[Telepathic Intruder]

"Water vapor is the most powerful green house gas in our atmosphere"

That said, it is also easily scrubbed from the atmosphere. It happens every time it rains. And when the temperature lowers a bit, it turns into clouds which reflect sunlight back into space. But then greenhouse gasses is not something that keeps be awake at night anyway.

[zeestephen]

The water vapor exhaust from planes would mostly collect in the stratosphere.

I wrote a separate post about the VERY significant difference between water vapor in the troposphere and water vapor in the stratosphere.