Algae farms in deserts to heal global warming

Algae produces most of the oxygen planet on the planet to begin with, why not plant up more deserts with algae farms.... you could even grow spirulina on the farms and turn it into a profitable health food product.

Also, if anyone's interested in how they can do their part to help protect the amazon rainforest, which also produces the vast majority of the oxygen on the planet(just going down there makes you feel high), visit - http://174486.amazonherb.net/RS_0_0_Main.aspx

 

Well, being that deserts, lack lots of water, and algae need water to live, I see where there would be a problem with that idea.