Introduction

The Australian continent is large and therefore exhibits a range of very different climatic zones. Broadly, the continent is characterised by arid climatic regimes: four-fifths of the landmass receiving an annual rainfall of less than 600 mm (Figure 12.1) and one-half of the continent receiving less than 300 mm. These arid and semi-arid regions form the greatest proportion of inland Australia, and are fringed by narrow, wet and temperate climatic zones along the southwestern, southern and eastern coastal zones (Figure 12.1). Tropical monsoonal rainfall characterises the northern coastal zones. Compared to other continents on Earth, Australia has by far the lowest average rainfall. This low precipitation rate is coupled with a high evaporation rate meaning that surface water availability is also anomalously low compared to global averages. Average annual temperature also shows significant variation (Figure 12.1) and in most areas there is also a high diurnal variation in temperature.

It is well known, however, that the currently arid areas of inland Australia were significantly wetter in the geological past, from the early Cenozoic (a period of geological time from c. 65 Ma until the present day; Gradstein et al. 2004) until at least the early Miocene (c. 23 Ma) (e.g. Kershaw et al. 1994; Martin 2006). Much of our current knowledge of climate change from the early Cenozoic to the present is deduced from observed variations in the isotopic signature of marine sediments (e.g. deMenocal 1995; Lisiecki and Raymo 2005; Raymo et al. 2006) as well as the distribution, chemistry and palynological assemblages of terrestrial and marine sediments and sedimentary rocks.