Through its interaction with radiation, water vapor provides an important link between the ocean and atmosphere. One way this occurs is through the greenhouse effect, and here we report on observations of water vapor greenhouse absorption in the Gulf of Mexico during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment during July 2002. The quantity dGa/dTs is the change in the amount of upwelling infrared flux absorbed by water vapor as the sea surface temperature increases, and therefore parameterizes the strength of the evaporative feedback between the ocean and atmosphere. Using hemispherical (IRBR) and narrow field of view (NFOV) radiometers aboard a NASA ER-2 aircraft, we have measured dGa/dTs during flights on July 9 and July 26 marked by large scale convective and quiescent conditions, respectively. Using the NFOV over the wavelength range 4-40 microns, we measured dGa/dTs=13.4 +/- 1.0 W/m^2/K on July 9, while on July 26 we measured dGa/dTs= 9.7 +/- 0.3 W/m^2/K. NFOV measurement of dGa/dTs in the 8-12 micron wavelength range yielded values of ~2.5 W/m^2/K for both days, indicating that most of the change in greenhouse absorption with increasing ocean temperature occurs in the rotational and vibrational spectral regions of water vapor. IRBR measurements yielded higher values of dGa/dTs on both days, but were likely affected by cold clouds in the hemispherical radiometer field of view. These results support the link between greenhouse efficiency, mid to upper tropospheric water vapor concentration, and convection.