I’m sorry, I’m unable to even parse that statement. The fact is that (a) the relative humidity of the atmosphere is maintained in a fairly constant balance dependent only on temperature, and that (b) the absolute humidity increases as the air temperature increases.
Water vapor is a very important consideration in radiative transfer computations in climate models, but its relevance is strictly as a feedback. Your statement that it’s “a potent if not persistent greenhouse gas” is just hugely misleading. Show me where in any IPCC graphs of greenhouse gas radiative forcings water vapor is even mentioned.