Submesoscale Eddies Buffer the Atlantic Niño/Niña Weakening Under Greenhouse Warming

The Atlantic Niño/Niña is a leading mode of tropical climate variability with profound global environmental and socioeconomic impacts. Conventionally, its variability is projected to weaken under greenhouse warming, primarily attributed to suppressed basin‐scale air–sea interactions. However, the modulating role of sub‐basin‐scale ocean dynamical processes remains largely unexplored. Here, using an ensemble of high‐resolution climate simulations, we show that submesoscale ocean eddies substantially dampen Atlantic Niño/Niña variability by regulating vertical heat transport. Under greenhouse warming, this eddy‐induced damping is projected to diminish due to the suppressed Atlantic cold tongue and enhanced upper‐ocean stratification. Consequently, this attenuation of damping buffers approximately one‐third of the variability weakening driven by basin‐scale processes. This mechanism is corroborated by comparison with standard‐resolution climate simulations, which fail to resolve submesoscale eddies, and is further supported by CMIP6 model outputs. These findings highlight the critical importance of resolving fine‐scale ocean processes to improve the fidelity of future climate projections.