A warm tongue of water stretches along the equatorial Pacific, and within weeks, Peru sees torrential rains while Australia's pastures dry out. That is how El Niño begins: a natural conductor that, at critical moments, makes only a few orchestra members play, but much louder. Scientists have long known that this phenomenon sends its cues across the planet, but they could not say precisely how far these cues spread, nor why some regions respond while others stay silent.
To find out, researchers built a climate network from 10,512 points on a map, connected by threads of statistical dependence. Each thread had a direction: from the El Niño basin (57 points in the warm tongue) to any other point on the globe. It turned out that during El Niño and its cold counterpart La Niña, these threads do not spread evenly but bundle into ropes. The number of points receiving any cue drops sharply, but for those that remain, the strength of the cue increases severalfold.
The test confirmed: the map of these 'incoming' strikes matches the map of actual temperature anomalies. North America, South America, Europe, India, South Africa, and Australia: those are exactly where thermometers show the largest deviations. The similarity coefficient was 0.63 for warm events and minus 0.59 for cold ones. It is as if the conductor knew exactly which rows of seats to wake up.
Previously, scientists knew that El Niño affects remote regions, but they did not see that this influence contracts like a flashlight beam and strikes with precision. Now it is clear: during events, the impact intensifies but covers a smaller area, and the specific affected regions change from one event to the next. The method that revealed this is simple: consider only the outgoing links from the El Niño basin and see where they land. This approach can be applied to precipitation, pressure, or ocean temperature to improve seasonal forecasts of anomalies in specific regions. The conductor does not always wave the baton the same way, but now we can hear whom he is calling this time.
During the strong El Niño of 2015–2016, one of the strongest since 1948, researchers were able to confirm most of the affected regions using data from previous events only, demonstrating the method's predictive potential.
In Kim Stanley Robinson's novel 'Forty Signs of Rain', climate networks and chaotic ocean dynamics play a key role in understanding abrupt climate change, echoing attempts to capture El Niño teleconnections.