3) Ocean Afforestation via macro-algae forests covering 9% of the world’s ocean surface can produce sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 billion tons of CO2 per year from the atmosphere, restoring pre-industrial levels. This amount of biomass could also increase sustainable fish production to potentially provide 200 kg/yr/person for 10 billion people.
https://www.researchgate.net/publication/259892834_Negative_...
Offsetting current carbon emissions would require some 50 trillion trees. An alternative offset would be to cultivate kelp forests. Kelp can grow at 2 feet per day, 30 times faster than terrestrial plants. Planting kelp across 9% of the oceans (4.5 x the area of Australia) could provide the same offset. Additionally, the kelp would support a fish harvest of 2 megatons per year and reduce ocean acidification. Large scale open ocean forestry would require engineered substrate and added nutrients.
https://www.resilience.org/stories/2019-04-29/nitrogen-crisi...