Apparently, water vapor is "an important greenhouse gas," according to this RealClimate post, but that doesn't mean that it's reduction holds the same level of importance as other global warming agents. RC scientist Gavin explains how water vapor is "a feedback and not a forcing," and gives lots of evidence and statistics to demonstrate his point. A little technical for me (as always), but you science types should love it. If you'd like, feel free to explain...
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