I think that the global warming "naysayers" are not saying that GW is a sham, they are saying that it isn't cause solely by humans. Meaning, it isn't cause we drive cars, or fart. And good luck ever reversing the effects of GW. I'm actually more concerned with what crap we need to do in order to "reverse" anything. I'm not going to pay more in order to be more "green."
I believe GW is happening, I just don't believe we'll ever change it, and I certainly don't think the big bad evil humans are the sole cause of it.
*Cue the name calling*