Future Changes in the South Asian Summer Monsoon: An Analysis of the CMIP3 Multimodel Projections

The projected future behavior of the South Asian summer monsoon (SASM) is analyzed for the 720-ppm stabilization experiments [Special Report on Emissions Scenarios (SRES) A1B] of phase 3 of the Coupled Model Intercomparison Project (CMIP3) simulations. The multimodel ensemble collectively exhibits a clear tendency for weakening SASM circulation and strengthening SASM precipitation during the twenty-first century. These tendencies are consistent, moreover, among multiple realizations for the same model where available. An annual correlation analysis and thermodynamic energy budget analysis are used to investigate the changes in the monsoon circulation, precipitation (latent heating), and dry static stability across time scales of variation. The strength of the SASM circulation is interpreted in terms of two competing factors: convective latent heating and dry static stability. It is found that on interannual time scales the latent heating wins out over the dry static stability to dominate the interannual fluctuations of the monsoonal circulation. However, the long-term trends in the SASM circulation are governed by the competing effects of the convective latent heating term and the adiabatic term to modify dry static stability in the thermodynamic energy budget.