Climate variations on time-scales of decades and longer have been a characteristic feature of Australian climate during the 20th Century. These in turn have had major impacts on climate-sensitive activities, including agriculture and water resource management, among others, and have been associated with several major incidents of land degradation and other environmental problems within Australia.

Some of the major variations, and their impacts, have been:

1. A continent-wide period of reduced rainfall over the entire country between the mid 1920s and 1940s, with major dust-storms, bushfires and land degradation. Also during this period, the normally strong ENSO influence on Australian rainfall became very weak.

2. Prolonged wet spells during the 1950s and again in the 1970s, associated with frequent and widespread flooding. These were also periods of extensive disease outbreaks in both the human and animal populations.

3. A tendency for rainfall to be below average over the northwestern portion of Australia between the 1930s and 1960s, followed by an extended (and essentially ongoing) wet spell from the 1970s onward, with particularly wet conditions since the mid 1990s. By contrast, a marked decrease in rainfall has occurred over southwestern Australia since the late 1960s, with important implications for water supply management and some ecological systems.

4. Following a brief cooling in the 1940s, there has been a distinct rising trend in temperatures over most of the country since 1950, with the rise in minimum temperatures (0.97ºC since 1950) being somewhat greater than the rise in maximum temperatures (0.62ºC). The rise in minimum temperatures has been greatest over the northeastern interior and has been reflected in a marked decrease in frost frequency since the 1950s. This has already impacted on agricultural activity.

A key challenge for the future is dissociating “natural” climate variability on the decadal and multidecadal time-scales from anthropogenic climate change. An example illustrating the problem will be presented, along with a brief summary of modelling approaches to this problem. On the longer time-scale, the experiences of the 20th century have important implications for adaptation to likely future climate change. Some results from a conference on managing with climate variability, which illustrates the issues associated with factoring long-term climate variability into planning in climate-sensitive industries, will be presented.