Ah cha, one must be understanding what is "partial pressure" of a gas, in a mixture, if one is wanting to be saying something about the dynamics of such. Vapour pressure is connected to insolation, but also to the capacity of a gas to absorb heat and 'accommodate' the added partial pressure; in this case the partial pressure of water vapour against all the other pressures/concentrations. This is much like finding a 'centre' from which something extends linearly, however it has non-linear 'amplification' pushing it too. So which is the 'signal' and which is the amplifier, and how does it make the signal larger - what is the amplitude? I think it resembles a voltage-amplifier, which means the voltage resembles H2O pp, and the signal is the 'induced' voltage across the input (resembling the 'heat' current/potential produced by CO2/methane pp). Heat density scales with H2O vapour density, which transports the excess heat via convection; Voltage potential 'transports' excess charge/current via 'electron convection'. This is, however an extremely simplified explanation - but not out of the cricket ground altogether. It's within the boundary.