The Case for Seaweed

Photo: Carol da Riva

Photo: Carol da Riva

In the two years since Alexandra inspired my interest in seaweed, I have found that the more you learn about seaweed, the more excited you get about its potential to be restorative to the oceans, the climate, the planet, and all of us who live on it. I hope you will feel the same at the end of this brief piece on the potential of seaweed to address the climate crisis and the ocean crisis, which are inextricably linked.

Seaweed captures carbon as it grows during the photosynthesis process like any other plant. Plants in the ocean (including kelps and seaweed, seagrasses, and mangroves) represent just 0.05% of the plant biomass on land, but they grow so quickly that they cycle through a similar amount of carbon every day as all land-based plants. The ocean is a major carbon sink - it has absorbed 25% of the carbon emitted since the Industrial Revolution – but that has come at the cost of a 30% increase in acidification, which makes it harder for marine organisms to live. Seaweed and other marine plants increase the ability of the oceans to absorb carbon, and do it in a way that decreases acidification, addressing two profound problems at once.

Seaweed can be an ally in the work to restore balance to the climate in three main ways: sequestering carbon as it grows; avoiding emissions by using harvested seaweed to displace more climate-intensive products; and producing negative emissions by applying seaweed to increase absorption of carbon from the atmosphere.

Some of the carbon that seaweed captures is released through the normal carbon flux process in the oceans and atmosphere. During the growth process, some seaweed biomass breaks off, and some of the carbon in that biomass is sequestered in sediment, both nearby and in deep ocean sinks. Under the leadership of Professor Carlos M. Duarte, a renowned marine biologist who is the world expert on seaweed and carbon and Oceans 2050’s Chief Scientific Adviser, last month we launched a global study with 19 farms in 12 countries on five continents to quantify the sequestration by seaweed of carbon in sediment. By the end of 2021, we hope to be able to provide guidance supported by rigorous scientific research and analysis on how much carbon seaweed sequesters in sediment as it grows, and what the main factors are that drive that sequestration rate – whether it might be species, geography, environmental conditions, farming practices, a combination of all of these things, or something else entirely. That information will enable the optimization of seaweed farming to maximize carbon sequestration. It will also be the basis for a new voluntary carbon methodology, to allow seaweed farmers to monetize the carbon impact of their work. We hope that this project will create a new blue carbon market that is much more scalable than the alternatives available today, giving carbon offset buyers the opportunity to achieve their climate goals by investing significant amounts in seaweed solutions that advance both climate and ocean restoration. Advancing the science will also allow us to move towards the goal of including seaweed farming in regulated carbon markets down the road.

But sequestration in sediment is not seaweed’s only potential contribution to climate restoration. When seaweed is farmed and harvested, the carbon stored in that harvested material may remain sequestered from the atmosphere or be released, depending on what it is used for. If it is used in a way that displaces more climate-intensive products, the result is avoided emissions. Seaweed is primarily grown for food, but there are a range of other potentially significant uses that could drive much bigger demand, and have net positive climate impacts: displacing agricultural feed that is now grown on land with seaweed, for example, which requires no application of water or fertilizer, and much less energy to grow than soy or corn; replacing petroleum-based plastics with home compostable bioplastics; or, everyone’s favorite (because it is seemingly the only funny story in the climate change community), feeding seaweed to cows to reduce their burping, which is a significant contributor to the climate crisis. 

In addition to avoiding emissions, seaweed-based products can also contribute to negative emissions, for example by using seaweed-based biostimulants to increase the carbon retention of soil. 

Seaweed can also help us adapt to climate change, by improving coastal resiliency in the face of more frequent, more intense storms, and rising seas. 

The oceans crisis is a climate crisis, and vice versa, and reducing the concentration of CO2 in the atmosphere is fundamental to enabling the restoration of the oceans. In addition to seaweed’s contributions to carbon sequestration, it has other benefits for ocean restoration, including reversal of dead zones / absorption of nitrogen and phosphorus, and increasing biodiversity. Oceans 2050 will work to advance the understanding of these effects, and to build markets that value them and channel investment to take them to scale.

There is also a compelling social and climate justice story to tell with seaweed farming. Seaweed farming has low barriers to entry for people with access to the ocean and experience on it. Fishermen facing the decline of their fisheries due to overfishing and the growing effects of the climate crisis, can grow seaweed in the off season to complement their earnings, or in some cases replace their fishing activity entirely. Small island nations without an intensive industrial sector they can decarbonize, can use seaweed farming as part of their Nationally Determined Contribution to meeting the goals of the Paris agreement. Indigenous coastal communities are natural partners in seaweed farming, given their commitment to place, their interest in economic development opportunities that are consistent with their values, and often their water and coastal rights. Seaweed farming is also often women’s work: 80% of the seaweed farmers on the island of Zanzibar, for example, are women. In our work to catalyze the scale up of seaweed farming, Oceans 2050 will prioritize partnering with indigenous and other coastal communities that have historically been excluded from economic benefits and are least able to insulate themselves from the pain of the climate crisis.

By some estimates, nature-based solutions have the potential to absorb 100-200 GT of CO2 over the remainder of the 21st century, which is a meaningful number in the context of the ~750 GT of CO2 emitted into the atmosphere (of which ~500 GT has already been absorbed by land and ocean ecosystems). We believe seaweed can contribute meaningfully to this work, by sequestering up to 10 GT of CO2 in the coming 30 years and expanding its reach to over 1 million km2 of ocean. It can do so in a way that does not compete with land needed for other uses like agriculture – and in fact enhances food and resource security by providing low carbon, plant-based materials to animals, fish, and humans.

This is why I am excited about seaweed. If you are too, please sign up for updates on our seaweed carbon farming project, and reach out if you have ideas about how to catalyze the scale up of seaweed farming to reach its potential to restore the oceans and the climate – and help ensure our children and grandchildren have a livable planet.

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Alexandra Cousteau Wants To Restore The Oceans By 2050