Published data were used to analyse the long-term annual temperature trends at eight locations located in northern Australia. Stations are located in states of Western Australia, Northern Territory and Queensland. All of the stations are located at latitudes north of 26 deg S. Similarities in the trends for individual stations enabled a comprehensive trend to be established for the whole region.
The data used were all from the website of BOM (the Australian Bureau of Meteorology). Only raw data were used (ie as originally recorded, without any adjustments). Data were only used from stations located in rural areas or in small towns so as to avoid the possible influence of urbanisation on the temperatures.
The periods of the data ranged from 108 years to 138 years(the earliest record, at Alice Springs, commencing in 1872).
Two stations, Darwin and Alice Springs, had major relocations near the middle of their records but were used in the present analysis because of their longevity and geographical representativeness:
- The recorded temperatures at Darwin Post Office, which commenced in January 1882, ceased suddenly on 19 February 1942 with the Japanese bombing that destroyed much of the city. Fortunately temperature records had commenced in February 1941 at Darwin Airport, a distance of about 6 km inland from the Post Office station. No useful correlation could be deduced from the short period of overlapping records. However, a comparison of the annual mean trendlines before and after 1941 allowed an approximate adjustment for consistency to be made. An adjustment of -0.6 deg C (ie a reduction) was therefore made to the Darwin Post Office annual mean temperatures for the period 1882-1941.
- The recorded temperatures at Alice Springs Post Office, which commenced in March 1878, ceased in December 1953. Temperature records had commenced in November 1941 at Alice Springs Airport, a distance of about 13 km south from the Post Office station. A correlation of the annual mean temperatures at the two stations indicated that no adjustments were nececessary to attain consistency, although there were seasonal differences. No adjustments were therefore made to the Alice Springs Post Office annual mean temperatures for the period 1882-1953.
The plots shown below are of the annual mean temperatures at each of the eight locations. On each plot a polynomial “best fit” trendline has been added. It should be noted that the trendlines near each extremity (ie near the start and end of the records) are quite sensitive to individual data points, whereas trendlines within the main body of the record are much more stable and reliable.
COMPARISON OF TRENDLINES
Annual Mean Temperature Trends
[ The basis of these trendlines can be seen from the analyses for the eight individual stations – see next section ]
Annual Mean Temperature Residual Trends
[ The individual trend-lines have been adjusted by constant amounts to be approximately zero at trend peaks around 1960 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Marble Bar (Western Australia) 1901-2015
Darwin (Northern Territory) 1882-2015
Alice Springs (Northern Territory) 1872-2015
Burketown (Queensland) 1890-2009
Richmond (Queensland) 1893-2015
Innisfail (Queensland) 1981-2015
Boulia (Queensland) 1888-2015
Gayndah (Queensland) 1910-2009
DISCUSSION AND COMMENTS
- The annual mean temperature trend-lines for eight stations are similar, especially since about 1920. Prior to about 1920 the trendlines are more variable.
- A cyclical pattern in the trend-line is apparent at the eight stations. A Low occurred in around 1960, and Highs occurred in around 1920 and 2000, indicating a cyclical wavelength of about 80 years.
- The ~2000 peak was generally about 0.5-1.0 deg C higher that that in ~1960.
- The ~1980 trough was generally about 0.5-1.2 deg C less than the peak in ~1950.
- The general consistency of the annual mean temperature trend-lines of the eight widely separated stations provides support for the good quality of the data and the conclusions drawn from the analysis.
- The increase in the annual temperature trend since around 1960 is typically around 0.5-1.0 deg C with indications of a cyclical peak around 2000.
- Another cyclical peak around 1920 is less well defined, with a median temperature about 0.2 deg C higher than around 1960.
- None of the eight stations show any abnormal increase in annual mean temperature in recent decades.
This article was written by Brian Gunter of Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.