green granite, you need to look a little deeper than that. The 6% is annual and roughly 60% of that 6% stays in the atmosphere. Add that up year on year.....
H20 is the major greenhouse gas but it isn't a driver - the amount is dependent on atmospheric conditions driven by other greenhouse gases. It is removed from the atmosphere too rapidly to be a driver. Throw a lot more water in the atmosphere and it precipitates out rapidly. Throw more CO2 in the atmosphere and it takes on the order of 100 years to be removed.
More CO2 means more H2O means more warming. H2O amplifies the effect of other greenhouse gases, but doesn't drive things.