Just consider for a moment both sides of the issue. You either believe that global warming is real or you don't.
Doesn't your view that it may not be real gaurantee that if it is real that mankind would not act quick enough to stem and manage climate changes due to global warming?
The reason I ask this is because for the non-believers, the only way you would be convinced that global warming is real would be well after global warming enters the phase where you can't reverse or slow down and manage the changes.
I have no idea of your knowledge level of the history to the climate on this planet. For all I know, you could be one of those "The earth is only 6500 years old" folks. But science has clearly demonstrated periods in the earths climate where the levels of CO2 shot up dramatically at the same time the earth experienced mass extinctions. And as far as time goes, it can and has happend quickly.