A better way of stating the claim is as Dr. Galvin A. Schmitt does on this [NASA site][1]: >as temperature rises, the **maximum sustainable water vapor concentration** increases by about 7% per degree Celsius Then, [look at a water vapor pressure table][2] Near 0 degrees C, the per cent increase per degree is about 8%. At 25 degrees C, the increase is about 6% per degree. [1]: https://www.giss.nasa.gov/research/briefs/schmidt_05/ [2]: http://intro.chem.okstate.edu/1515sp01/database/vpwater.html