In his carefully-crafted movie, Mr. Gore leads off with what many consider the most persuasive data: 650,000 years of correlation between CO2 and warming/cooling trends. Problem is, that data actually shows that the trends in atmospheric CO2 trail the warming-- by a few hundred years. Clearly CO2 is not in the climatic driver's seat.
I have seen a response that goes something like this: "OK, so CO2 didn't cause those temperature variations, but it was a positive feedback, amplifying the warming trends." At first, this seems reasonable. But a second look reveals it as dubious at best. First of all, the argument doesn't survive Occam's razor. The oceans heat very slowly. If you want to cause them to give up dissolved carbon dioxide, you have to be able to warm the planet significantly for several hundred years. And if you've got a mechanism that can warm the Earth for several hundred years, what need is there in your theory for this feedback mechanism? Second, making this argument concedes that the warming observed in the 20th century is nothing unusual, well within the range of natural variation.
I think it's reasonable to ask why Gore & company are so clearly trying to lead their audience to a conclusion ruled out by the very data they present? If their case is a total no-brainer like they claim, why do they need to?