Abstract Increased atmospheric CO 2 affects climate through radiative and physiological forcing, but their specific roles in the transient changes in future potential evapotranspiration (PET) and dryness/wetness remain unclear. Using simulations from seven Earth System Models of the Coupled Model Intercomparison Project Phase 6, we quantify the contributions of radiative forcing, physiological forcing, their interaction, and the direct CO 2 physiological effect on surface resistance to projected changes in annual PET and dryness/wetness relative to a historical baseline. Annual PET is projected to increase globally over land, affecting approximately 98 ± 6% of land. Global land shows an overall drying tendency, with wetting and drying projected over 41 ± 9% and 59 ± 9%, respectively. The increases in PET and the drying trend are primarily attributed to radiative forcing through surface warming. Spatially, radiative forcing dominates PET increases across 98 ± 6% of land by modulating temperature and net radiation. For dryness/wetness changes, radiative forcing, physiological forcing, their interaction, and the direct CO 2 physiological effect dominate over 73 ± 5%, 4 ± 3%, 3 ± 3%, and 20 ± 6% of land, respectively. Radiative forcing exerts its dominant influence mainly through its effects on precipitation (22 ± 4% of land) and temperature (51 ± 6%). In regions where physiological forcing or its interaction with radiative forcing prevails, dryness/wetness changes are primarily linked to associated precipitation variations. Overall, this study clarifies how radiative forcing, physiological forcing, their interaction, and the direct CO 2 physiological effect shape the transient changes in future PET and dryness/wetness.
Sun et al. (Wed,) studied this question.