The possibility that human influences could affect climate at a local level was recognised last century in Australia. The debate over whether 'rain follows the plough' was as intense as in the USA. By the mid-20th century attention was turning to the climatic effects of cities (Handcock and Nailon 1963; Royal Meteorological Society Australian Branch 1978). The Australian debate about the climatic influence of forests was mentioned earlier.

Monitoring Australian climate for evidence of climate change has been underway since at least the late 1970s (e.g. Coughlan 1979). In recent years, the National Climate Centre has released, each year, a time-series of east Australian average temperatures, to provide information on whether the climate is changing. Recently, a 'high-quality' dataset of stations which have passed extremely rigorous quality-control testing (Lavery et al. 1997) has been used to prepare spatial averages of rainfall for this monitoring. The data from these stations are believed to be capable of detecting even small changes in climate (Nicholls and Lavery 1992; Nicholls and Kariko 1993). They have been used to prepare time-series of all-Australia mean rainfall, as well as means for each State and various regions. A high-quality temperature dataset has also been produced (Torok and Nicholls 1996) and used to prepare spatial averages of annual mean minimum and maximum temperatures, and is now used as the basis for the regular annual monitoring of Australian mean temperature. Figure 2 shows the annual average maximum and minimum temperatures, and rainfall, averaged across Victoria, for each year from 1910 to 1992. Minimum temperatures have increased gradually since about the middle of the century. Maximum temperatures have remained relatively stable, while rainfall increased quite suddenly in the middle of the century.

Monitoring climate extremes (e.g., droughts), to determine whether the climate is becoming more extreme or variable, has commenced recently. Karl et al. (1995) found little consistency in patterns of change in temperature variability for Australia since 1961, apart from statistically significant decreases in interannual variability in spring, especially in temperate regions. Suppiah and Hennessy (1996) found an increase in the frequency of extreme rainfall events at a majority of stations in northern Australian summers since 1910. Few of the increases were statistically significant. Stone et al. (1996) report an apparent decrease in the number of frosts affecting inland eastern Australia during the twentieth century. Neil Plummer (National Climate Centre) is now coordinating a study to monitor changes in a variety of indices of extreme weather and climate.

There has been considerable focus on the possible causes of any changes in Australian climate, as well as the possible consequences for the future. In 1975 the Australian Academy of Science, at the request of the Australian Government, established a committee to report on whether the climate was changing. The Committee (Australian Academy of Science 1976) concluded that there was no evidence that the world was on the brink of a major climatic change. They also noted the existence of a new factor in climatic change, namely that 'man's activities are now developing on a scale and in direction, that could have an appreciable effect on the climate within decades'. These 'activities' included the enhancement of the 'greenhouse effect', through increases in carbon dioxide content in the atmosphere, and increases in particulate matter in the atmosphere. Pearman (1978) noted that a doubling of the atmospheric concentration of carbon dioxide could lead to an increase of 2–3°C in global temperature. Tucker (1981) reviewed the current state of knowledge regarding the possible climate effects of increased carbon dioxide production and concluded that 'it seems inevitable that life on earth will be affected by changing atmospheric carbon dioxide concentrations but it is too soon yet to give more than a general indication of the size of the effects and of their net beneficial or deleterious nature'. Since then, Australian involvement in international programs and studies (such as those of the Intergovernmental Panel on Climate Change) and national programs (e.g., Pearman 1988) has attempted to address the question of a human impact on global climate in more depth, as well as looking at its southern hemisphere implications (Giambelluca and Henderson-Sellers 1996). Despite this work, major uncertainties still remain (e.g., Houghton et al. 1996).

Bureau of Meteorology