This is the seventh in a series of posts in which I directly compare the most recent version of Australia’s temperature record, ACORN-SAT 2, with that of the previous version, ACORN-SAT 1. Daily data are directly downloaded from the Bureau of Meteorology. I do not analyse against raw data (available at Climate Data Online), except for particular examples, as I am interested in how different Acorn 2 is from Acorn 1. The basis for the new version is in the Research Report. The Bureau has published a new station catalogue with more detailed information, the adjustment summary for each station, plus lists of comparative stations for adjustments and all comparison stations for each site, with explanations of adjustment terminology. Well worth a look.
See my previous posts for Western Australia, the Northern Territory, Queensland, South Australia, Tasmania, and Victoria for a general introduction. It is important to highlight this paragraph on the new ACORN-SAT home page:
The purpose of updating datasets like ACORN-SAT is principally to incorporate data that has been recorded since the last analysis was released, as well as historical paper records that have been recently digitised. ACORN-SAT version 2 also incorporates the findings and recommendations of the Technical Advisory Forum, applies the latest scientific research and understanding and, where applicable, introduces new methodologies. The overall aim of the update to ACORN-SAT is to provide improved estimates of historical changes in climate.
As well, in the ACORN-SAT FAQs, the Bureau says:
“… The important question is not which one (version) represents the absolute truth, but whether those estimates produce wildly different results, and whether the range of estimates provides a reasonable guide to what has actually occurred.”
Therefore, the Bureau has set their own criterion for whether Acorn 1 and Acorn 2 are at all useful and valuable. To repeat:
“whether those estimates produce wildly different results, and whether the range of estimates provides a reasonable guide to what has actually occurred.”
The Context – New South Wales
Figure 1 is a map of Australia showing all of the Bureau’s ACORN-SAT climate monitoring stations. New South Wales is the oldest and most populous state with climates varying from semi-desert to montaine.
Figure 1: Australian ACORN-SAT stations
There are 25 Acorn stations in the NSW BOM database. Differences between Acorn 1 and Acorn 2 are summarized in the following sections.
Additional data
An extra 27 years of data have been digitised for Canberra, and 45 years for Moree, which has had an enormous effect on annual temperature trends (see below). Some locations had changes to new sites, with Acorn 1 data merged to Acorn 2 data, including Tibooburra and Wilcannia.
Largest temperature differences
In maxima, changes to Acorn 1 daily data ranged from +8.3 ℃ at Scone in 1996 to -9.6 ℃ at Cabramurra in 1998 applied to individual daily figures.
Remarkably, there were NO changes from Acorn 1 to Acorn 2 at Gunnedah.
Figure 2: Daily changes in maxima from Acorn 1 to Acorn 2 at Cabramurra
Minima adjustments ranged from -13.4 ℃ at Wagga Wagga in 1946 to +9.6 ℃ at Scone in 1996 on individual days but with many days adjusted by -2 ℃ or greater.
Figure 3: Daily changes in minima from Acorn 1 to Acorn 2 at Wagga Wagga:
(Remember, these are adjustments to Acorn 1, which was supposed to be “world’s best practice” seven years ago. How did the Bureau get it so wrong the first time? Has world’s best practice changed so much in seven years?)
Record temperatures
New record maxima were established at nine stations, with the highest at Bourke (48.9 ℃) while other stations’ record highs were unchanged or reduced. There were two notable changes. Figure 4 shows maxima at Sydney in 1939, where the record was increased by 2.5 ℃ to 47.9 ℃.
Figure 4: Three versions of maxima at Sydney in 1939
(The temperature was below 20 ℃ on 16th and 17th.)
Figure 5 shows Port Macquarie, whose record maximum was reduced by -4.1 ℃ from 48.1 ℃ to 44 ℃ in 1944.
Figure 5: Two versions of maxima at Port Macquarie in 1944
There is NO daily raw data for any Port Macquarie site from 1921 to 1956 at Climate Data Online, so there is no way of replicating these adjustments.
Such “wildly different results” are beyond rational explanation.
New record low temperatures were established at 15 stations, and a new record low for Acorn stations was set, not at Cabramurra in the Snowy Mountains, but at Inverell in the north: -13 ℃. Canberra’s minimum was reduced by 2.9 ℃ to -11.5 ℃.
Figure 6: Three versions of minima at Inverell
Raw minimum of -10 ℃ is cold enough. Acorn version 1 had cooled this further by 1.4 ℃, but version 2 cools version 1 by another 1.6 ℃, making it three degrees cooler than the raw figure. Strange things happen in the past!
Quality Control: especially minimum temperatures higher than maximum.
In Acorn 1, 15 out of the 25 stations had at least one example of minimum higher than maximum- including 12 times at Bourke and Sydney, 15 at Tibooburra, and 212 times at Cabramurra. The worst example was minimum 2.2 ℃ above maximum in October 1913 at Tibooburra. Blair Trewin claims he has “fixed” this problem (which he concedes was “physically unrealistic”) by adjusting temperatures in Acorn 2 so that the maximum and minimum are the same, so that DTR for the day is zero. In his words:
A procedure was therefore adopted under which, if a day had a negative diurnal range in the adjusted data, the maximum and minimum temperatures were each corrected to the mean of the original adjusted maximum and adjusted minimum, creating no change in the daily mean.
That is almost how he “corrected” the worst NSW example in Acorn 1 (minimum 2.2 ℃ above maximum at Tibooburra). Here is a plot of the raw data and changes made by Acorn 1 and Acorn 2 at Tibooburra in 1913.
Figure 7: Tibooburra temperatures October-November 1913
Acorn 1 maxima (orange line) were reduced too far below Raw (brown). Acorn 1 minima (grey) were too far above raw minima (light blue). Result: garbage. Acorn 2 has changed maxima (dark red) back to 0.1 ℃ below the raw value, and reduced minima (dark blue) from 17 ℃ to 16 ℃. This is not the “mean of the original adjusted maximum and adjusted minimum”- but at least the DTR is not negative.
The problem was caused by far too large adjustments to both maxima and minima, and was fixed by more arbitrary adjustments.
Not all Acorn 2 adjustments resulted in an increase in warming- in several, the warming trend was reduced. For example, Figure 8 shows annual temperature trends at Sydney.
Figure 8: Maxima Trends in Sydney 1910-2017
The warming rate of +1 ℃ per 100 years in Acorn 1 has been reduced to +0.79 ℃ in Acorn 2.
However, at Coffs Harbour the warming trend in minima was more than doubled, from +1.47 ℃ to +3.17 ℃ per 100 years.
Figure 9: Minima trends at Coffs Harbour 1952-2017
Figure 10 shows the effect of including an extra 27 years of data on annual trends at Canberra, with Acorn 1 adjusted downwards from 2011.
Figure 10: Trends in Canberra minima 1914-2017
Acorn 1 starts in 1940. Canberra’s warming trend has been increased from +1.48 ℃ to +2.18 ℃ per 100 years.
Conclusion:
There are no additional stations, but additional digitised data at several stations has a large impact on annual trends. As well, several Acorn 1 stations closed and their data merged with data from new sites in Acorn 2.
Large differences between Acorn 1 and Acorn 2 daily data of many degrees Celsius are found at several stations. Interestingly, no changes were made to Version 1 in Gunnedah maxima, and only a few in minima.
New record maxima were established at nine stations, with the remaining stations’ records being reduced or unchanged. The largest increase was of +2.5 ℃ at Sydney, and the largest decrease was at Port Macquarie where the record high was reduced by -4.1 ℃.
The issue of instances of minima being higher than maxima caused by too vigorous adjustments at 15 stations (including 12 times at Bourke and Sydney, 15 at Tibooburra, and 212 times at Cabramurra) has been “fixed”- only seven years after the problem was pointed out.
Not all Acorn 2 adjustments resulted in an increase in warming- in several, the warming trend was reduced. However, excessive adjustments have resulted in Coffs Harbour’s Acorn 1 minima trend of +1.47 ℃ per 100 years being more than doubled to +3.17 ℃ in Acorn 2.
The size of the adjustments only seven years after the “world’s best practice” dataset was launched, is incredible, and demands explanation. The explanation that Acorn Version 2 “applies the latest scientific research and understanding and, where applicable, introduces new methodologies”, is beyond belief, as most datasets so far examined are vastly different from Acorn Version 1. This is not incremental improvement.
In the ACORN-SAT FAQs, in the answer to:
“Why should the adjustments change, weren’t they correct the first time?”
the Bureau says:
“… The important question is not which one (version) represents the absolute truth, but whether those estimates produce wildly different results, and whether the range of estimates provides a reasonable guide to what has actually occurred.”
By their own words they have condemned themselves- “wildly different results” is exactly what has been produced. Adjustments made in Version 1 were apparently made in error as they have been “corrected” by adjustments in version 2. Will these adjustments be in error and corrected in version 3?
The Bureau officers responsible for Acorn version 2 appear to be blissfully unaware that they have made adjustments of up to 13.4 ℃ to temperatures in the dataset they proudly claimed to be world’s best practice just seven years ago.
What a mess.
I will next show a summary of Version 2 changes across the whole network, and then look at annual trends at all stations.
kenskingdom 