The Quick Fix for Global Warming

I recently came across a theory to combat global warming in a marine biology class. Noticing the outbreak of algae and plankton blooms in the ocean caused by nutrient runoff, some scientists started thinking about what it would take to create a large enough plankton bloom to stop the greenhouse effect. Everyone that had fourth grade science knows that plants use carbon dioxide for photosynthesis. Carbon dioxide is also the largest contributing greenhouse gas. While it is impractical to grow enough plants on land to use up carbon dioxide at the rate we are releasing it, plankton in the open ocean could be grown quickly and cheaply. Apparently the most economical way would be to add large amounts of iron to the ocean waters near the north and south poles. Iron seems to be the limiting resource in these areas, and even a little bit added would result in vastly greater amounts of plankton. The cons to this solution are many. The biggest downside is that we don't know exactly how this would impact the rest of the environment.