One of my biggest complaints about Al Gore's hysterical "documentary" is his intentional logical error of assuming that if CO2 concentrations have gone up more or less simultaneously with a global temperature increase, then 1) CO2 caused the increase, and 2) any causal relationship must be linear and maintained through any increase in CO2.
Both of these are probably wrong, but #2 is certainly wrong.
Each subsequent increase of X parts per million of CO2 in the atmosphere will have less "greenhouse" effect than the prior increase.
If a CO2 concentration increase of X ppm causes a Y degree temperature change, than the next increase of X ppm CO2 would cause a temperature change of less than Y, eventually to the point where increasing CO2 by X would have effectively zero impact on climate.
Again, there is real data showing that CO2 changes follow and don't lead temperature changes. But even if you believe CO2 causes climate change, it is absolutely wrong to believe the relationship is linear or exponential. Instead it is logarithmic, with each new molecule or ton of CO2 doing less than the prior molecule or ton.
Steve Milloy has another excellent article on this subject, in which he shreds the incorrect conclusions made about a recent study of human CO2 emissions. It's well worth a read:
Junk Science: Hot Air Study Melts Global Warming Theory, 5/24/05, by Steven Milloy for Fox News and JunkScience.com
http://www.foxnews.com/printer_friendly_story/0,3566,275267,00.html