A case is made that taken together, the 0.9 km lowering of tropical snow lines and the 8? reduction in the &dgr;18O for tropical mountain Huascar¿n snowfall point to reductions in the water vapor inventory of the glacial atmosphere large enough to account for a several degree global cooling. The major weakness in this argument is that as no means exists to estimate the change in the magnitude of the radiative cooling term in the tropical atmosphere's heat budget, the assumption must be made that during glacial time the magnitude of this term was close to its present value. Changes in the inventory of atmospheric water vapor are tantalizing for they offer not only a means of cooling the glacial Earth but also a means of producing the abrupt changes in global climate, now well documented in climate record.¿ 1997 American Geophysical Union