Australian climate change projections derived from simulations performed for the IPCC 4th Assessment Report

In this study, we present climate change projections based on the results from 23 climate model simulations performed for the IPCC 4th Assessment Report. Statistical methods are used to test how well each model simulated observed average (1961-1990) patterns of mean sea-level pressure, temperature and rainfall over the Australian region. The 15 models with the highest pattern correlations and smallest rms errors are identified. The 21st century simulations are driven by the IPCC 'SRES' greenhouse gas and aerosol emission scenarios. Using the 15 best climate models, annual and seasonal average projections of Australian rainfall and temperature change are derived for various decades. Results are highlighted for 2030 and 2070 for comparison with projections published by CSIRO in 2001. The projections are expressed as ranges, incorporating uncertainty in both global warming and regional differences between climate simulations over Australia. Inland regions show greater warming, compared to coastal regions. There are large decreases in the number of days below 0 degree C and large increases in the number of days above 35 degree C or 40 degree C. Rainfall changes are more complex than temperature changes. Although increases and decreases in rainfall are projected in the future, decreases dominate the overall pattern, especially in the south in winter and spring. CSIRO's earlier projections, based on nine climate models, appear robust when compared with the updated projections. The patterns and magnitudes of warming are similar, although the updated projections have slightly less warming in coastal regions. The pattern of rainfall change is also similar, particularly the strong decrease in winter and spring over southern Australia, but the updated projections give a more widespread tendency for increases in summer in eastern Australia and a clearer tendency for decreases in autumn in Queensland and the eastern Northern Territory.