The Pacific Ocean breathes, and that breath has a pulse. Every few years, its surface warms more than usual, bringing downpours to Peru and drought to Australia. This is El Niño, the warm phase of the ocean temperature oscillation. Predicting it in advance has long been a goal, but in spring the ocean and atmosphere behave so unpredictably that forecasts often miss the mark.

Instead of listening to individual points, scientists came up with a way to listen to the whole ocean at once. They took 14 points in the El Niño region and 193 points around it, and connected those that warmed and cooled in the same rhythm. The result is a network. When the connections in this network become too strong, it means the ocean is gearing up for a warm event a year later. The threshold for connection strength was set in advance, using historical data, and has not been changed since.

Now this ocean pulse can be monitored every year. Farmers in Peru know in advance that heavy rains are coming and can choose different crop varieties. Water authorities in Australia prepare for drought. The method is not perfect, but it has shown for the first time that long-term El Niño forecasting is possible not just on paper.