Distinct effects of global mean warming and regional sea surface warming pattern on projected uncertainty in the South Asian summer monsoon

Significant uncertainties in the projected South Asian summer monsoon (SASM) have been observed in the released Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) data set. Knowing what factors dominate the uncertainties is critical to constraining the local climate changes. Analyzing state‐of‐the‐art climate model simulations under the RCP8.5 scenario, we find that uncertainties in the circulation primarily result from the divergent global mean warming across models. In contrast, the compensation between dynamic and thermodynamic effects makes the spread in monsoon rainfall independent of the global temperature change. Via a suite of sensitivity experiments, we identify that the uncertainties in the SASM rainfall are dominated by the Indo‐Pacific sea surface temperature (SST) warming pattern, especially around the western central Pacific. The SST warming pattern plays its role by changing the zonal temperature gradient over the SASM region and modulating the interhemispheric moisture transport. We highlight that the SST warming patterns require more attention in constraining the projected regional rainfall changes. Key Points Divergent global mean warming renders key uncertainty to the projected monsoon circulation Indo‐Pacific warming patterns, not the mean warming, contribute to the rainfall spread in models Monsoon rainfall spread is mainly controlled by the zonal gradient of tropospheric temperature