Hyping Maximum Daily Temperatures (Part 3) | Watts Up With That? (2023)

Jennifer Marohasy

If maximum temperatures are the same, whether measured by platinum resistance probes or mercury thermometers, why does the Bureau make an adjustment of 0.5 °C in the homogenisation of temperatures from Cape Otway Lighthouse?

On Friday (3rd February 2023), I will be appearing as an expert witness in the Administrative Appeals Tribunal in Brisbane. The hearing is about a Freedom of Information (FOI) request that has been denied my husband, Dr John Abbot, for over three years. The information, I will argue, needs to be made public, to enable some assessment of the reliability, or otherwise, of temperatures as recorded at official Australian Bureau of Meteorology weather stations.

Claims that we are facing a climate catastrophe because temperatures will soon be exceeding 1.5 °C is driving the closure of coal mines, caps on the price of gas and a mental health epidemic amongst children who increasingly fear global warming.

Temperature measurements as published by the Australian Bureau of Meteorology, and other such weather bureaus around the world, are at the heart of the concern, because they purportedly show an unprecedented increase, particularly over recent years.

On the one hand, the Bureau claims temperature measurements from the platinum resistance probes, which now replace mercury thermometers at most official recording stations, are equivalent and therefore there is no need for scrutiny of the parallel measurements that exist for 34 weather stations. On the other hand, the Bureau has made changes to official temperatures as recorded at Cape Otway Lighthouse theoretically of 0.5 °C for the 84 years from 1910 to 1994 based on this instrument change. According to theACORN-SAT Station Adjustment Summarytemperatures have been dropped down from 15th April 1994 back to 1st January 1910 by 0.5 °C, citing installation of an automatic weather station (AWS) that involves a change from mercury thermometer to probe.

It is note worthy that the direction of the adjustment contradicts the expected affect of changing to a probe, which would be that the probe might measure warmer than the mercury. This is stated in the Bureau’s own Research Report No. 032The Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) Version 2 (October 2018)by Blair Trewin:

In the absence of any other influences, an instrument with a faster response time [a probe] will tend to record higher maximum and lower minimum temperatures than an instrument with a slower response time [a mercury thermometer]. This is most clearly manifested as an increase in the mean diurnal range. At most locations (particularly in arid regions), it will also result in a slight increase in mean temperatures, as short-term fluctuations of temperature are generally larger during the day than overnight.” (Page 21) End quote.

Because of the difficulty in achieving consistency between temperature recordings from the probes with traditional mercury thermometers the Indonesian Bureau of Meteorology (BMKG) records and archives measurements from both devices with a policy of having both types of equipment in the same Stevenson Screen at all its official weather recording stations.

It is important to note that by cooling past temperatures at Cape Otway by 0.5 °C, rather than, for example, increasing the value recorded from the probe each day, the Bureau has been theoretically under reporting the temperatures from Cape Otway lighthouse by 0.5 °C since 15th April 1994.

This difference of 0.5 °C – that is one third of the dread 1.5 °C that is driving the closure of coal mines, caps on the price of gas and a mental health epidemic amongst children who increasingly fear global warming – is only an estimate by the Bureau.

The Bureau cannot know the exact amount because the mercury thermometer was removed at the same time the probe was installed at the weather station at Cape Otway lighthouse. The mercury thermometer that was removed on 15th April 1994 had been faithfully used to measure maximum temperatures at Cape Otway lighthouse since 1865 – for 129 years. Information on equipment changes can be found in theMetadata for Cape Otway, available online.

The Australian Bureau has a policy of maintaining mercury thermometers with probes in the same Stevenson Screen for a period of at least three years when there is a change over. This policy, however, is not implemented and was completely ignored on 15th April 1994 at Cape Otway.

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While the mercury thermometer had been reliably recording temperatures at Cape Otway for 129 years, the probe needed replacing after just 14 years, on 11th November 2010 according to theMetadata for Cape Otway.

According to theACORN-SAT Station Adjustment Summaryno additional changes were made to the official historical temperatures following the installation of the second probe.

It is therefore reasonable to assume that temperatures at Cape Otway light house, temperatures that are incorporated into global databases used to calculate global warming, are still reliably 0.5 °C cooler than the ‘real temperature’, in other words the temperature as it would be recorded by a mercury thermometer.

If we add this 0.5 °C to 1.47 °C, which is how much the Bureau estimates Australia has warmed since 1910, then the tipping point of 1.5 °C has already been exceeded!

This should be of immense concern to climate activists. They should be screaming for an audit of temperature measurements.

Because the only way we can know for sure whether the tipping point of 1.5 has been exceeded, or not, is if the parallel data from the 34 weather stations where the Bureau claims to be recording temperatures from mercury thermometers and temperature probes in the same Stevenson Screen is made public. Then we can know if the probes really do record 0.5 °C cooler than mercury thermometers that were historically used to measure temperatures.

This is the essence of the FOI request that has been refused: that the parallel data be released.

The Bureau has variously claimed that it cannot make this parallel data public because it would be too onerous to scan all the A8 Forms that have the maximum temperatures recorded manually (written by hand onto paper) from the mercury thermometer each day next, to the digitally recorded temperature from the probe. An example ofan A8 Form is provided in Part 2of this series.

More recently the Bureau has claimed that it cannot make this information public because it doesnotexist, or variously that an A8 Form is not a document and therefore not subject to John Abbot’s FOI request. All the while the Bureau’s director, Andrew Johnson, writes to me that the measurements from the probes are equivalent to the measurements from the mercury.

Following the intervention of then Environment and Energy Minister Josh Frydenberg back in October 2017, I was provided with over 10 681 scanned A8 pages for the period from 1 January 1989 to 31st January 2015 for the official weather station at Mildura. With the assistance of colleagues, I manually transcribed over 4 000 of these A8 Forms beginning 1 November 1996.

Analysis of this data indicates that the first probe at Mildura did indeed record temperatures too cool relative to the mercury thermometer, but the third probe that is now in place records temperatures too hot sometimes by as much as 0.4 °C. If this is indeed the case more generally at weather stations across Australia, then it is possible that the tipping point of 1.5 °C may have already been exceeded and by more than two whole degrees Celsius, specifically by 2.37 °C (1.47 + 0.4 + 0.5).

We can only know if the parallel data is made public, facilitating a more accurate assessment of the change in temperatures across the landmass of Australia since at least 1910.


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The 1.5 °C tipping point is usually understood to be a mean temperature which is the average of the minimum as well as the maximum. In the above post I have compared it relative to just the maximum temperatures at Cape Otway as this blog series focuses on maximum temperatures. Of note, a problem comparing with the mean is that the alcohol thermometer, which measures minimum temperature, was also removed from the Cape Otway weather station in 1994. The Bureau only seemed to replace the maximum in 2002 and for a period of just ten years.

While the 2014ACORN-SAT Station Adjustment Summaryclaims that the only change to Cape Otway maximum temperatures for the period before 15 April 1994 is a dropping-down of 0.5 °C, in reality, scrutiny of the ACORN-SAT data relative to the original measurements shows the changes to be more complex than that. Chris Gillham who ownsWAClimate.nethas emailed me:

Each day is treated differently by the algorithm within ACORN-SAT.

For example, Cape Otway …

6 January 1985
ACORN 2.3 : 15.4C / RAW 16.0C

7 January 1985
ACORN 2.3 : 17.6C / RAW 18.0C

8 January 1985
ACORN 2.3 : 18.3C / RAW 18.5C

9 January 1985
ACORN 2.3 : 15.9C / RAW 16.5C

15 April 1994
ACORN 2.3 : 17.0C / RAW 17.2C

ACORN cooling those five days by 0.4C on average.

Alternatively …

6 August 1931
ACORN 2.3 : 11.0C / RAW 10.8C

7 August 1931
ACORN 2.3 : 11.0C / RAW 10.8C

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8 August 1931
ACORN 2.3 : 11.9C / RAW 12.3C

9 August 1931
ACORN 2.3 : 12.9C / RAW 12.8C

10 August 1931
ACORN 2.3 : 14.1C / RAW 14.3C

Both 12.2C on average.

Mind you, ACORN v RAW dailies never make sense.

All Cape Otway dailies from 1 Jan 1910 to 13 April 1994 average 16.7C in ACORN 2.3 and 16.6C in RAW.

All Cape Otway dailies from 15 April 1994 to 31 December 2022 average 17.2C in ACORN 2.3 and 17.1C in RAW.

[end Note from Chris]

I show the effect of the different versions of ACORN-SAT on the original ADAM values in myinteractive tableunique to this website, and specifically for Cape Otway here: https://jennifermarohasy.com/wp-content/uploads/2022/03/Tmax_090015.png

The ADAM values can be found here:http://www.bom.gov.au/climate/data/
The ACORN-SAT values can be found here:http://www.bom.gov.au/climate/data/acorn-sat/#tabs=Data-and-networks
Metadata for Cape Otway Lighthouse including instrument changes can be found here:http://www.bom.gov.au/clim_data/cdio/metadata/pdf/siteinfo/IDCJMD0040.090015.SiteInfo.pdf

In the following tables I annotate the relevant information in Metadata document andACORN-SAT Adjustment Summary.

Table 1.

Table 2.

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The ACORN-SAT Station Adjustment Summary, as provided to me in 2014 can bedownloaded here.

The feature image at the top of this blog post is of Cape Otway lighthouse. Cape Otway Lighthouse is the oldest surviving lighthouse on mainland Australia. Built in 1848, the lighthouse sits 90 metres above the ocean of Bass Strait.




Filed Under:InformationTagged With:Temperatures

Reader Interactions


  1. Hyping Maximum Daily Temperatures (Part 3) | Watts Up With That? (5)John & Suzanne SmeedsaysJanuary 28, 2023 at 4:43 pmGood on Ya – Jen, I am sure you will give them hell !Happy New Yearfond regards JOHN
  2. Hyping Maximum Daily Temperatures (Part 3) | Watts Up With That? (6)SamsaysJanuary 28, 2023 at 5:24 pmJenniferHow many instances have the BOM ‘increased’ historic temperatures?
  3. Hyping Maximum Daily Temperatures (Part 3) | Watts Up With That? (7)Patrick DonnellysaysJanuary 29, 2023 at 1:34 amWell done!Exposing lies and obfuscation is tiring. I admire your energy. Stay well!
  4. Hyping Maximum Daily Temperatures (Part 3) | Watts Up With That? (8)richard bennettsaysJanuary 29, 2023 at 7:47 amThe BOM has a real problem with reporting actual measured data when it does not agree with the political narrative on climate. People around the world now recognise that the climate debate has become a toxic narrative on how to be a corrupt public sector in one easy step.

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What causes rise in temperature? ›

Greenhouse Gases

Carbon dioxide, methane, and nitrous oxide concentrations are now more abundant in the earth's atmosphere than any time in the last 800,000 years. These greenhouse gas emissions have increased the greenhouse effect and caused the earth's surface temperature to rise.

What is the rise in temperature due to global warming? ›

Earth's temperature has risen by an average of 0.14° Fahrenheit (0.08° Celsius) per decade since 1880, or about 2° F in total. The rate of warming since 1981 is more than twice as fast: 0.32° F (0.18° C) per decade.

What affects temperature? ›

The temperature characteristics of a region are influenced by natural factors such as latitude, elevation and the presence of ocean currents. The precipitation characteristics of a region are influenced by factors such as proximity to mountain ranges and prevailing winds.

What are the 5 major factors that affect climate change? ›

Causes of Climate Change
  • Generating power. Generating electricity and heat by burning fossil fuels causes a large chunk of global emissions. ...
  • Manufacturing goods. ...
  • Cutting down forests. ...
  • Using transportation. ...
  • Producing food. ...
  • Powering buildings. ...
  • Consuming too much.

Will global warming make it colder? ›

But the scientific jury is still out. The data is clear: Rising global temperatures mean winters are getting milder, on average, and the sort of record-setting cold that spanned the country Friday is becoming rarer.

How much has global warming increased in 2022? ›

Continuing the planet's long-term warming trend, global temperatures in 2022 were 1.6 degrees Fahrenheit (0.89 degrees Celsius) above the average for NASA's baseline period (1951-1980), scientists from NASA's Goddard Institute for Space Studies (GISS) in New York reported.

How hot will the earth be in 2050? ›

Since 1880, average global temperatures have increased by about 1 degrees Celsius (1.7° degrees Fahrenheit). Global temperature is projected to warm by about 1.5 degrees Celsius (2.7° degrees Fahrenheit) by 2050 and 2-4 degrees Celsius (3.6-7.2 degrees Fahrenheit) by 2100.


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