During the last three decades, tropical sea surface temperature (SST) has shown dipole-20 like trends, with warming over the tropical Atlantic and Indo-Western Pacific but cooling 21 over the Eastern Pacific. Competing hypotheses relate this cooling, identified as a driver 22 of the global warming hiatus 1,2 , to the warming trends in either the Atlantic 3,4 or Indian 23 Ocean 5. However, the mechanisms, the relative importance, and the interactions between 24 these teleconnections remain unclear. Using a state-of-the-art climate model, we show 25 that the Atlantic plays a key role in initiating the tropical-wide teleconnection, and the 26 Atlantic-induced anomalies contribute ~55%-75% of the tropical SST and circulation 27 changes during the satellite era. The Atlantic warming drives easterly wind anomalies 28 over the Indo-Western Pacific through the Kelvin wave, and westerly anomalies over the 29 eastern Pacific as Rossby waves. The wind changes induce an Indo-Western Pacific 30 warming via the wind-evaporation-SST effect 6,7 , and this warming intensifies the La 31 Niña-type response in the tropical Pacific by enhancing the easterly trade winds and 32 through the Bjerknes ocean-dynamical processes 8. The teleconnection develops into a 33 tropical-wide SST dipole pattern. This mechanism, supported by observations and a 34 hierarchy of climate models, reveals that the tropical ocean basins are more tightly 35 connected than previously thought. 36 37 3 The tropics have experienced marked climate change since 1979 when the era of 37 global satellite observations began. Sea surface temperature (SST) trends exhibit a pan-38 tropical dipole-like pattern (Fig. 1a), with extensive warming from the tropical Atlantic 39 to the Indo-Western Pacific, and a triangular cooling pattern in the Central-Eastern 40 Pacific. This tropical-wide gradient in the SST trend interacts with the atmospheric and 41 oceanic circulation throughout the tropics (Fig. 1c, e), with an enhanced Walker 42 circulation 9-11 and a La-Niña-like Pacific sub-surface response. These changes further 43 contribute to global climate change 1,12,13 via multiple atmospheric teleconnections 8,14. 44 The tropical ocean basins are connected through atmospheric bridge 15 into an 45 interactive system. On interannual time scales, El Niño-Southern Oscillation (ENSO) 46 dominates the tropical inter-basin teleconnections 15,16 , although the Indian 17,18 and 47 Atlantic 19-21 Oceans experience regional effects that can feedback to the Pacific. In this 48 inter-basin teleconnection, El-Niño warming heats the Indian and Atlantic basins 13. Were 49 the same relationship to hold on multidecadal time scales, the cooling of the Eastern 50 Pacific would be linked to decreased SSTs in the Indian and Atlantic basins 51 (Supplementary Fig. 1), contrary to the observed trends. This discrepancy implies that 52 other mechanisms are required to compensate the Eastern Pacific induced tropical 53 cooling. 54 The north and tropical Atlantic has experienced a continuous warming trend...

The El Niño–Southern Oscillation (ENSO), which originates in the Pacific, is the strongest and most well-known mode of tropical climate variability. Its reach is global, and it can force climate variations of the tropical Atlantic and Indian Oceans by perturbing the global atmospheric circulation. Less appreciated is how the tropical Atlantic and Indian Oceans affect the Pacific. Especially noteworthy is the multidecadal Atlantic warming that began in the late 1990s, because recent research suggests that it has influenced Indo-Pacific climate, the character of the ENSO cycle, and the hiatus in global surface warming. Discovery of these pantropical interactions provides a pathway forward for improving predictions of climate variability in the current climate and for refining projections of future climate under different anthropogenic forcing scenarios.

No abstract