Two pendulums hang side by side, connected by a spring. Give one a push, and through the spring the other starts to swing. That's how the two regions of the equatorial Pacific are arranged, where sea-surface temperature rises and falls in the rhythm of El Niño.

Each region on its own resembles a pendulum with a delay: the water warms, the warm current drifts west, and a few months later a wave returns to cool the surface. The return time ranges from 237 to 439 days, depending on the basin's width. When the regions are linked, as if by a spring, one can pass its rhythm to the other.

The scientists built a model of two coupled pendulums with different delays and self-damping strengths. It turns out that a too-stiff spring, meaning strong coupling between the regions, damps oscillations in both: the pendulums freeze. A weak spring, by contrast, lets the region with the longer delay swing its neighbor, which on its own would have settled long ago. That's how irregular but persistent temperature oscillations arise.

Moreover, the regions don't have to be identical. If their parameters differ, more often than not one pendulum freezes while the other keeps swinging, or both come to rest at different positions. When oscillations do occur, their period is shared by both, even if the delays differ.

This work changes how we view the predictability of climate oscillations. If the ocean's two pendulums are weakly linked, the system stays sensitive to the slightest nudges without falling apart. Understanding which regions influence each other more strongly will help climatologists better interpret observational data and anticipate where synchronous temperature anomalies might appear. The pendulum analogy brings us back to a simple rule: sometimes, to make a system oscillate, you need to weaken the coupling, not strengthen it.