I just got around to reading Wally Broecker’s interesting piece in the March 9 Science about “the carbon pie.” One of Broecker’s arguments is that market carbon emissions trading will be insufficient to meet atmospheric carbon goals, and that carbon capture will inevitably be required:

Because CO₂ sales would serve only as a temporary stopgap, capture of CO₂ from the atmosphere would be necessary. CO₂ capture from the atmosphere is feasible, but has yet to be implemented, and faces several technological challenges.