Hyping Maximum Daily Temperatures (Part 4)

Written by:
4 February 2023
Hyping Maximum Daily Temperatures (Part 4) - Featured image
Originally Appeared In

his article was originally published the author’s website.

This article reflects the author’s ongoing research into the methods used by the Australian Bureau of Meteorology to collect, collate, adjust and publish temperature and rainfall data. Research into this topic have been published in the IPA Climate Change The Facts Publications, with an updated working paper shortly to be published.


John William Abbot versus Director of Meteorology was to be heard in the Administrative Appeals Tribunal, Brisbane, yesterday, Friday 3rd February 2023 – a focus of this series of blog posts. While it was to be a public hearing, and I was to be the expert witness, before I could present my evidence, the case was taken back into mediation and the public asked to leave.

I am now a part of the mediation that was not resolved yesterday. I am now legally bound to not comment on this ongoing mediation. That is set down to resume on Tuesday.

I am very grateful to Caroline, Gideon, Charles and Howard, for attending the public hearing yesterday – albeit so brief.

This saga has been ongoing for me in some form since 25th August 2015 when I first requested parallel data for Wilsons Promontory Lighthouse from the electronic weather station relying on platinum resistance probes since September 2000 and as a check from the original liquid-in-glass thermometers (including the mercury), which were installed back in 1872 and theoretically still recording temperatures. I specifically asked:

Could you please also provide me with the complete temperature record (maximum and minimum) as measured from each of these different thermometers for the period of their available record.

I am particularly keen to know if there is a single continuous monthly record for the mercury thermometer installed in 1872, to the present. [end]

This requested was made through the [email protected] portal, and I followed up with phone calls, but my application was never formally acknowledged. We do know it was discussed by Bureau staff as it is mentioned in correspondence that was made public following a partially successful FOI request by Mulholland (#FOI30-6142) concerning limits set on how cold temperatures can be recorded at Goulburn. The correspondence is available online here.

Because a change in measuring equipment can potentially create discontinuities in a temperature record, it is Australian Bureau of Meteorology policy to have new equipment recording side-by-side with old equipment for a period of at least 2 years. In this way, readings from the new equipment can be compared with readings from the old equipment, including to check they are comparable – that there are no discontinuities. This is the parallel data.

It is reasonable to assume this data would be public, but it is guarded by the Bureau and kept secret. The Bureau also claim it is undigitized and only potentially available as hard copies of A8Forms and that the Bureau lacks the available resources for scanning to provide this on request. Access to this data for the Brisbane airport weather station was the objective of an FOI request by John Abbot and so began the current saga.

In 2017, I was successful in acquiring some parallel data for Mildura. After many late nights manually transcribing values from the scanned A8 Forms provided to me following the intervention of then Minister for Energy and Environment Josh Frydenberg I charted the data and did some analysis.

This analysis showed that the first probe, which became the official instrument at Mildura on 1 November 1996, was recording too cool relative to the mercury with some seasonal variability. On 3 May 2000, the Bureau changed the Stevenson screen to a smaller design, and while there is no record of a change in the type of probe, this almost certainly also occurred based on the very different recording pattern relative to the mercury, see Chart 1.

Chart 1 shows the changing pattern in the difference between recordings from the mercury versus probe for maximum daily temperatures at the official recording station in Mildura (Victoria) shown as monthly averages.
Chart 1 shows the changing pattern in the difference between recordings from the mercury versus probe for maximum daily temperatures at the official recording station in Mildura (Victoria) shown as monthly averages.

Initially the temperatures as recorded at Mildura, from 3 May 2000 from what I am assuming was a new second probe in the new shelter, were more consistent with the measurements from the mercury thermometer. But then I could see from the data that the temperatures from the probe started to cool relative to the mercury thermometer for the period to 27 June 2012. Cooling was at a rate of nearly 1°C per 100 years.

Then on 27 June 2012 the probe which had been recording the official temperature at Mildura for 12 years while drifting to record ever cooler, was changed. The limited available parallel data indicates that this third probe records too hot relative to the same mercury thermometer – often by 0.4 °C.

This is the extent of the available parallel data, and it suggests:

1. The change from a mercury thermometer to a probe makes a material difference to the reliability of the historical data.

2. This matters for understanding climate variability and change – the trend.

3. This information is in the public interest – given far reaching public policy decisions are being made on the basis of a 1.5C tipping point.

4. We know the data exists because I received the scanned A8 Forms for Mildura with recordings from both probes and the mercury back in 2017. We also know the data exists according to the Bureau’s own referencing of this data and discussion of this data.

On 12th December 2019, John Abbot made a request to access the parallel daily maximum and minimum temperature datasets for the Brisbane airport weather station; that is the measurements recorded using the mercury thermometer as a potential check on the measurements from the platinum resistance probe.

That data has never been provided and is the origin of the current saga to be resumed on Tuesday through private mediation.

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