[tonycarreon]

in essence the sun's radiation (mostly as light) passes through the atmosphere and hits the ground where it is partially absorbed and partially reflected back into space (as light). the absorbed radiation is eventually emitted back up towards space. if there was no atmosphere then the radiation would pass on into space. however the earth's atmosphere absorbs and releases the radiation back towards the surface (including the oceans and ice caps) or out into space. the more "greenhouse gases" in the atmosphere, the higher the chance the radiation will be emitted back towards the surface instead of into space.

yes plants absorb carbon dioxide and release oxygen, and we're are cutting down forests and planting smaller trees that will take hundreds of years to have an appreciable effect on CO2 absorption all the while we're putting more CO2 into the atmosphere. the oceans are also responsible for capturing CO2 but in doing so they change the pH which has an ill effect on marine life. ice is also a good captor of CO2 but with warmer temperatures the ice melts and releases the CO2 back into the atmosphere.

the reason CO2 is a target is because it's the second highest contributor to the "greenhouse effect" behind water vapor and one we can "do something about." in addition, CO2 remains in the atmosphere for a lot longer than other gases so doing something now will have a positive effect many years from now.