A warm ocean off the coast of Peru can make winter in Moscow unusually mild. Climate scientists call these invisible threads that link weather in distant corners of the planet teleconnections. For a long time, they were thought of as something like permanent wiring: the signal sources may pulse, but the wires themselves lie still. New research shows that greenhouse gases have already rewired that circuitry.

The authors compared two thirty-year periods: 1960–1990 and 1990–2020. They took temperature maps for every point on the globe and looked at how strongly those maps are linked to five major climate modes, including El Niño, the Indian Ocean Dipole, and the Pacific Decadal Oscillation. It turned out that over thirty years, the connections changed across one-fifth of the planet's surface. For El Niño, significant shifts affected 20% of grid cells; for the Indian Ocean Dipole, 15%; and for global mean temperature, 28%.

To distinguish an anthropogenic shift from natural variability, the scientists used covariance fingerprinting. This method projects the observed change in connections onto the change simulated by an ensemble of climate models with historical forcing. Then the observed shift was compared with a thousand random shifts drawn from a control model run without anthropogenic forcing. The observed shift exceeded all one thousand random ones, meaning the probability of explaining it by natural variability is less than one in a thousand.

Before this work, it was unclear whether the teleconnections themselves change under greenhouse gas forcing or whether the observed shifts are random. Now it is clear: the global restructuring of teleconnections between 1960–1990 and 1990–2020 cannot be explained by natural variability. It is attributed to human influence. Moreover, the changes are not just about overall warming: in some regions, El Niño, which used to bring warmth, now brings cooling. For example, in northeastern Africa, the sign of the connection has reversed.

By the end of the century, under a high-emissions scenario, the restructuring will intensify. A warm ocean off the coast of Peru will tug at those threads in ways quite different from half a century ago. And the wiring once thought permanent will continue to be rewritten.