Net Zero

Australia’s Broken Temperature Record (Part 5)

Written by
31 March 2022
Jennifer at Goulburn weather station in August
Originally appeared in JenniferMarohasy.com

All 224 Homogenised Temperature Series – Including the Bombing of Darwin

I can hardly be accused of cherry picking if I present all the temperature series – all four iterations of the homogenised ACORN-SAT temperature series charted with the raw historical series from the Australia Data Archive for Meteorology (ADAM). ADAM is a little-known data set that contains the unhomogenised values: the temperature values as they were recorded.

The extent of their remodelling is mind boggling, including for Darwin, where in the most recent iteration temperatures in the historical record are artificially cooled including for the period of World War 2.

Darwin was bombed 64 times by the Japanese during World War 2. The first air raid destroyed the weather station at the post office and killed the postmaster, but Darwin also had a weather station at the airport that had been in operation almost a year.

The Australian War Memorial would never change important historical war records, yet the Australian Bureau of Meteorology has remodelled Darwin’s temperature record dropping down maximum temperatures during World War 2 by on average 1°C for 1941 and on average 0.5 °C for 1942. The Bureau has done this by changing daily temperatures. For example, on 18th February 1942 – the day before the first air raid and the day of the last evacuation of civilians – the maximum temperature was recorded as 31.1 °C at the airport in the Australian Data Archive for Meteorology (ADAM). But when I look in the official Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) database the maximum temperature for that day has been cooled to 30.1 °C. This revisionists approach to our climate history affects Australia’s war time record because weather and climate are critical to military strategy.

In March 2012, when Version 1 of ACORN-SAT was published, the Bureau was claiming in its catalogue that there was abnormal cooling of the Darwin temperature record before 1 January 1937 because of shading from trees. Somewhat peculiarly, this was then used as a justification for adjusting all the temperatures down before this date back to 1910, in effect further dramatically cooling the early record. At that time, there were no changes to the daily temperatures during WW2. The changes to the war record were made in 2018, in the development of ACORN-SAT version 2.0 and have been carried forward into the current version ACORN-SAT 2.2.

Just this month I’ve updated the interactive table at my website that shows the extent of the remodelling of the temperature record by plotting the annual maxima and minima series from each of the 112 homogenised ACORN-SAT sites (versions 1, 2.0, 2.1 and most recently 2.2) with the actual maxima and minima values from the Australian Data Archive for Meteorology (ADAM). There are 224 charts with at least five temperature series in each chart (more when the raw/ADAM data includes post office as well as airport series etc.). Click across and have a play:

https://jennifermarohasy.com/acorn-sat-v1-vs-v2/

There is a lot of work in those charts and this is the only place on the internet that you will find them!

The Darwin maximum temperature comparison is the feature image and does look a bit messy because initially temperatures were recorded at the post office (green series), and temperature were cooling following the cyclone in 1937. The Bureau have completely remodelled this cooling out of the official record with the latest iteration that is ACORN-SAT version 2.2 (pink series) showing gradual warming from 1910 through until the present. Considering the original series from the post office (014016 green) and then the airport (014015 blue) there is cooling and then warming.

It is the completely remodelled (pink series) not the original historic (green and then blue series) that are incorporated into the Annual Climate Statement to lament catastrophic human-caused global warming.

Homogenisation of the data is not the only factor that affects overall warming trends. The Bureau truncates the historical record to begin in 1910. Considering Darwin there is a perfectly good historical temperature record beginning in 1895 when temperatures were recorded using a mercury thermometer in a Stevenson Screen. There is no reason to truncate or change this record, but the Bureau completely remodels it removing the hot early record (pre-1910) and then dropping down/cooling daily values from 1980 until a linear trend is created (pink series).

The maximum temperature series for Darwin airport based on the ADAM data.
The maximum temperature series for Darwin airport based on the ADAM data.

This is part 5 of the series, Australia’s Broken Temperature Record. You can read part three here: https://ipa.org.au/netzero/australias-broken-temperature-record-part-4

This blog post blew-out to 4,300 words in a draft that incorporated information about Darwin’s early war history and the story of the telegraphic office in Darwin that became the post office. The much longer version will be published as part of book that I am writing about how to fix Australia’s broken temperature record.

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Jennifer Marohasy

Jennifer Marohasy is a Senior Fellow at the Institute of Public Affairs

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