Finally something to address!
First off we generally do talk about water vapor being an “emission”. It’s a forcing.
Second the bulk of greenhouse gas warming is actually a good thing. Without it the planet would be an iceball.
In the chart below note that without a greenhouse atmosphere the temperature of the earth should be -18C. Instead it’s around 15C.
The problem with your assumption on the water vapor is it’s a lagging indicator of climate change in this case.
Atmospheric water vapor is dependent on the temperature of the atmosphere. With warmer air being more able to hold more water vapor.
Water vapor has been a part of the earth’s atmosphere since it cooled off after formation. We are looking at what’s happened in the last century or so.
For the amount of atmospheric water vapor to increase over that time frame the average atmospheric temperature would have to increase first.
As
@Maxima1 pointed out there is no other natural phenomenon that could account for the temperature rise other than CO2 from man-made activity.
The injection of CO2 into the atmosphere starts the atmosphere warming which naturally causes more water vapor to accumulate in the atmosphere which causes more warming.
This is a feedback cycle but it’s root cause is due to human CO2.