Every day, temperatures at different points on Earth fluctuate, and often these changes coincide even over great distances. Climate scientists connected such points with lines, as if stretching a web across the planet. In normal years, the web is neatly divided into sections, but when El Niño occurs in the Pacific Ocean, the lines break and new ones emerge that stretch across the entire globe.

To build such a web, the researchers used temperatures from 1948 to 2015 at 10,242 points. For each pair of points, they calculated how strongly their temperatures vary together, keeping only the strongest correlations, just 0.5% of all possible pairs. Then they measured how densely the lines cluster into knots and how far they reach.

During strong El Niño and La Niña events, the web loses its usual regional breakdown. Instead, long-distance links appear, for example between the eastern Pacific and Indonesia or West Africa. But after the 1991 eruption of Mount Pinatubo, connections became denser only in one region and did not extend far.

This way of looking at climate helps us understand when a change affects the whole planet and when it remains local. If a computer climate model reproduces the same rewiring of the web, it can be trusted more.