The official mean temperatures before 1910 for Australian capital cities listed above by Commonwealth Meteorologist H.A. Hunt can be compared with BoM mean raw minima and maxima:
PERTH pre 1910
Mean Max – 22.8C
Mean Min – 12.8C
Perth Airport 9021 / 1944-2012
Mean Max – 24.4C (1961-1990: 24.3C)
Mean Min – 12.1C (1961-1990: 12.3C)
Perth Metro 9225 / 1992-2012
Mean Max – 24.6C
Mean Min – 12.7C
ADELAIDE pre 1910
Mean Max – 22.8C
Mean Min – 11.7C
Adelaide Airport 23034 / 1955-2012
Mean Max – 21.5C (1961-1990: 21.5C)
Mean Min – 11.4C (1961-1990: 11.3C)
Adelaide Kent Town 23090 / 1977-2012
Mean Max – 22.3C
Mean Min – 12.2C
BRISBANE pre 1910
Mean Max – 25.6C
Mean Min – 15.6C
Brisbane Aero 40223 / 1996-2000
Mean Max – 25.4C (1961-1990: 25.4C)
Mean Min – 15.7C (1961-1990: 15.8C)
Brisbane 40913 / 2000-2012
Mean Max – 26.4C
Mean Min – 16.2C
SYDNEY pre 1910
Mean Max – 21.1C
Mean Min – 13.3C
Sydney Observatory Hill 66062 / 1858-2012
Mean Max – 21.7C (1961-1990: 22.1C)
Mean Min – 13.8C (1961-1990: 14.2C)
Sydney Airport AMO 66037 / 1929-2012
Mean Max – 22.2C (1961-1990: 22.2C)
Mean Min – 13.4C (1961-1990: 13.1C)
MELBOURNE pre 1910
Mean Max – 19.4C
Mean Min – 9.4C
Melbourne Regional Office 86071 / 1908-2012
Mean Max – 19.8C (1961-1990: 20C)
Mean Min – 10.2C (1961-1990: 11C)
Essendon Airport 86038 / 1929-2012
Mean Max – 19.6C
Mean Min – 9.2C
Melbourne Airport 86282 / 1970-2012
Mean Max – 19.7C (1961-1990: 19.6C)
Mean Min – 9.5C (1961-1990: 9.4C)
HOBART pre 1910
Mean Max – 16.7C
Mean Min – 7.8C
Hobart (Ellerslie Rd) 94029 / 1882-2012
Mean Max – 16.9C (1961-1990: 17.1C)
Mean Min – 8.3C (1961-1990: 8.7C)
Hobart Airport 94008 / 1958-2012
Mean Max – 17.5C (1961-1990: 17.4C)
Mean Min – 8.1C (1961-1990: 8C)
Average Maxima
Pre-1910 average mean maximum for all six Australian capital cities - 21.4C
13 nearby ACORN/airport/same stations for all years - 21.6C / for 1961-1990 - 21.7C.
Average Minima
Pre-1910 average mean minimum for all six Australian capital cities - 11.8C
13 nearby ACORN/airport/same stations for all years - 11.9C / for 1961-1990 - 12.2C.
Many of the pre-1910 temperatures were recorded without a Stevenson Screen for part or all of their record whereas after 1910 the thermometers were screened. In turn, these are all capital city stations with abundant modern UHI and airport warming influences.
In Australia’s new ACORN-SAT dataset, between 30% and 50% of all Fahrenheit degrees recorded before 1972 metrication were rounded to .0F, creating a probable downward bias up to .3C before that year. The BoM has already acknowledged but not adjusted for a .1C metrication bias in 1972.