Dr Bill Johnston
Mount Isa post office (Bureau of Meteorology, BoM ID 29125), and Mount Isa airport (Aero, 29127; Latitude -20.72o, Longitude 139.49) joined 1 January 1967; temperature data from 1 January 1957 to 31 December 2024; and separately, Mount Isa Mine (29126), Latitude – 0.7361, Longitude 139.4817; temperature from January 1965 to July 1992.
Although mining is due to cease in the near future, Mount Isa in central Queensland is home to one of the most productive single mines in the world. A post office opened in 1924, and the railway to the port of Townsville opened in 1929. An aerodrome constructed for the United States Army Air Force in 1943 became a major military camp during WWII. Post office data from 1957 were merged with Aero site data from January 1967.
While little seems known about conditions in the post office yard, site summary metadata suggests the Aero site was partially automated in September 1996, but a humidity probe was apparently not installed until March 2009. An Almos automatic weather station (AWS) has replaced manual observations but the changeover date is not available. Metadata also ignores when 60-litre Stevenson screens replaced 230-lite screens at the previous or current site; however, it is likely to have been before data for the earlier manual comparison site was so-designated. As metadata cannot be trusted, analysis is best undertaken using objective statistical methods.
While not an Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) dataset used to monitor Australia’s warming, together with up to nine other sites including some ACORN-SAT ones, maximum temperature (Tmax) observed at the post office, airport and the mine were used by scientists at the BoM to homogenise ACORN-SAT sites as far afield as Victoria River Downs (1015 km), Rabbit Flat (987 km) and Longreach (571 km) (Figure 1).
Figure 1. In addition to Victoria River Downs, Rabbit Flat and Longreach, maximum temperature data for Mount Isa post office, Aero and the mine were used to homogenise ACORN-SAT sites at Tennant Creek, Camooweal, Burketown, Normanton and Richmond.
As no attempt is made by ACORN-SAT to assess the quality of data used to construct comparator datasets, as a subset of Victoria River Downs, this study aimed to determine whether the combined Tmax dataset for the post office, airport (Aero), and the mine were fit for the purpose of homogenising other sites.
Conclusions
Possible site changes include undocumented site moves, removal of vegetation in the vicinity of screens using herbicide or mechanically, replacement of 230-litre Stevenson screens with 60-litre ones, introduction of the Almos AWS at the airport and the withdrawal of staff that maintained sites and instruments.
Checks and balances that are part of the BomWatch approach provide assurance that step-changes in 1966, 1980, 1996 and 2013 in the combined post office/Aero dataset, and in 1980 at the mine, are unrelated to the climate. Post hoc tests verified that data consist of non-trending segments delineated by step-changes that are unrelated to the weather.
Importantly, accounting for step-changes and rainfall simultaneously left no residual trend or change that could be attributed to CO2, coal mining, electricity generation or anything else.
The use of correlated, faulty data that are not homogeneous, to adjust faults in ACORN-SAT has no statistical or scientific merit and should be abandoned.
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Click here to download the full paper with photos, graphs and data