How ENSO and its Impact on Climate May Change
With Increasing Greenhouse Gases


Soon-Il An

Department of Atmospheric Sciences, Yonsei University, Seoul, Korea


Abstract: The multi-decadal modulation of the El Nino-Southern Oscillation (ENSO) due to the greenhouse warming has been analyzed herein by means of diagnostics of IPCC-AR4 coupled general circulation model (CGCMs) and the eigen analysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multi-decadal time scale. The climate system model outputs suggest that the multi-decadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigen analysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multi-decadal modulations of the ENSO’s amplitude and period. In particular, the change in the vertical contrast, i.e., change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.