In 1972, anchovies vanished off the coast of Peru. Fishermen were left empty-handed, and the world learned the word El Niño. Since then, scientists have been looking for ways to predict when the warm current will again upend the planet's weather. It turns out that this phenomenon has a hidden conductor, one that lives in the western Pacific and breathes with a period of several decades.

The climate of the Indo-Pacific region is like a symphony orchestra without a conductor. The violins play their melody, the cellos theirs, and together they create the complex music of weather. Until recently, scientists could only hear the loud parts: El Niño, monsoons, the Indian Ocean Dipole. But this music also has quiet, slow themes that last for decades. They are nearly drowned out by the noise of short-term fluctuations, yet they set the tempo for the whole orchestra.

To make out this slow theme, the researchers took a 1300-year climate record generated by a computer model. It's like having an audio recording of the orchestra spanning a thousand years. Then they applied nonlinear spectral analysis, a method that does not require prior filtering and can separate the voices of instruments even when their frequencies are close. Previously, principal component analysis was used, but it could mix signals, like a poor microphone that records all instruments into a single jumble.

The results showed that in the western Pacific there is a slow mode of temperature variability, which they named the Western Pacific Multidecadal Mode (WPMM). When it is in its cold phase, meaning the temperature in the western Pacific is below normal, the amplitude of El Niño and monsoons increases. In other words, a cold western Pacific amplifies warm events in the east. This connection is not accidental: the correlation between WPMM and decadal rainfall over Australia reaches −0.62, which is much stronger than that of the classic Pacific Decadal Oscillation (0.44).

Such a result means that multi-year droughts and floods in Australia could be predicted by monitoring slow temperature swings in the western Pacific. It's as if we learned to predict the orchestra's volume by watching the conductor's baton, even though the conductor stands behind the scenes. In the 1300-year model record, the cold phase of WPMM can trigger anomalously wet periods over Australia lasting nearly a century.

The study shows that internal multidecadal climate oscillations exist and can be extracted from data without prior filtering. This opens the way to more accurate indices of climate oscillations and to improved forecasts on decadal horizons. The orchestra without a conductor turns out not to be so chaotic after all: it has its own slow rhythms, which can be heard if you listen properly.