The Pacific Ocean works like a seesaw: water warms up near one coast, then the other. When it gets unusually warm off South America, that's El Niño—a year of weird weather across the planet. Wind rocks this seesaw. Short bursts of westerly wind, lasting just one to two weeks, are especially important. A single burst hits the water like a palm on a taut sheet, sending a wave racing across the entire ocean.

Scientists used to describe these bursts as steady background noise, as if the wind always blew the same way. But before a major El Niño, bursts come in series, like someone tossing stone after stone into a pond. The new model says: while the water is cold, the wind stays calm. But once the ocean warms about one and a half degrees above normal, it starts triggering new bursts on its own. Warm water changes the air above it, and that air breaks into short, powerful jolts.

Testing against 153 years of data confirmed that this model correctly shows more bursts before a strong El Niño than before a weak one. That helps better predict dangerous warm years. Now the ocean's seesaw is less of a mystery: you can see where the hand that pushes it comes from.