By David Mason-Jones
Upon finding a 13-year gap in its data for an important weather station in Queensland, the Australian Bureau of Meteorology homogenised data from 10 other locations to fill-in the missing years. One of these places was more than 400km away and another almost 2.5 degrees of latitude further South.
Is the resulting data credible? No, is the conclusion reached in a research Report by Australian scientist, Dr. Bill Johnston.
When the US Army Air Force (USAAF) closed its heavy bomber transit base at Charleville at the end of the Second World War the aerodrome reverted to civilian status. The base had been a link in the ferry route delivering aircraft from factories in the US to the war zone.
The whereabouts of any weather observations taken by the Americans is unknown and history is somewhat vague about the dates and times but a 13-year slice of data for Charleville airport from 1943 to 1956 has apparently gone missing.
From as early as July 1940 as the possibility of war with Japan grew, and then when the Pacific War actually broke out, the urgency of the situation resulted in a period when weather observations at Charleville were marked by multiple site relocations, instrument changes and changes in organisational responsibly. After the war there also followed a period of turbulence in the management of aerodromes with the Royal Australian Air Force handing over control to Civil Aviation authorities.
Around 30 years ago as global warming worry grew, so did the demand for accurate temperature data from the past. But this created a problem for the Bureau: How to create a continuous and reliable temperature record at Charleville for the missing raw data?
The solution was simple – make it up. Fill in the 13-year gap with your best guess, create some numbers and fill in the blank spaces. In essence, this is what happened. But to be fair to the Bureau, it wasn’t just a totally whimsical pure guess. On the face of it, it was more sophisticated and used homogenisation.
As Dr. Johnston’s research Report shows in detail, there are severe limits to the usefulness of homogenisation in this instance.
Using aerial photographs and archived maps and plans, Johnston thoroughly investigated the Charleville airport weather station and the way homogenisation was carried out. The Report, backed with tables of data and graphs of weather data from the ten stations used in the homogenisation process, is briefly summarised at http://www.bomwatch.com.au/bureau-of-meterology/charleville-queensland/ At the end of the brief summary a link is available to a PDF of the full Report, complete with tables of data. It is a long, detailed and thorough Report covering many factors and is well worth the investment in time needed to fully understand it.
Homogenisation of temperatures is where you take temperature data from ‘nearby’ weather stations and then estimate what the numbers may have been in the middle. As Johnston points out, this can introduce problems in data analysis because it assumes the nearby weather stations are close enough to make a valid comparison. It also assumes that there are no embedded errors in the other stations’ data which can corrupt the process. In addition, it assumes there are no sudden step changes in the data from the other stations that are not related to climate.
In the case of the stations used to homogenise Charleville the distances are enormous and the data from the other locations contains embedded errors and step changes which can then become homogenised into the Charleville temperature reconstruction.
A glaring problem with homogenisation at Charleville involves the word ‘nearby’. ‘Nearby’ as it applies to Charleville is not just another town or weather station ten or twenty kilometres away. The ‘nearby’ stations are hundreds of kilometres away.
The Report lists distances as: Mungindi – 390 km away. By way of comparison, the distance between London and Paris is 344 km. Would it be statistically sound to homogenise daily temperature readings in Paris by reference to what the temperature was that day in London? It is also notable that Mungindi is 2.46 degrees of latitude South from Charleville.
The others are: Blackall – 234 km distant: Bollon Post Office – 216 km: Injune – 238 km: Longreach – 238 km: Cunnamulla – 192 km: Collarenebri – 414 km: Surat – 291 km: Tambo – 196 km and Mitchell – 171 km.
Please consider whether the use of these distant stations is valid to establish a highly accurate baseline of maximum temperature to identify a slowly rising temperature trend.
With the distances involved, and with the other problems with metadata at the ten ‘nearby’ sites, it may be implausible to rely on the 13 years of infilled data at Charleville to identify the fine degrees of temperature trend needed as evidence of catastrophic anthropogenic global warming at Charleville.
Dr Bill Johnston is a former NSW Department of Natural Resources senior research scientist and former weather observer. www.bomwatch.com.au or [email protected]
To read a summary of Dr. Johnston’s paper go to http://www.bomwatch.com.au/bureau-of-meterology/charleville-queensland/ click on the link at the end of the summary to access the full paper.