The uncertainty associated with tropical sea surface temperatures (SSTs) during past greenhouse climates may have important and unaccounted for effects. We explore early Paleogene climatic sensitivity to changes in tropical-subtropical SSTs with a general circulation model. We demonstrate that tropical SST changes have local and far-field climatic effects, underscoring their importance in understanding greenhouse climates. The responses of winds, upwelling, and surface water balance to tropical SST changes are substantial. Our results indicate that current tropical SST reconstructions may have a significant cool bias despite corrections and that the existence of hot (>30 ¿C) tropical SSTs may be realistic for greenhouse climate intervals, including the Eocene. ¿ 2000 American Geophysical Union