The strongest natural fluctuation of climate on interannual time-scales is the El Niño-Southern Oscillation (ENSO) phenomenon,
and ENSO-like fluctuations also dominate decadal time-scales (sometimes referred to as the Pacific decadal oscillation).
ENSO originates in the tropical Pacific but affects climate conditions globally.
The importance of changes in ENSO as the climate changes, and its potential role in possible abrupt shifts have only recently been appreciated.
Observational and modelling results suggest that more frequent or stronger ENSO events are possible in the future.