This post sets the scene for a series of forthcoming ones on climate reconstruction of the years before 1910 in South East Australia.
Temperature measurements began to be recorded and retained systematically in Australia in the 19th century, but it was only after 1908 that most thermometers were enclosed in standard Stevenson screens. Many monthly MAXIMUM temperature records in South East Australia show sudden and substantial step changes around 1908, 1898 and earlier dates. It is likely that some of the steps down reflect the installation of either Stevenson screens or one of the alternatives in use at the time, such as “Thermometer Sheds”.
This post shows a plot of RAW Tmax data from the following stations (Australian BoM station ids in brackets, see the map below for the positions)
- Melbourne Regional Office (86071), Cape Otway Lighthouse (90015), Wilsons Promontory Lighthouse (85096)
- Adelaide West Terrace (23000), Hay Miller Street (75031), Deniliquin Wilkinson Street (74128)
The following figure shows 12-month moving averages of RAW Tmax data, with constant offsets applied in order to better reveal the steps and the generally high degree of correlation of temperature fluctuations.
For the nearby pair of Hay and Deniliquin there appears to be steps down in 1898 (at very similar times) and again in 1908, but this time with a noticeable delay. There also appears to be a transition around 1916 to a noticeable reduction in correlation with Adelaide.
Cape Otway also appears to have a step down around 1898 and another around 1908.
To the author these sudden and large steps in both absolute and relative (to neighbours) temperature cannot be climatic in origin, and probably reflect system changes and/or moves. The similarity of the timing of the steps, but with significant differences, suggests the hand of human organisation. The only alternative hypothesis I can offer involves Martians with heat rays operating only in certain locations.
Subsequent posts will examine the temperature steps in more detail, estimating their seasonal profiles, correcting the monthly averages, and presenting the resulting regional climate histories back to at least 1890.