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GHCN Temperature Adjustments Affect 40% Of The Arctic

March 11, 2012

By Paul Homewood

 

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                                       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/

 

 

 

 

 

 

 

 

 

 

 

                                                         APPENDIX A

                                        Annual  Mean Temperature Centigrade in 1940

Station Country Actual Temperature Adjusted Temperature Difference Longitude/
Latitude
Upernavik Greenland -3.97 -5.94 -1.97 56 W / 72 N
Jakobshavn Greenland -2.77 -3.07 -0.30 51 W / 69 N
Nuuk Greenland -0.07 -1.17 -1.10 51 W / 64 N
Angmagssalik Greenland -0.82 -1.02 -0.20 37W / 65 N
Stykkisholmur Iceland 3.72 3.62 -0.05 22 W / 65 N
Reykjavik Iceland 5.08 2.88 -2.20 21 W / 64 N
Vestmannaeyja Iceland 5.43 3.63 -1.80 20 W / 63 N
Akureyri Iceland 3.90 2.80 -1.10 18 W / 65 N
Teigarhorn Iceland 4.88 3.98 -0.90 14 W / 64 N
Lerwick Shetland Isles 7.46 6.96 -0.50 1 W / 60 N
Jan Mayen Norway -0.06 -0.34 -0.28 8 W / 70 N
Bodo Norway 4.14 3.94 -0.20 14 E / 67 N
Tromso Norway 2.23 2.23 NIL 19 E / 69 N
Karasjok Norway -2.76 -3.36 -0.60 25 E / 69 N
Vardo Norway 0.88 0.88 NIL 31 E / 70 N
Kandalaksa Russia -0.31 -1.01 -0.70 32 E / 67 N
Murmansk Russia -0.40 -0.77 -0.37 33 E / 68 N
Archangel Russia 0.00 -0.60 -0.60 40 E / 64 N
Kanin Nos Russia -1.38 -1.74 -0.36 43 E / 68 N
Ust Cilma Russia -2.36 -2.29 +0.07 52 E / 65 N
Malye Karmaku Russia -4.51 -5.11 -0.60 52 E / 72 N
Narjan Russia -3.24 -3.88 -0.64 53 E / 67 N
Salehard Russia -5.96 -7.06 -1.10 66 E / 66 N
Tarko Russia -6.30 -7.50 -1.20 77 E / 64 N
Ostrov Dikson Russia -11.10 -11.39 -0.29 80 E / 73 N
Dudinka Russia -9.71 -10.81 -1.10 86 E / 69 N
AVERAGE -0.70

 

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.

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14 Comments
  1. Coldish permalink
    March 11, 2012 1:42 pm

    Astounding! Have you looked at any Canadian stations? Alert, Clyde?

    • March 11, 2012 1:57 pm

      I could not see anything obvious. The GHCN system is down for maintenance today, but I will check tomorrow.

  2. Björn permalink
    March 12, 2012 11:02 am

    I had the monthly data from the Icelandic Weather Bureau ( = IWB in the follwing text ) since 1830 for station Stykkishólmur,Iceland lying around in my computer ( had been plying with it some weeks back) , so I pulled in the monthly GHCN data on offer ( form 1883 – onward ) for that station and did a quick comparision. There are some very big disreparancies, which to me look like fouled up metadata either by GISS or IWB. Here is a small sample of the biggest offenders:
    Monthly mean temp. in °C
    Year Jan Feb Mar
    1927 0 0 -4
    1928 0 0 -2.6
    1929 -3.6 0 -10.8
    1932 0 0 -3.4
    1933 -1.8 0 -0.8
    1935 -3.2 0 -3.6
    1939 0 0 -3.8
    1941 0 0 -0.6
    1942 -3 0 -2.6
    1944 0 0 -1.2
    1945 0 0 -5.8
    1946 -5 0 -3
    1948 0 0 -5.6
    1949 0.3 0.3 0.1
    1950 -3.8 0.2 -0.8
    1953 -0.6 -0.6 -0.6
    1954 -0.6 -0.6 -0.6
    1955 -0.6 -0.6 -0.6

    The Table above shows the columnar diffrence of monthly_means from GHCN and IWB,
    on close inspection I noticed that the IBW table and GHCN table for the above entries have the same numerical value but diffrent signs for .ex the the 1929 values for january and marz are +1.8 and +5.4 according to IWB and -1.8 and -5.4 ( °C ) IN GHCN, resulting in a diffrence of double that size. There are only few other places than these shown here above, with such multidegree diffrences, but a good deal more with -0.4 to -0.6 degree diffs, and some 10 to 12 consequent years at the older end of the table all have a -0.1 °C lower entry in all months at GiSS , and at the other end ( i.e. 1970 – 2011) there are some 20 years with a +0.1 degree bias in all monts of the GHCN data.
    As the daily raw data used for the calculation are not accessible either at IWB or at GISS it is not possible make sure what is causing them but I suspect that the small value +/- 0.1 diffrences are simply caused by different rounding off procedures at either place of origin or because of diffrences in how many days with valid mesurement are needed for a valid and retained monthly value, the GISS claims to require at least 20 dayvalues for each month , and I have no idea how IBW do their means . And it is also not possible to say if the ( suspected ) metadata foul-up happens at GISS or IWB, But the consistency of the one sided disreparences for 23 stations really do point the finger somwhat in direction of the GHCN beeing the baddy, as it is is more unlikely that there likesiszed unidirectional error at all 23 stations. There is of course a theoretical possibilty of it being the case , so the CHCN crew should have the benefit of doubt , until otherwise shown in error or not.

    It is of course obvious these diffrences will propagate into the final results and skew them f.ex the -10.8°C 1929 marz value will lower the seasonal M-A-M (spring) value for that year by 3.3 °C and that again propagates into their anaomalie calculation e.t.c. but I did not go any further into this, an I am not sure I will either because like the man said it should not be the job of us, innocent spectators as we are , to quality check the work of those who are paid for it.

  3. March 13, 2012 3:26 pm

    The GHCN data retrieved by BEST has many errors in it compared to the same station data available from Environment Canada.

    BEST drops 10s of thousands of data points between its Singe Value repository and its Quality Controlled repository.

    Data seems a bit off for the one station I checked – Malahat BEST # 7973

    BEST single value compared to Environment Canada

    EC data scraped from:

    http://climate.weatheroffice.gc.ca/prods_servs/cdn_climate_summary_report_e.html?intMonth=12&intYear=2002&prov=BC&txtFormat=text&btnSubmit=Submit

    Sorted by biggest ABS difference

    17.89 2002 12
    8.55 2003 2
    7 1995 11
    2.7 2011 12
    1.6 2000 6
    1.183 2008 4
    0.867 2001 6
    0.793 2007 4
    0.789 2008 6
    0.782 2000 7
    0.759 2002 3
    0.746 2001 4
    0.722 2008 5
    0.667 2003 9
    0.659 1991 12
    0.633 2010 4
    0.633 2004 9
    0.605 1996 1
    0.604 2008 8
    0.602 1997 6
    0.602 2006 3
    0.587 2008 2
    0.572 2000 4
    0.555 2008 7
    0.528 2003 5
    0.465 2010 6
    0.461 2006 2
    0.43 2006 9
    0.406 2000 10
    0.391 2000 9
    0.358 1998 11
    0.341 2000 1
    0.318 1996 11
    0.314 1999 12
    0.276 1999 11
    0.263 2007 3
    0.244 1994 3
    0.243 2004 12
    0.242 1995 12
    0.233 2006 11
    0.232 1994 12
    0.231 2006 12
    0.231 1997 9
    0.206 2007 10
    0.204 2000 5
    0.195 1993 5
    0.195 1999 3
    0.188 1999 5
    0.187 2005 12
    0.175 1996 4
    0.172 1995 6
    0.171 1998 6
    0.165 1992 5
    0.154 1999 10
    0.15 1995 3
    0.148 1997 5
    0.146 2001 12
    0.144 2007 11
    0.132 1999 7
    0.129 2000 12
    0.125 1994 1
    0.123 1992 1
    0.123 1993 3
    0.122 1996 9
    0.122 2006 1
    0.118 1993 12
    0.117 1997 3

    …. etc

  4. Lou S permalink
    March 20, 2012 9:40 pm

    This is yet another illustration of why the only reliable record
    of global temperature is the satellite record.

    The surface network will always suffer from limited and irregular sampling
    and be prone to fudging some measurements differently from others.
    The satellite record has uniform coverage of the earth and,
    although not without fudge, at least it’s a uniform fudge.

  5. March 21, 2012 5:37 am

    I have made an assessment of the long-term temperature trends in the colder areas of the Northern Hemisphere. I selected 30 stations extending through Alaska, Canada, Greenland, Iceland, Scandinavia and Siberia that had long-term records. The data was obtained from the Dutch Meteorological Institute (KNMI) website and (I think) were the raw data without any adjustments having been made.

    The results indicate that there has been an oscillating trend of increasing temperature over the past 150 years, but there is no evidence that the trend in recent decades is any different to that that had been recorded in earlier times. So where is the big problem?

    http://members.westnet.com.au/brigun/cold_north_temps.html

    Any comments would be appreciated. Brian

  6. June 17, 2012 6:09 pm

    Paul, I caught your letter in today’s Sunday Telegraph regarding the Royal Society. Nice one.

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