16 A cold tongue mode (CTM) formed in the 1980s as a La Niña-like stepwise response 17 to recent global warming; however, a consensus has not been reached on the mechanism 18 underlying the CTM formation. Here, we attribute the CTM to the enhanced deep 19 convection of the warm pool regions over the western Pacific and south of North 20 America. Increases in the sea surface temperatures in the two Pacific warm pool regions 21 that occurred due to global warming exceeded the threshold of deep

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... hreshold of deep convection after 22 the 1980s, which resulted in two opposite anomalous vertical circular circulation 23 patterns and induced the CTM via the intensification, contraction, and westward shift 24 of the Walker circulation and the uplift of the thermocline. Our results provide a novel 25 explanation of the La Niña-like response under recent global warming.