A few people, (I think Little Hawk was one) have asked the question 'how come a small amount of CO2 can have such a large impact on our climate? I've been trying to find a good reference for this that doesn't get terribly technical very quickly.
This is the best I can find so far
How do we know CO2 is causing warming?

My understanding (as a chemist not a physicist) is that, molecule for molecule, CO2 is a much stronger greenhouse gas than water. That is, its infra-red absorption bands will be more intense. There is generally more water in the atmosphere so that will have more impact in total than CO2. Some people quote 98% of total contribution from water, others say its more like like 60%. If you believe the first figure, then CO2 is about as strong a greenhouse gas as water, if you believe the second figure, then its hundreds of times stronger (which is apparently what the basic physics would suggest).

So we (global humanity) are currently conducting a world-wide experiment to see what happens when you dramatically increase the amount of CO2 in the atmosphere - you might say the ultimate 'field trial'!

Hope this is useful
KP