About 125 scientists from 11 countries met in Jekyll Island, Ga., in October to discuss the unique role that water vapor plays in the climate system. Water vapor links the surface and atmospheric branches of the global hydrologic cycle. Its horizontal and vertical fluxes are key to the energy cycle, and its radiative effects are the major factor in the atmospheric greenhouse effect.
Theoretical calculations indicate that global climate is highly sensitive to small changes in humidity at all levels in the atmosphere, but observations to test this hypothesis are lacking. Because few high-quality humidity observations exist, especially in the upper troposphere, researchers are uncertain of the nature and strength of climate feedback mechanisms involving water vapor and its distribution and long-term changes. Consequently, water vapor is not well treated in global climate models and requires more attention.