Simulations with the NCAR Climate System Model (CSM), a global, coupled ocean-atmosphere-sea ice model, for the last glacial-interglacial cycle reproduce recent estimates, based on alkenones and Mg/Ca ratios, of sea surface temperature (SST) changes and gradients in the tropical Pacific and predict weaker El Ni¿os/La Ni¿as compared to present for the Holocene and stronger El Ni¿os/La Ni¿as for the Last Glacial Maximum (LGM). Changes for the LGM (Holocene) are traced to a weakening (strengthening) of the tropical Pacific zonal SST gradient, wind stresses, and upwelling and a sharpening (weakening) of the tropical thermocline. Results suggest that proxy evidence of weaker precipitation variability in New Guinea and Ecuador are explained not only by changes in El Ni¿o/La Ni¿a but also changes in the atmospheric circulation and hydrologic cycle.