A commercial venture to create a plankton bloom and suck up some carbon out of the atmosphere is being planned by a company called Planktos. The way it works is that you drop iron into the ocean to encourage a bloom. I can only hope that this works, but many scientists are in doubt. And I have to wonder.... it seems to me to be a trial and error sort of approach. Do it now, ask questions later. When our environment is in play it seems like a dangerous game.
Further reading:
International Herald Tribune