A barrel floating in the ocean will grow a seaweed farm. It would be easy to create rainforest sized algae farms mid ocean. The seaweed farms would photosynthesize, as well as the lifeforms themselves would be made of carbon.

Cheap. Proactive. Harmless.

Also mid ocean seaweed (algae) farms could be towed to countries in need for emergency food, fuel.

No downside.

Build seaweed farms from shore and tow them out to sea and anchor them. Polluting companies could sponsor the low costs.

Win Win Win