William M. Gray
Professor Emeritus, Dept of Atmospheric Science,
Colorado State University
..Recent GCM global warming scenarios assume that a slightly stronger hydrologic cycle (due to the increase in CO2) will cause additional upper-level tropospheric water vapor and cloudiness. Such vapor-cloudiness increases are assumed to allow the small initial warming due to increased CO2 to be unrealistically multiplied 2-4 or more times. This is where most of the global warming from the GCMs comes from – not the warming resulting from the CO2 increase by itself but the large extra warming due to the assumed increase of upper tropospheric water vapor and cloudiness. As CO2 increases, it does not follow that the net global upper-level water vapor and cloudiness will increase significantly. Observations of upper tropospheric water vapor over the last 3-4 decades from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and the International Satellite Cloud Climatology Project (ISCCP) data show that upper tropospheric water vapor appears to undergo a small decrease while Outgoing Longwave Radiation (OLR) undergoes a small increase. This is opposite to what has been programmed into the GCMs. The predicted global warming due to a doubling of CO2 has been erroneously exaggerated by the GCMs due to this water vapor feedback.....