A hammock woven from thousands of cords is stretched between continents. Each cord is a link between two points on the planet: when it warms in one place, it cools in another, day after day. As long as the hammock holds, it keeps the climate in its familiar rhythm. But every few years El Niño arrives, a warm current off the coast of Peru, and the cords begin to snap.
Climate network is not a metaphor but a working tool. Scientists took daily temperature measurements from 1979 to 2006 in four regions: the tropical Pacific, North America, Europe, and Southeast Asia. For each pair of points, they calculated how synchronously temperature changes, accounting for delays up to 200 days. If the connection was strong and held for five consecutive periods, they considered it stable. Such cords in the hammock turned out to be numerous, linking even very distant regions.
During eight known El Niño events, the number of surviving links dropped sharply in all four regions, even though average temperature in most of them barely changed. For example, in the North American region, the average temperature anomaly showed no signal, but the network clearly sagged in 1997 and 2005. The hammock lost cords but remained taut: average temperature did not jump; only the connections between points broke.
The connections that broke were almost indistinguishable in correlation strength from those that survived. However, they had noticeably longer time delays, typically more than a few days. This means El Niño primarily destroys slow, long-range connections, while fast local responses remain. The hammock does not fall entirely, but its weave changes: long cords snap, short ones hold.
This view of climate opens something new: previously it was unclear how El Niño affects regions where average temperature does not change. Now it is clear that it restructures the very fabric of interactions, and this is visible in the number of surviving links. The method can be applied to monitor climate anomalies and possibly to provide early warning of El Niño onset. The hammock woven from cords continues to hold the climate, but now we can count how many cords are still intact.
The correlation significance threshold of 2 was not chosen arbitrarily: in calm years, correlations below this value are almost nonexistent, so any drop below 2 immediately signals an anomaly. It is like a sensor that only triggers on a real alarm.