The effect of stratospheric ozone loss on Southern Hemispheric extratropical circulation is explored using an atmosphere-only model. The main tropospheric response is a sudden shift in the leading mode of month-to-month variability, the Antarctic Oscillation, during November and December towards its high phase. Therefore, this change consists of a shift in atmospheric mass from high-latitudes poleward of 60 ¿S to a mid-latitude band centred on 45 ¿S. This response provides a plausible explanation for the increase in westerly circulation at 60 ¿S observed since the early 1980's. There is also a strong response in January--March but this may be unrealistic as the observed lower stratospheric temperature changes are poorly simulated in that season. ¿ 2001 American Geophysical Union