Yves here. I do try to keep up, but I must confess to not having heard of kelp cultivation as a carbon capture strategy. I had assumed the article would be about the merits of kelp and seaweed as highly nutritious foods versus their cost of cultivatiion compared to other health-enthusiast-preferred greens, notably kale and spinach (if you are from the South, you know that collard rates, as does chard). As one might infer, kelp for carbon capture doesn’t work so well unless it is interred in some fashion. It turns out that garden variety burial does not suffice. This piece explains why really getting kelp or any biomass out of the carbon cycle is not trivial.
By Veronique Carignan, an environmental chemist and former academic researcher in chemical oceanography. She now works as an environmental activist and freelance climate journalist. Originally published at Undark
Champions ofthe kelp industry have made bold claims that farming the fast-growing seaweed will alleviate the climate crisis. But those claims are not substantiated by the science of how kelp removes and sequesters atmospheric carbon. Kelp farming is a Band-Aid solution to mitigating global climate change, pushed to the forefront by decades of insufficiently modifying human behavior to cut carbon emissions.
Instead, the United States has focused its efforts on strategies that are largely centered around carbon capture, which removes carbon dioxide from the atmosphere and from emission point sources such as large industrial facilities and power plants. Most of these carbon capture strategies are costly, complex to implement, and not well studied, whereas kelp farming is cheap and technologically simple, making it an appealing option for those looking to use carbon capture as a climate change mitigation strategy.
Like almost all plants, kelp removes carbon dioxide from the atmosphere via photosynthesis. As one of the fastest growing organisms in the world (some species can grow up to 2 feet per day), kelp gains biomass quickly and thus sequesters carbon quickly. Natural kelp forests capture 5.4 million tons of carbon dioxide annually and are worth an estimated $500 billion, including their value in the food and materials industries. But even more money likely lies in the unexploited coastal ocean suitable for growing kelp, which spans an area of around 18 million square miles. Given the space available for aquaculture and the tremendous value of kelp, it is no surprise that seaweed is one of the fastest growing components of global food production, increasing on average 8 percent per year.
Companies seeking to capitalize on the obvious value of kelp farming are using its supposed carbon sequestration potential as a hook to expand the practice, raise funds, or sell carbon credits. However, scientists have questionedwhether kelp farming acts to store carbon long term. Although kelp does absorb carbon dioxide through photosynthesis, the long-term sequestration of that carbon is limited by a process called the slow carbon cycle.
Global carbon cycling refers to the movement of carbon between the atmosphere, biosphere, ocean, and land. This cycling happens on two timescales: fast and slow. In the fast cycle, carbon is absorbed by plants and sequestered as organic matter. When plants die or are consumed (burned as biofuel, eaten, used as feed, or to make materials, for example), that carbon is usually released back into the atmosphere. This cycle takes years to decades and does not remove carbon from the atmosphere long term.
By contrast, the slow carbon cycle takes 100-200 million years and moves carbon from the atmosphere to rock material and fossil fuels. Carbon moved via the slow carbon cycle is considered truly “removed.” Note that burning fossil fuels (that is, roughly 300-million-year-old carbon) has been adding billions of tons of carbon dioxide annually to natural emissions from the respiration of organisms, disrupting the slow carbon cycle. That is why human perturbations to the carbon cycle have such dire and permanent consequences for the planet.
For kelp to be useful in storing carbon, it needs to be stored as part of the slow carbon cycle, which means kelp needs to be deposited in the deep ocean where it won’t interact with the atmosphere for centuries to millennia. That doesn’t happen if the kelp is being used as food, a biofuel, or in materials production because all those pathways lead to the carbon dioxide being emitted back to the atmosphere via the fast carbon cycle.
To solve this issue, some companies plan or purport to deliberately sink seaweed, thereby enhancing its long-term storage capacity. Then, they profit from this sequestration by selling carbon credits to companies with large carbon emissions. The repercussions of sinking millions of tons of kelp to the seafloor are unknown, but changing the nutrient balance of the deep sea is dangerous because organisms living there can be particularly vulnerable to shifts in things like pH and oxygen availability. What’s more, the technology required to achieve this will likely involve using fossil fuels. In fact, the potential environmental outlook for sinking seaweed is so bad that some scientists have called for a moratorium on the practice, but companies are charging ahead anyway.
For example, Maine-based Running Tide Technologies was the one of the world’s largest kelp-based carbon removal startups but failed to deliver on its promises, going out of business in 2024, only seven years after being founded. Running Tide raised $54 million in funding to grow kelp on flotation devices designed to sink to the deep ocean. When its plan became too costly and its proof of concept failed, the company instead sunk some 21,000 tons of wood chipsoff the coast of Iceland to fulfill the carbon credit promises it sold to large corporations, including Microsoft and Shopify.
Even if we ignore the many pitfalls and unknowns of farming kelp for carbon sequestration, we would need an enormous amount of space to sequester just a fraction of the carbon dioxide emitted each year. One analysis calculated that 300-foot-wide kelp farms running along 63 percent of all global coastlines would be needed to sequester 0.1 billion tons of carbon dioxide per year — a mere 2 percent of annual U.S. emissions.
Some supporters of kelp farming suggest that kelp should not be sunk but rather used to replace fossil-fuel dependent systems. There is potential in using kelp biofuel or kelp-based animal feed to reduce carbon emissions. However, farming kelp on a large scale for such purposes would have negative repercussions on ocean ecosystems and could actually exacerbate climate change. Shading from kelp reduces phytoplankton growth, which could reduce the efficiency of sinking kelp for carbon sequestration by 37 percent. Adding massive amounts of organic carbon to the deep ocean would deplete oxygen, shifting the nutrient balance of the deep ocean and of upwelling regions which supply global ocean fisheries. When kelp grows, it emits halocarbons, which are short-lived but highly potent greenhouse gases. Kelp farming is far from a green solution and puts our oceans at further risk of deterioration.
Ocean governance is notoriously relaxed and difficult to enforce, but the ocean is the primary regulator of the Earth’s climate. It is imperative that we take caution before undertaking global-scale modifications to the ocean’s delicate balance. Ultimately, efforts placed into changing human behavior and developing technologies to disentangle our global systems from their reliance on fossil fuels are far more valuable than working on temporary strategies that allow us to continue business as usual.
Kelp harvesting has a very long history. Wander anywhere along the western coast of Ireland and Scotland and you’ll see the remains of drying frames and processing factories (often in very remote areas) which were used up to the early 19th Century to produce soda ash, and later Iodine and other chemicals. It was also used to make soil – many fields in the west of Ireland were produced by mixing sand and seaweed, then covered with a very thin layer of precious topsoil in order to make the lazy beds needed for potato cultivation. Its not an exaggeration to say that in the 18th to 19th century millions of people depended directly or indirectly on kelp to keep food on the table.
Apart from food – various seaweeds associated with kelp forests are widely used in food processing, including bulking up cheap beefburgers Its also a potentially very useful source of animal feed. The main problem is that some species are very efficient at soaking up toxins, including arsenic (one reason why you shouldn’t eat too much kombu).
Surprisingly little is known of its ecology, specifically why kelp beds grow profusely in some parts of the ocean, while others are bare sand or rock. It seems to be related to a combination of water temperature (they prefer cooler waters), and nutrient enrichment. This seems to be the main reason that the many attempts to establish kelp forests have had very mixed results. Its complicated by the very wide range of seaweed species that falls under the general term ‘kelp’. Rising sea temperatures are wiping out kelp beds in many parts of the ocean, which is having a major impact on fisheries. However, it may be that they will be replaced by natural (or man-made) new kelp beds in the vast areas of northern Canada and Russia that are now becoming increasingly ice free. Hudson Bay alone has something like 300 million hectares of shallow waters with potential for use.
As the article points out (and is elaborated in depth in the excellent paper linked in the article – this is a must read for anyone interested in ocean based carbon sequestration techniques), kelp forests can at best be only a minor direct contributor to sequestration, especially if somewhat stupidly the proposers are simply dumping the seaweed in deep water). However, as an integrated whole, there can be no question that there are potentially a lot of benefits for growing kelp, especially in areas degraded by existing dredging techniques (which are astonishingly destructive – we just don’t talk about it much because we can’t see the damage to seafloor ecosystems). Or put another way, if you are worried about the health of our seas, don’t eat scallops.
Or only eat sustainably dive-harvested scallops….
I have never heard of kelp as a viable carbon sequestration method. It will have more effect as a cattle feed additive to reduce cow burps.
My in-laws’ friends were pioneers of kelp farming (off ropes hung in the water column), first away in Vancouver and then back in Ireland, but for food and fine chemical purposes.
The history of kelp in agriculture also extends to Southwest England, particularly Scilly, and the Channel Islands. I suspect Wales has the same history too, probably the whole Atlantic coast if Europe frankly. From memory, in Jersey the kelp is called “vraic” (a cognate of “wrack”).
My California coastal town once informed tourists with signs in the sand that kelp on the beach was “beach wrack’ and a normal, environmentally useful happenstance. As the number of tourists has overwhelmed beach acreage the ‘wrack’ is now removed by tractor-pulled sand screens. The beach signs are no longer—but we’re still a certified ‘Tree City’.
Environmentalism is easily inconvenienced!
https://english.news.cn/20240516/b4fdf114d8114c5d9122aaa95e3f3ccb/c.html
May 16, 2024
Booming seafood industry mirrors China’s “blue granary” development *
FUZHOU — In a coastal county in east China’s Fujian Province, fishermen are fully immersed in harvesting kelp, while trucks loaded with fresh seaweed bustle back and forth.
“This year’s kelp harvest season started after the Spring Festival and is nearing its end,” said Lin Zhexian, a 61-year-old fisherman in Lianjiang County, adding that he set off around midnight, collecting nearly 5.4 tonnes of fresh kelp in a single day.
Spanning a sea area of 3,112 square km, Lianjiang saw its output of aquatic products, including seaweed and abalone, reach nearly 1.29 million tonnes in 2023, with a total output value of around 30.69 billion yuan (about 4.32 billion U.S. dollars).
The booming seafood industry exemplifies Fujian’s efforts to promote its marine economy. Situated by the East China Sea, the province boasts a sea area of 136,000 square km, a rugged coastline and numerous bays and islands, making it an optimal place for developing mariculture.
In China’s “No. 1 central document” for 2023, the Chinese government called for accelerating the development of deep-sea and far-sea mariculture as it makes efforts to safeguard the country’s food security by stocking its “blue granary.”
* https://onlinelibrary.wiley.com/doi/10.1111/raq.12524 …
https://onlinelibrary.wiley.com/doi/10.1111/raq.12524
February 12, 2021
Kelp aquaculture in China: a retrospective and future prospects
https://onlinelibrary.wiley.com/doi/full/10.1111/raq.12871
November 1, 2023
Kelp breeding in China: Challenges and opportunities for solutions
God Bless Fuzhou and the rice scientists at FAFU. The pond in the center of campus was lovely. A charming young lass fetched me a lotus pod for snacking. Beautiful plants… and an even more beautiful girl.
I’m starting to write like amfortas…
I’ve seen it promoted as a supplement or even replacement for lobstering. It can use the boats, the seasons don’t overlap, and the cap ex is cheaper than lobster pots and lines.
The environmental impact has to be better than fish farms, so a net win there.
Kelp for food, kelp for fertilizer. People have mentioned the need for longest-term recapture and reuse/recycling of those nutrients which slowly flow off the ” land” into the “sea”. Kelp would be a way to recapture those nutrients and move them back onto the land.
Kelp shouldn’t need concepts of “carbon sequestration” to justify its beneficial use in various circular biocarbon bionutrient biocycles.
Seek kelp!
There is a cream for that
https://x.com/OFalafel/status/1240596787108499456
There’s an app for that.
In California, reconstituted kelp forests are useful in getting otters to eat the sea urchins that destroy the kelp, but I’m not sure those qualify as farms. Kelp forests also create an ecosystem that some fish can thrive in.
Another significant experiment, is that adding certain kelps to cow feed, significantly reduces the methane produced in cattle, when they “pass gas”. That may be a far more useful contribution to lowering greenhouse gases than, the carbon sink angle, but farmers will have to be convinced to use it. That would likely require legislation and government subsidies (and the taxes to fund it), to get it to scale.
Kelp powder can be used to replace 20% of cement in concrete.
It seems kind of stupid to grow kelp to sink in the ocean when they could just as easily collect some of the millions of tons of sargasso from beaches in Mexico, Central America, and the Caribbean, and accomplished the same thing with the added benefit of cleaning up those beaches.
In my youth, I spent considerable time diving for abalone in California. Abalone thrive on kelp, as do sea urchins, which are considered a delicacy in Japan for uni sushi (the edible gonads are spread on rice). Cultivated abalone have to be fed kelp, so harvesting kelp is integral to production. I also harvested sea palm in Mendocino, helping a friend who made a business of harvesting, drying, and packaging sea palm for local ‘health food’ stores.
This coastal bounty has a fragile balance and is easily disrupted. When divers overfished abalone, sea urchins filled in to the niche. Due to different feeding methods, they tended to wipe out the kelp. Ironically, Japanese tastes drove the elimination of abalone, then Japanese tastes for uni will probably lead to sea urchin’s destruction. The result will be an overabundance of kelp, which is when humans will step in with vain hopes of illusive carbon capture.
For many years I have studied organic farming and gardening, and have practiced both. Studies (by organic enthusiasts) show that a healthy soil is loaded with carbon, while soil found in industrial, chemical-based agriculture is bereft of carbon. So, just as planting trees is a carbon sink, transitioning to organic farming and gardening is, too. Studies also show that organic methods can produce the quantity of food our world needs, especially as if done locally.
Small but vital changes in life ways can do more to reduce carbon emissions than any fanciful carbon-capture or even the industrialized ‘Green New Deal’, although the residents of the rich Global North have become accustomed to their ways. The problem is that those ways will kill them.