Climate Dynamics

, Volume 37, Issue 1–2, pp 83–101 | Cite as

Effects of increased CO2 levels on monsoons

  • Annalisa Cherchi
  • Andrea Alessandri
  • Simona Masina
  • Antonio Navarra


Increased atmospheric carbon dioxide concentration provided warmer atmospheric temperature and higher atmospheric water vapor content, but not necessarily more precipitation. A set of experiments performed with a state-of-the-art coupled general circulation model forced with increased atmospheric CO2 concentration (2, 4 and 16 times the present-day mean value) were analyzed and compared with a control experiment to evaluate the effect of increased CO2 levels on monsoons. Generally, the monsoon precipitation responses to CO2 forcing are largest if extreme concentrations of carbon dioxide are used, but they are not necessarly proportional to the forcing applied. In fact, despite a common response in terms of an atmospheric water vapor increase to the atmospheric warming, two out of the six monsoons studied simulate less or equal summer mean precipitation in the 16×CO2 experiment compared to the intermediate sensitivity experiments. The precipitation differences between CO2 sensitivity experiments and CTRL have been investigated specifying the contribution of thermodynamic and purely dynamic processes. As a general rule, the differences depending on the atmospheric moisture content changes (thermodynamic component) are large and positive, and they tend to be damped by the dynamic component associated with the changes in the vertical velocity. However, differences are observed among monsoons in terms of the role played by other terms (like moisture advection and evaporation) in shaping the precipitation changes in warmer climates. The precipitation increase, even if weak, occurs despite a weakening of the mean circulation in the monsoon regions (“precipitation-wind paradox”). In particular, the tropical east-west Walker circulation is reduced, as found from velocity potential analysis. The meridional component of the monsoon circulation is changed as well, with larger (smaller) meridional (vertical) scales.


Carbon dioxide forcing Monsoon precipitation Coupled model experiments 



This work was done in the “Numerical Application and Scenarios” division of CMCC in the framework of the activity “Understanding of the climate system.” We are grateful to the anonymous reviewers whose comments greatly improved the analysis and to C. Cagnazzo for her advice related to radiative issues. A. Cherchi thanks G.A. Vecchi and H. Annamalai for useful discussion and suggestions in the preliminary part of the study.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Annalisa Cherchi
    • 1
  • Andrea Alessandri
    • 2
  • Simona Masina
    • 1
  • Antonio Navarra
    • 1
  1. 1.Centro Euro-Mediterraneo per i Cambiamenti Climatici and Istituto Nazionale di Geofisica e VulcanologiaBolognaItaly
  2. 2.Centro Euro-Mediterraneo per i Cambiamenti ClimaticiBolognaItaly

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