Previous studies on future scenarios identified two key effects of increasing CO2 on the African summer monsoon (ASM): Rising CO2 leads to an enhancement in moisture supply, favoring an increase in ASM precipitation (the thermodynamic effect). However, it also results in a weakening in mean atmospheric flow, thus facilitating a dryness across the ASM region (the dynamic effect). Therefore, the ultimate change in ASM precipitation stems from the balance of both the thermodynamic and dynamic effects. This study further examines the impact of rising CO2 on ASM rainfall, by taking into account various climate states. Our results suggest that an increase in CO2 during warm interglacial periods has a stronger influence from thermodynamic factors than from dynamic factors, resulting in an enhancement in ASM rainfall. In contrast, if CO2 increases under cold glacial climate backgrounds, its dynamic impact dominates a reduction of rainfall in most ASM region.