One thing that has hurt the global warming hypothesis, aside from data, is that the supporters blame everything that happens on "climate change." This despite what seems obvious to me, specifically that in a world where diurnal temperature changes of 30or 40 degrees F are common and annual variations are 80 to 100 degrees F, that a change of less than 0.1 F in the annual average between 1990 and 2008 would have any effect at all. Some of the rational people who believe in the global warming hypothesis also see this, as indicated in this article.

http://www.spiegel.de/international/0,1518,596019,00.html