If you have seen the articles on the NZ temperature adjustments and Nordic temperature adjustments you might be interested in the Australian data.

The issue with NZ and Nordic data that the raw temperature data for weather stations do not show the temperature increases indicated by the IPCC, raising the question of how the data have been adjusted.

As Prof. Karlen states in the ClimateGate email #1221683947, temperature at many stations has not exceeded early 20th century temperatures:

.. data sets show an increase after the 1970s to the same level as in the late 1930s or lower. None demonstrates the distinct increase IPCC indicates.

Here is the plot of means of Australian raw data for 103 temperature stations, based on the file Aus.tab downloaded from the Australian BoM web site and collated by Steve McIntyre.

The red line is the annual temperatures from 1910 to 2008 based on a simple average of the data in each year. The temperature is strongly increasing, and there seems to be some sort of glitch around 1940 where temperatures increase suddenly.

The problem with averaging all these stations is that the any tendency in stations to change with latitude introduces bias. That is, if stations are introduced in warmer climates late in the century, the average will be biased to warmer temperatures.

To get around this problem, I have simply normalized each of the station records (i.e. subtracted a station’s mean value) before averaging each year. This puts all of the stations on a even playing field, so to speak, no-matter whether it is normally warm or cold.

The blue line shows the normalized result. The temperatures are only slightly increasing.

Whats more, current day temperature has yet to exceed the peak temperature achieved in 1914 (blue dotted line and marked with blue crosses).

While averages of the raw Australian data appear to be increasing strongly, a simple normalization procedure to remove the bias introduced by station changes virtually eliminates all trace of temperature increases.

One would expect a similar situation in Australia to the Nordic stations, with a lack of individual stations with strongly increasing temperatures.

For interest, here is the figure supporting the temperature curves in IPCC and also published in e.g. Forster, P. et al. 2007: Assessing uncertainty in climate simulation. Nature 4: 63-64.

Here is the data object Aus.tab, and here is the script.R. Save the data object to a directory and then run the R script in that directory.

I have a similar view to Willis Eschenbach on this issue, and don’t claim that the BoM is actually altering the global temperature figures. However, issues in New Zealand and the Fennoscandian region are also found in Australia, proving the point that the compiled data cannot be taken at face value, and the adjustments to get them into the form we usually see need to be comprehensively audited.