[labster]

But ultimately on Earth, even in the dry polar latitudes, there’s certainly enough water to absorb everything in the H2O spectrum lines. The atmosphere is lousy with water, generally 1-3%, meaning it is usually the third most abundant gas.

[Xylakant]

Sure, but the question here is “does the water vapor from burning Methane add to the vapor in the atmosphere?”, which is different from “is water vapor the most important contributor to the greenhouse effect?”