Farming seaweed

Harvesting macroalgae
Developing marine farms

Context

Seaweeds can grow very fast – at rates more than 30 times those of land-based plants. By drawing CO₂ out of the ocean waters (thereby allowing the oceans to absorb more CO₂ 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.

Implementation

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.

Claim

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 CO₂. A further 34 gigatonnes per year of CO₂ could be taken from the atmosphere if the methane is burned to generate electricity and the CO₂ 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 CO₂ 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.

Counter-claim

Farming seaweed is not an important problem; it’s a niche activity that distracts from pressing global issues like food security and climate change. While some tout its benefits, the reality is that seaweed farming lacks the scale and impact needed to address significant environmental challenges. Instead of focusing on this minor agricultural trend, we should prioritize sustainable practices in more critical sectors that directly affect millions of lives and the health of our planet.