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Climate Variability and Change (continued)

Temperature

In general, Australia experiences higher temperatures at locations close to the equator and over the desert regions, and lower temperatures in southern Australia and in mountainous regions. Temperature shows greater ranges between highest and lowest temperatures, both daily and annually, with increasing distance from the sea and with increasing latitude. Average annual air temperature ranges from 29C along the Kimberley coast in north-west Australia to about 4C in the alpine areas of the south-east. July is the coldest month over the whole continent, with the coldest regions being the mountainous regions of the south-east.

Temperature trends [A Indicator 1.5]

Globally, surface temperature, measured in standard meteorological screens at 1.5 m above the ground, has increased since 1861. During the 20th century, the increase was 0.6-0.2C (IPCC 2001). This value is about 0.15C larger than the figure estimated by the Second Assessment Report of IPCC (1996). Globally, the 1990s was probably the warmest decade and 1998 the warmest year in the instrumental record dating back to 1861. About 0.25 to 0.4C of the temperature increase has occurred in the past 20 years (National Research Council 2000). This estimate takes into account types of instruments and their changes with time, as well as urban heat island effects, mainly by excluding data from stations affected by these problems.

A time series of global and hemispheric temperatures, which are based on surface air temperature (measured by land stations and represented over the ocean by sea surface temperatures from ships and buoys) shows that the rise in temperature was greater in the Northern Hemisphere than in the Southern Hemisphere (Figure 23). Variations in Australian annual mean, maximum and minimum temperature anomalies (Figures 24, 25 and 26) are based on data derived from about 130 high-quality non-urban temperature observing stations located throughout the country. This network of stations was developed to monitor long-term temperature trends in Australia and is a subset of the network identified by Torok and Nicholls (1996). Temperature values are shown as anomalies from the reference period 1961 to 1990, directly comparable with global temperature anomalies shown in Figure 23. Records at these stations have been corrected for discontinuities caused by changes in instrumentation, site location and urban influences. Temperature over Australia during the 20th century shows an increasing trend, consistent with global trends (Jones 1994; Torok and Nicholls 1996) (compare Figures 23 and 24). Long-term trends and interannual variations in the Southern Hemisphere annual mean temperature are closely related to Australian temperature trends and variations, since many Australian stations contribute to Southern Hemispheric temperature statistics.

Average annual mean temperature generally increased throughout Australia since 1910 and the second half of the century shows greater warming than the first half. However, the amount of warming has not been uniform across the country, nor has it been the same for maximum and minimum temperatures (Figures 25 and 26). The past 20 years have been particularly warm, with many of the warmest years on record occurring during the 1980s and 1990s.

Australian average surface temperature has increased by 0.76C over 90 years. Minimum temperature has increased by 0.96C and maximum has increased by 0.56C over 90 years. Annual average temperature increase is consistent with the global temperature trend reported by IPCC (2001).

Spatial patterns of maximum and minimum temperatures [A Indicator 1.5]

Trends in the spatial patterns of annual mean, annual mean maximum and annual mean minimum temperatures have been calculated, based on data from 1910 to 1999. Mean annual temperature shows an increase of about 0.1C per decade at some locations, but the all-Australian average temperature increase is 0.76C during the last 90 years. The increase is largest over western and northern Australia, and smallest in the south-east (Figure 27). Mean annual maximum temperatures show increases over the western half of the continent and small increases or decreases in the eastern half (Figure 28). Trends in annual minimum temperatures indicate largest increases in eastern Australia (Figure 29).

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