Unraveling tropical Indian Ocean influences on El Niño-driven Northwest Pacific anomalous anticyclone projections under global warming

Summer climate over East Asia is strongly influenced by the Northwest Pacific anomalous anticyclone (NWPAC) associated with El Niño events. Understanding how this anticyclone responds to global warming is key to predicting future climate risks such as floods and heatwaves. However, current climate models exhibit substantial uncertainty in their projections. This study reveals that a major source of this uncertainty stems from how models simulate changes in climatological atmospheric circulations over the tropical Indian Ocean (TIO). These circulations modulate a series of air-sea interactions in the TIO, which in turn shape the response of the NWPAC during El Niño decay summers under global warming. Models projecting a stronger weakening of climatological TIO circulations tend to project a stronger NWPAC, while those with weaker changes project a weaker NWPAC. These findings reveal that how well we project Indian Ocean states crucially affects the reliability of future summer climate projections in East Asia.