The El Ni–Southern Oscillation (ENSO) is a major coupled ocean-atmosphere climate phenomenon that affects tropical regions globally. It is characterized by periodic fluctuations in sea surface temperatures and atmospheric pressure patterns across the equatorial Pacific Ocean. The cycle operates in three primary phases: the neutral phase, where conditions are near average; the warm phase, known as El Ni, characterized by warmer-than-average sea surface temperatures and changes in wind patterns; and the cool phase, or La Ni, marked by cooler-than-average temperatures. These large-scale oscillations profoundly influence global weather, contributing to shifts in precipitation, temperature extremes, and oceanic circulation patterns across the world's major climate zones.