Committed and Irreversible Humid Heat Stress Risk in China Despite Carbon Dioxide Removal

Carbon dioxide removal (CDR) is critical to net-zero pathways achieving the Paris Agreement 1.5°C target, yet its effectiveness in reducing humid heat stress risks remain uncertain. Here we examine the hysteresis and reversibility of humid heat stress in China under CDR scenarios. Humid heat responds asymmetrically during warming and CO2 removal especially in eastern and southern China, producing a hysteretic and partially reversible trajectory. This results from unequal adjustments of temperature and relative humidity, which constrain heat-stress recovery even as global temperatures decline. Moist static energy analysis indicates suppressed vertical energy export over eastern China and enhanced transport of warm moisture from tropical oceans, sustaining humid heat during CO2 removal. Consequently, severe humid heat stress persists, with over 6.4 billion people affected, more than 66% of which is due to hysteresis. These findings highlight enduring heat-related risks and the urgent need for adaptation alongside mitigation.