I am not associated with any of the following, but there are organizations attempting to build devices that will bring colder, nutrient rich waters to the surface to cause phytoplankton blooms (or use the same nutrients for seaweed farming):
1) ocean-based.com 2) http://www.climatefoundation.org/
We should of course do everything we can to stop emitting carbon. But projects like these may an important part in our future.