Hype about most each day temperatures (half 4)

From Jennifer Marohasy’s blog

By Jennifer Marohasi

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

I am now part of the mediation that was not resolved yesterday. I am now required by law not to comment on this ongoing mediation. This is to continue on Tuesday.

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

This mode has been in progress for me in some form since August 25, 2015, when I first requested parallel data for Wilson’s Promontory Lighthouse from the electronic weather station, which has relied on platinum resistivity probes since September 2000, and as a verification from the original liquid-in-glass thermometers (including the mercury one) installed as early as 1872 and theoretically still recording temperatures. I specifically asked:

Also, could you please provide me with the full temperature records (maximum and minimum) taken by each of these different thermometers for the period of their available record.

I am particularly interested in whether there is a single continuous monthly record for the mercury thermometer installed in 1872. [end]

This request was made through the climatedata@bom.gov.au portal and I followed up with phone calls, but my application was never officially confirmed. We know it has been discussed by Bureau staff as it is mentioned in correspondence released following a partially successful FOI request from Mulholland (#FOI30-6142) regarding the set limits for cold temperature recording at Goulburn. The correspondence is available online here.

Because a change in measuring equipment can potentially cause discontinuities in a temperature record, it is Australian Bureau of Meteorology policy to record new equipment alongside old equipment for a period of at least 2 years. In this way the readings of the new equipment can be compared to the readings of the old equipment, also to check that they are comparable – that there are no breaks. This is the parallel data.

It is reasonable to assume that this data is public, but it is guarded and kept secret by the Bureau. The Bureau also claims that it is not digitized and may only be available as paper copies of A8 forms and that the Bureau lacks the resources available to scan to provide this upon request. Access to this data for the Brisbane Airport weather station was the target of an FOI request from John Abbot and this is how the current saga began.

In 2017 I managed to collect some parallel data for Mildura. After many long nights of manually transcribing values ​​from the scanned A8 forms that were provided to me following the intervention of then-Energy and Environment Secretary Josh Frydenberg, I recorded the data and did some analysis .

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

Initially, temperatures recorded at Mildura from May 3, 2000 by a new second probe at the new shelter from May 3, 2000 more closely matched the readings from the mercury thermometer. But then I could see from the data that the probe’s temperatures were beginning to cool relative to the mercury thermometer for the period up to June 27, 2012. Cooling occurred at a rate of nearly 1°C per 100 years.

Then, on June 27, 2012, the probe that had recorded the official temperature at Mildura for 12 years as it drifted to become progressively cooler was replaced. The limited parallel data available suggests that this third probe is reading too hot — often by 0.4°C — compared to the same mercury thermometer.

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

1. Changing from a mercury thermometer to a probe makes a significant difference in the reliability of historical data.

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

3. This information is in the public interest – as major policy decisions are made based on a 1.5 degree tipping point.

4. We know the data exists because I received the scanned A8 forms for Mildura with records from both probes and the mercury in 2017. We also know that the data exists because of the Bureau’s own referencing of and discussion of that data.

On December 12, 2019, John Abbot requested access to the parallel daily high and low temperature records for Brisbane Airport weather station; these are the measurements recorded using the mercury thermometer as a possible verification of the measurements from the platinum resistance probe.

This data was never provided and is the origin of the current saga, which is due to continue on Tuesday through private mediation.

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