3 Further complicating the response of the different atmospheric levels to increases in greenhouse gases are other processes such as those associated with changes in the concentration and
distribution of atmospheric water vapor and clouds.
Aires, F., C. Prigent, W.B. Rossow, and M. Rothstein, 2001: A new neural network approach including first - guess for
retrieval of atmospheric water vapor, cloud liquid water path, surface temperature and emissivities over land from satellite microwave observations.
Non-condensing greenhouse gases, which account for 25 % of the total terrestrial greenhouse effect, thus serve to provide the stable temperature structure that sustains the current
levels of atmospheric water vapor and clouds via feedback processes that account for the remaining 75 % of the greenhouse effect.
This provides a stable reference temperature structure for the fast feedback processes to operate and maintain the
amounts of atmospheric water vapor and clouds at their quasi-equilibrium concentrations.
The effect of the increased volume
of atmospheric water vapor is not knowable because until recently there were only very crude estimates of atmospheric water vapor levels.
By several meteorological measures, the airmass associated with this storm is pretty extraordinary: the amount
of atmospheric water vapor (precipitable water) expected to be present near San Francisco on Saturday morning may be close to the all - time record value for any time of year.
They describe «water vapor and clouds as the fast feedback processes in the climate system,» whereas the «noncondensing greenhouse gases... provide the stable temperature structure that sustains the current levels
of atmospheric water vapor and clouds» (p. 356); in terms of direct effects on radiation, they estimate water vapor accounts for about half the greenhouse effect, clouds for about a quarter, CO2 for 20 % and other greenhouse gases 5 %.