Surface humidity refers to the amount of moisture or water vapor present in the air that is close to the Earth's surface. It measures how sticky or damp the air feels on our skin. Full definition
It is hard for me to imagine this large a reduction in tropical mean near surface humidity with warming — but one only has to get this reduction in the convecting regions. (gfdl.noaa.gov)
One study, published in today's edition of the journal Nature, found that the overall increase in worldwide surface humidity from 1973 - 99 was 2.2 %, which is due «primarily to human - caused global warming,» according to study co-author Nathan Gillett of the University of East Anglia, in Norwich, U.K. (climate-skeptic.com)
Willett, K. M., P. D. Jones, N. P. Gillett, and P. W. Thorne, 2008: Recent changes in surface humidity: Development of the HadCRUH dataset. (nca2014.globalchange.gov)