Atlantic-Pacific SST Gradient Change Responsible for the Weakening of North Tropical Atlantic-ENSO Relationship due to Global Warming

The changes in the negative relationship between the boreal spring North Tropical Atlantic (NTA) and the subsequent El Nino Southern Oscillation (ENSO) event are examined. While the NTA's triggering of ENSO events has strengthened in the observed period during 1992–2002 compared to 1967–1987, it is projected to be weakened in the Representative Concentration Pathway (RCP) 4.5 scenario. The relative change in the climatological Atlantic sea surface temperature (SST), compared to those in other ocean basins, can explain the negative NTA-ENSO relationship changes in both the observations and RCP4.5 scenario. In RCP4.5 scenario, the climatological Atlantic SST weakly increases relative to other ocean basins; therefore, the increase in the SST threshold for convection is greater than the increase in Atlantic SST, which suppress Atlantic convection. This suppresses NTA-related local convection anomalies associated with the weakened negative NTA-ENSO relationship. In the observed recent decades, the climatological Atlantic SST is further increased than those of other oceans, and thus, the NTA-related teleconnection is enhanced.