Seaweeds can grow very fast – at rates more than 30 times those of land-based plants. By drawing COâ‚‚ out of the ocean waters (thereby allowing the oceans to absorb more COâ‚‚ from the atmosphere) they help fight climate change. The seaweed farms buffer the ocean’s growing acidity and provide ideal conditions for the cultivation of a variety of shellfish. Despite the huge expansion in aquaculture, and the experiences gained in the United States and China of integrating kelp into sustainable marine farms, this farming methodology is still at an early stage of development.
Globally, in 2017 around 12 million tonnes of seaweed is grown and harvested annually, about three-quarters of which comes from China where over 500 square kilometres of seaweed farms exist in the Yellow Sea. The current market value of the global crop is between US$5 billion and US$5.6 billion, of which US$5 billion comes from sale for human consumption. Production is expanding very rapidly.
If 9% of the ocean were to be covered in seaweed farms, the farmed seaweed could produce 12 gigatonnes per year of biodigested methane which could be burned as a substitute for natural gas. The seaweed growth involved would capture 19 gigatonnes of COâ‚‚. A further 34 gigatonnes per year of COâ‚‚ could be taken from the atmosphere if the methane is burned to generate electricity and the COâ‚‚ generated captured and stored. This, they say:…could produce sufficient biomethane to replace all of today’s needs in fossil-fuel energy, while removing 53 billion tonnes of COâ‚‚ per year from the atmosphere… This amount of biomass could also increase sustainable fish production to potentially provide 200 kilograms per year, per person, for 10 billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity.