Obama may think that greenhouse gas emissions have been causing solar heat to be trapped inside the atmosphere more than is convenient. If increases in carbon dioxide and other gases have indeed had that effect, reversing the trend could be a matter of reducing the gases. However, information I've heard with regard to carbon dioxide is that human industry is not the main source of it.
Insufficient CO2 in the atmosphere would be a problem for green plants, which use it for photosythesis, producing food for man and beast. I doubt, however, our efforts would reduce it that far.
I hear that some city is actually drilling to force CO2 into the crustal rocks beneath. A great caution is in order there. About a generation ago a lake in an internal drainage in Africa accumulated carbon dioxide in its depths, according to National Geographic, and released it suddenly. The denser-than-oxygen CO2 displaced the oxygen in the valley, killing animals, from humans down to ants. The plants did just fine. Vast amounts of CO2 under pressure beneath a city is asking for a disaster.
