Weakened influence of ENSO on the East Asian summer monsoon since the early 2000s

ENSO typically reaches its peak during the boreal winter but can exert a lasting influence on the East Asian summer monsoon (EASM) for up to six months. The remarkably prolonged impact of ENSO establishes it as a valuable precursor for predicting the EASM, which is beneficial to approximately 1.6 billion people. Over the past three decades, scientists have made significant strides in understanding this relationship, benefiting not only from their own efforts but also from the heightened role of ENSO on the EASM since the late 1970s.However, our present study discovered that the influence of ENSO on the EASM has been diminishing in the last two decades. Moreover, we revealed that this interdecadal weakening of ENSO's impact is linked to changes in ENSO's decaying rate around the early 2000s. From 1977 to 1999, ENSO events peaking in the boreal winter frequently displayed a gradual decay, which triggered robust positive feedback in the tropical Indian Ocean and the western North Pacific, resulting in pronounced EASM anomalies. In contrast, during the period of 2000 to 2022, ENSO events exhibited a faster decay, leading to a substantial decrease in the ENSO-induced anomalies in the Indo-western Pacific and the associated EASM anomalies. These findings are well supported by model simulations.The recent decline in ENSO's impact on EASM anomalies poses a significant challenge for predicting EASM in the coming decades. At a time when global warming is causing severe heatwaves and droughts in the EASM region, the changing role of ENSO in influencing the EASM introduces new uncertainties in our efforts to adapt to the global warming crisis.