The December 09 issue of National Geographic has a very clear diagram of our greenhouse gas and global warming problem. You can see it below on:

www.NGM.com/bigidea

It starts with:

"It's simple, really: As long as we pour CO2 into the atmosphere faster than nature drains it out, the planet warms. And that extra carbon takes a long time to drain out of the tub."

I suggest you study this short article that is on the web site above even if you do understand the criticality of GW because it is presented in an effective and clear-to-understand way.

Please look for the second diagram on the second page too.