Is it possible for water vapour to become the main driver without CO2?The easy answer is: by reducing CO2. The increase in water vapour is a function of the CO2 driven temperature increase. Climate sensitivity dictates a 1C increase for a doubling of CO2. The effect of the water feedback is to amplify that to around 3C as a best estimate. The range of projections is between 2.5 and 4.5.
If CO2 were dropped to specified levels tomorrow, would water vapor follow suit automatically? Yes or no?