Substantial variability exists between El Nino events, in terms of their strength, location, and persistence. The degree to which all of these properties will respond to future climate change remains unclear, partially due to the complexity of interactions between greenhouse gas and other anthropogenic and natural forcing factors. We are using the LME greenhouse gas and ozone/aerosol single-forcing ensembles to investigate the mechanisms for changes to ENSO characteristics in the 20th century relative to the pre-industrial period.