The three most intense El Niño events of the last century probably all occurred in the last 25 years (1972/3,1982/83 and 1997/8). El Niño events have also become longer-lasting since 1976. These observations raise the question, is this due to global warming?
Previous model studies have been unable to throw light on this because their coarse resolution of equatorial conditions prevented adequate simulation of ENSO events. A new and more refined model indicates that increased greenhouse-gas concentrations may well cause more frequent El-Niño-like conditions and more extreme low sea-surface temperatures in the tropical Pacific Ocean.
(1) Timmermann, A., et al. 1999. Increased El Niño frequency in a climate model forced by future greenhouse warming. Nature, 398, 694-7.