Increasing probability of humid-heat extremes outpaces that of dry-heat extremes in global land monsoon regions under anthropogenic warming

A growing concern under global warming is that humid-heat extremes (HHE) present a more severe health hazard than dry-heat extremes (DHE). However, the difference in probability acceleration between HHE and DHE over global land monsoon regions, and their anthropogenic attribution, remain unclear. Using station observations and Coupled Model Intercomparison Project Phase 6 multi-model ensembles, this study quantifies the probability, human contribution, and population exposure of HHE and DHE in monsoon and non-monsoon regions. Results show that during 1979–2020, the rate of increase in the occurrence probability of HHE (5.38 × 10 −2 per year) in monsoon regions substantially exceeds that of DHE (3.84 × 10 −2 per year), with the gap widening under warming. At a global warming level of 2.0 °C, HHE probability rises to 7.66 times pre-industrial levels, far surpassing DHE (5.36 times). This disparity may be attributed to the fact that soil drying amplifies near-surface warming, while its effect on reducing atmospheric humidity is constrained in monsoon regions. Simultaneously, wet-bulb temperature exhibits heightened sensitivity to warming under high-temperature conditions, thereby accelerating the increasing rate of HHE. Approximately 87% of HHE are attributable to human-induced climate change, higher than the 81% for DHE. The anthropogenic signal of HHE emerges about a decade earlier than that of DHE; by 2040, 94% of the global monsoon region will face substantial anthropogenic influence on HHE. Population exposure analysis reveals that under high-emission scenarios leading to a global warming level of 2 °C, the difference in exposure changes between HHE and DHE reaches 164.63% in monsoon regions. Limiting warming to 1.5 °C more effectively reduces HHE exposure. These findings highlight that population exposure to HHE increases faster than that to DHE in global monsoon regions, calling for targeted adaptation strategies to mitigate their asymmetric health threats.