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[post_content] => Carbon dioxide removal (CDR) is a term used to describe anthropogenic activities that directly or indirectly remove carbon dioxide (CO2) from the atmosphere and durably store it in geological, terrestrial, or ocean reservoirs, or in products. Marine carbon dioxide removal (mCDR) is a subset of CDR approaches that leverage the ocean to remove CO2 and/or store captured CO2 in ocean reservoirs.
Microalgae cultivation for carbon dioxide removal (CDR) is emerging as a potential solution to the climate crisis. Microalgae are fast-growing organisms that convert carbon dioxide (CO2) into biomass and various other organic compounds through photosynthesis. Microalgae play a critical role in the global carbon cycle, capable of fixing CO2 10 - 50 times more efficiently than terrestrial plants (Bhola et al., 2014). Proposed strategies to utilize microalgae for carbon dioxide removal take advantage of the physiology of microalgae and their role in the carbon cycle and seek to achieve long term (>100 years) sequestration and storage of carbon. The two primary strategies for microalgae CDR are:
- Open systems where the open ocean is directly manipulated to enhance biological production, capture atmospheric CO2, and export the captured carbon to the deep ocean. In open systems, CO2 fixation is facilitated by the addition of limiting macronutrients (e.g., phosphorus, nitrogen, silica) and/or micronutrients (e.g., iron) to the ocean’s surface to augment biological production (Williamson et al., 2012). Open system techniques accelerate natural processes already occurring in the ocean. Most approaches in the open ocean fall into the following two categories (some proposals that do not fit into these categories are also explored).
- Surface nutrient addition: the direct addition of nutrients (macro or micro) into ocean waters in situ to increase microalgal growth
- Nutrient upwelling: artificial upwelling of nutrient-rich deep ocean waters to the surface to increase microalgal growth
- Closed systems where inputs and growth conditions are controlled, and outputs (microalgae) are harvested within the confines of a pond or a photobioreactor. In closed systems, CO2 fixation is facilitated by the mixing of required inputs (sunlight, nutrients, CO2, water) and the introduction of microalgae culture with the intention of reproduction and continuous fixation in a contained system (Beal et al., 2018). This can be accomplished on shore in cultivation ponds or photobioreactors, or afloat in photobioreactors either stationary or towed at sea (Zhai et al., 2020; Kim et al., 2016; Zhu et al., 2017).
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- Onshore: encompasses more established methods of microalgae cultivation, including photobioreactors, cultivation ponds, and hybrid onshore configurations. In these systems, all inputs are tightly controlled and regulated, and outputs must be directly managed through either storage or utilization of byproducts. While cultivation techniques are well-established and show high technological readiness, storage and utilization pathways remain underdeveloped and scale is a major consideration. Social and environmental risks for closed onshore systems are easier to monitor and mitigate due to the controlled nature of the system.
- Offshore: includes floating photobioreactors (PBRs) that are incorporated into a floating platform which can be stationary or towed behind a ship. In these systems, cultivation occurs in the photobioreactor, inputs are regulated, and outputs can be actively managed or directed. While at sea, these photobioreactors operate much like their onshore counterparts to cultivate microalgae, however nutrients and energy are provided by the ocean water and wave action, respectively. After microalgae are cultivated, they can be sunk into the deep ocean for sequestration or hauled to shore to be used as biomass. This is an area that has garnered much attention in startup communities (see this Y Combinator request for startups), however, little is available about the technologies in the open-sourced or peer reviewed literature.
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Regardless of approach or technology, there are two fundamental questions that make up the “CDR Potential” for a given pathway:
1) How much carbon can this approach sequester? 2) How long can it stay sequestered?
How much carbon can be sequestered?
- Carbon fixation rates and storage capacity of the microalgae species
- The capacity of microalgae to fix carbon differs across species and selecting appropriate species for different approaches remains an area of study. Genetic modification of carbon fixation rates and carbon storage capacity may expand the CDR potential for microalgae (Li et al., 2022).
- Scalability of the approach (for example, offshore cultivation has fewer spatial imitations than onshore cultivation)
- The expense of acquiring, transporting, and delivering nutrients, as well as the bioavailability of those nutrients, and the resulting carbon-to-nutrient ratio in the microalgae
- Additional considerations for closed systems include:
- Harvesting Considerations: The energy necessary for harvesting algae from cultivation set-ups (e.g., raceway ponds) can be an impediment to scaling. Current estimates from the US Department of Energy cite energy usage as ~1.4 kWh/m3, and high capital costs, ~$152,000/million gallons per day. Automated harvesters, such as the Zobi Harvester, have the potential to cut time and costs significantly, using less than 0.14 kwh/m3 and a capital cost of less than $106,000 per million gallons per day of capacity, unlocking harvesting barriers (Hazlebeck & Rickman, 2019). Utilizing gravity-based systems is another way of increasing energy efficiency for harvesting (Muylaert et al., 2017).
- Planktonic Cultivation vs Biofilms: Microalgae can be cultivated in two forms: planktonic or on biofilms. Planktonic microalgae are suspended in water and are highly diluted (less than 1%). Planktonic microalgae have been more extensively studied and can be cultivated in photobioreactors or ponds (Morales et al., 2020). Biofilms are aggregates of microorganisms attached to a surface and are much more concentrated than planktonic cultivation. The areal productivity for biofilms of microalgae is about two-fold the one for planktonic microalgae (Morales et al., 2020). New techniques with biofilms are in development (Mantzorou & Ververidis, 2018).
How durable is the carbon sequestration?
- Deep ocean: wherein microalgae, and their embedded carbon, cultivated via ocean fertilization or on land in photobioreactors or ponds are stored in the ocean for long-term storage. If purposely placed or injected into the water column at depth (>1,000 meters), many parts of the global ocean can offer 100 to 1,000 years-scale permanence. Sequestration durability is reduced to 10 to 100 years-scale for microalgae participating in the biological carbon pump due to high rates of remineralization in the upper ocean and during transit to the deep ocean as microalgae are grazed or decompose. There is extensive basin-scale variability in sequestration durability (Siegel et al., 2021). Areas of the ocean best suited to long carbon storage are places where surface waters and sinking matter can reach depths greater than 1,000 meters. The Southern Ocean south of the biogeochemical divide separating the Antarctic from the sub-Antarctic would be one such suitable location as well as much of the North Pacific (Siegel et al., 2021). Findings also suggest the North Atlantic and North Pacific oceans have the greatest carbon storage potential, while subtropical oceans have the least (Nowicki et al., 2022). Continued thorough measurements and models are needed to quantify the durability of sequestration for any given site, accounting for the fact that durability is likely best defined as a probability distribution given the various transit times of water masses.
- A number of large-scale campaigns are underway to improve our understanding of deep ocean carbon storage. These include EXPORTS (USA), COMICS (UK), and ONCE (China). Also note work being done to remediate harmful algal blooms and the potential applicability of findings on the efficacy of sinking algal biomass to mCDR research (see BlueGreen Water Technologies as an example).
- In addition, there are a number of studies underway to investigate ways to accelerate deep ocean carbon storage, among them:
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- Investigating Carbon Storage in Microalgae Polysaccharides: Scientists at the MARUM MPG Bridge Group Marine Glycobiology recently won the European Research Council’s Consolidator Grant to research carbon storage in marine algal polysaccharides and their role in the marine carbon cycle.
- Work from Mukul Sharma’s lab at Dartmouth College is investigating the use of clay minerals to enhance the removal of carbon from the euphotic zone and sequester it in the deep ocean (Bates et al., 2019). The principal idea behind this research is the formation of clay-gel hybrids when clay comes into contact with dissolved organic matter produced by microalgae and bacteria. These hybrids may facilitate the conversion of dissolved organic matter to particulate organic matter and rapid export out of the mixed layer. While clay additions are very underexplored in open ocean environments, they have long been recognized to interact with, and flocculate, in the presence of microalgae (Avnimelech et al., 1982; Chen et al., 2018).
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- Long-lived bioproducts: wherein carbon sequestered in microalgae is incorporated into products such as bioplastics for long-term storage.
- Biochar: Microalgal biomass can be processed via pyrolysis, gasification, or hydrothermal carbonization and turned into biochar. Biochar is a carbon-rich product that can be used in soils for agriculture (helping to prevent leaching of pesticides and nutrients) or as absorbents in air/water treatments for pollutant removal (Bi & He, 2022; Lee et al., 2020; Wang et al., 2023).
- Burial & land-based sequestration: Algal biomass that is sufficiently salty, dry, acidic, and rich in natural preservatives can be stored on land (buried) for long-term sequestration (OpenAir, 2022).
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Nutrient Fertilization
CDR Potential: >1 Gt CO2/year (NASEM, 2022; GESAMP, 2019), 0.1 – 1.0+ Gt CO2/year (NOAA, 2023) Technology Readiness: Field studies still necessary to determine fate of carbon, net carbon sequestration, and sequestration durability {{4}}{{5}} Nutrient fertilization refers to the addition of micronutrients (e.g., iron) and/or macronutrients (e.g., phosphorous, nitrogen, silica) to the ocean surface to increase photosynthesis by marine phytoplankton and, in turn, accelerate the uptake of carbon dioxide from seawater and enhance the transfer of organic carbon down the water column for sequestration. Note that there is a larger research focus on micronutrient fertilization (e.g., iron) because less nutrient is needed to sequester the same amount of carbon, making it more financially feasible and scalable. While increased photosynthetic uptake of CO2 via ocean nutrient fertilization has been well studied and documented for decades, the transfer of carbon from the atmosphere to the deep ocean resulting in sequestration is a challenge to measure, and to date has not been effectively demonstrated for a deliberately perturbed system (NASEM, 2022). Long-term sequestration depends on a variety of factors including location, export depth, and the remineralization rates of the sinking particles, all of which need additional research. The ultimate CDR potential of large-scale microalgal cultivation and sequestration in the open ocean with nutrient fertilization is currently difficult to determine, in large part because many original scientific studies were not designed or well suited to measure carbon sequestration efficacy or durability (Buesseler, et al., 2008). A broad review suggests that cultivating and sequestering microalgae could be scaled to 3.67 Gt CO2 equivalent (1 Gt of carbon) removed per year (GESAMP, 2019), however, in practice CDR may vary based on a variety of factors including:- The depth of remineralization for carbon, iron, and other macronutrients (NASEM, 2022).
- Factors affecting carbon sequestration that remain uncertain (NASEM, 2022):
- Net primary productivity in the vicinity of nutrient fertilization and downstream (to address issues associated with “nutrient robbing”).
- Efficiency of export of materials out of the euphotic zone, related to the attenuation of the particle flux
- Ratio of iron to carbon (Fe:C) in exported materials and how that ratio changes with depth
- Ecosystem / trophic level interactions
- The effectiveness of particular methods of delivering nutrients
- Pulse (one-time) versus continuous (repeated) experiments will likely change carbon capture efficiency
- Field-trials have yet to observe full growth cycles of microalgae including the bloom demise
- Artificial iron fertilization: The first observations of a relationship between iron and atmospheric CO2 came from geological records that revealed a correlation between CO2 in ice cores and iron rich dust (Martin et al., 1990). John Martin conducted pioneering work in the late 1980s to identify iron-limited regions of the ocean. The next decade (1993 – 2004) was spent executing studies in the Equatorial Pacific, Southern Ocean, Subarctic North Pacific, and Subarctic North Atlantic to explicitly examine the primary biological response of adding iron to surface waters. What resulted were thirteen studies in the open ocean accompanied by decades of analysis (Yoon et al., 2018), rendering artificial iron fertilization the most studied and well-understood approach in this road map. The application of iron to the ocean surface to investigate the relationship between iron limitation and phytoplankton growth suggests potentially high global capacity for iron fertilization to result in gigaton scale carbon dioxide sequestration (Martin et al., 1988; Morel & Price, 2003; ExOIS, 2022) and has led scientists to look to iron as a strategy to enhance the ocean’s biological carbon pump (Martin et al., 1990; Martin & Fitzwater, 1988). Most of the open ocean experiments conducted to date were largely focused on the immediate biological response to added iron in the form of a microalgae bloom and not the geochemical response (in the form of carbon fluxes), thus there is limited knowledge on the efficacy of this technique for net carbon dioxide removal. However, there are a handful of groups around the globe currently investigating the fate of carbon from net primary production. In addition to the efficacy of such methods, biogeochemical and ecological impacts remain unknown. A 2022 whitepaper by ExOIS (Exploring Ocean Iron Solutions) lays out a number of questions that remain to be answered by science including: What controls the efficacy and durability of ocean iron fertilization as a CDR strategy? How can ocean iron fertilization efficacy be accurately and efficiently monitored and verified? What are the intended and unintended ecological consequences of ocean iron fertilization and how can they be mitigated?
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- Engineered nanoparticles: Babakhani et al. (2021) propose the application of engineered nanoparticles in addition to iron fertilization in an attempt to enhance phytoplankton growth and possibly mitigate environmental risks posed by iron fertilization (e.g., nutrient robbing). Here, the goal is for the engineered nanoparticles to control the rate of nutrient release. Nanoparticles may be more expensive to deploy but may also be more effective at CDR. Focused field trials of engineered nanoparticles with artificial ocean fertilization are still needed to fully understand the impacts and efficacy of this technique.
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- Triggering the formation of marine snow: The GEA275 Project (Croatia) is investigating if adding iron chelates to high-nitrate, low-chlorophyll regions of the ocean can induce the formation of marine snow (organic detritus) for carbon removal and storage in the deep sea. Unlike other forms of iron fertilization, this approach does not aim to stimulate phytoplankton growth but rather to accelerate the release of extracellular organic carbon by existing communities of phytoplankton and heterotrophic bacteria.
- Macronutrient fertilization: Compared to iron fertilization, macronutrient fertilization has received less attention from the scientific community (but note Harrison 2017), with one clear disadvantage of this method being that larger quantities of nutrient material are needed per ton of carbon removal due to the higher cellular ratios of nitrogen and phosphorus to carbon (as compared to iron to carbon). However, ideal locations for macronutrient fertilization (low-nutrient, low-chlorophyll) may be more accessible than hard-to-reach locations ideal for iron fertilization, such as the Southern Ocean. In general, macronutrient fertilization presents general concerns around acquiring sufficient quantities of nutrients (some of which are nonrenewable, like phosphate), ecosystem impacts, and the fate of carbon once sequestered in phytoplankton. More work is needed to better understand macronutrient fertilization’s potential as a scalable CDR technique (NASEM, 2022).
Artificial Upwelling
CDR Potential: <0.1 Gt CO2/year. There is low confidence that artificial upwelling will be effective, durable, or scalable for CDR (NASEM, 2022) Technology Readiness: The technology necessary to conduct field trials is not ready for deployment (NASEM, 2022). Artificial upwelling, the pumping of nutrient rich water to the surface for increased photosynthetic activity, has been proposed as a mechanism by which to remove atmospheric carbon dioxide. In general, the overall CDR potential of artificial upwelling is thought to be low because of the coincident upwelling of high CO2 water alongside nutrients and the potential for off gassing. Off gassing of upwelled high CO2 deep water from the ocean to the atmosphere is anticipated to offset some or all the carbon sequestration supported by the introduction of new nutrients into the surface ocean. The NASEM Report (2022) on ocean-based carbon dioxide removal estimated that artificial upwelling / artificial downwelling projects could remove and sequester between 0.1 and 1.0 gigatons of atmospheric carbon dioxide per year, noting however, that estimates are limited to modeling studies and there exists no proof of concept that artificial upwelling could sequester carbon below the pycnocline. A 2022 modelling study of artificial upwelling systems with current technology estimated global potential for carbon dioxide removal using microalgae was less than 50 megatons (0.05 gigatons) of carbon dioxide annually (Koweek, 2021). Pilot-scale field trials that examine carbon flux are needed to assess potential efficacy of artificial upwelling as a CDR approach. Other barriers to this technology include high costs of energy, construction, and maintenance, and a 2016 review paper by Pan et al. found that while devices have been successfully deployed in the field for months at a time, they pose a significant disturbance to ecosystems which limits scaling potential as well as introducing many unknown ecosystem risks.Floating Photobioreactors
CDR Potential: unknown Technology Readiness: Many designs and configurations have been proposed, but more field trials are needed to assess carbon capture efficiency and scalability, as well as address the issue of carbon supply. Floating photobioreactors are systems for cultivating microalgae that are either stationary or towed behind ships in the open ocean. These systems, while still in early stages of development, show great potential of efficient microalgal production with low manufacturing and operating costs. This is primarily attributed to lower fabrication, operating, and maintenance costs than conventional cultivation systems, free wave energy to provide mixing, and nutrients, space, and temperature controlled by the surrounding water (Zhu et al., 2020). Several designs have been proposed which effectively incorporate photobioreactors as floating platforms towed behind ships. These photobioreactors are powered by wave energy and incorporate nutrients from the ocean water as inputs into the microalgal cultivation (Zhai et al., 2020; Kim et al., 2016; Zhu et al., 2018). Currently, the biggest challenge to commercialization for floating photobioreactors technology is carbon supply which is typically supplied by aerating CO2-enriched air and does not represent a carbon negative pathway (but rather a carbon neutral pathway). One example of past work done in this field is the NASA Offshore Membrane Enclosures for Growing Algae (OMEGA) Project. This project deployed plastic enclosures out in the water with photobioreactors incorporating semi permeable membranes that allow for osmosis from saltwater to freshwater and allowing the water to provide cooling and mixing from wave action, avoiding land costs and incorporating wastewater rich in nutrients and CO2. Such technology could be adapted in future iterations to be towed behind ships.- Combining cultivation with wastewater treatment: Wastewater is a nutrient-rich medium that has been explored as a nutrient source for microalgae cultivation {{26}}. Wastewater is rich in nitrogen, phosphorous, heavy metals, etc., which are often costly and energy-intensive to remove through traditional methods {{27}}. Many species of microalgae can remove these compounds by accumulating and/or using them in their cells. One challenge in this approach is providing microalgae with enough CO2 for optimal growth. There is potential for wastewater treatment to be paired with onshore cultivation systems such as raceway ponds or with offshore systems such as photobioreactors, however more research is needed to assess the feasibility of such set-ups. Most studies into coupling wastewater treatment with microalgae have looked at end products such as biofuels and not the permanent removal of carbon dioxide. As such, there is limited data on the actual carbon dioxide removal potential of this approach. While closed microalgae cultivation is widely considered to be an economically non-viable way to make fuels {{28}}{{29}}, it may be viable for CDR purposes.
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- Current Projects: Algae Systems (US) grows microalgae in bags of disinfected wastewater and CO2. The bags are deployed offshore in Mobile Bay, Alabama, and the combination of wave energy and sun create the necessary conditions for algae to grow. Currently, the algae are harvested and used for diesel and jet fuel, while the water is cleaned for re-use. The plant is currently at demo-scale and treats 40,000 gallons of wastewater per acre per day.
Cultivation Ponds
CDR Potential: Largely unknown, Brilliant Planet projects 5 Gt CO2/year (OpenAir, 2022) Technology Readiness: Techniques and methods are well studied, and many are well established (though very few have been intended for CDR). Raceway ponds are largely ready to be scaled. Onshore ponds in which microalgae is cultivated through controlled inputs of water and nutrients are the most established method of cultivating microalgae. More frequently, cultivation ponds are used to grow microalgae for end uses other than carbon removal, such as for high value bioproducts for use in cosmetics, food, and feed. Recently, there has been growing interest in using seawater to grow microalgae on land and sequester the carbon as a means of reducing atmospheric CO2. While the technology for growing microalgae on land is relatively well developed, questions remain around scalability due to many factors like competition with other land-uses/land-users and the cost of water and energy. Although closed microalgae cultivation is considered an economically non-viable way to make biofuel (Lane, 2022), these same barriers may not apply to CDR where the “final product” has an entirely different value.- Current Projects: Brilliant Planet (London) began growing microalgae in 2013 on the shores of St Helena, South Africa and now have a thirty-thousand square meter production facility in the coastal desert of Morocco which has been operating for over five years. Their systems use seawater to cultivate microalgae in large ponds and are monitored with high-frequency satellites. Permanent carbon sequestration is achieved by burying resulting biomass in ultra-dry desert landfills and sealing it with a geomembrane liner (OpenAir, 2022).
Microalgae-based Bioenergy for Carbon Capture and Storage (MBECCS / ABECCS)
CDR Potential: unknown Technology Readiness: Early stages of development Microalgae production can be paired with ‘bioenergy with carbon capture and storage’ (BECCS) wherein microalgae is used as the source of bioenergy and its associated carbon is sequestered for long-term storage. Traditionally, BECCS takes terrestrial plants that absorb atmospheric CO2 via photosynthesis and then extracts the energy embedded in the biomass while the resulting CO2 is captured and stored. Microalgae are an intriguing substitution for terrestrial plants due to their high photosynthetic efficiencies. Even et al. (2022) models the firing of microalgae grown with only atmospheric CO2 and shows that MBECCS uses four times less cultivation area than BECCS. If this method can become cost-effective, it would increase the scalability of bioenergy with carbon capture and storage by decoupling it from land use. Another way of pairing microalgae with BECCS is by injecting the CO2 captured through traditional BECCS into microalgae ponds to increase productivity. Beal et al. (2018a) modeled a system that paired a 121-hectare algae facility with a 2,680-hectare eucalyptus forest for algae-based bioenergy with carbon capture and storage (ABECCS), sequestering 29,600 t of CO2 per year. Theoretically, the carbon captured by the microalgae could be durably sequestered in the ocean, however, it should be noted that in these models, microalgae were used for high value bioproducts and may not count as CDR.- Current Projects: The Johnson Lab at the Duke Nicholas School of the Environment was awarded a grant for a pilot demonstration of carbon capture/storage technology based on ABECCS. The project uses a combined system that generates CO2 from forest products (bark/sawdust) and then uses that CO2 to grow algae for carbon sequestration in valuable bioproducts. Preliminary analysis of this process shows it to be carbon negative and economically viable.
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[post_content] => Manipulating microalgae at the scale necessary for meaningful carbon removal brings a host of known and unknown environmental risks and co-benefits. This is true regardless of the approach used or where the intervention is located. These risks must be weighed against the risks of no action (i.e., continued ocean acidification, warming, sea-level rise, etc.).
General Risks of Open Systems
Ocean fertilization and artificial upwelling are, in part, characterized by intentionally perturbing the natural ecosystem to encourage an increase of photosynthesis and the production of organic matter. Approaches that take place in the open ocean will very likely impact the surrounding ecosystems and ecology, including biological, chemical, and physical changes. As such, these disturbances will very likely change species composition and biodiversity. Other downstream impacts include potential for ocean acidification, hypoxia, the production of greenhouse gases, and mid-water oxygen depletion. Ocean fertilization and artificial upwelling share many of the same potential environmental impacts (risks and co-benefits) with a key difference being that artificial upwelling also affects the ocean’s density field and sea surface temperature, and ecological shifts would likely result from the influx of cold, nutrient-rich waters to the ocean surface (NASEM, 2022). While these potential impacts have either been observed from models or during small-scale field experiments, more controlled field trials are necessary for a better characterization of environmental impacts from artificial upwelling.Harmful Algal Blooms
One of the most prominent concerns with artificial iron fertilization is the possibility that it will increase the abundance of Pseudonitzschia, a genus of diatom that is known to produce the neurotoxin domoic acid, leading to a harmful algal bloom (HAB). However, there is not data that suggest significantly higher levels of domoic acid after an artificial iron fertilization event (Marchetti et al., 2009; Trick et al., 2010; Silver et al., 2010). While it’s possible that HABs may occur on land in pond cultivation systems, risks from contained systems would likely be far easier to manage and control.Land-Use
An obvious difference between onshore and offshore approaches is land use. Offshore methods of cultivating microalgal growth require no land, although will likely face barriers in the form of permitting and governance. Onshore cultivation methods such as ponds will require vast swaths of land to scale meaningfully. This presents a number of environmental impacts including land use change and the energy required to clear areas and build and operate facilities. All these impacts will need to be fully considered when assessing true net carbon removal as well as tolerance for environmental change. Onshore cultivation may also pose a risk to coastal habitats from spills, leakage, and ruptures.Summary Table of Potential Impacts
Below is table with a summary of some of the possible risks and co-benefits associated with multiple approaches as well as an estimate of their likelihood of occurring and the severity of resulting consequences. It is important to note that environmental risks likely vary greatly across scales. For example, a pilot-scale experiment likely brings about substantially lower risks and less severe consequences than a commercial operation. [post_title] => Environmental Impacts [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => environmental-impacts [to_ping] => [pinged] => [post_modified] => 2024-05-03 15:07:20 [post_modified_gmt] => 2024-05-03 15:07:20 [post_content_filtered] => [post_parent] => 3575 [guid] => https://www2.oceanvisions.org/?page_id=3643 [menu_order] => 3 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )WP_Post Object
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[post_content] => As with any new technology or innovation, there exist known and unknown social risks as well as potential co-benefits from microalgae CDR. It is critical that these risks and co-benefits are considered with relevant stakeholders and groups who would be impacted throughout the process of developing, testing, and deploying any proposed solution. Risk tolerance or aversion will vary between locations and communities with different communities viewing different risks as “acceptable” or “unacceptable” (Gannon & Hulme, 2018). Similarly, if there are economic (or other) co-benefits associated with a CDR approach, other risks may be seen as more acceptable. A holistic understanding of the short-term and long-term consequences of any approach will be necessary to adequately assess risks to society and culture. Any risks presented by microalgae-based CDR approaches must be weighed against the risk of “no-action”. Co-development of planning, testing, and deployment of any approach with all stakeholders may help to evaluate risks while maintaining transparency and equity. Adherence to a code of conduct that governs research activities will be critical to ensuring responsible research into any of these proposed approaches. Currently, work in this area is being led by the Aspen Institute (development of a code of conduct to govern ocean-based carbon dioxide removal research) and the American Geophysical Union (see an Ethical Framework for Climate Intervention and a response from scientists) (Loomis et al., 2022).
Social Risks
- Lack of public support & social license: There are currently low levels of public support and/or acceptance of CDR broadly in the United States and beyond, particularly with activities viewed as “geoengineering” or “climate engineering” (Carlisle et al., 2020; Cox et al., 2020). Other factors that may affect public support include perceptions of scale and perceptions of capture versus storage. These are areas that require more focused study to better understand. Early experiments are opportunities to adopt best practices and avoid mistakes when building public support and stakeholder engagement.
- Risk to culturally significant landscapes: CDR interventions that alter marine landscapes may lead to disruptions (e.g., native species populations) to cultural, spiritual, or cosmological landscapes and other non-tangible uses or relationships to the ocean and its inhabitants. The introduction of any new technology that interacts with natural ecosystems is likely to always be contested due to the diversity of ways in which people view the relationship between humans and the non-human world (Gannon & Hulme, 2018; Abate, 2016).
- Human health risks: Exposure to aerosolization of toxins from harmful algal blooms (HABs) have been known to cause respiratory symptoms in humans (Stewart et al., 2006). Although HABs have not been observed during artificial iron fertilization experiments, their occurrence is not impossible across many microalgae-based CDR approaches, including shore-based cultivation operations.
- Irreversible consequences: Negative impacts (environmental or social) of an approach that are irreversible may impact future generations, raising concerns regarding intergenerational justice (Cooley et al., 2022). This concern highlights the need for appropriate procedures so that any field trials that are approved and deployed do not have irreversible consequences.
- Decreased equity and social welfare due to financing: The creation of financing systems like carbon markets for forest carbon sequestration caused tensions around land rights and had implications on human rights and equity for Indigenous and forest-dependent communities (Cooley et al., 2022). These issues will likely vary greatly for closed systems on land, coastal closed systems, and open ocean/deep ocean commons.
- Location considerations: Just as there are different governance implications for activities occurring in exclusive economic zones versus the high seas, these geographical differences may also carry importance for social impacts. Environmental or ecological impacts from activities taking place in near-shore waters may have more direct social impacts than activities taking place in the open ocean.
- Food security: Microalgae-based interventions that risk disturbing food supply chains (e.g., fisheries) may threaten food security. This is especially relevant for communities that rely on the ocean for sustenance.
- Impacts on livelihoods from tourism and fisheries: Activities that use or interfere with near-shore environments and ecology may impact industries like tourism and fisheries, thus impacting livelihoods. This is particularly important in areas that depend heavily on these industries economically and/or are socioeconomically vulnerable in general (e.g., the Global South).
Social Co-Benefits
- Economic incentives: The various potential utilization pathways of microalgae could create avenues for wealth generation and emissions-free economic growth – namely economic incentives within existing carbon markets, preventing costly environmental disasters resulting from uncontrolled climate change, and converting a damaging waste product (CO2) into a value-added product (Daneshvar et al., 2022).
- Job creation: Economic value-addition is likely to also create jobs in new and existing industries in aquaculture and beyond (Mayo-Ramsay, 2010).
- Ownership and benefits accruing from uses of genetic resources: Many microalgae-based innovations bring with them a suite of potential biotech and genomic-based approaches. It will be important to understand when and how local benefits rights holders (e.g., coastal communities, Indigenous communities) can benefit from the use of marine-based genetic resources. This is an inherently complex subject that questions ownership of marine resources and is rich with justice and equity implications.
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[post_date] => 2023-02-13 16:27:30
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[post_content] => Governance considerations will vary across microalgae approaches based on where key activities take place (exclusive economic zones, high seas, on land, etc.) and on the nature of the activity (fertilization, pumping water, carbon injection, etc.). While robust governance around ocean-based carbon dioxide removal in general is lacking, there are existing laws, regulations, and policies that may be applicable to certain activities (see below). Governance will be multi-scale including local, regional, national, and international governance structures. International governance may be particularly relevant here as more recent global agreements assert the need for carbon dioxide removal and are explicitly supportive of carbon dioxide removal activities. Examples include the Glasgow Climate Pact and recent draft text prepared by UNFCCC (United Nations Framework Convention on Climate Change) at COP27 for carbon removal in Article VI of the Paris Agreement (source: Carbon Removals at COP). However, ocean-based CDR is not specifically referenced or supported and a number of international agreements and statements by international bodies could end up restricting ocean-based CDR. Also important is that, generally speaking, international law doesn’t bind private parties.
The Sabin Center for Climate Change Law at Columbia Law School is currently developing a set of model laws to facilitate responsible ocean CDR research in US waters. Presently, there is no legal framework in the United States specific to ocean CDR which can hinder research and development. Attempting to use existing environmental laws can fail to capture the unique environmental and social risks associated with ocean CDR. See the Sabin Center’s 2022 white papers “Removing Carbon Dioxide Through Artificial Upwelling and Downwelling: Legal Challenges and Opportunities” and “Removing Carbon Dioxide Though Ocean Fertilization: Legal Challenges and Opportunities” for specific legal considerations related to microalgae CDR.
Existing Governance Structures that May be Applicable to Microalgae for CDR
- United Nations Convention on the Law of the Sea (UNCLOS): Adopted/ratified by 167 countries and the European Union, UNCLOS defines countries’ rights and responsibilities in terms of use and management of offshore areas. Provisions that may be relevant to microalgae cultivation and/or sequestration in the open ocean include:
- Part XIII of UNCLOS which establishes rules for “marine scientific research”
- Part XII of UNCLOS which requires countries to “protect and preserve rare or fragile ecosystems as well as the habitat of depleted, threatened or endangered species and other forms of marine life” and includes a number of specific provisions on marine pollution from vessels, land-based sources, activities in the area, and dumping, among others. Without clear distinctions on what is or is not considered “pollution”, these provisions may be relevant for microalgae-based CDR interventions.
- Proelss (2022) investigates the United Nations Convention on the Law of the Sea and finds that although it covers ocean fertilization research stages, it does not apply to ocean fertilization for CDR, leaving the legality of ocean fertilization unclear under international law.
- Convention on Biological Diversity (CBD): Adopted in 1992, the CBD aims to protect biological diversity. 195 countries and the European Union have ratified it; the United States has signed but not ratified it. In 2008 the Conference of the Parties of the Convention on Biological Diversity recommended that ocean fertilization activities not take place until there exists a sufficient scientific basis to justify it. The term “ocean fertilization” was not defined. In 2010 a decision was made to regulate “geoengineering activities” such that no geoengineering activities take place that may impact biodiversity until there is a scientific basis to justify such actions. An exception is made for small-scale scientific experiments in controlled settings (the definition of “controlled settings” may prevent research in the open ocean) after thorough assessment and justification, though key terms in the exceptions for scientific experimentation are not defined, resulting in significant uncertainty as to when it will apply.
- London Protocol / London Convention: Adopted in 1972, this convention aimed to control all sources of human-caused pollution in the ocean, with a particular focus on the dumping of waste or other materials in the ocean. There is a lack of clarity and general disagreement concerning what the future of policy and governance application of ocean iron fertilization may look like, particularly with the precedent of the London Protocol, which has banned nonscientific application outright (Rohr, 2019). The London Protocol has not yet ruled on closed offshore systems and represents an opportunity to bring attention back to issues of ocean utilization for carbon dioxide removal.
- Amendment on Ocean CDR: This amendment, not yet entered into force, states: “Contracting Parties shall not allow the placement of matter into the sea from vessels, aircraft, platforms or other man-made structures at sea for marine geoengineering activities listed in annex 4 (an amendment that regulates the placement of matter into the ocean for marine geoengineering) unless the listing provides that the activity or the subcategory of an activity may be authorized under a permit.”
- Statement on Marine Geoengineering: In October of 2022, parties to the treaties which regulate marine dumping adopted a statement calling out the need for evaluation of four marine geoengineering techniques that have potential to mitigate the effects of climate change but could also threaten marine ecosystems. The four techniques given priority are: ocean alkalinity enhancement, macroalgae cultivation and sequestration (including artificial upwelling), marine cloud brightening, and microbubbles/reflective particles/materials. The London Protocol and London Convention Parties are conducting a technical and legal analysis to evaluate the next steps and future regulation. (See the International Maritime Organization’s briefing)
- GESAMP (Group of Experts on the Scientific Aspects of Marine Environmental Protection) Working Group 41: Ocean Interventions for Climate Change (formerly Marine Geoengineering): In early 2022, GESAMP’s Working Group 41 formally advised the London Protocol Parties to consider marine geoengineering techniques to list in the new annex 4 of the protocol. These geoengineering techniques are those that may assist in mitigating or reversing the impacts of climate change. Included in this list are approaches that utilize microalgae to sequester carbon for long-term storage. (Timeline of Ocean Fertilization under the London Protocol)
Other Considerations
- Creation of new frameworks: In many cases it may be most efficient and effective to create new frameworks that put controls on research to ensure it occurs in a safe and responsible way that aren’t unnecessarily restrictive or hindering.
- Modification of existing policy: Examine, and consider reforming, existing policies that have the potential to inhibit the research and development of this technology, e.g., the London Protocol.
- Scale considerations: Pilot-scale experiments will likely have different associated risks than full-scale implementation. This may translate into policy and governance frameworks that consider the scale of manipulation or experimentation as a critical variable.
- Government subsidies: Subsidies from the government could provide incentive to researchers as well as the funds necessary to accelerate research.
- Bias amongst approaches: How will the ability to monitor and verify impacts and efficacy of a particular approach influence support from governance and policy? An approach-neutral stance (with financing, policy etc.) will help ensure that all approaches are given an opportunity to reach their full potential.
- Resource competition for onshore cultivation: There is potential for competition for nutrients with traditional agriculture and other societal priorities. Although microalgae can be grown on marginal lands unsuitable for agriculture, land competition with human settlement, industrial processes, and other infrastructure may pose a challenge if microalgae production is scaled up significantly (Scott-Buechler, in preparation).
- Using existing frameworks for onshore cultivation: Onshore cultivation of microalgae may look similar to established aquaculture or desalination plant policies/laws and thus have a more straightforward path for research and development.
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- Measurement, reporting, and verification (MRV) procedures will need to be developed following advances in research and development. Advances in research and development will inform what parameters need to be monitored and verified, and how to do so. MRV protocols should include measurements of key ecological parameters as well as carbon fluxes to ensure that microalgae CDR activities do not exceed accepted limits of environmental impact.
- Life cycle analyses will need to be conducted for any approach that uses microalgae for CDR to determine the net carbon removal potential after accounting for process and embedded emissions.
- Social co-benefits are not well understood or identified. While research into social impacts is growing, there remain large uncertainties around the range of potential impacts that may result from large-scale environmental interventions. Integrating social risks and co-benefits into CDR research agendas may help this area of knowledge grow alongside the technical research and development.
- Environmental co-benefits have not been well studied or articulated across microalgae-based CDR methods (NASEM, 2022). Identifying and understanding the potential array of co-benefits may help offset other risks, both environmental and social, and aid in decisions around which methods are to be pursued further.
- Location and siting: Siting analyses are needed to identify optimal locations for microalgae CDR and address potential synergies and/or conflicts with other marine resource users (e.g., fisheries, renewable energy, etc.) (Map optimal locations for microalgae-based approaches and engage with interested and affected constituents)
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Open Ocean Systems
- Export and fate of carbon from net primary production in the upper ocean to understand sequestration efficacy and durability: A fundamental understanding of the export and fate of net primary production from the upper ocean is critical to any development, testing, or deployment of approaches that hope to accelerate this process. Currently a number of field campaigns are working on answering these questions, including EXPORTS (USA), COMICS (UK), and ONCE (China). In addition to these large campaigns focused on fundamental understanding of the biological carbon pump, these questions must be answered in the context of purposeful nutrient additions (Accelerate the design, permitting, and execution of the next generation of controlled field trials to answer questions specifically pertaining to carbon sequestration)
- Natural iron cycle / anthropogenic iron input: There is a lack of knowledge about the current state of iron cycling in the ocean system, particularly how much anthropogenic iron is already input into the system and what the spatially specific distribution of impacts are likely to be (Liu et al., 2022). Research must prioritize understanding inputs and refining existing iron-cycle models. This will be critical work for ocean iron chemistry models to measure future changes in anthropogenic iron loading. Future research must also seek to better understand natural and pre-existing anthropogenic analogs that may be analyzed as simulations of future ocean iron fertilization (Bach & Boyd, 2021; Weis et al., 2022). Analogs may include volcanic ash and wildfire ash deposits into ocean systems.
Closed Systems
- Harvesting efficiency: In the cultivation stage, harvesting microalgae from closed systems contributes to 20–30% of the total cost of microalgal biomass production, so opportunities to increase efficiency present the greatest opportunity for cost reductions through innovation (Singh & Ahluwalia, 2013). (Optimize and/or efficiently automate all approaches for scalability and economic feasibility)
- Strain optimization: The algal industry is still relatively small, and primarily optimizes for lipid and/or protein content in microalgae strains. More research is thus needed to identify ideal species, strains, and specific growth conditions to maximize microalgal CO2 uptake; and to estimate associated costs. (Optimize and/or efficiently automate all approaches for scalability and economic feasibility)
- Fertilizer efficiency: High fertilizer needs are likely to be the most substantial constraint on closed onshore cultivation systems (Huntley et al., 2015). Research is needed into options to maximize fertilizer recycling and other strategies to lessen fertilizer needs. (Optimize and/or efficiently automate all approaches for scalability and economic feasibility)
- Overall CDR potential: There exists virtually no information on overall CDR potential of closed offshore systems (e.g., towed photobioreactors). (Accelerate the design, permitting, and execution of the next generation of controlled field trials to answer questions specifically pertaining to carbon sequestration)
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[post_date] => 2023-02-06 21:54:37
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- Mapping interested and affected constituencies: It will be important to identify the diverse stakeholders for microalgae CDR, including producers, potential buyers for carbon removal, potential buyers for other useful co-products, and communities where projects may be sited. Understanding perceptions, needs, concerns, and opportunities across multiple stakeholder groups is necessary to scale microalgae-based CDR.
- Industry transitions: Microalgae is already cultivated around the world today but is done so for non-CDR purposes—primarily feeds and fuels. Analysis of industry willingness and needs for transitioning from CO2 reuse to CO2 removal could ease the creation of onshore microalgae CDR pathways, but more research is necessary to determine if this is possible and under what conditions.
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- For open ocean systems, under various conditions
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- Determine the effectiveness (including bioavailability) of nutrient delivery at supporting new primary production
- Determine the efficacy of export from the surface ocean into the deep ocean, and the associated estimates of carbon sequestration durability
- Determine the resulting air-sea fluxes of carbon dioxide and other greenhouse gases to quantify the additionality of the nutrient fertilization
- Characterize the environmental impacts, both intentional and unintentional, of any nutrient fertilization activity, including:
- Changes to upper ocean biology, chemistry, and physics (especially for artificial upwelling)
- Impacts to upper trophic levels and food web interactions
- Impacts to existing marine industries and resource needs (e.g., fisheries)
- For closed systems
- Demonstrate net negative carbon removal pathways in closed system cultivation
- Determine sequestration efficacy and durability from various carbon storage possibilities, including land-based burial, storage in the deep ocean, and storage on the seafloor
- Characterize the environmental impacts, both intentional and unintentional, of any cultivation and sequestration activity, including:
- Land-based impacts from onshore cultivation construction and operation
- Impacts from leakage or spill of onshore systems
- Impacts to other marine-based operations (e.g., fisheries)
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- Perform siting analyses to identify optimal locations for microalgae CDR that consider the suite of technical, economic, social, and political factors necessary for deployment, as well as potential conflicts and co-benefits with other marine industries (e.g., fisheries, renewable energy, etc.)
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- Develop tools and instruments to increase harvest efficiency for microalgae grown in contained systems
- Determine and/or develop optimal microalgae strains for maximally efficient CO2 uptake for various environments and settings
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- There has yet to be widespread adoption of a single code of conduct for CDR research, development, and deployment, although some organizations have proposed guidelines for the development of such a code (see American Geophysical Union and the Aspen Institute) or have an internal code of conduct to which they adhere (see Planetary).
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- Clear frameworks that allow for responsible field trials of microalgae-based CDR to take place on land, in coastal waters, and in the open ocean are critical to accelerate progress. Without such frameworks there is risk of inappropriate experimental siting and delays in moving research out of the lab and into the real world. Climate interventions are time sensitive and responsible research, development, and deployment relies on comprehensive, cohesive, and effective government structures.
Microalgae Cultivation and Carbon Sequestration
Microalgae-based techniques to capture and store carbon
About the Microalgae Road MapFirst-Order Priorities
Accelerate design, permitting, and execution of controlled field trialsMap optimal locations for microalgae-based approachesOptimize or automate approaches for scalability and feasibilityCreate and adopt of a code of conduct for responsible researchCreate frameworks that facilitate responsible field trials