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ACORN 2.1 influence on Tasmania temperature trends

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In October 2020 the Bureau of Meteorology again rewrote Australia's temperature history with the release of ACORN 2.1, an update to its homogenised ACORN 2 dataset (Australian Climate Observations Reference Network - Surface Air Temperatures) released in late 2018 that significantly increased the rate of climate warming since 1910.

There are seven ACORN stations in Tasmania. This page analyses the daily temperatures at all seven weather stations and averages the three with a start year of 1910 to ensure a uniform timescale. The other four excluded stations have temperature recordings starting in years after 1910, the most recent being Grove with a start year of 1955.

The three long-term weather stations analysed on this page (with a start year of 1910) had a 1910-1964 average maximum of 16.79C in ACORN 2 and a 1910-1964 average maximum of 16.79C in ACORN 2.1 - meaning ACORN 2.1 has not altered the historic maxima of ACORN 2.

The three long-term weather stations had a 1910-1964 average minimum of 8.31C in ACORN 2 and a 1910-1964 average minimum of 8.31C in ACORN 2.1 - meaning ACORN 2.1 has not altered the historic minima of ACORN 2.

Daily temperatures in ACORN 2.1 and RAW have been annualised, and below are charts showing the difference between the ACORN 2.1 homogenised dataset when compared to original raw annual temperatures. This analysis only allows the inclusion of years within which there were no months with less than 15 days of recorded temperatures, as is the ACORN protocol.

Three Tasmanian stations begin in 1910 and end in 2017 in ACORN 2.1 and RAW - Eddystone Point, Launceston and Low Head. The first charts below show maximum and minimum temperature trends at these three stations with associated data.

Excel files at the bottom of each station chart and data summary can be downloaded to compare how the ACORN 2.1 algorithms influence daily, monthly and annual temperatures at all seven sites since 1910.

acorn 2.1 tasmania maximum temperatures

1910-1964 - ACORN 2.1 16.79C / raw 16.75C

1965-2019 - ACORN 2.1 17.34C / raw 17.17C

ACORN 2.1 warmed 0.55C / raw warmed 0.42C

Average change per decade : ACORN 2.1 0.08C / raw 0.07C

Tasmania 2000-2019 - ACORN 2.1 17.68C / raw 17.58C

The first decade, 1910-1919, averaged 16.95C in ACORN 2.1 and 17.11C in raw

The final decade, 2010-2019, averaged 17.79C in ACORN 2.1 and 17.79C in raw

1961-90 - ACORN 2.1 - 17.14C / raw 16.88C

Download Excel spreadsheet for three Tasmanian weather stations in ACORN 1, ACORN 2.1 and RAW

acorn 2.1 tasmania minimum temperatures

1910-1964 - ACORN 2.1 8.31C / raw 8.74C

1965-2019 - ACORN 2.1 8.94C / raw 8.92C

ACORN 2.1 warmed 0.63C / raw warmed 0.18C

Average change per decade : ACORN 2.1 0.09C / raw 0.03C

Tasmania 2000-2019 - ACORN 2.1 9.20C / raw 9.20C

The first decade, 1910-1919, averaged 8.41C in ACORN 2.1 and 8.99C in raw

The final decade, 2010-2019, averaged 9.27C in ACORN 2.1 and 9.27C in raw

1961-90 - ACORN 2.1 - 8.84C / raw 8.85C

Download Excel spreadsheet for three Tasmanian weather stations in ACORN 1 and ACORN 2.1 and RAW

Station menu

Butlers Gorge, Cape Bruny, Eddystone Point, Grove, Hobart, Launceston, Low Head

Butlers Gorge

acorn 2.1 butlers gorge maximum temperatures

1945-1981 - ACORN 2.1 12.34C / raw 12.68C

1982-2019 - ACORN 2.1 13.25C / raw 13.24C

ACORN 2.1 warmed 0.91C / raw warmed 0.56C

Average change per decade : ACORN 2.1 0.29C / raw 0.21C

Butlers Gorge 2000-2019 - ACORN 2.1 13.49C / raw 13.43C

1961-90 - ACORN 2.1 12.79C / raw 12.96C

Pre 1972 .0 F rounding ACORN 2.1 - 17.19% / raw - 87.75%

Post 1972 .0 C rounding ACORN 2.1 - 9.63% / raw - 29.86%

The first decade, 1945-1954, averaged 11.69C in ACORN 2.1 and 12.24C in raw

The final decade, 2010-2019, averaged 13.57C in ACORN 2.1 and 13.57C in raw

ACORN catalogue: The original site at Butlers Gorge (also numbered 096003) operated from 1944 at the Hydro-Electric Commission settlement. The site appears to have been unchanged during the 1944–1993 period. In the early years of observations a HEC-pattern screen (single-louvred and lower than a Bureau standard screen) was used; this was replaced with a Bureau standard screen some time between 1973 and 1976. Observations appear to have been made at non-standard times (earlier than 9 am) on occasions. The settlement was abandoned, with all buildings removed, by 1969. Observations continued until October 1993. The current site is an automatic weather station which was installed about 150 m east of the previous site. It commenced observations in May 2008. Data from Lake St Clair (096071) was used in the 1993–2008 period, with the overlaps at both ends of this period used to merge the datasets. Lake St Clair is approximately 20 km north of Butlers Gorge but the overlap data indicates that temperature differences between the two locations are minimal. The site is over marshy tussock grass about 200 m southeast of the visitors’ centre.

1998-2007 raw max averaged 13.37C and post AWS 2009-2018 averaged 13.57C

Butlers Gorge max Excel spreadsheets

acorn 2.1 butlers gorge minimum temperatures

1945-1981 - ACORN 2.1 3.09C / raw 2.94C

1982-2019 - ACORN 2.1 3.16C / raw 2.92C

ACORN 2.1 warmed 0.07C / raw cooled 0.02C

Average change per decade : ACORN 2.1 0.11C / raw 0.12C

Butlers Gorge 2000-2019 - ACORN 2.1 3.27C / raw 3.15C

1961-90 - ACORN 2.1 3.26C / raw 2.91C

Pre 1972 .0 F rounding ACORN 2.1 - 19.29% / raw - 86.45%

Post 1972 .0 C rounding ACORN 2.1 - 10.15% / raw - 28.83%

The first decade, 1945-1954, averaged 2.65C in ACORN 2.1 and 2.57C in raw

The final decade, 2010-2019, averaged 3.38C in ACORN 2.1 and 3.38C in raw

1998-2007 raw min averaged 2.94C and post AWS 2009-2018 averaged 3.41C

Butlers Gorge min Excel spreadsheets

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Cape Bruny

acorn 2.1 cape bruny maximum temperatures

1923-1970 - ACORN 2.1 15.21C / raw 14.49C

1971-2019 - ACORN 2.1 15.87C / raw 15.58C

ACORN 2.1 warmed 0.66C / raw warmed 1.09C

Average change per decade : ACORN 2.1 0.15C / raw 0.22C

Cape Bruny 2000-2019 - ACORN 2.1 16.15C / raw 16.11C

1961-90 - ACORN 2.1 15.71C / raw 15.14C

Pre 1972 .0 F rounding ACORN 2.1 - 20.50% / raw - 74.42%

Post 1972 .0 C rounding ACORN 2.1 - 10.57% / raw - 20.08%

The first decade, 1923-1932, averaged 15.00C in ACORN 2.1 and 14.44C in raw

The final decade, 2010-2019, averaged 16.34C in ACORN 2.1 and 16.34C in raw

ACORN catalogue: The site appears to have been close to its current location before a move in April 1939. It also moved on 13 November 1961, and 45 m east in March 1969. An automatic weather station (094198) has been operating since 1997 at Cape Bruny. This is expected eventually to supersede the current site. It is about 50 m west of the current site, close to the 1961–1969 location of the manual site, but is in a more exposed location on top of the ridge. This exposure has clearly reduced rainfall readings but impacts on temperature are less clear.

94010 1987-1996 average max 15.13C vs 94198 AWS 1998-2007 (50 metres west) average max 15.47C

Cape Bruny presents an interesting comparison of an Automatic Weather Station and a manual Stevenson screen both observing daily temperatures over 20 years. The Cape Bruny analysis raises questions about the warming influence of AWS temperature readings in all latitudes across Australia.

Cape Bruny max Excel spreadsheets

acorn 2.1 cape bruny minimum temperatures

1923-1970 - ACORN 2.1 8.04C / raw 8.45C

1971-2019 - ACORN 2.1 9.03C / raw 9.18C

ACORN 2.1 warmed 0.99C / raw warmed 0.73C

Average change per decade : ACORN 2.1 0.17C / raw 0.12C

Cape Bruny 2000-2019 - ACORN 2.1 9.29C / raw 9.32C

1961-90 - ACORN 2.1 8.69C / raw 9.03C

Pre 1972 .0 F rounding ACORN 2.1 - 22.92% / raw - 74.05%

Post 1972 .0 C rounding ACORN 2.1 - 10.27% / raw - 21.21%

The first decade, 1924-1933, averaged 7.89C in ACORN 2.1 and 8.38C in raw

The final decade, 2010-2019, averaged 9.37C in ACORN 2.1 and 9.38C in raw

94010 1987-1996 average min 8.88C vs 94198 AWS 1998-2007 (50 metres west) average max 9.48C

Cape Bruny min Excel spreadsheets

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Eddystone Point

acorn 2 eddystone point maximum temperatures

1910-1964 - ACORN 2.1 17.28C / raw 16.65C

1965-2019 - ACORN 2.1 17.91C / raw 17.34C

ACORN 2.1 warmed 0.63C / raw warmed 0.69C

Average change per decade : ACORN 2.1 0.07C / raw 0.13C

Eddystone Point 2000-2019 - ACORN 2.1 18.22C / raw 18.21C

1961-90 - ACORN 2.1 17.67C / raw 16.76C

Pre 1972 .0 F rounding ACORN 2.1 - 17.77% / raw - 67.46%

Post 1972 .0 C rounding ACORN 2.1 - 15.73% / raw - 29.61%

The first decade, 1910-1919, averaged 17.72C in ACORN 2.1 and 17.09C in raw

The final decade, 2010-2019, averaged 18.39C in ACORN 2.1 and 18.39C in raw

ACORN catalogue: There is little documentation on the site prior to the 1990s, but it is believed that there were no significant site moves between 1908 and 1996. An automatic weather station was installed in late 1996, with an associated site move about 70 m southeast. Parallel observations were carried out with the former site (using the station number 092115), but some observations from the new site were incorrectly recorded against the comparison number, making it impracticable to use the parallel observations to assess the impact of the move.

Assuming the AWS was operational from 1996, 1986-1995 raw max averaged 17.09C and post AWS 1997-2006 averaged 17.88C

Eddystone Point max Excel spreadsheets

acorn 2 eddystone point minimum temperatures

1910-1964 - ACORN 2.1 9.94C / raw 9.78C

1965-2019 - ACORN 2.1 10.54C / raw 10.53C

ACORN 2.1 warmed 0.60C / raw warmed 0.75C

Average change per decade : ACORN 2.1 0.08C / raw 0.10C

Eddystone Point 2000-2019 - ACORN 2.1 10.72C / raw 10.72C

1961-90 - ACORN 2.1 10.38C / raw 10.41C

Pre 1972 .0 F rounding ACORN 2.1 - 16.66% / raw - 67.62%

Post 1972 .0 C rounding ACORN 2.1 - 23.74% / raw - 32.18%

The first decade, 1910-1919, averaged 9.96C in ACORN 2.1 and 9.80C in raw

The final decade, 2010-2019, averaged 10.79C in ACORN 2.1 and 10.79C in raw

Assuming the AWS was operational from 1996, 1986-1995 raw min averaged 10.37C and post AWS 1997-2006 averaged 10.60C

Eddystone Point min Excel spreadsheets

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Grove

acorn 2.1 grove maximum temperatures

1955-1986 - ACORN 2.1 17.37C / raw 16.85C

1987-2019 - ACORN 2.1 17.59C / raw 17.56C

ACORN 2.1 warmed 0.22C / raw warmed 0.71C

Average change per decade : ACORN 2.1 0.09C / raw 0.19C

Grove 2000-2019 - ACORN 2.1 17.66C / raw 17.68C

1961-90 - ACORN 2.1 17.49C / raw 16.99C

Pre 1972 .0 F rounding ACORN 2.1 - 17.33% / raw - 44.03%

Post 1972 .0 C rounding ACORN 2.1 - 9.73% / raw - 12.19%

The first decade, 1955-1964, averaged 17.28C in ACORN 2.1 and 16.74C in raw

The final decade, 2010-2019, averaged 17.79C in ACORN 2.1 and 17.79C in raw

ACORN catalogue: The original site (094069) was also on the Research Station grounds and began operating in 1952. New buildings had been built approximately 15 m away from the site at some point between 1966 and 1985, most likely after 1980. The instruments were relocated 100 m west on 17 January 1990 in anticipation of a new building which was never constructed. The site closed in 2010. The current automatic weather station was established 190 m southwest of the previous site, and has been operating since June 2004.

94069 overlap with 94220 16 June 2004 to 9 February 2010 : 94069 17.43C / 94220 17.42C

1994-2003 raw max averaged 17.46C and post AWS 2005-2014 averaged 17.62C

Grove max Excel spreadsheets

acorn 2.1 grove minimum temperatures

1955-1986 - ACORN 2.1 5.19C / raw 5.79C

1987-2019 - ACORN 2.1 5.59C / raw 5.86C

ACORN 2.1 warmed 0.40C / raw warmed 0.07C

Average change per decade : ACORN 2.1 0.18C / raw 0.07C

Grove 2000-2019 - ACORN 2.1 5.78C / raw 5.94C

1961-90 - ACORN 2.1 5.31C / raw 5.91C

Pre 1972 .0 F rounding ACORN 2.1 - 18.93% / raw - 49.73%

Post 1972 .0 C rounding ACORN 2.1 - 9.68% / raw - 12.96%

The first decade, 1955-1964, averaged 4.93C in ACORN 2.1 and 5.52C in raw

The final decade, 2010-2019, averaged 5.91C in ACORN 2.1 and 5.91C in raw

94069 overlap with 94220 17 June 2004 to 10 February 2010 : 94069 6.03C / 94220 5.59C

1994-2003 raw max averaged 5.84C and post AWS 2005-2014 averaged 5.76C

Grove min Excel spreadsheets

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Hobart

acorn 2.1 hobart maximum temperatures

1918-1968 - ACORN 2.1 16.90C / raw 16.69C

1969-2019 - ACORN 2.1 17.62C / raw 17.41C

ACORN 2.1 warmed 0.72C / raw warmed 0.72C

Average change per decade : ACORN 2.1 0.12C / raw 0.15C

Hobart 2000-2019 - ACORN 2.1 18.01C / raw 17.82C

1961-90 - ACORN 2.1 17.27C / raw 17.06C

Pre 1972 .0 F rounding ACORN 2.1 - 18.89% / raw - 27.46%

Post 1972 .0 C rounding ACORN 2.1 - 10.09% / raw - 11.69%

The first decade, 1918-1927, averaged 17.03C in ACORN 2.1 and 16.81C in raw

The final decade, 2010-2019, averaged 18.15C in ACORN 2.1 and 18.15C in raw

Hobart has annual max temps back to 1883: 1883-1891 + 1894 + 1896-1907 16.79C

ACORN catalogue: The site has been on the same property since its establishment in 1882. A new building was built in the area in 1966 and the screen was moved approximately 5 m to be clear of this. An automatic weather station was installed on 29 June 1992, and became the primary instrument on 1 November 1996.

1986-1995 raw max averaged 17.25C and post AWS 1997-2006 averaged 17.33C

Hobart max Excel spreadsheets

acorn 2.1 hobart minimum temperatures

1918-1968 - ACORN 2.1 8.59C / raw 8.13C

1969-2019 - ACORN 2.1 8.92C / raw 8.89C

ACORN 2.1 warmed 0.33C / raw warmed 0.76C

Average change per decade : ACORN 2.1 0.05C / raw 0.10C

Hobart 2000-2019 - ACORN 2.1 9.11C / raw 9.10C

1961-90 - ACORN 2.1 8.76C / raw 8.65C

Pre 1972 .0 F rounding ACORN 2.1 - 16.78% / raw - 31.79%

Post 1972 .0 C rounding ACORN 2.1 - 9.82% / raw - 12.41%

The first decade, 1918-1927, averaged 8.80C in ACORN 2.1 and 8.31C in raw

The final decade, 2010-2019, averaged 9.25C in ACORN 2.1 and 9.25C in raw

Hobart has annual min temps back to 1883: 1883-1891 + 1894 + 1896-1907 7.80C

1986-1995 raw min averaged 8.72C and post AWS 1997-2006 averaged 8.90C

Hobart min Excel spreadsheets

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Launceston

acorn 2 launceston maximum temperatures

1910-1964 - ACORN 2.1 17.33C / raw 17.88C

1965-2019 - ACORN 2.1 17.84C / raw 17.32C

ACORN 2.1 warmed 0.51C / raw cooled 0.56C

Average change per decade : ACORN 2.1 0.09C / raw -0.02C

Launceston 2000-2019 - ACORN 2.1 18.14C / raw 17.85C

1961-90 - ACORN 2.1 17.63C / raw 16.99C

Pre 1972 .0 F rounding ACORN 2.1 - 17.82% / raw - 34.68%

Post 1972 .0 C rounding ACORN 2.1 - 9.72% / raw - 11.98%

The first decade, 1910-1919, averaged 17.32C in ACORN 2.1 and 18.43C in raw

The final decade, 2010-2019, averaged 18.19C in ACORN 2.1 and 18.19C in raw

Launceston 91049 has annual max temps back to 1901: 1901-1902 + 1904-1909 17.78C

91049 overlap with 91104 1 April 1939 to 30 December 1959 : 91049 18.18C / 91104 16.61C

91104 overlaps with 91311 29 July 2004 to 16 June 2009 : 91104 17.59C / 91311 18.27C

ACORN catalogue: The original site (091049) was at several locations around the centre of Launceston. There was a site move in December 1929 and further site moves on 29 March 1941, 29 September 1942 and 26 February 1948. Temperature observations continued at this location until 1959 but they were not used in ACORN-SAT after 1947. The first airport site (091104) was close to the terminal building and operated from 1939. It moved at some point in 1968–1969 to a location on the western side of the runway and north of the terminal. An automatic weather station was installed at this location on 19 May 1992 and became the primary instrument on 1 November 1996. The site continued until June 2009. The current site (091311) began operating at its current location 1.4 km southeast of the previous site on 12 July 2004. The airport is 160 m higher in elevation than the town, and is also further from the ocean. This results in markedly lower temperatures than those in the town, especially overnight.

1986-1995 raw max averaged 17.05C and post AWS 1997-2006 averaged 17.43C

Launceston max Excel spreadsheets

acorn 2 launceston minimum temperatures

1910-1964 - ACORN 2.1 5.13C / raw 7.00C

1965-2019 - ACORN 2.1 5.99C / raw 6.26C

ACORN 2.1 warmed 0.86C / raw cooled 0.74C

Average change per decade : ACORN 2.1 0.11C / raw -0.13C

Launceston 2000-2019 - ACORN 2.1 6.28C / raw 6.28C

1961-90 - ACORN 2.1 5.73C / raw 6.32C

Pre 1972 .0 F rounding ACORN 2.1 - 19.29% / raw - 40.79%

Post 1972 .0 C rounding ACORN 2.1 - 10.16% / raw - 12.88%

The first decade, 1910-1919, averaged 5.24C in ACORN 2.1 and 7.56C in raw

The final decade, 2010-2019, averaged 6.31C in ACORN 2.1 and 6.30C in raw

Launceston 91049 has annual min temps back to 1898: 1898 + 1902 + 1906-1909 6.20C

91049 overlap with 91104 1 April 1939 to 31 December 1959 : 91049 6.68C / 91104 5.95C

91104 overlaps with 91311 30 July 2004 to 17 June 2009 : 91104 6.39C / 91311 6.28C

1986-1995 raw min averaged 6.34C and post AWS 1997-2006 averaged 6.09C

Launceston min Excel spreadsheets

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Low Head

acorn 2 low head maximum temperatures

1910-1964 - ACORN 2.1 15.80C / raw 15.74C

1965-2019 - ACORN 2.1 16.37C / raw 16.86C

ACORN 2.1 warmed 0.57C / raw warmed 1.08C

Average change per decade : ACORN 2.1 0.09C / raw 0.10C

Low Head 2000-2019 - ACORN 2.1 16.67C / raw 16.68C

1961-90 - ACORN 2.1 16.18C / raw 16.90C

Pre 1972 .0 F rounding ACORN 2.1 - 19.67% / raw - 65.03%

Post 1972 .0 C rounding ACORN 2.1 - 10.18% / raw - 24.86%

The first decade, 1910-1919, averaged 15.94C in ACORN 2.1 and 15.82C in raw

The final decade, 2010-2019, averaged 16.80C in ACORN 2.1 and 16.80C in raw

Low Head 91057 has annual max temps back to 1895: 1895-1899 + 1901-1909 = 15.61C

91057 overlap with 91293 8 January 1998 to 5 December 2001 : 91057 17.58C / 91293 16.65C

ACORN catalogue: The original site (091057) was in the grounds of the Low Head lighthouse, which is on a small hill south of the headland. Prior to June 1937 the screen did not strictly meet Stevenson screen specifications, and was painted brown for a time around 1933, a period when the standard of observations was poor for a few years. Comparison of documentation from 1933 and 1940 indicate either a site move or new buildings during that time, with the latter being more likely. The site moved by 8 m in April 1949. At some point between 1968 and 1986 a gravel driveway was built in close proximity to the screen (the data suggest this occurred in about 1970). The site moved by 25 m on 15 August 1988. The automatic weather station (091293) began operating on 8 January 1998 at a site 200 m north of the previous location.

Assuming the AWS was operational from 1998, 1988-1997 raw max averaged 17.12C and post AWS 1999-2008 averaged 16.59C

Low Head max Excel spreadsheets

acorn 2 low head minimum temperatures

1910-1964 - ACORN 2.1 9.91C / raw 9.50C

1965-2019 - ACORN 2.1 10.28C / raw 10.04C

ACORN 2.1 warmed 0.37C / raw warmed 0.54C

Average change per decade : ACORN 2.1 0.07C / raw 0.11C

Low Head 2000-2019 - ACORN 2.1 10.60C / raw 10.60C

1961-90 - ACORN 2.1 10.11C / raw 9.71C

Pre 1972 .0 F rounding ACORN 2.1 - 15.95% / raw - 63.08%

Post 1972 .0 C rounding ACORN 2.1 - 10.10% / raw - 28.49%

The first decade, 1910-1919, averaged 10.02C in ACORN 2.1 and 9.62C in raw

The final decade, 2010-2019, averaged 10.72C in ACORN 2.1 and 10.72C in raw

Low Head 91057 has annual min temps back to 1895: 1895-1899 + 1901-1909 = 8.58C

91057 overlap with 91293 9 January 1998 to 12 December 2001 : 91057 10.07C / 91293 10.61C

Assuming the AWS was operational from 1998, 1988-1997 raw min averaged 9.85C and post AWS 1999-2008 averaged 10.46C

Low Head min Excel spreadsheets

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