Abstract
The Southern Hemisphere climate system is changing rapidly with anthropogenic climate change. The two external forces driving these changes are the greenhouse gas emissions and the stratospheric ozone levels. Previously, the combination of stratospheric ozone depletion over Antarctica and an increase in greenhouse gas emissions led to changes in the Southern Hemisphere climate, such as a poleward shift and intensification of the westerly jet, a poleward expansion of the Hadley cell, a poleward shift of the storm tracks, an increase in sea surface temperatures, and an increase in sea ice melting. With the implementation of the Montreal Protocol, however, the stratospheric ozone is expected to recover by mid-century. As the ozone recovers, the greenhouse gas and ozone forces will oppose each other and the changes observed previously will begin to weaken or reverse. How the Southern Hemisphere climate system then responds to the ozone recovery is the goal of this thesis. This thesis investigates the changes observed in both the atmosphere and ocean, and in turn, how these global changes affect the regional and local climate, such as changes in precipitation. Understanding what drives the changes seen in local precipitation in regions prone to flooding and droughts, such as South Africa, is important for agricultural areas and farming populations throughout the world. In this thesis, a new estimate of Agulhas leakage is calculated first, using observed and simulated Lagrangian drifters and floats. Then, the Southern Hemisphere climatic response to the ozone recovery in an ocean eddy-parameterizing coupled climate model is explored next. And lastly, to determine which of the external forces is more dominant in the Southern Hemisphere climate system, the role the greenhouse gases and the ozone recovery play in the Southern Hemisphere climate system is examined using CCSM4 coupled ocean eddy-parameterized and eddy-resolving simulations.