Greenhouse warming exacerbates El Niño-induced Indian monsoon droughts.

The inverse relationship between the El Niño‒Southern Oscillation (ENSO) and the Indian summer monsoon has weakened since the early 1980s. Here, we demonstrate that the historical weakening of the ENSO-monsoon relationship was caused by two unusual events (in 1983 and 1997), and greenhouse warming has actually strengthened rather than weakened this link between 1902 and 2023 and is projected to continue doing so. However, confidence in the projection of this enhancement remains relatively low. We attribute the model spread in ENSO-monsoon links to variations in ENSO-induced Walker circulation anomalies, primarily through zonal wind feedback processes. Through the use of multiple observations to constrain such atmospheric dynamic processes, we find that the observation-constrained sensitivity of monsoons to the ENSO by the end of this century will become almost 40% greater than that from 1963-2023. Such intensification occurs because, even if the degree of El Niño-induced sea surface warming remains unchanged, the response of tropical precipitation to sea surface warming will increase, causing further eastward displacement of Walker circulation anomalies and an increased subsidence over the Indian subcontinent, which will reduce monsoon precipitation further. Our findings suggest intensified hydrological extremes and increased risks for food security in India in a warmer future.