Global circulation model (GCM) experiments carried out for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) predict that as the Earth undergoes global warming, humidity will increase in subtropical regions.
Hurley and Galewsky use an IPCC AR4 GCM simulation to study the source of this increased atmospheric water vapor under global warming. The authors find that the increased subtropical atmospheric water vapor can be attributed primarily to the warmer temperatures encountered by air parcels at the time the parcels were last saturated with water vapor.
Furthermore, the researchers note that increased evaporation does not explain the increased subtropical humidity and that circulation changes have only a minimal impact on humidity in their simulations.
Title: A last-saturation diagnosis of subtropical water vapor response to global warming, John V. Hurley: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA; Joseph Galewsky: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA.Geophysical Research Letters (GRL) paper DOI: 10.1029/2009GL042316, 2010