Irreversibility of extreme precipitation intensity in global monsoon areas under multiple carbon neutrality scenarios

The Global Monsoon Areas (GMAs), home to over half of the world's population, face escalating socio-economic risks from extreme precipitation events intensified by rising atmospheric carbon dioxide (CO₂). While previous studies have examined the irreversibility of the climate system following carbon neutrality, most have focused on single carbon neutrality scenarios with limited attention to these vulnerable areas. This study assesses the irreversibility of extreme precipitation intensity across seven GMA sub-regions under eight future scenarios, incorporating four carbon neutrality targets and two reduction rates, using simulations from a state-of-the-art climate model. Our results reveal that extreme precipitation intensity exhibits irreversible behavior in response to carbon neutrality forcing, failing to return to its initial level even when atmospheric CO₂ is reduced. This irreversibility is particularly pronounced when carbon neutrality timing is delayed, and the emission reduction rate is slow. Moreover, the irreversible response is nonlinear to the magnitude of carbon forcing, leading to distinct regional vulnerabilities, with some areas experiencing sharp increases in irreversibility by even small delays in reaching carbon neutrality. This region-specific behavior is largely attributed to increases in mean and variability of precipitation linked to irreversible El Niño-like warming and interhemispheric differential warming. Moisture budget analysis further shows that the intensified precipitation arises from the relative influence of thermodynamic (moisture flux) and dynamic (wind) drivers across regions. These findings highlight the urgency of rapid policy implementation in vulnerable regions and can provide a scientific basis for developing regional adaptation strategies to mitigate growing extreme precipitation risks.