El Niño / Southern Oscillation (ENSO) Index Since 1951

The El Niño / La Niña cycle has been documented for centuries, but has actually been shaping the Earth's weather for at least 250 million years. In more recent times the Southern Oscillation Index (SOI) has measured changes in atmospheric circulation across the tropical Pacific. It's one of the key indicators used to monitor the El Niño / La Niña cycle.

Some researchers have suggested that climate change may influence ENSO behaviour, but the data doesn't indicate greater recent volatility compared with its historical range. Instead, it illustrates the natural swings between El Niño (negative values) and La Niña (positive values) that influence weather patterns around the world. While the underlying ENSO cycle remains broadly consistent with its historical range, its interaction with a warmer climate may make weather-related impacts less predictable, and historic planning assumptions less reliable.