Uncertainty in the CMIP5 Projections over South Asia

We analyze Global Climate Models (GCMs) simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to investigate the response of South Asian summer monsoon to increases in greenhouse forcing. The analysis covers 1970-1999 as the baseline period and 2010-2039 as the near-term, 2040-2069 as the mid-term and 2070-2099 as the long-term future periods under the Representative Concentration Pathway (RCP) 8.5. Our preliminary analysis suggests an increase in the South Asian summer monsoon precipitation in the ensemble mean of GCMs in all future periods. However, not only do most of the GCMs disagree on the sign of the precipitation change, the inter-model spread is also much larger than the multi-model mean. The disagreement is particularly significant over the western and northeastern parts of South Asia. This uncertainty in monsoon projections is partly associated with the fact that many GCMs show substantial biases in the simulation of spatial and temporal distribution of seasonal precipitation, as well as in the representation of local and large-scale processes that govern precipitation variations at intra-seasonal to inter-annual time-scale. Given the uncertainty in the CMIP5 ensemble mean projections, a skill-based analysis approach is necessary to improve the reliability of 21st century climate projections over the monsoon region.