Only an idiot believes that human activity is responsible for global warming. The fact that CO2 and temperatures are both going up at the same time is not proof that one is causing the other. The earth's temperature has gone up and down throughout its history. Hell, in the 70's, scientists were convinced that the world was entering a new ice age, so which is it? The fact is, these people have no idea, but that won't stop them from inventing one.
Time and time again, people who support this idea also support stupid ideas like Live Earth, the "Green Industry" and political candidates and scientific institutions that are pushing this shallow agenda. Is it possible that all these people are correct? Probably not. I think it is far more likely that "green industry" is being used a a fake issue so politicians can get elected, so failed politicians (Al Gore) can create their own little empires and feel important by putting on concerts that events that probably cause a lot more pollution than would have been otherwise, and so scientific institutions can continue to get funding to do more "research" which probably includes financing greenhouse-gas-spewing trips from one cushy environmentalist conference to another.
The part that probably pisses me off the most is how people are now blaming everything on global warming. Hurricane Katrina? Global warming. Huge blizzard on the east coast? Global Warming. Drought in the southwest? Global Warming. Fires in So California? Global warming. Evidence was recently found that the SoCal fires were deliberately started, and the brainwashed sheep still won't let up. Global warming has become the new "bogeyman" issue that is going to decide yet another election, just like "gay marriage" was last time.
The fact is, the temperature of the globe is increasing and there is a very good chance that there is nothing that humans can do about it - even if CO2 is responsible for it, the Kyoto treaty and other such rot won't pull it out of the air fast enough. I will only take a politician or scientist seriously when they stop talking about how to stop global warming and start talking about how to survive an inevitable climate change by changing our own way of life.