Climate model predictions for global warming exhibit regional changes in tropical rainfall, including regions of drought. Regional rainfall reductions are also among the tropical remote impacts of El Niņo. A mechanism creating regional reductions in precipitation at the margins of convection zones during warming has been identified using an intermediate climate model. In this "upped-ante mechanism", a warm troposphere increases the value of surface boundary layer moisture required for convection to occur. In regions of plentiful moisture supply, moisture rises to maintain precipitation, but this increases the moisture gradient relative to neighboring subsidence regions. Reductions in rainfall then result for those margins of convection zones that have strong inflow of air from the subsidence regions and less frequently meet the increased "ante" for convection. This new mechanism is the leading cause of simulated tropical drought in the global warming case and is dominant in certain El Niņo drought regions.