by Carybeth Reddy, MBA ’22
This article was written in response to a seminar given by Marcius Extavour, VP of Energy and Climate at XPRIZE, in an EDGE Seminar on Sept. 29, 2021 at Duke University’s Fuqua School of Business. This article voices one student’s perspective and does not necessarily represent the views of either Duke University or the seminar speaker.
During a recent conversation in our EDGE Seminar class, Marcius Extavour, VP of Energy and Climate at XPRIZE, stated that carbon reduction is a must, as is carbon removal. Marcius shared various projects and initiatives that have high potential, as well as XPRIZE’s partnership with the Musk Foundation for a $100 million prize searching for viable and scalable carbon removal projects. Marcius said that there’s no silver bullet for the climate situation we’re in, but rather we need to find the best solutions that are scalable and that these may be different in different places. Marcius touched on seaweed in the conversation, noting that it may not be scalable. This led me to want to look further into seaweed as a nature-based solution–one that I thought had promise, but I admittedly knew little about carbon removal.
Is seaweed a solution that may be best in some places, and is it a scalable solution? I found that seaweed farming has drawbacks and will not be enough on its own, but we are not looking for a silver bullet, and it has enough positive impacts that it deserves investment alongside other carbon removal technologies.
Overview of Seaweed as Carbon Removal
There are various companies currently piloting seaweed farming as a form of carbon removal. Kelp is one of the most commonly farmed types of seaweed because it grows rapidly, up to two feet per day. Seaweed absorbs carbon dioxide through photosynthesis. This naturally occurring process is thought to sequester about 200 million metric tons of carbon dioxide every year, a rate up to 50 times greater than forests on land and equivalent to New York’s annual emissions.
The seaweed must be sunk at least 1,000 meters to the deep ocean to keep the carbon from rejoining the carbon cycle. Running Tide, a start-up based in Maine, is farming seaweed and plans to sink it to the ocean floor to become a provider of carbon offsets. The company is working closely with scientists to develop technology and reliable carbon accounting for seaweed as carbon removal. Other companies have also entered the market and are still testing the best ways to easily and cost effectively sink seaweed.
The Promise of Seaweed
Seaweed is a promising option for carbon removal because it is fast growing and does not require fertilizers or fresh water that some other nature-based solutions require. Seaweed also does not take up land that could be used for food production, one of the drawbacks to solutions like planting trees (though seaweed could be cultivated on land to increase farming capacity).
In addition to carbon removal impacts, seaweed farming has other positive climate and environmental impacts. Seaweed can help regenerate ocean ecosystems and reduce acidification of the ocean. It also is an option to sustainably increase the global food supply by as much as 10% by 2050 according to the World Bank. Utilizing seaweed as a food source does not result in permanent carbon removal, but is still a positive impact of seaweed cultivation. Adding seaweed to cow feed can reduce methane emitted by cows. These positive environmental impacts make a case for seaweed farming for uses in addition to carbon removal.
Seaweed farming can also positively impact farming communities, providing a social benefit. Farming seaweed provides jobs and economic growth to farming communities. Cascadia Seaweed, a company based in British Columbia, is collaborating with First Nations communities to provide jobs and training to communities living on Vancouver Island in hopes of becoming North America’s largest seaweed provider. Communities that rely on the ocean for economic growth can be brought in as part of the seaweed for carbon removal process to benefit from the jobs and profits this may provide.
While seaweed presents much promise in terms of carbon removal and other environmental and social benefits, there are some risks, some of which may not yet be known. If seaweed is grown on a global scale, it could reduce the sunlight that reaches other species, impacting photosynthesis in a way that could be dangerous to ecosystems. Since seaweed has not been grown on this scale before, there are other ecosystem impacts we may not know about, including potential negative impacts of disturbing the ocean floor.
Farming seaweed and sinking it is a new idea and the companies in the new industry are still figuring out the best way to sink seaweed in order for the carbon to be sequestered. This process may be costly, and that funding could be better spent developing technology that could remove carbon on a larger scale. It is also possible that farming seaweed could have unintended consequences or risks for shipping, fishing, or ocean wildlife.
One major criticism of seaweed cultivation for carbon removal is that it cannot be scaled to the level required to meet the need. The average square kilometer of seaweed can sequester more than a thousand metric tons of carbon dioxide. The Sierra Club found that this could potentially scale up to offset carbon produced by the aquaculture industry (300,000 metric tons per year), though this doesn’t begin to make a dent in the goals in the Paris Climate Accords. Other studies have found seaweed to have larger scale potential, including Energy Futures Initiative estimate that kelp could remove one to nine billion metric tons of carbon dioxide per year. Existing uses of the ocean such as shipping may prevent the ability to scale up, and scaling up too much could impact marine animals’ migration patterns. Because of all of this, seaweed farming on its own is not the solution to meet global carbon removal demand, but has potential as part of a suite of removal options.
Net Positive Environmental Impact?
Seaweed farming has promise. It’s not a silver bullet and further research and development is needed to test out the best ways to farm and sink seaweed. It could be costly and there are potential drawbacks to farming too much seaweed, but with its many positive impacts for both carbon removal and broader environmental and ecosystem concerns, it should be one among the many solutions to carbon removal.
 Gerretsen, Isabelle. “The Remarkable Power of Australian Kelp.” BBC Future Planet, April 14, 2021. Accessed October 2, 2021. https://www.bbc.com/future/article/20210406-how-kelp-can-help-solve-climate-change
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 Smith, Heather. “Can Farming Seaweed Put the Brakes on Climate Change?” Sierra Magazine, June 28, 2021. Accessed October 2, 2021. https://www.sierraclub.org/sierra/2021-2-summer/stress-test/can-farming-seaweed-put-brakes-climate-change
 Godin, Melissa. “The Ocean Farmers Trying to Save the World with Seaweed.” Time Magazine, September 4, 2020. Accessed October 2, 2021. https://time.com/5848994/seaweed-climate-change-solution/
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