It is well documented that the stratosphere acts as an ‘early warning system’ for climate change, as signatures of changes are often more robust in the stratosphere than in the troposphere. Thus the monitoring and detection of stratospheric changes is of special relevance for the attribution of climate change. For example, lower stratospheric water vapour (H₂O) showed an unexpected but significant decline since 2001. Concurrently a significant decrease in tropical tropopause temperatures was measured which suggests that the low H₂O values are the result of an increase in tropical upwelling (Randel et al., 2006) possibly due to increased GHG concentrations. Important current research issues are how stratospheric O₃, H₂O,and other constituents evolve in a future atmosphere with enhanced GHG concentrations, and how these changes in stratospheric composition will affect climate.