Global warming- i dont really believe it... but?

ookay so i am thirteen. ive heard alot about global warming. right now im kinda thinking it isnt real. it just doesnt add up! ive studied that if you condensed the history of all life up until now (from the first tiny life form to dinos, to cavemen, to humans) in to one hour, human life would only be in the last ten seconds! and more than half of that time we didnt even have the things that they say "cause global warming". it doesnt seem possible that we destroyed the world so quickly! second if you took all the cars. and factories and planes in the WORLD and put them all together in one place it would only fill the state of california! third all the carbon deoxcide thats "trapped in the atmosohere " plants use to make more oxygen! n fourth the sun goes through 12 year cycles of heat and in the ice age it got suddenly warm and there was nothing to polute the atmosphere then! but now im a little confused with all the stuff going on with global warming and adevertising? what's the truth