Finding the cause? We should at least look at the elephant in the room. In other words look at that big flaming ball in the sky that appears every day.
I found this interesting site that appears to be an earth science textbook. Seems very "technical," maybe a little less biased than Al Gore & the NY times, though I do see some opinions thrown in there.
What I wanna know, is how scientists know exactly how many parts per million of each listed substance there was in the atmosphere in the 1700's in order to compare! Hmmm... (scratching my head). I have a feeling it must involve calculus.
http://www.physicalgeography.net/fundamentals/7y.html
http://www.physicalgeography.net/fundamentals/7h.html