Xianghui Fang

An orchestra of three conductors governs the Pacific climate. The first conductor is intraseasonal wind bursts, blowing now from the west, now from the east, like random plucks on strings. The second is the interannual ocean dynamics, slowly rocking warm and cold waves.

A flashlight beam in fog reaches some objects and fades before touching others. So it is with El Niño forecasts: for events in the central Pacific, the light reaches almost two years ahead, but for eastern events it gets lost in random wind gusts within six months.

Three pendulums hang from a long rope attached to the ceiling. One swings fast, another slow, and the third sometimes freezes and then lurches. But the rope is shared, so each jerk of one is felt in the motion of the others.

Every few years, a huge pool of warm water in the western Pacific Ocean shifts eastward, like water in a bathtub when you tilt it sharply to one side. That is El Niño. But each tilt is different: sometimes the water sloshes against the shores of Peru, sometimes it stalls in the middle, sometimes it pours out in a powerful surge, and sometimes it barely creeps.

A warm patch off the coast of Peru does not appear every year, but when it does, deserts are drenched with rain and Australia is plagued by wildfires. This is El Niño, a phenomenon that climate models struggle to reproduce. Simple models do well at estimating how often it occurs but lose spatial details.