How does a lot of noise eliminate the signal?
In phase sensitive detection the initial input from the signal is much less than that of the noise. After integrating the signal over a few thousand cycles, however, the signal is much larger than the noise. The noise doesn't integrate / accumulate and eventually vanishes.
H2O isn't a gas like CO2. H2O a condensable _vapor_ and any excess H2O precipitates out of the atmosphere.
CO2 is a gas and any excess CO2 hangs around for decades or centuries.
That's why H2O only enters the AGW equation to the extent that CO2 has _already_ warmed the atmosphere. The higher temp. due to CO2 allows more water vapor in the atmosphere.
This is a _positive_ feedback.
Bret Cahill