Linking Centennial Surface Warming Patterns in the Equatorial Pacific to the Relative Strengths of the Walker and Hadley Circulations

This study analyzes representative concentration pathway 4.5 projections by 18 models from phase 5 of the Coupled Model Intercomparison Project to show that surface warming patterns in the equatorial Pacific during the twenty-first century (centennial warming) are influenced by the relative strengths of the Walker and Hadley circulations. The stronger the Hadley (Walker) circulation is, the greater the surface warming in the central Pacific (CP) [eastern Pacific (EP)]. The EP warming is associated with the Bjerknes feedback, while the CP warming is associated with the wind evaporation sea surface temperature feedback. This atmospheric circulation influence on the centennial warming is similar to that found for the EP and CP El Nino. This suggests a methodology to constrain the estimate of the projected surface warming patterns in the equatorial Pacific using recent El Nino activity. The constraint indicates that the "most likely" centennial warming patterns have a maximum in the EP and are 39% weaker than the warming projected by the 18-model mean. The most-likely projection also shows alternating stronger and weaker warming in the subtropical North Pacific, which is not predicted by the 18-model mean projection. Nevertheless, the two projections agree on the minimum warming in the southeastern subtropical Pacific.