Monitoring changes in Australia’s climate requires observational datasets that are not only good quality, but also homogeneous through time.
A homogeneous climate record is one in which all observed climate variations are due to the behaviour of the atmosphere, not other influences, such as changes in location, exposure of the observation site, instrumentation type or measuring procedure.
A change in the type of thermometer shelter used at many Australian observation sites in the early 20th century resulted a sudden drop in day time temperature an increase in minimum temperatures which is entirely spurious. It is for this reason that these early data are currently not used for monitoring climate change. Other common changes at Australian sites over time include location moves, construction of buildings or growth of vegetation around the observation site and, more recently, the introduction of Automatic Weather Stations.
The impacts of these changes on the data are often significant at the individual station level, so they need to be removed before long-term trends are investigated. Procedures to identify and adjust for non-climatic changes in historical climate data generally involve a combination of:
- investigating historical information (metadata) about the observation site,
- using statistical tests to compare records from nearby locations, and
- using comparison data recorded simultaneously at old and new locations, or with old and new instrument types.
"High-quality" Australian climate datasets have been developed in which homogeneity problems have been reduced or even eliminated. These datasets represent only a small fraction of the total Australian climate archive.
Further details are available from Australian Climate Observations Reference Network – Surface Air Temperature.
NOTE: The Daily and Annual temperature datasets below have been superseded by the Australian Climate Observations Reference Network – Surface Air Temperature ( ACORN-SAT) dataset.