GISS raw and BoM High Quality adjusted temperature comparisons
The charts below are sourced to data from the GISTEMP recordings by the Goddard Institute of Space Studies and the Australian Bureau of Meteorology High Quality database.
The GISS data is sourced from raw GHCN data with USHCN corrections. The original source is raw temperature data from the Australian Bureau of Meteorology. Temperatures in the BoM HQ database are adjusted by the bureau.
Note that in most but not all charts the BoM HQ temperatures trend above the GISS data as of 1993, and temperatures in many of the locations are the same or similar in 2008 and 2009. Various locations in the GISS database, particularly those with long records preceding 1940, have missing data beginning in 1993.
Why do temperatures in the BoM HQ data, upon which Australia's historic warming trends are based, consistently rise above the actual raw temperatures in the GISS database, usually from 1993 to 2008?
Similar trends have been observed by researcher Ken Stewart within the Reference Climate Station sites maintained by the BoM - see BOM vs GISS - Who's Right?
Note: see Climategate memo re Cobar
All GISS locations in Australia
Above is a chart of the average temperature of all 41 Australian locations combined annually in the GISS database with records current to 2008/09. In essence, this is a chart that averages all the charts above.
This chart in no way represents temperature increases across Australia since 1910 because of the changing number of locations since that year ... 1910 - seven, 1920 - seven, 1930 - 10, 1940 - 14, 1950 - 30, 1960 - 35, 1970 - 40, 1980 - 41, 1990 - 41, 2000 - 41.
All 41 locations are not included in the chart source until 1971, due to the GISS selection of locations and timeframes, so the chart does not present temperatures from the same locations all the way back to 1910.
The BoM and GISS records separate in 1993 but, unlike all of the 41 charts above on this page, it is the GISS temperatures that are higher than BoM temperatures. How can this be?
The answer lies in the data source itself, where GISS has missing annual data beginning in 1993 at 12 locations.
The 12 locations missing annual temperature data in the GISS source are mostly in southern latitudes with cooler climates - Yamba, Amberley, Gladstone, Richmond Post Office, Moruya Heads, Richmond RAAF, Cape Otway, Wilson's Promentary, Robe, Tarcoola, Cape Bruny and Cape Leeuwin.
These 12 locations had a combined average temperature of 17.47 C, compared to an average 19.09 C among the other 29 locations.
The 12 locations with missing data are mainly long-record locations as far back as 1910, whereas the 29 others have shorter records, the earliest back to 1942. Note that the BoM raw temperature records for the missing GISS years are available (view charts)
The missing data after 1993 in the 12 locations causes the GISS averaged temperatures to rise above the BoM records, which have no missing years of data.
It appears that to counter this bias caused by locations with missing data since 1993, GISS has lowered temperatures in most other locations without missing data so that the trend lines are equal across the full historic record.
But there is another explanation which has come to light since the so-called ClimateGate 2 leak of documents including the following email from Blair Trewin at the Bureau of Meteorology to Phil Jones at the University of East Anglia:
This series of errors is also referenced within the Independent Peer Review of the ACORN-SAT data-set (p24) as below:
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