Published data were used to analyse the long-term annual temperature trends at ten locations located in southern Australia. Stations are located in states of Western Australia, South Australia, New South Wales, Victoria and Tasmania. All of the stations are located at latitudes south of 28 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).
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 ten 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 1930 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Cape Leeuwin (Western Australia) 1897-2015
Northam (Western Australia) 1902-2015
Tibooburra (New South Wales) 1910-2014
Wicannia (New South Wales) 1881-2014
Yamba (New South Wales) 1910-2015
Moruya Heads (New South Wales) 1910-2015
Robe (South Australia) 1884-2015
Maryborough (Victoria) 1899-2015
Wilsons Promontory (Victoria) 1880-2015
Cape Bruny (Tasmania) 1923-2015
DISCUSSION AND COMMENTS
- The annual mean temperature trend-lines for ten stations show an increase since about 1930.
- A cyclical pattern in the trend-line is apparent at several of the stations, particularly Moruya Heads and Tibooburra. A Low occurred around 1930, and a High around 2010.
- The ~2010 peak was generally about 0.4-1.1 deg C higher that that in ~1930.
- Four of the stations (Cape Leeuwin, Yamba, Maryborough and Cape Bruny) show no evidence of a peak being reached around 2010.
- The general consistency of the annual mean temperature trend-lines of nine of the ten widely separated stations (Moruya heads is the exception) 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 1930 is typically around 0.4-1.2 deg C with indications of a cyclical peak around 2010.
- Seven of the ten stations either show no abnormal increase in annual mean temperature in recent decades or have a cyclical peak around 2010. The other three stations (Cape Leeuwin, Yamba and Wilsons Promontory) show no cyclical peak around 2010, although in future years such a peak may be evident.
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.