I just finished reading a fascinating article on Wired from November 2000 about an entrepreneur's plan to reduce greenhouse gases by stimulating phytoplankton growth with iron. It's a very interesting article. The idea of iron fertilization
looks good at first, but it has the potential to screw up marine ecology very severely and to cause many more problems than it solves.
Most of these problems are covered in the article, but one that's not mentioned there is the fact that producing the iron to fertilize the phytoplankton would release greenhouse gases (from coal-burning), not all of which would be re-trapped by the phytoplankton. Not a winning proposition.
The other bone I have to pick with this Markels fellow is that he doesn't believe in global warming at all; he simply wants to make money off the people who do. Unfortunately, his ideas are bound to be popular with the current Administration. No worries about changing current practices about fossil fuels; just grow some more phytoplankton!
As Jeff likes to say, every problem has a simple, easy, and wrong solution.