The reason the ocean far from land is a beautiful clear blue colour is because there is no life in it. The reason there is no life is that it lacks the nutrients necessary for algae to start photosynthesis - and algae are right at the start of the food chain. Numerous experiments have shown that with the right nutrients the algae take off and with them the whole food chain fills out. A relatively small increment in ocean plant productivity could offset all the human contribution of greenhouse causing carbon dioxide. The ideal source of nutrients is coal ash - after all it's composed of the very minerals that supported plant life all those hundreds of millions of years ago. The idea of spreading coal ash over wide areas of the deep ocean would horrify many people - but actually it's far more benign than our current unplanned poisoning of the atmosphere. How could we get people to accept this idea?