"Gore's credibility is damaged early in the film when he tells the audience that, by simply looking at Antarctic ice cores with the naked eye, one can see when the American Clean Air Act was passed. Dr. Ian Clark, professor of Earth Sciences at the University of Ottawa (U of O) responds, "This is pure fantasy unless the reporter is able to detect parts per billion changes to chemicals in ice." Air over the United States doesn't even circulate to the Antarctic before mixing with most of the northern, then the southern, hemisphere air, and this process takes decades. Clark explains that even far more significant events, such as the settling of dust arising from the scouring of continental shelves at the end of ice ages, are undetectable in ice cores by an untrained eye."
http://www.canada.com/nationalpost/financialpost/story.html?id=d0235a70-33f1-45b3-803b-829b1b3542ef&p=1

Yes, Gore is lying sack- but he has an excuse, he's a political.

The article goes on to say:
"CO2 is plant food, an ingredient essential for photosynthesis without which Earth would be a lifeless, frozen ice ball."

Now, if the atmosphere lacked CO2 would that result in Earth being a frozen ice ball?
Lifeless yeah, because it's not possible to have plant life without CO2- plants need it or they die- without plants we and all animal life couldn't exist. You could argue about the lifeless aspect- for instance miles beneath solid rock there is life- but whatever. The main point I'm having a problem is the frozen ice ball part.
Now, Earth has apparently been a frozen ice ball and Earth has been a nearly iceless ball. Now, CO2 may play a role in global temperature, but at 380 ppm or lower it seems it doesn't play a dominate role. Removing all CO2 from Earth atmosphere would be practically impossible- the oceans are filled with it, the soils are filled with it, volcano belch it, and it even falls to Earth from space. But assuming one could wave a wand and banish all CO2 from the atmosphere, it's unknown if this would significantly effect global temperatures.

Now, this bring up an interesting question, what is the lowest level of CO2 in the atmosphere that a plant can survive?
I wouldn't be in the least surprised if no one knew the answer.