The ability of coupled GCMs to correctly simulate the climatology and a prominent mode of variability of the West African monsoon is evaluated, and the results are used to make informed decisions about which models may be producing more reliable projections of future climate in this region. The integrations were made available by the Program for Climate Model Diagnosis and Intercomparison for the 4th Assessment Report of the Intergovernmental Panel on Climate Change. The evaluation emphasizes the circulation characteristics that support the precipitation climatology, and the physical processes of a “rainfall dipole” variability mode that is often associated with dry conditions in the Sahel when SSTs in the Gulf of Guinea are anomalously warm.
Based on the quality of their 20th century simulations over West Africa in summer, three GCMs are chosen for analysis of the 21st century integrations under various assumptions about future greenhouse gas increases. Each of these models behaves differently in the 21st century simulations. One model simulates severe drying across the Sahel in the later part of the 21st century, while another projects quite wet conditions throughout the 21st century. In the third model, warming in the Gulf of Guinea leads to more modest drying in the Sahel due to a doubling of the number of anomalously dry years by the end of the century. An evaluation of the physical processes that cause these climate changes, in the context of our understanding about how the system works in the 20th century, suggests that the third model is providing the most reasonable projection of 21st century climate.

Full Article: http://http://www.geo.cornell.edu/geology/faculty/Cook/Cook_Vizy_CMEP.pdf

Last Updated: 2007-07-25