Journal Article

Climate‐Dependency of Impact of Increased Carbon Dioxide on African Monsoon Rainfall: Insights From Model Simulations

Liu, Jiping, Lohmann, Gerrit, Pausata, Francesco S. R., Werner, Martin, Yang, Hu, Wang, Hang, Yang, Chaoyuan, Shi, Xiaoxu, D’Agostino, Roberta, Hu, Yongyun

2025

Overview

Previous studies on future scenarios identified two key effects of increasing CO2${\\text{CO}}_{2}$on the African summer monsoon (ASM): Rising CO2${\\text{CO}}_{2}$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${\\text{CO}}_{2}$on ASM rainfall, by taking into account various climate states. Our results suggest that an increase in CO2${\\text{CO}}_{2}$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${\\text{CO}}_{2}$increases under cold glacial climate backgrounds, its dynamic impact dominates a reduction of rainfall in most ASM region. Plain Language Summary The increase in carbon dioxide (CO2${\\text{CO}}_{2}$ ) levels influences African monsoon rainfall mainly via two processes. First, the warming induced by rising CO2${\\text{CO}}_{2}$leads to enhanced evaporation, thereby increasing atmospheric water vapor content, which provides a greater moisture supply for precipitation formation (the “thermodynamic effect”). Second, rising CO2${\\text{CO}}_{2}$also weakens the tropical circulation, which influences the dynamics of monsoon rainfall (the “dynamic effect”). Consequently, the final changes in monsoon rainfall are determined by the combined effects of these two processes. In this study, through a set of sensitivity simulations, we investigated the impact of rising CO2${\\text{CO}}_{2}$on African summer monsoon (ASM) rainfall during different climatic periods. Although the response in monsoon precipitation is not spatially uniform, our results generally indicate that increased CO2${\\text{CO}}_{2}$levels exert a greater thermodynamic impact than a dynamic one during relatively warm interglacial periods, resulting in strengthened monsoon rainfall. Conversely, a dryness over most of the ASM region is dominated by the dynamic effect when CO2${\\text{CO}}_{2}$increases during cool glacial periods. This research contributes to our understanding of the complex interplay between CO2${\\text{CO}}_{2}$levels, thermodynamic processes, and dynamic processes in shaping African summer monsoon rainfall. It also underscores the importance of considering climatic periods and the relative strengths of different mechanisms when assessing the impact of CO2${\\text{CO}}_{2}$on monsoon systems. Key Points The impact of rising CO2${\\text{CO}}_{2}$on African summer monsoon rainfall is climate dependent Under interglacial climate background, a rise in CO2${\\text{CO}}_{2}$can enhance northern Africa precipitation by increasing atmospheric moisture content In glacial times, a rise in CO2${\\text{CO}}_{2}$facilitates a dryness over most northern Africa, primarily due to a weakened tropical circulation

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: African monsoon / African summer monsoon / Carbon dioxide / Climate / CO2 effects / glacial climate / Glacial climates / interglacial climate / Interglacial periods / Monsoon rainfall / Monsoons / paleoclimate modeling / Precipitation / Rainfall / Rainfall simulators / Summer monsoon / Thermodynamics