ENSO

ENSO — the El Niño–Southern Oscillation — is the full, formal name for the climate cycle this site tracks. The two halves of the name record a scientific merger: "El Niño" was the fishermen's term for the warm ocean current off Peru, while the "Southern Oscillation" was the seesaw in atmospheric pressure between the eastern and western Pacific that Sir Gilbert Walker documented in the 1920s. By the 1960s, scientists — Jacob Bjerknes foremost — established that the two were one phenomenon: the ocean and atmosphere of the tropical Pacific, locked in a feedback loop.

ENSO has three phases. El Niño is the warm phase: weakened trade winds, warm water spreading east, tropical rainfall following it. La Niña is the cool phase: strengthened trades and an exaggerated version of the normal pattern. Neutral is everything in between. The cycle repeats irregularly, every two to seven years, with each phase typically peaking in Northern Hemisphere winter.

It matters because the tropical Pacific is the planet's largest source of atmospheric heating, and ENSO is the biggest thing that changes it. The 2026–27 El Niño now underway is ENSO's warm phase at unusual strength — its progress runs live on the dashboard.