Temperature change in Australia

The rates of temperature change in Australia at rural and non-rural weather stations are compared. Over those periods in which there were increasing temperatures, the rural stations appear to have warmed at about 60-70% of the warming rate of the non-rural stations.

Data

Data from the Australian Bureau of Meteorology (BOM) is used, and is assumed to be sufficiently accurate for the purpose. It is not known whether any original measurements have been adjusted in the BOM records.

The data values downloaded from BOM are monthly mean max and monthly mean min. These are used in preference to monthly max and monthly min, as being more representative of each month’s temperature.

Weather Stations

47 weather stations were active from 1940 to 2000, ie. from 1940 or earlier to 2000 or later. Of these, 10 were rural.

Station Number Station Name Latitude Longitude Start Year Last Year Is Rural? 3003 BROOME AIRPORT -17.9475 122.2353 1939 2009 No 4020 MARBLE BAR COMPARISON -21.1756 119.7497 1901 2006 Yes 8025 CARNAMAH -29.6889 115.8869 1940 2009 No 8093 MORAWA -29.2103 116.0089 1925 2005 No 9510 BRIDGETOWN COMPARISON -33.9575 116.1375 1907 2009 No 9518 CAPE LEEUWIN -34.3728 115.1358 1907 2009 Yes 9534 DONNYBROOK -33.5719 115.8247 1907 2009 No 9581 MOUNT BARKER -34.625 117.6361 1907 2009 No 10073 KELLERBERRIN -31.6183 117.7217 1910 2009 Yes 10111 NORTHAM -31.6508 116.6586 1907 2009 No 10579 KATANNING COMPARISON -33.6886 117.5553 1907 2009 No 10614 NARROGIN -32.9342 117.1797 1913 2009 No 10648 WANDERING COMPARISON -32.6814 116.6756 1901 2003 No 12038 KALGOORLIE-BOULDER AIRPORT -30.7847 121.4533 1939 2009 No 12071 SALMON GUMS RES.STN. -32.9869 121.6239 1932 2009 Yes 12074 SOUTHERN CROSS -31.2319 119.3281 1907 2007 No 17031 MARREE COMPARISON -29.6481 138.0637 1939 2009 No 17043 OODNADATTA AIRPORT -27.5553 135.4456 1940 2009 No 18012 CEDUNA AMO -32.1297 133.6976 1939 2009 No 18044 KYANCUTTA -33.1332 135.5552 1930 2009 Yes 18070 PORT LINCOLN -34.7225 135.8558 1892 2002 No 21046 SNOWTOWN -33.7844 138.2133 1908 2001 No 26026 ROBE COMPARISON -37.1628 139.756 1884 2009 No 29004 BURKETOWN POST OFFICE -17.7425 139.5475 1890 2009 No 30018 GEORGETOWN POST OFFICE -18.2922 143.5483 1894 2007 No 30045 RICHMOND POST OFFICE -20.7289 143.1425 1893 2009 No 32040 TOWNSVILLE AERO -19.2483 146.7661 1940 2009 No 33047 TE KOWAI EXP STN -21.1642 149.1192 1908 2009 Yes 37010 CAMOOWEAL TOWNSHIP -19.9225 138.1214 1939 2009 No 38003 BOULIA AIRPORT -22.9117 139.9039 1888 2009 No 39039 GAYNDAH POST OFFICE -25.6258 151.6094 1893 2009 No 39083 ROCKHAMPTON AERO -23.3753 150.4775 1939 2009 No 46037 TIBOOBURRA POST OFFICE -29.4345 142.0098 1910 2009 No 55023 GUNNEDAH POOL -30.9841 150.254 1876 2009 No 66037 SYDNEY AIRPORT AMO -33.9411 151.1725 1939 2009 No 66062 SYDNEY (OBSERVATORY HILL) -33.8607 151.205 1859 2009 No 70014 CANBERRA AIRPORT -35.3049 149.2014 1939 2009 No 74128 DENILIQUIN (WILKINSON ST) -35.5269 144.952 1858 2003 No 78031 NHILL -36.3347 141.6367 1897 2008 No 82039 RUTHERGLEN RESEARCH -36.1047 146.5094 1912 2009 Yes 86071 MELBOURNE REGIONAL OFFICE -37.8075 144.97 1855 2009 No 90015 CAPE OTWAY LIGHTHOUSE -38.8556 143.5128 1864 2009 Yes 91057 LOW HEAD (COMPARISON) -41.0567 146.7883 1895 2001 Yes 91104 LAUNCESTON AIRPORT COMPARISON -41.5397 147.2033 1939 2009 No 94029 HOBART (ELLERSLIE ROAD) -42.8897 147.3278 1882 2009 No 200283 WILLIS ISLAND -16.2878 149.9652 1921 2009 Yes 200288 NORFOLK ISLAND AERO -29.0389 167.9408 1939 2009 No

Whether each station was rural or non-rural was determined using Google Earth. The decisions were necessarily subjective. The Google Earth views of the stations are shown in RSelectedStationsGoogleMaps (10.7mb PDF)

Note : Station 9581 Mount Barker is obscured by cloud in the Google Earth view. The population of Mount Barker is over 4,000, and the weather station appears to be in or very near the built-up area, so it is classified as Non-Rural.

The monthly mean max and monthly mean min temperatures for all these stations were downloaded from the BOM website http://www.bom.gov.au/. The temperatures were downloaded in January and February 2011, but unfortunately the December 2010 temperatures for some of the stations had not then been posted. For those stations, data was in fact complete to November 2010. Note that “Last Year” for stations that are still open is given as 2009, and that 10 of the stations closed between 2000 and 2009. A further 3 stations (29004, 39039, 91104) appear to have closed in 2009.

The data as downloaded is in http://members.westnet.com.au/jonas1/QMeanTemps.pdf

(2.8mb)

Please see the Acknowledgements and Licence information

Product code “IDCJAC0002″ is Monthly Mean Maximum Temperature, and “IDCJAC0004″ is Monthly Mean Minimum Temperature.

Calculations

Temperature trends (least-squares linear fit) over various periods were calculated separately for each calendar month, for each station, using only the monthly temperatures that were given. There was no attempt to fill in any missing data.

For each period, only the stations active for the whole of the period were used (there could be some missing data, but the test was that there was data for the first year of the period or for an earlier year and that there was data for the last year of the period or for a later year).

The overall trend for each period was then taken as the average of all trends for that period – ie, the average across all calendar months and all active stations.

The reasons for using this method are:

If an attempt was made to fill in missing data, then there would be a risk that the filling-in method used could introduce errors or biases.

Each calculated trend is for one calendar month only (eg. all Januaries), so has no seasonal bias.

If trends were calculated on annual averages, instead of by calendar month, then any year with a missing month’s data could not be used, because that would introduce a selection bias.

If trends were calculated on all months, instead of by calendar month, then the least-squares algorithm would bias the result towards the hottest and coldest calendar months. The previous issue – a missing month’s data affecting a whole year – also applies.

Each calculated trend is for one station only. If station data was averaged before calculating the trend, then it would not be possible to use any month for which any station’s data was missing, because it would introduce a selection bias.

The station / calendar month trends for each period were only calculated for stations active in that calendar month over the whole of the period (individual months’ data may still be missing). Thus when trends are averaged for any given period, there is no station selection bias. Note that the number of selected stations can be different for different periods.

It is possible that there may be a geographical bias in the data, ie. the stations used may have different geographical distributions for different periods, or that the geographical distribution of stations is not representative of the region. It is also possible that missing data could affect results, especially if missing values are clustered (eg. same calendar month missing over consecutive years, for a given station).

The full results, where there were at least 5 stations used in each trend average, are given in this table:

Also in: http://members.westnet.com.au/jonas1/RAverageMeanTempTrendsSummary5.pdf (42kb)

and are as follows:

Trends are given in deg C per year. So, for example, the first number, 0.0036, for the period 1910-2000, means that the average trend of Monthly Mean Max temperatures from 1910 to 2000 for Non-Rural stations was 0.0036 deg C per year. (All results are given to 4 decimal places, so there may be rounding errors).

For stations whose Dec 2010 data was missing, the average trend shown to 2010 is the average of the Jan-Nov trends. Stations are only included for periods over which they have both “Max” and “Min” temperature data.

These figures indicate that over those periods in which there were increasing temperatures, the rural stations only warmed at about 60-70% of the warming rate of the non-rural stations.

There are some curious numbers in the results, which could deserve further analysis – for example, the rural trends for 1980-2000 and 1990-2000 are much lower than the non-rural, yet for 2000-2010 they are about the same as the non-rural. Also, there is no warming trend from 1910-1940, a period of quite rapid global warming (see, eg.,

http://www.cru.uea.ac.uk/cru/info/warming/gtc.gif).

Where there were at least 2 stations used in each trend average, the results are given in

http://members.westnet.com.au/jonas1/RAverageMeanTempTrendsSummary2.pdf (43kb)

and all trend averages are given in

http://members.westnet.com.au/jonas1/RAverageMeanTempTrendsSummary.pdf (45kb)

All of the individual station / calendar-month trends (rounded to 4 dec places) are given in this document:

http://members.westnet.com.au/jonas1/QMeanTempTrends.pdf (734kb)

This too could deserve further analysis, eg. there may be significant summer / winter trend differences.

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For further information and discussion, see

http://members.westnet.com.au/jonas1/AustraliaTemperatureChangeNotes.pdf

This document includes:

List of the 47 weather stations.

Google Earth maps used for Rural/Non-Rural identification. [link]

BOM website (data source). [link]

Source data. [link]

Individual station / calendar-month trends. [link]

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