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Methodology
Temperatures for 38 weather stations in the 1953 Year Book were converted from Fahrenheit to Celsius at Grafton, Armidale, Port Macquarie, Broken Hill, Dubbo, Newcastle, Bathurst, Jervis Bay, Albury, Cooma, Mildura, Benalla, Bendigo, Horsham, Ballarat, Bairnsdale, Cairns, Townsville, Cloncurry, Mackay, Longreach, Rockhampton, Charleville, Toowoomba, Streaky Bay, Port Pirie, Yongala, Mt Gambier, Wyndham, Geraldton, Kalgoorlie, Collie, Albany, Burnie, Launceston, Darwin, Daly Waters and Alice Springs.
The weather stations at Leeton, Swansea and Zeehan were excluded either due to a lack of comparable data or relocated stations too far from the 1911-40 original to be meaningful.
Raw temperature data from the BoM online database was averaged for 1911-40 and 2000-11, as well as intervening periods for comparison with trends during the 20th Century.
Only the 1911-40 and 2000-11 periods were compared within the results which you can download as an Excel spreadsheet, and intervening data is listed below within the station breakdowns.
The 1911-40 and 2000-11 timeframes were also compared against the same periods within the Australian Climate Observations Reference Network - Surface Air Temperatures (ACORN).
Discussion
The 1953 Australian Commonwealth Year Book has reliable source data for 1911-40 temperature averages at various weather stations not available in the BoM's digitised database of old logbook records.
Among the 38 stations analysed, 27 have BoM database records for the period 1911-40. In the Year Book and BoM raw tables, the maxima for these 27 both average 24.4C. Minima average 12.8C in the Year Book and 12.9C in the BoM raw tables.
Among the 53 maxima and minima at these 27 stations (1911-40 raw minima not available at Mt Gambier), 34 or 64% of Year Book averages are identical to BoM raw averages in 1911-1940.
Among the eight stations that differ in maxima during 1911-40, five were 0.1C higher in raw than their Year Book equivalents and three were 0.1C lower in raw than their Year Book equivalents.
Among the 11 stations that differ in minima during 1911-40, four were 0.1C lower in raw than their Year Book equivalents, two were 0.1C higher in raw than their Year Book equivalents, two were 0.2C higher in raw than their Year Book equivalents, and two were 0.3C higher in raw than their Year Book equivalents.
In maxima, the differences represent a sum 0.2C increase within a total 658.7 degrees among the 27 stations. In minima, the differences represent a sum 1.1C increase within a total 334.9 degrees among the 27 stations.
The reason for the 19 differences between Year Book and digitised BoM raw temperatures is unknown but the book was compiled to the highest standard of statistical analysis possible in 1953 for official Australian data references on the world stage, and its 1911-1940 temperatures are most likely accurate.
The averaged influence of the 36% of slightly different data is statistically insignificant and 1911-1940 Year Book temperatures can be considered accurate substitutes for comparison.
Some of the BoM raw station records have years missing but not within the 1911-40 and 2000-11 periods except for Dubbo ACORN which started in 1921, Jervis Bay 68151 raw which started in 2002 and Collie East 9994 raw which started in 2003.
Most stations have relocated, many to nearby town airports, introducing warmer or cooler environmental variables to minima and maxima that are adjusted in the ACORN database.
Among the 38 weather stations, 15 are in the ACORN database.
The comparison is between a 30 year climate period 1911-40 and the 12 years up to and including 2011. The BoM had not digitised all 2012 months at the time of this analysis. 2001-10 is considered the hottest ever decade in Australia.
Results
The average raw maximum of 38 stations in 1911-40 was 24.2C and in 2000-11 it was 24.6C.
The average raw minimum of 38 stations in 1911-40 was 12.5C and in 2000-11 it was 12.5C.
The average raw maximum of 15 ACORN stations in 1911-40 was 25.1C and in 2000-11 it was 25.4C.
The average ACORN maximum of 15 ACORN stations in 1911-40 was 24.8C and in 2000-11 it was 25.6C.
The average raw minimum of 15 ACORN stations in 1911-40 was 14.0C and in 2000-11 it was 13.2C.
The average ACORN minimum of 15 ACORN stations in 1911-40 was 12.3C and in 2000-11 it was 13.9C.
See Excel spreadsheet for further details.
Conclusion
The 1953 Commonwealth Year Book provides what was considered a representative national distribution of Australian average temperatures in the early 20th Century, and these can be compared with the same locations in the 21st Century - both 38 stations raw and 15 stations adjusted within ACORN.
All 38 station 1911-40 Year Book minima and maxima averaged 18.35C and all 2000-11 BoM raw minima and maxima averaged 18.56C, suggesting an increase in mean temperature of 0.21C over 100 years for residents of the towns.
Within the 15 ACORN stations, adjusted 1911-40 minima and maxima averaged 18.53C and 2000-11 adjusted minima and maxima averaged 19.74C, suggesting an increase in mean temperature of 1.21C over 100 years.
The general trend within raw temperatures during the 100 years was for an increase in maxima at most stations and a greater proportion of reduced minima.
This is at odds with claims that Australia's warming climate has been influenced more by minima than maxima.
ACORN adjustments by the BoM are considerably larger among minima than maxima. This is apparent in a 0.3C downward adjustment of maxima at the 15 ACORN stations in 1911-40 and a 0.2C upward adjustment in 2000-11, compared to a 1.7C downward adjustment of minima in 1911-40 and a 0.7C upward adjustment in 2000-11.
The most significant ACORN adjustment was at Launceston where the 1911-40 average raw minimum of 7.1C was adjusted down by 2.4C to 4.7C.
As the 1911-40 temperatures within this analysis were recorded in regulated Stevenson Screens, it is assumed the main ACORN justification for substantial downward adjustment of early minima was the influence of station relocations, a majority to airports, and Urban Heat Influence at the original town post office locations.
Australia's climate as experienced within the 38 representative towns warmed by a mean 0.21C over the 100 years from 1911-40 to 2000-11, according to unadjusted thermometer readings, whereas their significance in those timeframes to Australian averages influenced by grid cell weighting within the national ACORN dataset increased by one degree to a mean 1.21C.
NSW - Grafton, Armidale, Port Macquarie, Broken Hill, Dubbo, Newcastle, Bathurst, Jervis Bay, Albury, Cooma
Victoria - Mildura, Benalla, Bendigo, Horsham, Ballarat, Bairnsdale
Queensland - Cairns, Townsville, Cloncurry, Mackay, Longreach, Rockhampton, Charleville, Toowoomba
South Australia - Streaky Bay, Port Pirie, Yongala, Mt Gambier
Western Australia - Wyndham, Geraldton, Kalgoorlie, Collie, Albany
Tasmania - Burnie, Launceston
Northern Territory - Darwin, Daly Waters, Alice Springs
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