Committed and irreversible humid heat stress risk in China despite carbon dioxide removal

Carbon dioxide removal is critical to net-zero pathways achieving the Paris Agreement 1.5 °C target, yet its effectiveness in reducing humid heat stress risks remains uncertain. Here, we examine the hysteresis and reversibility of humid heat stress in China under carbon dioxide removal scenarios. Humid heat responds asymmetrically during warming and 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 the removal. Consequently, severe humid heat stress persists, with over 0.2 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. Severe humid heat stress threatens over 0.2 billion people in China during carbon dioxide removal, driven by unequal temperature/humidity adjustments, as sustained warm moisture transport prevents rapid recovery, according to moist static energy analysis.