Bureau ‘Cooling The Past To Declare Record Heat’

Written by
20 December 2019
Originally appeared in Jennifer Marohasy Blog

In September 2017, the Bureau declared the hottest ever September on record for the state of Victoria based on temperature data from Mildura.

I’ve since shown that this was helped along by the Bureau replacing a mercury thermometer with an electronic probe that can record a good 0.4 degrees hotter for the same weather.

There is not only the issue of the Bureau not providing any information on how the electronic probe was calibrated, but as I’ve explained to the Chief Scientist, there is also the issue of averaging:

There is a lot of natural variability in air temperature (particularly on hot sunny days at inland locations), which was smoothed to some extent by the inertia of mercury thermometers. In order to ensure some equivalence between measurements from mercury thermometers and electronic probes it is standard practice for the one-second readings from electronic probes to be averaged over a one-minute period, or in the case of the US National Weather Service the averaging of the one-second readings is over 5 minutes.

The Australian Bureau began the change-over to electronic probes as the primary instrument for the measurement of air temperatures in November 1996. The original IT system for averaging the one-second readings from the electronic probes was put in place by Almos Pty Ltd, who had done similar work for the Indian, Kuwaiti, Swiss and other meteorological offices. The software in the Almos setup (running on the computer within the on-site shelter) computed the one-minute average (together with other statistics).

This data was then sent to what was known as a MetConsole (the computer server software), which then displayed the data, and further processed the data into ‘Synop’, ‘Metar’, ‘Climat’formats. This system was compliant with World Meteorological Organisation (WMO) and the International Civil Aviation Organisation (ICAO) standards. The maximum daily temperature for each location was recorded as the highest one-minute average for that day. This was the situation until at least 2011.

I have this on good advice from a previous Bureau employee.

It is likely to have been the situation through until perhaps February 2013 when Sue Barrell from the Bureau wrote to a colleague of mine, Peter Cornish, explaining that the one-second readings from the automatic weather station at SydneyBotanical Gardens were numerically-averaged. At some point over the last five years, however,this system has been disbanded. All, or most, of the automatic weather stations now stream data from the electronic probes directly to the Bureau’s own software. This could be an acceptable situation, except that theBureau no-longer averages the one-second readings over a one-minute period.

Indeed, it could be concluded that the current system is likely to generate new record hot days for the same weather, because of the increased sensitivity of the measuring equipment and the absence of any averaging/smoothing. To be clear, the highest one-second spot reading is now recorded as the maximum temperature for that day at the 563 automatic weather stations across Australia that are measuring surface air temperatures.

Just yesterday, the Bureau fed that “hottest ever” meme with a claim that analysis of data from about 700 weather stations across the country showed Wednesday was the hottest day recorded in Australia, with the nationally averaged maximum daytime temperature reaching 41.9C.

That was apparently a full degree higher than the previous record of 40.9C set on Tuesday, which itself broke the mark of 40.3C from January 2013.

But how exactly are the temperatures being measured, and which stations are being combined?

The Bureau has deleted the hottest day ever recorded with a mercury thermometer in a Stevenson screen, which was 51.6 degrees Celsius at Bourke in 1909.

Then there is the issue of the Bureau cooling the past.

For example, it is a full 1.4 degrees cooler in Darwin on 1st January 1910 in the official ACORN-SAT version 2, temperature data base, relative to the actual temperature recorded back then in a Stevenson Screen with a mercury thermometer.

I have also documented how the Bureau put a limit on how cold a temperature can be recorded.

Not to mention closing stations in high altitude regions that may record colder temperatures. So the 700 weather stations used to calculate the hottest day on Wednesday may be skewered warmer since the closure of stations in the coldest places:

During June and July 2017, blizzard conditions were experienced across the Australian Alps, but we will never know how cold it actually got. Because a MSI1 card reader prevented the equipment – able to record down to minus 60 – from recording below minus 10 at Thredbo and probably also at many other locations.

It is also impossible to know how cold this last winter was relative to 1994 because the weather station at Charlotte Pass was closed in March 2015 – it is no longer in operation.

I’ve written to the National Audit Office about only some of these issues and that was some years ago now.

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Jennifer Marohasy

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

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