Every few years, the warm El Niño current in the Pacific Ocean alters weather worldwide: in some places, rains flood fields; in others, the sun scorches crops. Scientists have long known that the atmosphere behaves chaotically: a tiny change today can lead to a storm a week later. But now it turns out that chaos can spread from ocean to air and back again, like a cold in a crowded bus.
Mathematicians took three simple models: one for warm water carried by currents, another for El Niño, and a third for the air. They linked them together and ran them on a computer. It turned out that if you add a bit of chaos to one model, the neighboring model, previously calm and predictable, also starts behaving erratically. Chaos propagates along the chain, like a crack spreading through glass.
Previously, scientists thought unpredictability originated in a single place: either in the atmosphere or in the ocean. Now it's clear that it's not about location but about connections. The climate system is a network where chaos runs from node to node. Therefore, accurate weather forecasts beyond a few days are impossible, even with perfect instruments. This knowledge doesn't yet help predict weather better, but it changes the question itself: instead of "where does chaos originate?" we now ask "how does it spread?"
Lorenz, who discovered chaos in the atmosphere, posed the famous question: 'Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?' This work shows that chaos can also travel through the ocean: warm water in the Pacific can make weather in the distant Atlantic unpredictable.
The idea of global climate connectivity echoes Kim Stanley Robinson's novel 'Forty Signs of Rain', where scientists try to understand and predict abrupt climate changes caused by nonlinear interactions between ocean and atmosphere.