"Global humidity" refers to the amount of water vapor present in the Earth's atmosphere all around the world. It measures the overall level of moisture present in the air worldwide. Full definition
Natural swings in the power of the greenhouse effect occur all the time as total global humidity changes. (newclimatemodel.com)
The power of the weather systems is well able to cope with large variations in oceanic energy output and the variations in the power of the greenhouse effect in the air arising from natural changes in global humidity. (newclimatemodel.com)
AFAICS, the only negative feedbacks are: 1) the increase in precipitation of snow with increased global humidity levels; and 2) the physical fact that as snow melts and water evaporates, those endothermic processes cool the surrounding area (but again I am doubtless missing a few). (realclimate.org)