Regional Patterns of Sea Surface Temperature Change : A Source of 2 ! Uncertainty in Future Projections of Precipitation and Atmospheric 3 ! Circulation

1! Precipitation change in response to global warming has profound impacts on 2! environment for life but is highly uncertain. Effects of sea surface temperature (SST) 3! warming on the response of rainfall and atmospheric overturning circulation are 4! investigated using Coupled Model Intercomparison Project simulations. The SST 5! warming is decomposed into a spatially uniform SST increase (SUSI) and deviations 6! from it. The SST pattern effect is found important in explaining both the multi-model 7! ensemble mean distribution and inter-model variability of rainfall change over tropical 8! oceans. In ensemble mean, the annual rainfall change follows a " warmer-get-wetter " 9! pattern, increasing where the SST warming exceeds the tropical mean, and vice versa. 10! Two SST patterns stand out both in the ensemble mean and inter-model variability: an 11! equatorial peak anchoring a local precipitation increase, and a meridional dipole mode 12! with increased rainfall and weakened trade winds over the warmer hemisphere. These 13! two modes of inter-model variability in SST account for one third of inter-model spread 14! in rainfall projection. 15! The SST patterns can explain up to four fifth of the inter-model variability in intensity 16! changes of overturning circulations. SUSI causes both the Hadley and Walker circulation 17! to slow down as articulated by previous studies. The weakening of the Walker circulation 18! is robust across models as the SST pattern effect is weak. The Hadley circulation change, 19! by contrast, is significantly affected by SST warming patterns. As a result, near and south 20! of the equator, the Hadley circulation strength change is weak in the multi-model 21! ensemble mean and subject to large inter-model variability due to the differences in SST 22! warming patterns.