El Ni�o warming corresponds to an eastward extension of the western Pacific warm-pool, one thus naturally wonders whether an increase in the warm-pool SST will result in stronger El Ni�os. This question, though elementary, has not drawn much attention. The observation that the two strongest El Ni�os in the instrumental record occurred during the last two decades when the warm-pool SST was anomalously higher, however, has added some urgency to answering this question. Here we show observational as well as model results which support a positive answer to this question. An increase in the warm-pool SST implies an enhanced heating across the equatorial Pacific. In response, stronger El Ni�o develops to "pump" more heat out of the tropics and thereby regulates the warm-pool SST. Comparing the variations in the warm-pool SST with those in the global mean surface air temperature over the last 100 years suggests that the warming trend in the warm-pool SST may also have an anthropogenic origin. Preliminary analysis of climate simulations by the NCAR CCSM supports this suggestion.