The Pacific Ocean is like a giant swing: warm water piles up in the west, then slides toward the east, and the temperature off the coast of South America jumps. Such warm years are called El Niño, and cold ones La Niña. But the swing doesn't move on its own: it's pushed by the wind. Especially important are short, one-to-two-week bursts of westerly wind near the equator. They hit the ocean surface like a palm slapping water in a bathtub, sending a wave that reaches the other shore months later.

For a long time, these bursts were modeled as smooth noise, like a gentle breeze that always blows a little. But real bursts come in clusters: before a major El Niño, their number rises sharply. The authors of the new study compared three ways to describe this noise. The first is the usual smooth one. The second includes rare strong spikes, like stones thrown into a pond: silence, then a splash. The third is trickier: while the ocean is cold, the noise remains smooth, but once the temperature crosses a threshold, the model switches to spikes.

Testing against 153 years of data showed that the third option matches the overall temperature picture as well as the first, but it does much better at describing what happens before a big El Niño. For the strongest warm events, the model produces noticeably more bursts in the year before the peak than for weak ones. Previously, this discrepancy was unexplained; now it is built into the mathematics of the noise itself.

This approach changes the outlook for forecasting. If we know that a warm ocean itself triggers new bursts, we can spot the approach of a strong event earlier. The model has been tested on a simplified ocean scheme, but it can already be embedded in large climate models. The swing is no longer a toy of chance: we see the hand that pushes it.