ferd berple says (quoting someone or other):
August 18, 2014 at 12:02 pm
the effect of increasing the concentration of the two main GHGs, water vapor and carbon dioxide, from about 303 to 304 molecules per 10,000 molecules of dry air would not be measurable.
due to partial pressure law, increasing CO2 by 1 molecule will tend to reduce H2O by 2.4 molecules, all else remaining equal. Otherwise the increased CO2 would increase the mass of the atmosphere, increasing the surface pressure, making it harder to evaporate water, until such time as the same weight of water failed to evaporate, bringing the weight of the atmosphere back into equilibrium.
Since the molecular weight of CO2 is 44, and the molecular weight of H2O is 18, it takes (44/18) = 2.44 molecules of H2O to equal the weight of 1 CO2 molecule. What is interesting is that this would yield a negative H2O feedback of 2.4, which almost exactly balances the 3 time positive water feedback assumed by climate science. Since the H2O will tend to come out of the atmosphere more rapidly than temps will rise, it could well be that partial pressure law causes a net negative feedback.
Which would explain why the models are running hot. They fail to allow for partial pressure law to reduce H2O in their calculations, as CO2 increases.
Usually deniers talk about CO2 being so small it can't have any effect. Ferd takes a different tack. He's run this argument before, that CO2 pressure is so great that it presses on the sky's walls and floor and ceiling and stops water evaporating :) (Shades of our friend, Mack!)