Hiroyasu Ando

A translator in a conference room hears not only the words but also the echo of previous phrases still bouncing around the ceiling. If they get distracted by every reverberation, an hour of conversation turns into two. Similarly, a complex system, whether an ocean or a power grid, receives random jolts that do not vanish instantly but drag behind them a tail of memory.

Every winter, the Pacific Ocean warms slightly off the coast of Peru, and every summer it cools. This rhythm is set by the gears of the climate machine, but some turn fast, others slow, and still others speed up or stall. Linear inverse models have helped us glimpse these gears in data for decades, but they were blind to seasonal changes in pace.

Glasses with flat lenses show a symmetric world: rise and fall, heat and cold look the same. For decades, climatologists have viewed El Niño through such glasses, using linear inverse models. These captured the rhythm of oscillations but missed that the warm phase of El Niño is typically sharper and stronger than the cold La Niña.