On the island of Tahiti and in the city of Darwin in northern Australia, barometers stand. The difference in their readings is called the Southern Oscillation Index, and it indicates the state of the tropical Pacific Ocean. This index is like a swing: if you give it a push, it will keep swaying gently for a long time, even after the person has walked away.

Scientists tested how long the index remembers its past values. It turns out that the connection between what happened a month ago, or even two years ago, and what is happening now persists. This is not random: a random series would have no such memory. But neither is there complete certainty, because the index behaves chaotically, like a stream where two identical leaves can drift in different directions.

For rocket launches, every meter per second matters. If it is known months in advance that the Pacific is warm, windier weeks can be expected, and the launch can be rescheduled to a calmer time. Thus, the climate pendulum swinging thousands of kilometers away helps plan operations at the launch site.