Hey, here's a scheme I read about in one of the Freakonomics books. There was research into the idea of something like giant inner tubes floating along in the ocean. They had long tubes deep into the ocean. Now, warm surface water would be splashed into the floating inner tubes, slowly forcing warm water below the surface. The warm water displaced the cold water at depth, resulting in a cooler surface, which was supposed to eliminate hurricanes.
I've no strong opinion on this one, but some parts of the world rely on hurricanes for the annual rainfall. If this thing were really effective, would it also affect the great ocean currents?
I did not make this up.