Here is what did it for me:
https://www.youtube.com/watch?v=-JIuKjaY3r4
This 6 minute clip made me question the entire thing, because it was so full of half truths, innuendo, false conclusions, and then topped off with a politician's favorite rhetorical device--morality.
So when Al Gore started caricaturing the "so-called skeptics" I started listening closely. Because that's what you do when someone is trying to bamboozle you. And at every turn, when he laid down reason and picked up rhetoric, there was an "inconvenient truth" that he knew he could not hide so he resorted to lame arguments and hand waving.
Al Gore's inconvenient truths, just from that clip:
1:30 - The medieval warm period was actually quite warm, and you can't simply will it away by adjusting your chart or appealing to humor. Did you notice the chart goes from big smooth lines to little jagged lines? I did. Apparently it's a reconstruction where scientists have attempted to compare prehistoric temperatures to modern ones. I fundamentally reject that this is a fair way to present data to make your case. Those jagged lines should have error bars at least. The "hockey stick" has since been removed from IPCC reports out of embarrassment (see the 'Climategate' scandal and efforts by McIntyre and McKitrick to reproduce the hockey stick study).
2:55 - "In all of this time, 650,000 years, the CO2 level has never gone above 300 parts per million". First of all this is wrong. The Holocene has seen an oscillation from 210 to 385 ppm. I don't know where he's getting his numbers. What he also does not say is that this trend is actually quite rare. In most of the Earth's history the CO2 level has been many many times higher, from 2000 to 8000 ppm in the last 500 million years.
3:00 - The two charts very clearly fit together because of the opposite relationship that Gore is implying: A warmer climate means more biological activity, therefore more CO2. Duh. But somehow he is bamboozling his audience into believing that the relationship goes the other way. An elementary scientific attitude would at least say "hey wait a minute, correlation does not imply causation."
6:00 - After the elevator gag, he responds to "so-called skeptics" with hand-waving. "If this much on the cold side is a mile of ice over our heads, what would that much on the warm side be?" The audience is left to conjure doomsday scenarios in their minds. The answer could very well be "far more economic growth due to great swaths of land opened up for farming" but no, Al Gore is sure it's going to be a catastrophe.
6:15 - Then here comes the "this is not politics, this is a moral issue" which is a politician's favorite thing to say. Love the finger pointing and lowered tone of voice. Again this is the kind of behavior that makes a reasonable person question the basis of the whole thing.
I get that Gore really believes he needs to stop Manbearpig and needs to do it ASAP. But he and everyone else on the political left that wants vast international control over economies (and that's really what his political plan is) should have expected some blowback from this kind of rhetoric. And that's my answer to chasing's question of "how could it be Gore's fault" that there is skepticism over his crazy agenda.