The warm bias in the west and cold bias in the east over the  Indian Ocean weakens the zonal asymmetry of the observed SST. This weakening is not unique to the Indian Ocean but can also be seen over the Pacific and Atlantic Oceans (Fig. \ref{fig:tsClimDif}a). The annual mean SST zonal asymmetry bias is weak over the Indian Ocean due to pronounced seasonality, but very strong over the Pacific and Atlantic Oceans due to dramatic warming over the tropical eastern basins especially nearby the western coasts of South America and Africa. The warm biases over the tropical eastern Pacific and Atlantic in coupled climate models have also been reported in previous studies and explained by excess heat flux into the ocean due to insufficient low-level clouds \citep{Mechoso_1995, HuangBohua_2007}, and insufficient cooling by ocean dynamical processes \citep{Colas_2012}. The general weakening of the zonal SST asymmetry over all the tropical ocean basins in coupled climate models suggests that these coupled models might have difficulty in capturing the correct ocean processes that are important in determining the SSTs in equatorial and coastal upwelling regions. Consequently, these coupled models might underestimate the thermostat mechanism as proposed by \citet{Clement_1996}.  Fig. \ref{fig:tsClimDif}b shows the change of multimodel mean annual mean SST from the 1979--2005 historical runs to the  2070--2099 RCP8.5 runs in CMIP5 (colors, the 30$^{\circ}$S--30$^{\circ}$N tropical mean has been removed to emphasize the non-uniform component). This also implies a weakening of the zonal SST asymmetry near the equator over all the ocean basins.  The projection of much faster SST warming off the coast of East Africa than over the equatorial eastern Indian Ocean might partly explain the wetting projection in East Africa. However, if the response of SSTs to anthropogenic forcings in coupled models  is biased by their bias in simulating current tropical zonal SST asymmetry then the reliability of these SST projections and the associated precipitation projections are questionable.