This is a very poor substitute for trees. Trees convert gaseous carbon dioxide into solid organic molecules [1]. I am pretty suspicious of the idea that humans

This is a very poor substitute for trees. Trees convert gaseous carbon dioxide into solid organic molecules [1]. I am pretty suspicious of the idea that humans (especially the humans who come up with the lowest bids to win these contracts) can store planetary-scale amounts of carbon dioxide over geologic time. This may very well accomplish nothing. [1] http://en.wikipedia.org/wiki/Carbon_fixation http://en.wikipedia.org/wiki/Carbon_fixation