11.7.3.1 Mean Temperature

In both the southern and northern Australia regions, the projected MMD-A1B warming in the 21st century represents a significant acceleration of warming over that observed in the 20th century (Figure 11.16). The warming is larger than over the surrounding oceans, but only comparable to, or slightly larger than the global mean warming. Averaging over the region south of 30°S (SAU), the median 2100 warming among all of the models is 2.6°C (with an inter-quartile range of 2.4°C to 2.9°C) whereas the median warming averaged over the region north of 30°S (NAU) is 3.0°C (range of 2.8°C to 3.5°C). The seasonal cycle in the warming is weak, but with larger values (and larger spread among model projections) in summer (DJF). Across the MMD models, the warming is well correlated with the global mean warming, with a correlation coefficient of 0.79, so that more than half of the variance among models is controlled by global rather than local factors, as in many other regions. The range of responses is comparable but slightly smaller than the range in global mean temperature responses, and warming over equivalent time periods under the B1, A1B, and A2 scenarios is close to the ratios of the global mean responses The warming varies sub-regionally, with less warming in coastal regions, Tasmania and the South Island of New Zealand, and greater warming in central and northwest Australia (see Figure 10.8).

Figure 11.16. Temperature anomalies with respect to 1901 to 1950 for two Australian land regions for 1906 to 2005 (black line) and as simulated (red envelope) by MMD models incorporating known forcings; and as projected for 2001 to 2100 by MMD models for the A1B scenario (orange envelope). The bars at the end of the orange envelope represent the range of projected changes for 2091 to 2100 for the B1 scenario (blue), the A1B scenario (orange) and the A2 scenario (red). More details on the construction of these figures are given in Box 11.1 and Section 11.1.2.

These results are broadly (and in many details) similar to those described in earlier studies, so other aspects of these earlier studies can be assumed to remain relevant. For the CSIRO (2001) projections, pattern-scaling methods were used to provide patterns of change rescaled by the range of global warming given by IPCC (2001) for 2030 and 2070 based on the SRES scenarios. By 2030, the warming is 0.4°C to 2°C over most of Australia, with slightly less warming in some coastal areas and Tasmania, and slightly more warming in the northwest. By 2070, annual average temperatures increase by 1°C to 6°C over most of Australia with spatial variations similar to those for 2030. Dynamically downscaled mean temperature change typically does not differ very significantly from the picture based on AOGCMs (e.g., see Whetton et al., 2002). Projected warming over New Zealand (allowing for the IPCC (2001) range of global warming and differences in the regional results of six GCMs used for downscaling) is 0.2°C to 1.3°C by the 2030s and 0.5°C to 3.5°C by the 2080s (Ministry for the Environment, 2004).