Digging deeper into the Australian Temperature Adjustments, below are data from 224 stations in the Torok and Nicholls network. It looks like most of the increase in Australian temperature in the last 150 years is due to a step-like increase in the mean annual minimum temperature since 1975!
CA examined the sometimes considerable adjustments of individual stations here and here. Steve also plotted up the raw station data. I don’t know how he did the plots for ‘before adjustment’ as all the data seems to be ‘post adjustment’ by Torok.
Here I use a differenced normalization method described previously to account for the differences in mean temperature at each station, without averaging over areas. Its not exactly the same, but it produces a similar trend result, as shown in the last figure below.
The Torok network contains the mean annual maximum and minimum temperatures of 224 stations, and these are plotted below with the ‘official’ BoM mean temperature (blue) of high quality network of 103 stations. While the minimum and mean temperatures are clearly increasing, the maximum temperature has not increased at all.
This has no doubt been observed before, but it raises some very interesting physical issues (ie temperature increase is self-limiting). Torok states that:
Maximum and minimum temperatures have increased since about 1950, with minimum temperatures increasing faster than the maximum temperatures.
However, its not clear from this graph that maximum temperatures have increased significantly since 1950. The graphs above have gone back to 1910 only so as to more closely resemble the BoM graphs. When all the data is plotted back to 1850, mean annual maximum temperatures look totally flat.
Moreover, the increase in minimum temperatures seems isolated to the period after 1975, associated with the change known as the Great Pacific Climate Shift.
Torok and Nicholls prepared this dataset from daily station maximums and minimums as follows.
A high-quality historical surface air temperature data set, for mean annual temperatures, has been prepared for Australia by adjusting data for inhomogeneities caused by station relocations, changes in exposure and other discontinuities.
I am reminded of this paper: MAXIMUM AND MINIMUM TEMPERATURE TRENDS FOR THE GLOBE: AN UPDATE THROUGH 2004 by Russell S. Vose*, David R. Easterling, and Byron Gleason showing a sharp increase in maximum temperatures globally, which does not seem to be apparent in the Australian data. More arguments for a comprehensive and independent audit of the global data sets?
The next step would be to audit the daily station data in this directory. Access seems to be blocked though.
Below is a comparison of the official BoM mean temperatures, and the result of my differenced normalization procedure on the 103 high quality stations (obtained from CA here), just to show that the simple method of normalization does produce similar trends as the official version, even if the details differ.
Oh and here is the script.R. You need to download the Torok files first, and uncomment sections as noted, as it takes awhile to run.
Torok, S. and Nicholls, N., 1996. An historical temperature record for Australia. Aust. Met. Mag. 45, 251-260.