Why is the El Niño so hard to predict?

A: The El Niño Southern Oscillation (ENSO) is a climate phenomenon with three phases: warm, cool, and neutral. Depending on the phase in a year, ENSO affects the climate in the world’s tropical and subtropical regions, including the monsoons, so scientists track it closely. But climate models have historically struggled to model the ENSO, leading to uncertainties in weather prediction worldwide.

Some reasons include the following. The conditions required for a clear ENSO signal only emerge in early summer, so forecasts before then quickly lose value. Short-lived westerly wind bursts can ‘kick’ the ENSO towards warm or cool phases and inject chaos into weather systems. Warm-water or wind anomalies in the Indian Ocean and other basins can reinforce or dampen ENSO. Scientists also disagree on which basin matters most when representing these links in models.

Recently, scientists with the CLIVAR Pacific Region Panel Working Group reported a potential advance. They reported a model called a recharge oscillator (RO) that treats ENSO as a contest between just two variables: sea-surface temperature in the central-eastern Pacific and the amount of warm water stored below the surface further west.

They reported in Reviews of Geophysics that RO was able to reproduce all of ENSO’s features, including its cycles, habit of peaking in December, and the difference in the sizes of its phases.