We analyzed eighty years of historical weather records and used a hierarchy of computer models to understand the cause of these swings and project future changes. We found that the variability of this pattern has already increased significantly, contributing to more intense weather, such as a 40% increase in extreme rainfall during certain events. Our work shows this amplification is driven by the growing temperature difference between the tropics and Antarctica. This trend is projected to continue, suggesting the Southern Hemisphere will likely face more frequent and intense weather extremes in a warming world.