Australia's most highly populated and associated agricultural centres rely on rains from frontal systems embedded in the mid-latitude westerlies. A long-term shift in these, and subsequent modification in rainfall, will create cause for new responses to water requirements and a shift in agriculture types and regions.

Understanding the causes of shifts in the westerlies is imperative to future management issues. Meteorological records are relatively short, and thus understanding the mechanisms leading to shifts in the westerlies in an extreme climate prior to these measurements, confirmed with proxy data, will help extend our understanding of the variability possible in our climate system.

Using an AGCM, the present day and the last glacial maximum are simulated. The boundary conditions, such as the sea surface temperature and the extent of Antarctic sea-ice, were tested for their influence on the meridional shift in the westerlies. The pattern and change in the sea surface temperatures, and thus shifts in the baroclinicity, were found to be the major contributing factor. This is particularly true in winter, a very important time for those regions in the northward reach of the westerlies as this is when they receive most of their rain. Over the Australian region proxy evidence confirms the southward shift produced by the model, with evidence of enhanced aridity. The average shift is of the order of the extremes in the present day variability.