This is a fantasy solution touted on Slashdot and other techno-naive sites. There are several problems with it:
- A rapid increase of algae in the world's oceans would suck more than carbon dioxide out of the atmosphere. It would also suck a tremendous amount of nutrients from the world's oceans as well. Nutrients that other ocean life depends on.
We've already seen similar results in rivers, lakes, and at the mouth of the Mississippi where the algricultural fertilizer run-off from the Midwest has cause an algae bloom too. It's also refered to as a "dead zone" because the resultant algae bloom killed everything else and then died too.
- Although the algae would fall to the bottom of the ocean the carbon would still be added to the world's atmosphere, but at a later date.
The dead algae would be decomposed by microbes at the bottom of the ocean, slowly, but inevitably. The result of that decomposition is the production of methane, another greenhouse gas! And methane is actually a worst greenhouse gas than carbon dioxide!
So we remove a greenhouse gas, carbon dioxide, from the atmosphere only to add a another, worse, green house gas, methane, a century or so later! Hurrah for science!
- Finally, iron isn't cheap and we're not talking about a few pounds here and there. We're talking about metric tons of it. And how is this iron going to be paid for? Taxes? Gee, the techno-libertarians won't like that idea.
Face it folks, we need to reduce our levels of resource consumption, as a species. We can make investments into more efficient use of resources, not just power but all resources a priority or we can just keep partying until the lights go out.