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PERSPECTIVES 0 0 5 0 4 60 E 0 3 0 2 0 1 0 1 0 2 0 3 120 E 0 4 0 5 180 5 Rainfall mm per day sure at mid latitudes and decreased pressure at high latitudes 1 Increasing greenhouse gases have probably contributed to the observed Southern Hemisphere 60 W warming at mid and lower latitudes and to the observed circulation changes strengthening of the SAM in winter However the magnitude of the circulation response in these climate models is not nearly as strong as that found in the observations or in the ozone forced mod 120 W el response in summer 3 The recent changes in the Southern Hemisphere circulation at high latitudes have clear impacts on Antarctica and the Southern Ocean In addition there may be important links between SAM variations and rainfall in southern Australia New Zealand and South America see the figure Increases in the SAM with increasing pressure at mid latitudes are associated with decreases in rainfall between 35 and 50 S There has been a substantial reduction 15 to 20 in winter rainfall in southwest Western Australia over the past 50 years associated with a southward shift in the winter rain bearing weather systems 5 Fyfe has noted this southward shift in Southern Hemisphere extratropical cyclones in both observational data and model responses to increasing greenhouse gases 6 The observed rainfall trends in southwest Western Australia are much greater than expected from most climate model simulations with increasing greenhouse gases Furthermore they occur in a season when there is likely to be little influence from stratospheric Seasonal 11 year running mean 4 3 Climate connections Top Relation between variations of the southern annular mode SAM and rainfall in the Southern Hemisphere based on data from a long control climate model simulation 7 Similar results are obtained with the climate model of Gillett and Thompson 3 Bottom Time series of winter rainfall in southwest Western Australia The decrease in rainfall is consistent with the observed

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