Atmospheric aerosol particles act as cloud condensation nuclei, affording them the ability to influence cloud microphysics, planetary albedo, and precipitation. Models of varying complexity and satellite observations from NASA's A-Train constellation of satellites are used to determine what controls the precipitation susceptibility of warm clouds to aerosol perturbations. Three susceptibility regimes are identified: (i) clouds with low liquid water path (LWP) generate very little rain and are least susceptible to aerosol; (ii) clouds with intermediate LWP where aerosol most effectively suppress precipitation; and (iii) clouds with high LWP, where the susceptibility begins to decrease because the precipitation process is efficient owing to abundant liquid water. Remarkable qualitative agreement between remote sensing observations and model predictions provides the first suggestions that certain regions of the Earth might be more vulnerable to pollution aerosol. Targeted pollution control strategies in such regions would most benefit water availability via precipitation.