A rather abrupt change in the El Niño – Southern Oscillation behavior occurred around 1976/77 and the new regime has persisted. There have been relatively more frequent and presistent El Niño episodes rather than the cool La Niñas. This behavior is highly unusual in the last 120 years (the period of instrumental record). Changes in precipitation over the tropical Pacific are related to this change in the El Niño – Southern Oscillation, which has also affected the pattern and magnitude of surface temperatures. However, it is unclear as to whether this apparent change in the ENSO cycle is caused by global warming.