By this particular measure, water vapor can be thought of as providing 36% of the greenhouse effect, and carbon dioxide 12%
http://en.wikipedia.org/wiki/Greenhouse_effect
However, the amount of water vapor in the atmosphere isn't increasing, because the amount of water on Earth is always about the same. Maybe if the surface area of all the water on the Earth increased, I could see that happening. But there would have to be like an entire new ocean created.
Also, water vapour usually takes up far more of the atmosphere than CO2. Therefore, it could be argued that CO2 per unit has a greater effect - it's just that there's more water vapour. Regardless, CO2 is increasing, water vapour is not. And an increase of volume of the greenhouse gasses in the atmosphere by, like, 1%, will over time have a much greater effect on temperature on Earth than 1%.
I really couldn't see any university publishing a "study" saying that water vapour is a greenhouse gas. It's well known knowledge.