The Atlantic Niño/Niña, akin to the Pacific El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), is a dominant mode of interannual climate variability, exerting profound impacts on the global climate. Previous studies show reversed changes in ENSO and IOD variabil ity before and after 2100. However, the projected evolution of the Atlantic Niño/Niña beyond 2100 remains unknown. Here, we find that the Atlantic Niño/Niña variability displays a sustained weak ening toward the 23rd century under high- and low- emission scenarios. On the one hand, atmo spheric stratification is stabilized in the equatorial Atlantic, reducing the sensitivity of zonal wind to the anomalous sea surface temperature (SST) gradient. On the other hand, weakened equat orial upwelling decreases SST sensitivity to thermocline anomalies. These changes suppress the Bjerknes feedback in the tropical Atlantic, leading to a sustained weakening of Atlantic Niño/Niña variability under persistent greenhouse warming, in sharp contrast to ENSO and the IOD. Such weakening in variability may further influence the predictability and global impacts of the Atlantic Niño/Niña, with potentially far-reaching ramifications.