etc before sending the data onto GHCN.

Clearly the fact that nearly every station in the region has been adjusted disproves the idea that these sites are outliers, which give biased results not supported by nearby stations.

GHCN were asked in January to investigate this issue and so far have failed to come up with any explanation. Unless they can do this, the assumption must be that the adjustments have been created by faulty software.

Discussion

In global terms, these few stations make no tangible difference to overall temperatures. However, they do make a significant difference to temperatures in the Arctic, which are derived from a small number of stations such as these and then projected over hundreds of miles.

Across much of the Arctic, temperatures were as high in the years around 1940 as they are now. History should not be revised at the whims of an algorithm.

What should happen next? In my view, GHCN should immediately revert to Version 3.0 until the matter is properly investigated and any issues resolved. They maybe just need to put Version 3.1 down as a bad experience and start from scratch again. I believe they also need to seriously review their Quality Control procedures and question how these anomalies were allowed to arise without being flagged up.

It should not be up to independent observers to have to do this.

References

1) GISS still archive the Version 2.0 data here. (Also GISS, following requests by me and others, have included a link to Version 2.0 on their main site).

http://data.giss.nasa.gov/gistemp/station_data_v2/

2) And can be compared with Version 3.1 here.

http://data.giss.nasa.gov/gistemp/station_data/

3) The adjustments can also be seen in graph format at GHCN here. (The station numbers can be obtained at GISS)

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

Footnote

I originally set this table up yesterday, 9th March. Today I noticed a few had changed slightly, presumably at the monthly update, so have amended them. It appears GHCN are still fiddling with their algorithms as the same thing occurred last month.

Share this: Print

Email

Twitter

Facebook

Pinterest

LinkedIn

Reddit



Like this: Like Loading...