Perth 1940 Jan-Mar Historic Comparisons

Continuing the comparison of historic sources of temperature and contemporary records, Chris Gillham has compiled a list of maximum and minimum daily temperatures for Perth for the months of January, February and March 1940 and uncovered some strange discrepancies (highlighted – all months at perth-newspapers-mar-qtr-1940).

Chris notes that while BoM’s contemporary temperatures largely agree with temperatures reported in newspapers of the day, a couple of temperatures in each month disagree by up to a degree C!

File attached comparing the March quarter 1940 daily newspaper and BoM raw data for Perth Regional Office 9034 (Perth Observatory atop Mt Eliza at the time), plus an ACORN average for each month.

Combining all days in the March 1940 quarter, average max in The West Australian newspaper was 29.51C and average BoM raw max was 29.56C. Average min in the newspaper was 17.38C and average BoM raw min was 17.15C. Rounded, max up .1C and min down .3C in BoM raw compared to what was reported in 1940. There seems a tendency for just two or three temps each month to be adjusted in raw, sometimes up but obviously with a downward bias in min.

ACORN-SAT judged the three months to have an average max of 31.32C and an average min of 16.17C. So max has been pushed up about 1.8C and min has been pushed down about 1.2C or 1C, depending on your point of view :-) .

It always pays to go back to the source data.

  • cohenite

    Great work to all concerned. If this is a pattern whereby every month or so the raw data is either or both reduced at just one particular day or increased substantially then over the data stream you would think that a warming bias could be increased in the trend in contradiction to the raw data or any justification for homogenisation.

    So, the question would be if such a systematic pattern were present through ACORN was it just inadvertent. But even if it were such sloppiness is unacceptable.