Since late 2002 there has been a sharp decrease in the water vapor in the lower stratosphere. It has dropped .5 parts per million or around 10%. Scientists don't know what has caused this decrease, but regardless, it is good for us. Water vapor is a natural greenhouse gas, and because of the 10% decrease, the average global surface temperature was almost 25% lower than it other wise would have been. One idea is that the water vapor at tropical latitudes has changed because of a shift of patterns of sea-surface temperatures that effect rates of evaporation and water vapor movement globally.
http://www.sciencenews.org/view/generic/id/55762/title/Water_vapor_slowed_recent_global__warming_trend
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