El Niño events periodically wreak havoc on the world's weather, increasing the risk of hurricanes and flooding in some regions, and droughts and forest fires in others. But despite telltale signs of their presence in the Pacific Ocean, including a reversal of ocean currents and large temperature rises, it can be hard to tell where else El Niños are having an effect.
However, forecasting the weather during an El Niño event could soon be as simple as joining the dots, thanks to software that maps the world's climate as an interconnected network. The software, developed by a team led by Avi Gozolchiani from Bar-Ilan University in Ramat-Gan, Israel, plots daily temperature measurements for each of several locations to nodes of the network. It then calculates links between nodes if their measurements change in the same way.
By applying the technique to climate records from 1979 to 2005, the team found that the majority of these links are stable over time, forming a "skeleton" to the world's climate. Yet it's the weaker links, which break and then reform, that are of more interest. Under normal climate conditions this happens only occasionally, but disturbances from an El Niño event cause the links to "blink" on and off every few weeks (Europhysics Letters, DOI: 10.1209/0295-5075/83/28005).
"Their behaviour becomes much more erratic," says Gozolchiani, whose team includes researchers from the Tokyo University of Information Sciences in Japan. The location of the blinking links reveal where the El Niño is having an influence, he says.
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