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Who taught you geoscience? They failed that day. Water is only a greenhouse gas in the stratosphere well above the troposphere and any atmospheric weather pattern. Water vapor on the surface is and never will be a greenhouse agent. The oceans evaporate cubic miles worth of water per year that does effectively zero to the long term radiation balance of the planet it all rains back down eventually over land is the oceans themselves. Clouds have a short term effect of reflecting sunlight during the day and trapping long wave during the night the net effect is in a planetary scale a wash. The long term radiation balance gasses are all in the stratosphere where they trap heat at night and day. CO2, methane, hydroflorocarbons, and yes water vapor. There is no convective pathway for water vapor released or evaporated at the surface to get high into the stratosphere. Volcanism is one way with high powered eruptions. The largest source currently is aircraft exhaust above 55,000 feet get fuel burns to CO2 and water with high flying usually military jets at FL550+ commercial is nearly all below FL450. A new and growing source is rockets crossing the stratosphere into orbit. SpaceX has been putting up heavy lift once or more per month that burn kerosene and O2 right through the entire stratosphere the effects of thousands of launches per year will add up. It can take over 100 year
s for water vapor in the stratosphere to fall via gravity into the troposphere, a good portion leaks out the other way it gets energized by solar and cosmic radiation to energy levels where it can escape into space directly. Either way the residence time for stratosphere water vapor is decades to centuries.