Supported by the National Natural Science Foundation of China Excellent Research Group for Tibetan Plateau Earth System (continuation grant No. 42588201) and other programs, a research team led by Professor Tianjun Zhou from the Institute of Atmospheric Physics, Chinese Academy of Sciences, has made new progress in understanding the response of the South Asian summer monsoon (SASM) to climate warming. Their study, entitled “Past warm intervals inform the future South Asian summer monsoon”, was published online in Nature on May 14, 2025 (https://doi.org/10.1038/s41586-025-08956-6).

In the future, monsoon rainfall over densely populated South Asia is expected to increase, despite a weakening of monsoon circulation. In contrast, past warm intervals were marked by both heavier rainfall and stronger monsoon circulation. This apparent discrepancy presents a major challenge for understanding SASM dynamics in a warming world. To address this issue, the research team synthesized six warming scenarios spanning both the past and future periods, including the mid-Pliocene, the Last Interglacial, the mid-Holocene, and three future emission scenarios. Based on both climate modelling results and proxy datasets, the authors found a consistent monsoon response across these intervals: increased rainfall, weakened circulation over the Bay of Bengal, and enhanced circulation over the northern Arabian Sea. The overall increase in monsoon rainfall is driven by two primary mechanisms. Thermodynamically, global warming leads to higher atmospheric moisture content, following the “wet-gets-wetter” paradigm. Dynamically, enhanced surface warming over subtropical Eurasia and North Africa modifies the monsoon circulation, subsequently altering sensible heat advection and leading to a “south-dry, north-wet” rainfall pattern across South Asia.

Building on the physical relationships between surface warming and the SASM during past warm periods, the researchers have developed a regression model to project future changes in monsoon rainfall and circulation. Under a high-emissions scenario, the statistical model predictions show strong agreement with climate model outputs, with spatial correlation coefficients of approximately 0.8 for circulation and 0.7 for rainfall. This suggests that past warm climates, despite being driven by different forcing agents, can serve as analogues for the future SASM. Drawing on geological evidence, the study projects an overall increase in South Asian monsoon rainfall under future warming scenarios, particularly along the Himalayas. This implies an increasing risk of heavy rainfall-induced natural disasters in this relatively vulnerable region.

Figure. Future prediction of the South Asian summer monsoon based on past information. Using the regression model, predictions include: (a) thermodynamic and (b) dynamic components of monsoon rainfall; (c) total monsoon rainfall and 850 hPa horizontal winds. (d) Same as (c), but from multi-model projections