Down in the windswept wastes of the great Southern Ocean lies Base Orcadas, an Argentine naval outpost that boasts a weather station, and it’s a particularly important weather station because it’s the only one below latitude 60S with a long-term temperature record. The station was established by the Scottish National Antarctic Expedition in 1903 and transferred to Argentina in 1904 and it has been recording temperatures since April 1903. The station is located on a somewhat insecure-looking gravel spit on Laurie Island in the South Orkneys:
Figure 1: Base Orcadas Weather Station, South Orkney Islands: 60.7S 44.7W (Photo credit Noticias Ambientales)
The Orcadas record has another distinction: it’s one of the few records in the Southern Hemisphere where the homogeneity adjustments applied by GISS, NCDC and BEST generate a substantial cooling correction. Here we will look into whether this cooling correction is any more valid than the wholesale warming corrections, the adjustments applied elsewhere in the Hemisphere.
A note on data sources before proceeding. Here I use the GISS raw and adjusted GHCNv2 records from GISTEMP, the NCDC raw and adjusted GHCNv3.2 records from KNMI Climate Explorer and the BEST raw and adjusted records from BEST’s station data website. The three data sets give very similar results and are used interchangeably. However, BEST’s raw records contain more readings than those of GISS or NCDC and fill in gaps in the GISS and NCDC records. Where BEST got the extra data from is not stated.
Figure 2 shows the location of Orcadas relative to the two other reasonably complete temperature records in the area that go back to the early 1900s or before – Grytviken in South Georgia, located 900km to the northeast and Punta Arenas in Chile, located 1,800km to the northwest.
Figure 2: Location of Base Orcadas relative to Grytviken and Punta Arenas, Google Earth view.
The raw Orcadas record is a fairly good match to the raw records in the Antarctic Peninsula over the period of common readings after 1945, but not to Grytviken and Punta Arenas (Figure 3). Orcadas shows much larger short-term temperature swings than the other two records and also about 2C of net warming, compared to about a degree of net warming at Grytviken and effectively no warming at Punta Arenas:
Figure 3: Raw annual mean temperatures, Orcadas, Grytviken and Punta Arenas. Data NCDC.
It would be reasonable to conclude that these three records are located in areas with different temperature histories and should therefore not be homogenized, but they get homogenized anyway. The homogenization process adds about a degree of warming to Punta Arenas, subtracts about a degree of warming from Orcadas and leaves Grytviken substantially unchanged. The result is three reasonably congruous records, each of which shows about a degree of overall warming (Figure 4).
Figure 4: Adjusted annual mean temperatures, Orcadas, Grytviken and Punta Arenas. Data NCDC.
We will now take a closer look at the cooling corrections that the three data sets apply to Base Orcadas. We can quantify these corrections simply by subtracting the raw monthly data from the adjusted monthly data, and Figure 5 shows what we get when we do this. GISS identifies a 0.8C downward shift in the raw record (requiring a 0.8C warming “correction”) in September 1950, NCDC identifies a 0.7C downward shift in the same month and BEST, which adds some kind of a residual seasonal adjustment during the homogenization process – hence the wiggles – identifies a downward shift of 0.65C in December 1949:
Figure 5: Cooling corrections applied to Orcadas raw record
How do the homogenization algorithms come up with these corrections? BEST gives the most detail on procedures so I will use BEST as the example. First BEST presents a plot of the raw Orcadas record, which shows gradual warming since about 1930 and no obvious shifts:
Figure 6: BEST Orcadas raw record, monthly means
Then BEST subtracts the Orcadas raw record from a“regional temperature expectation” or “regional average” series constructed using records from up to 2,000km away, and from the result it deduces the existence of an artificial upward shift of about 0.7C in the Orcadas record in December 1949. Note that the shift is classified as an “empirical break”, i.e there is no record of a coincident station move or time of observation change:
Figure 7: Difference between BEST raw Orcadas record and BEST “regional average” for Orcadas
BEST then adjusts the shift out, and to confirm it did it right it presents a plot comparing the adjusted Orcadas record with its regional temperature expectation series. Not suprisingly, the two match:
Figure 8: BEST adjusted Orcadas record versus BEST regional average
However, this approach involves more than a little circular logic, and BEST also assumes that records from anywhere within a 12.6 million square kilometer area centered on Orcadas can be used to define the “regional expectation” in the South Orkneys, which is a stretch. Consequently we are left with the possibility that the shift is simply an artifact of the homogenization algorithms. How do we find out whether it is?
Well, we could do it fairly easily if there happened to be a station near Orcadas with a record covering the period around 1950. And as it happens, there is:
Figure 9: Signy Island Weather Station, South Orkney Islands: 60.7S 45.6W
Located according to BEST a mere 47.33km west of Orcadas is the Signy Island Research station, located on what appears to be somewhat firma terra than Orcadas. Signy is run by the British Antarctic Survey and is on the site of an old South Orkneys whaling station. It has been in operation since January 1947 and has a temperature record running from then to December 1995, when the station was put on a summer-occupancy schedule.
So how do the Signy and Orcadas records compare? Figure 10 plots BEST’s versions of the two raw records over the period of common readings. The records track each other remarkably well for most of the time considering the highly variable temperatures, which jump around from year to year as much here as anywhere else on Earth, particularly in the winter. The generally high level of congruity and the lack of any large displacements in the difference plot suggests that both records are measuring real temperature variations and are not significantly affected by artificial distortions:
Figure 10: Orcadas versus Signy raw records, BEST monthly data
The only feature that looks as if it might complicate matters is the “bust” in 1950, but this turns out to be a simple quality control failure. As shown in Figure 11 the Orcadas and Signy raw records are displaced by a month relative to each other during most of 1950 in all three data sets, and GISS’s, NCDC’s and BEST’s QC procedures didn’t pick up on it.
Figure 11: The one-month shift between the Orcadas and Signy raw records during 1950, BEST monthly data
I corrected the displacement by deleting the implausible-looking December 1950 value in the Signy record and moving the Signy values after February 1950 forward a month (I may have moved the wrong record but as a practical matter it makes no difference which one is shifted). The corrected comparison is shown in Figure 12:
Figure 12: Orcadas and Signy raw records after correction for shift
Subtracting Signy from Orcadas now yields the results shown in Figure 13. If the Orcadas record contains a ~0.7C artificial shift in or around 1950 we should see it clearly in the difference plot at the bottom, but we don’t.
Figure 13: Orcadas versus Signy raw records after correction for one-month shift.
But we see a clear displacement in late 1950 when we compare the raw Signy record with any of the three homogeneity-adjusted Orcadas records (Figure 14 compares it with the GISS version). There can be no clearer proof that the shift is manufactured by the adjustments:
Figure 14: Orcadas adjusted record versus Signy raw record, BEST data
And because the raw Signy record does not receive any adjustments what we see in Figure 14 is the end product of the homogenization process. Instead of turning a distorted raw record into an undistorted adjusted record homogenization has turned an undistorted raw record into a distorted adjusted record. And the adjusted record is supposedly the one that’s correct.