ACORN-SAT 2.0: Nation-wide Summary

This is the eighth 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.  Results for the whole network are summarised below.

Introduction:

The Bureau of Meteorology has released its latest revision of the Australian temperature record back to 1910.  Previous versions of our historic temperatures included “High Quality”, which I revealed in 2010 to have major flaws, not least being the strong warming bias; and ACORN-SAT 1, released in March 2012, proudly touted as being “World’s Best Practice”, which I (along with others) found to have very many severe problems.  (If you like, check these posts, hereherehere, and here.  There are many others.)

Stung by the public and media criticism which this generated, the Bureau set up a supposedly independent Technical Advisory Forum, which met on one day per year for three years and basically rubber-stamped Acorn.  They did, however, make some recommendations, particularly about transparency.  In the light of this recommendation, this latest release without any publicity at all is perplexing.

Nearly all of Australia’s climate analysis and modelling is based on the previous version, Acorn 1, including monthly, seasonal, and annual means, extremes, and trends.  Sometime in the near future, this will be based on Acorn 2 data.

As this an upgrade to an existing dataset, we might expect there would be a few small tweaks of maybe a few tenths of a degree in some records and any changes to temperature trends would be fairly small.  Perhaps there might be some extra stations in remote areas to improve the density of the sparse network, perhaps some records starting earlier because of newly digitized data, hopefully a sensible fix for the dreadful situation of many daily minimum temperatures being higher than the maximum.

Not so.

No wonder the Bureau has released Acorn 2 so quietly- it is a confusing mess, and completely alters Acorn 1.  Trends are vastly different, some temperatures altered by more than 10 degrees Celsius, and new records established.

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.

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.”

Daily data were directly downloaded from the Bureau of Meteorology for maxima and minima for each of the 112 stations.

The Context

Figure 1:  Australian ACORN-SAT stations

Oz map all

There are 112 Acorn stations in the BOM database.  Differences between Acorn 1 and Acorn 2 are summarized in the following sections.

Largest temperature differences between Version 1 and Version 2

All temperatures are shown in degrees Celsius.

The five stations with the largest increases to daily maxima were:

Orbost (Victoria) 14.60
Wandering (W.A.) 10.90
Alice Springs  (N.T.) 10.10
Port Lincoln  (S.A.) 9.70
Scone  (N.S.W.) 8.30

The five stations with the largest decreases in daily maxima were:

Wandering  (W.A) -10.90
Cabramurra  (N.S.W.) -9.60
Esperance  (W.A.) -9.40
Alice Springs  (N.T.) -9.20
Wyalong  (N.S.W.) -8.60

Gunnedah (NSW) was the only station that had no changes made to the Version 1 values for maxima.

The five stations with the largest increases to daily minima were:

Merredin  (W.A.) 14.40
Butlers Gorge  (Tas.) 11.30
Alice Springs  (N.T.) 11.00
Scone  (N.S.W.) 9.60
Snowtown   (S.A.) 9.10

Horn Island (Qld) was the only station with no increases to daily minima.

The five stations with the largest decreases in daily minima were:

Wagga Wagga (N.S.W.) -13.40
Merredin  (W.A.) -12.60
Alice Springs  (N.T.) -11.50
Esperance  (W.A.) -10.80
Butlers Gorge  (Tas.) -9.70

Adjustments made to daily data were mostly of the order of +/- 1 or 2 ℃.  However the figures in the above tables show how enormous some adjustments were at many stations- including a range of 27 ℃ in adjustments to minima at Merredin!  That must surely rank as “wildly different results”.

New temperature extremes:

New records were set.

In Acorn 2 40 stations had increased record high maxima, 35 had their record highs decreased, and the remaining 37 were unchanged.  In minima, there were 36 stations whose lowest temperatures were increased, and 66 had new record lows. 10 were unchanged.

The old Australian record for highest maximum in Acorn Version 1 was (improbably) 51.2 ℃ at Albany in the far south of Western Australia.  In version 2, that has been reduced to 49.5 ℃.  The Version 2 highest maximum is now 51.1 ℃ at Oodnadatta in the South Australian desert.

The lowest temperature in Version 1 was -12.7 ℃ at Butlers Gorge in Tasmania.  That has been surpassed in version 2 by Inverell in northern inland New South Wales with -13 ℃.  (In raw data, the lowest at Inverell was -10.6 ℃ in July 1882.)

Here are the five stations with highest daily maximum temperatures.

Oodnadatta 51.10
Carnarvon 51.00
Forrest 50.10
Marble Bar 49.80
Port Hedland 49.7

Coldest minima:

Inverell -13.00
Butlers Gorge -12.70
Bathurst -11.50
Canberra -11.50
Cabramurra -10.70

Warmest minima stations are all coastal or islands:

Cape Moreton 5.10
Cairns 6.00
Weipa 9.10
Darwin 10.50
Horn Island 15.00

In Acorn version 2 there are some other peculiarities:  the “improved estimate” of climate change in Australia shows that Nhill, in western Victoria, has probably never had a frost, as its coldest morning has only been 2.7 ℃, the same as Sydney and Tennant Creek.   Alice Springs has the 69th hottest temperature at 45 ℃: far cooler than Albany, Eucla, Ceduna, or Port Lincoln far to the south.

Changes to temperature trends

With such enormous changes made to the daily data at so many stations, there have also been some major changes to temperature trends, both at individual stations and across the whole network.  (Trends are shown as degrees Celsius per 100 years).

Highest trends in maxima in Acorn 1

Cabramurra 4.75
Birdsville 3.21
Wyalong 3.00
Cunderdin 2.97
Cape Borda 2.90

Highest trends in maxima in Acorn 2

Wyalong 3.78
Cabramurra 3.66
Cunderdin 2.96
Birdsville 2.82
Ceduna 2.78

A trend of +4.75 ℃ per 100 years at Cabramurra high in the mountains is astounding- and the trend has been decreased by over one whole degree in Acorn 2.  The top four warming stations are the same in both datasets, but Cape Borda has been replaced by Ceduna in Acorn 2.  (Cape Borda went from 5th fastest warming to 15th; Ceduna went from 22nd to 5th.)

Highest trends in minima in Acorn 1

Rockhampton 3.10
Barcaldine 3.03
Laverton RAAF 3.03
Moree 3.01
Townsville 2.96

Highest trends in minima in Acorn 2

Rockhampton 3.41
Camooweal 3.27
Coffs Harbour 3.17
Horn Island 2.90
Laverton RAAF 2.81

Rockhampton maintains top position as fastest warming, and is warming even more in Acorn 2.  Laverton RAAF slips from third to fifth, while the other three places are completely changed.  Barcaldine slips from second fastest warming to 49th, replaced by Camooweal which rises from 41st!  Coffs Harbour has risen from 46th to third, but the gong for “most improved” must go to Horn Island, rising to +2.9 ℃ per 100 years in fourth place from +1.03 ℃ per 100 years in 72nd place,.    Those are definitelywildly different results”.

Greatest warming change in trends in maxima from Acorn 1 to Acorn 2

Eucla 1.50
Wittenoom 1.43
Giles 1.10
Ceduna 1.05
Port Macquarie 0.98

It seems that the improved methods used to create Acorn 2 has changed Eucla’s record to the extent thata reasonable guide to what has actually occurred” means an increase of +1.5 ℃ per 100 years in the rate of warming- an increase of 557%.

Greatest warming change in trends in minima from Acorn 1 to Acorn 2

Horn Island 1.87
Scone 1.86
Camooweal 1.71
Coffs Harbour 1.70
Tarcoola 1.51

The same applies to minima, with Horn Island’s warming trend increasing from +1.03 ℃ to +2.9 ℃ per 100 years.  Five stations had warming trends increase by more than 1.5 ℃, and 14 increased by more than 1.0 ℃ per 100 years.

Greatest cooling change in trends in maxima from Acorn 1 to Acorn 2

Victoria River Downs -1.07
Sale -1.07
Cabramurra -1.08
Moree -1.29
Rabbit Flat -1.64

The changes were not all in the same direction.  Rabbit Flat’s very patchy record takes the gong for the greatest cooling change in trend.  Rabbit Flat went from 24th fastest warming (+1.69 ℃ per 100 years) in Acorn 1 to 110th (third last) in Acorn 2- at +0.05 ℃ per 100 years.

Greatest cooling change in trends in minima from Acorn 1 to Acorn 2

Moree -0.89
Rabbit Flat -0.94
Halls Creek -1.32
Barcaldine -1.42
Giles -1.55

Again there were some big movers.  Rabbit Flat and Moree were again in the top five for most cooling change.  Giles had a similar fall from grace to record the greatest change: from 71st fastest warming (+1.03 ℃ per 100 years in Acorn 1) to second last place in Acorn 2 at -0.52 ℃, but Barcaldine went from second fastest warming to 49th, and Halls Creek from 58th fastest to 110th.

National Trends

In order to aggregate data into a national mean, all stations’ data were converted to anomalies calculated from their 1981 -2010 means.  There are 112 Acorn stations, but the Bureau insists that Urban Heat Island (UHI) warming makes eight of them (Townsville, Rockhampton, Sydney, Richmond RAAF (NSW), Melbourne, Laverton RAAF (Vic), Adelaide and Hobart) unsuitable for regional and national analysis.  The next plots show the change in trend from Acorn 1 to Acorn 2: first in maxima.

Figure 2: National mean of maxima at all stations

Acorn trends tmax all

Acorn 2 produces an increase in trend from +0.88 ℃ to + 0.99 ℃ per 100 years- an increase of 12.5%.

Figure 3: National mean of maxima at 104 stations, excluding those with UHI effect

 Acorn trends tmax nonUHI

Excluding eight UHI warmed stations produces virtually no difference from the trend of all 112 stations: +0.88 to +1.00 ℃.

Figure 2: National mean of minima at all stations

Acorn trends tmin all

In minima, the trend increases from +1.16 ℃ to +1.35 ℃ per 100 years- an increase of 16.4%.

Figure 3: National mean of minima at 104 stations, excluding those with UHI effect

 Acorn trends tmin nonUHI

Again, exclusion of UHI warming stations has a small effect, with the trend for non-UHI stations increasing from +1.15 ℃ in Acorn 1 to +1.37 ℃ per 100 years in Acorn 2.  That’s an increase of 19.1%.

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 many stations.  The largest changes ranged from -10.9 ℃ to +14.6 ℃ in maxima and -13.4 ℃ to +14.4 ℃ in minima.  Interestingly, no changes were made to Version 1 in Gunnedah maxima, and to Horn Island in minima.

New record maxima were established at 40 stations, with the remaining stations’ records being reduced or unchanged.  Australia’s “new” record high temperature is 51.1 ℃ at Oodnadatta.  The largest increase was of +2.5 ℃ at Carnarvon.  Our “new” record low temperature is -13 ℃ at Inverell.  The largest decrease in record low is -2.7 ℃ at Alice Springs.

Trends at individual stations in maxima and minima have often seen spectacular changes: changes in trend over Acorn 1 of from -1.64 ℃ to +1.87 ℃ per 100 years.  These changes resulted in very large changes in relative placing of fastest warming or cooling.  Eucla’s trend in maxima was increased more than six and a half times: 557%.  Broome’s minima trend increased more than five and a half times: 461%.

The size of the adjustments only seven years after the “world’s best practice” dataset was launched, is incredible.  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 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 14.6 ℃ to temperatures in the dataset they proudly claimed to be world’s best practice just seven years ago.

Acorn 2, as the best estimate of Australia’s temperature record, is a failure.

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One Response to “ACORN-SAT 2.0: Nation-wide Summary”

  1. A C Osborn Says:

    Nice work Ken.
    Shocking results though.

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