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 ofENSOevents 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. Plain Language Summary The sea surface temperature (SST) warming over the North Tropical Atlantic (NTA) region during boreal spring can induce a La Nina event during subsequent winter. This negative relationship is reported to be weakened due to global warming. This study emphasizes the role of Atlantic SST climatology on the weakening of the negative NTA-El Nino Southern Oscillation relationship by controlling the local convective response to the NTA SST anomaly. Global warming is not directly linked to the enhanced convective activities, as the threshold SST for the convection is also increased due to global warming. This indicates that the change in convective activity over the Atlantic would be more closely linked to the relative SST changes compared to other ocean basins. Due to the weakening of the Atlantic Meridional Overturning Circulation as a result of global warming, the increase in the Atlantic SST is weaker than those in other ocean basins. As a result, the increase in the SST threshold for convection is greater than the Atlantic SST increase. This suppresses NTA-related convection anomalies and also weakens the negative NTA-El Nino Southern Oscillation relationship due to global warming.