220.127.116.11. Water Vapour Feedback
The importance of water vapour feedback in climate change has long been recognised (Manabe & Wetherald, 1967). The concentration of water vapour in the atmosphere increases rapidly with rising temperature (about 6%/�C); this is the basis for the strong positive water vapour feedback seen in current climate models (whereby increases in temperature produce increases in atmospheric water vapour which in turn enhance the greenhouse forcing leading to further warming). All current GCMs simulate a strong positive water vapour feedback (Cess et al., 1990) and are in agreement with observational data (Raval & Ramanathan, 1989).