Bureau of Meteorology analysis and forecasts
Since 1910, the Bureau estimates that average mean minimum temperatures in Western Australia have risen almost 1 degree C (.05-.2 degrees C per decade) while average mean maximum temperatures have risen by about .7 degrees C (.05-.2 degrees C per decade). See maps of minima and maxima or timelines of minima and maxima from 1910 to 2008. The bureau's calculations are based on readings from 26 locations, 12 coastal (Albany, Broome Airport, Cape Naturaliste, Cape Leeuwin, Carnarvon Airport, Derby Aero, Esperance, Geraldton Airport, Perth Airport, Port Hedland Airport, Roebourne, Rottnest Island) and 14 inland (Bridgetown Post Office, Giles Meteorological Office, Halls Creek, Jarrahwood, Kalgoorlie-Boulder Airport, Katanning, Kellerberrin, Marble Bar, Meekathara Airport, Merredin, Newman Aero, Southern Cross, Wandering, York). The development and application of Australia's High Quality climate datasets (PDF 270kb) provides an analysis of the methods used to "correct" climate readings for a more accurate historical comparison. The Bureau notes on its website that: The temperature timeseries are calculated from homogeneous or "high-quality" temperature datasets developed for monitoring long-term temperature trends and variability. Where possible, each station record in these datasets has been corrected for data "jumps" or artificial discontinuities caused by changes in observation site location, exposure, instrumentation or observation procedure. This involves identifying and correcting data problems using statistical techniques, visual checks and station history information or "metadata". The Bureau also notes: A change in the type of thermometer shelter used at many Australian observation sites in the early 20th century resulted in a sudden drop in recorded temperatures which is entirely spurious. It is for this reason that these early data are currently not used for monitoring climate change. Other common changes at Australian sites over time include location moves, construction of buildings or growth of vegetation around the observation site and, more recently, the introduction of Automatic Weather Stations. The impacts of these changes on the data are often comparable in size to real climate variations, so they need to be removed before long-term trends are investigated. Procedures to identify and adjust for non-climatic changes in historical climate data generally involve a combination of:
It should be noted that all WA temperature recordings for August 2009 shifted up by .4 to .5 degrees C after a database bug was corrected by the BoM on November 17, 2009. It should also be noted that recordings by the Goddard Institute of Space Studies, primarily for September 2009, are as much as 1.2 degrees C higher than the actual temperatures recorded by the BoM. For further information about anomalies between BoM and GISS temperature records, see historic charts for all Australian locations. Note that in 2012 and with no publicity, the High Quality dataset series was replaced by the Australian Climate Observations Reference Network - Surface Air Temperature (ACORN-SAT) series which recalculates Australia's temperature history. Analysis here. The Federal Government's Climate Change in Australia office estimates that Western Australia's average climate will warm (under medium carbon dioxide emissions and at the 50th percentile from the IPCC Special Report on Emission Scenarios) from the 1980-1999 period by 1 to 1.5 degrees C up to 2030, from 1.5 to 2.5 C by 2050 and 2 to 4 degrees by 2070. The Bureau's Climate Change Centre also provides a map of Western Australia showing the maximum temperature anomaly and minimum temperature anomaly for the most recent month. How our temperatures have changed (PDF 128KB) is a 2005 compilation by John Cramb from the Bureau of Meteorology that outlines climate change and variations in southern Western Australia since 1910. How Do We Know About the Climate in the Period Before Instruments? is an excellent analysis by the Australian Bureau of Statistics, and includes a note that "The data also suggest that the early part of the 20th century was rather cold by the standards of the last 3,600 years". Climate variability and change in south west Western Australia by the Indian Ocean Climate Initiative, published 2002. A historical annual temperature dataset for Australia by Simon Torok and Neville Nicholls, Bureau of Meteorology Research Centre, Melbourne, published 1996.
A BoM climate records audit shows data influenced by the Celsius metrication of temperature scales in 1972 and consistently inaccurate thermometer readings before and since. Urban heat island features of southeast Australian towns (PDF 221kb) published in 2001 shows concrete and bitumen heat retention around 7C in central Melbourne and 2C to 5C in regional towns. A 2012 thermal night scan of Perth CBD showed at least 4C concrete and bitumen heat retention compared to residential areas with tree cover varying UHI up to 2C in suburbs. Read more in Urban climates and heat islands: albedo, evapotranspiration and anthropogenic heat (PDF 573kb). Although the Bureau of Meteorology is conclusive that pre-1900 data is unreliable, largely because it was superseded by more accurate Stevenson temperature recording equipment, there is still debate about the validity of this position. The following text is extracted from Historical Thermometer Exposures in Australia: Western Australia: Cooke (1906) notes that at Perth ‘A set of meteorological instruments was first mounted in a Stevenson screen on 1st January 1897, and observations have been taken regularly at 9 a.m. and 3 p.m. since that time’. This comment refers to a set of observations commenced at the site of the Perth Observatory, which was under construction at that time. From August 1885 to the end of 1896 the official Perth observations were from another site in the Botanical gardens. At that site ‘The Thermometer house is of an octagonal form’ (Cooke, 1897), ‘built from plans supplied by C. Todd, Esq., C.M.G., Government Astronomer, South Australia, the principle of exposure being similar to that followed in the Adelaide Observatory ... Thermometers for recording the temperature of the air in the shade are placed in the Thermometer house in a revolving stand of Mr. Glaisher’s pattern’ (Fraser, 1886). Although observations continued at this latter site for some years after 1896, still using the same exposure, the data were not used for official purposes after this date. There are indications that Western Australian stations opened after 1897 were equipped with a Stevenson screen. It appears likely that stations operating at that date were refitted during 1896 and 1897, including the installation of a Stevenson screen. With the exception of the Perth Botanical gardens, stations operating prior to 1896 were described as having ‘Shade Screens ... of the same pattern as those recommended and used by the Board of Trade’ (Cooke, 1897). Cooke, the first Government Astronomer of the Colony, was appointed in February 1896 and he or a colleague visited most, if not all, the Western Australian meteorological stations during this year, replacing instruments. Cooke (1898) comments that on this tour he ‘found things in a more or less unsatisfactory condition’. This and subsequent annual reports contain a statement which strongly suggests that each out-station was provided with a Stevenson screen before the end of 1897. The term ‘Stevenson screen’ was not use in the earlier report (Cooke, 1897). The Board of Trade screens were small, single louvred, fully enclosed wall screens (Anonymous, 1877, Scott, 1875, 1907). Thermometers in these screens were found to record higher temperatures than thermometers exposed in a Stevenson screen in open ground (Scott, 1875). Climate change and global warming in Australian newspapers gives an amusing insight to how the climate has been warming since the 19th century, according to the Press. Is the US Surface Temperature Record Reliable? (PDF 3.9mb) is a comprehensive 2009 survey of America's climate-monitoring network that raises questions about the validity of Stevenson Screen recordings since the early 1900s. For further evidence of past climate change via tree rings, corals, ice cores, marine sediments, etc, see a 2005 CSIRO report detailing what palaeo-science can reveal about climate change and its potential impacts in Australia (PDF 1.3mb). This CSIRO report displays palaeo-scientific evidence that sea surface temperatures were considerably warmer during the 1700s and 1800s in Australia's northern waters, based on isotope readings from the Great Barrier Reef. Similar results can be seen in tree ring data from Tasmania and New Zealand, with inconsistent trends in South America. The influence of Pacific Sea Surface Temperatures on global warming and cooling can be further studied within Geophysical Research Letters or Making Holocene Spaghetti Sauce by Proxy (PDF 11.2mb). Research by the University of New South Wales Faculty of Science, reported in February 2009, suggests the long running drought in eastern Australia is caused by variable water temperatures in the Indian Ocean. An alternative explanation for Australian temperature trends in the late 20th century is the Great Pacific Climate Shift of 1976 (PDF 272kb). There is also evidence that massive land clearing (PDF 580kb) has contributed significantly to temperature increases and rainfall declines recorded in the south of Western Australia since the mid 20th century. Hide the Decline examines historic records across Australia showing differences between coastal and inland temperature trends due to ocean influences, as well as a clear divide in Australia's east/west temperature patterns. In 2010, research published in Nature Geoscience magazine presented evidence that high snowfall in the Antarctic over recent decades is having a previously unrecognised impact on rainfall in the south-west of Western Australia, mostly by restricting the northern range of oscillating cold fronts so that fewer are reaching the Australian mainland. The Australian Climate Science Coalition aims to promote open scientific debate on the causes of climate change. Australian temperature trends at different times of the day are analysed within the Gust of Hot Air blog of honourary science graduate Jonathan Lowe. For a quality Australian blog that dissects climate change and other issues, check JoNova. For the best quality climate change analysis blog in the world, check Watts Up With That?
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