An aftereffect of global warming on tropical Pacific decadal variability

Studies have shown that global warming over the past six decades can weaken the tropical Pacific Walker circulation and maintain the positive phase of the Interdecadal Pacific Oscillation(IPO).Based on observations and model simulations,another afteref fect of global warming on IPO is found.After removing linear trends(global warming signals)from observations,however,the tropical Pacific climate still exhibited some obvious dif ferences between two IPO negative phases.The boreal winter(DJF)equatorial central-eastern Pacific sea surface temperature(SST)was colder during the 1999–2014 period(P2)than that during 1961–1976(P1).This diff erence may have been a result of global warming nonlinear modulation of precipitation;i.e.,in the climatological rainy region,the core area of the tropical Indo-western Pacific warm pool receives more precipitation through the"wet-get-wetter"mechanism.Positive precipitation anomalies in the warm pool during P2 are much stronger than those during P1,even after subtracting the linear trend.Corresponding to the dif ferences of precipitation,the Pacific Walker circulation is stronger in P2 than in P1.Consequent easterly winds over the equatorial Pacific led to a colder equatorial eastern–central Pacific during P2.Therefore,tropical Pacific climate dif ferences between the two negative IPO phases are afteref fects of global warming.These afteref fects are supported by the results of coupled climate model experiments,with and without global warming.