Hysteresis and irreversibility of global drought patterns in response to CO₂ mitigation efforts

Drought is expected to intensify with rising CO₂, but its behavior under CO₂ mitigation, remains uncertain. The response of the climate system to CO₂ variation exhibits hysteresis and irreversibility, highlighting the difficulty of recovery and the potential for long-lasting impacts. We investigated the hysteresis and reversibility of global drought and the associated underlying drivers. The Community Earth System Model 2 was used to simulate CO₂ changes: linear increases, decreases (i.e. net negative), and restoration to the initial level. This paper incorporates three well-established indices based on atmospheric, meteorological and soil moisture data to reflect drought. Here, we show that drought is dominant during the CO₂ decrease phase, leading to strong hysteresis with irreversible behavior over more than half of the global land cover. The robust irreversible changes in drought are concentrated in specific areas, i.e. hotspots, covering over 11% of the global land and are particularly pronounced in Northern Africa, Southwest Russia, and Central America. A decrease in precipitation drives drought during the CO₂ increase phase, while an enhanced vapor pressure deficit (VPD) exacerbates it during the CO₂ decrease phase. This increased VPD exacerbates drought hysteresis by raising potential evapotranspiration. Our findings suggest that only CO₂ reduction is not enough to effectively mitigate drought impacts, rather advanced water management strategies are essential.