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 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:
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".
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. 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. 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? Top of page
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