Does new U.S. humidity study contradict greenhouse theory? Some skeptic blogs say so. The authors say no: 

Thank you for your interest in our recent paper and the response that it has been receiving. The skeptics have chosen to focus on one of our results and even here have taken it out of context.  Our paper can best be summarized by 3 conclusions:

1) Dewpoint/specific humidity has changed very little since the 1930s DUE mainly to the change from manual sling psychrometers to hygrometers in the late 1950s.

2) During the more recent period with more or less consistent observation technology and instrumentation, dew point and specific humidity has increased as expected in a warming climate

3) Local effects (both urbanization and irrigation) affect humidity trends at the some of the limited number of available airport locations analyzed.

- Paula Brown and Art DeGaetano (some of their earlier research collaborations)