The Role of Kelp Forests in Carbon Dioxide Removal and Climate Mitigation

The Role of Kelp Forests in Carbon Dioxide Removal and Climate Mitigation


Aaron Eger

Board Of Directors Program Director FounderKelp Forest Alliance

Albert Pessarrodona

Marine EcologistUniversity Of Western Australia Oceans Institute And School Of Biological Sciences

Catriona L. Hurd

ProfessorUniversity Of Tasmania Institute Of Marine And Antarctic Studies

Melissa Ward

Project DeveloperSilvestrum Climate Associates

With Support From

This webinar and report was made possible by support form SeaTrees and the Sustainable Surf Foundation

Key Takeaways

  • We need to remove CO2 from the atmosphere in addition to drastically reducing emissions.

  • Kelp forests are one of the most widely distributed marine primary producers that undoubtedly remove or sequester some amount of CO2 from the atmosphere. The amount will vary from place to place and over time.

  • For the purposes of climate change mitigation and carbon credits, we need to establish the long-term removal of CO2 from the atmosphere and its safe storage for >100 years.

  • Two sequential processes must be measured to quantify carbon dioxide removal or sequestration 1) The amount of kelp carbon that is stored long term and 2) The amount of CO2 that the kelp forest removed from the atmosphere.

  • A carbon methodology describes how carbon removal projects operate and quantify CDR, including robust reporting, monitoring, and verification (MRV) frameworks that are needed for future voluntary carbon markets and other climate change mitigation frameworks.

  • A kelp forest carbon methodology must be cost-effective, scientifically robust, and transparent.

  • Determining the exact quantity of carbon removed from the atmosphere by kelp forests is technically feasible but complex. Currently, linking specific actions (e.g., conservation, restoration) to specific amounts of CO2 removed has not been effectively done.

  • Once a methodology is established, making cost-effective, easy-to-use, and publicly available models of kelp CO2 removal potential should be a priority to relieve burdens of early project development and democratize access.

  • As efforts to increase blue carbon financing through the voluntary carbon market expand, it is vital that projects generate positive outcomes for people, nature, and climate.

  • Biodiversity credits are a promising avenue for kelp forest conservation finance. They are easier to attribute to kelp forests, quantify, verify, and may attract a higher per unit price than carbon credits. However the market mechanisms of biodiversity credits are poorly defined and generating low quality credits risks damaging the reputation of the field.

  • Carbon and-or biodiversity credits will likely be a useful tool in restoring and protecting kelp forests. While promising, it is unlikely that these credits will entirely fund kelp forest conservation efforts and they must be paired with other forms of conservation finance.

"Kelp forests are neither ‘the silver bullet to climate’ nor ‘completely ineffective at removing or sequestering carbon’. The truth lies somewhere in between."

Key Definitions

For the simplicity, this report will refer to both carbon sequestration and carbon dioxide removal as “carbon dioxide removal”, the only difference being that one is the result of a direct human intervention which is necessary to produce a carbon credit*.

Carbon fixation

Carbon storage

Carbon sequestration - long term

Carbon dioxide removal (CDR)

Frequently Asked Questions

The Most Asked Questions About Kelp Forests, Carbon Removal, and Biodiversity Credits

Kelp Forests and Carbon Cycling

Kelp Forests

Kelp forests, a type of marine brown alga, thrive in both the intertidal and subtidal zones, anchoring to rocky and hard substrates. Unlike terrestrial plants, kelps lack roots though they also showcase a remarkable diversity, ranging from small, shrub-like varieties to vast canopies that can stretch beyond 30 meters in length. This incredible adaptability not only allows kelp to dominate its marine environment but also contributes to the unique and complex habitats that support a wide array of marine biodiversity1.

Global models estimate that kelp forests cover an estimated area between 1.4 to 1.8 million square kilometres2. However, direct observations from satellites, underwater surveys, and drones record ~0.1 million square kilometres, though this number is certainly an underestimate3. Regardless, kelp's ecological footprint is undeniably vast, blanketing roughly 25 to 36 percent of the world's coastlines4. This expansive distribution underpins kelp's significant role in marine ecosystems and its potential impact on global carbon cycles.

Carbon Fixation

Kelp forests convert (fix) a significant amount of CO2 into biomass (organic carbon) with one study suggesting that globally, they fix as much as twice the carbon fixed in Canada’s boreal forests5. While the carbon fixation rate of kelp varies significantly by species and geography, we can estimate a global average of ~40 tons of CO2 per ha per year3. Such figures highlight the importance of kelp in coastal ocean carbon cycling and their status as one of the most productive ecosystems on the planet.

When kelp forests remove CO2 from seawater, a deficit in the seawater concentration of CO2 compared to the atmosphere is created. This deficit typically leads to a transfer of CO2 from the air to the sea, particularly in areas of intense photosynthetic activity6. Unlike seagrasses, kelp does not bury carbon where it grows. Instead, it contributes to the carbon cycle through the release of both dissolved organic carbon (DOC), which is microscopic, and particulate organic carbon (POC), consisting of larger pieces of kelp detritus biomass7.

Pathways to carbon storages

The long term storage of carbon by kelp can occur in two forms. Very small pieces of kelp (detritus) can drift away and be buried in marine sediments or exported to the deep sea, where the carbon will take time to cycle back to the atmosphere. Alternatively, kelp dissolved organic carbon that is resistant to microbial decomposition (refractory) can persist for long periods of time in the water column and are effectively long-term carbon pools7.

Measuring Carbon Dioxide Removal

Quantifying CO2 Uptake

In terrestrial systems, CO2 removal is a direct one-step process where CO2 is removed from the atmosphere and stored in woody tissues or soil. Marine systems, however, involve a two-step process. Initially, kelp removes CO2 from seawater, creating seawater “parcels” with a CO2 deficit, a step that occurs within seconds. The second step is the much slower transfer of CO2 from the atmosphere into this CO2-depleted seawater6.

Understanding the Terminology

While long term storage of kelp via DOC or POC plays an important role in the carbon cycle, these processes can only contribute to lowering atmospheric if that CO2 is ultimately removed from the atmosphere, not just the seawater. Carbon dioxide removal is therefore measured by determining the amount of CO2 that is covered to organic biomass, and stored long term, typically > 100 years, as well as the percent of that CO2 which was removed from the atmosphere. These are the processes that will help reduce CO2 in the atmosphere.

Therefore, CDR is the process which can mitigate the impacts of climate change and CDR needs to be quantified to generate a carbon credit. Any carbon credits will therefore need to quantify the amount of carbon stored in the ocean AND the amount of that carbon which was removed from the atmosphere.

The Equilibration Process

The equilibration process is determined by the weak partial pressure difference between CO2 in the air and water, resulting in slow transfer (diffusion) rates from atmosphere to ocean. The timeframe for this equilibration varies significantly based on geographic location and bathymetry, from weeks in coastal oceans to months in the open ocean to potentially more than a year in Arctic waters. In well mixed coastal waters, it is thought that there is a 1:1 or near 1:1 ratio of the amount of carbon that is stored and removed, while open ocean or Arctic systems may have a substantially lower ratio (1:3)8. Once this process is complete, any long-term carbon storage is considered removed or sequestered.

Pathways to Equilibrium

Once kelp removes CO2 from the water and a CO2-depleted seawater is established, several pathways can follow. The parcel of seawater, which has a CO2 deficit due to the kelp forest's absorption of CO2, will likely move away from that kelp forest:

  1. It may stay within a kelp forest bed or shallow coastal waters for several weeks and the amount of CDR can be relatively easily quantified (CO2 IS removed).
  2. It may move into an oyster or mussel bed that has CO2-rich water, and the deficit is filled without a transfer from the atmosphere (CO2 is NOT removed).
  3. It could sink below a less dense water body and full CO2 equilibration does not occur (CO2 is PARTIALLY removed).

The optimal scenario for CDR is when this CO2-depleted water remains at the surface until it fully equilibrates with the atmosphere. Methods for measuring air-sea CO2 equilibration include eddy co-variance9, along with oceanographic modelling of these processes.

Verifying CDR and Carbon Sequestration for Kelp Forests

Verifying CDR for kelp forests involves measuring complex processes. For each kelp forest under consideration for carbon credit schemes, two processes need to be quantified:

  1. The amount of kelp derived CO2 that is stored long term in sediments (POC) or the deep ocean (POC or DOC).
  2. The amount of that CO2 stored which was removed from the atmosphere via the equilibration of the “seawater parcel”.

What is Needed?

We require a considerable investment in technology and expertise to advance this field. Due to the large scales over which these processes occur, “an armada of sensors” is required to track kelp carbon storage and the subsequent air-sea CO2 equilibration. Further, the field requires physical oceanographers to measure and model the exchange described above. These steps are fundamental to better understand carbon cycling in kelp forests and quantify their impact on mitigating GHG emissions.

The simplified workflow of quantifying CDR is:

  1. How much CO2 is removed from seawater and fixed into living kelp tissue (biomass).
  2. How much of that kelp biomass is stored long-term (over 100 years) as Dissolved Organic Carbon (DOC) and Particulate Organic Carbon (POC).
  3. How much of that CO2 was removed from the atmosphere via equilibration with the seawater.

Combining these steps together,

Carbon dioxide fixed (kilograms) x carbon stored (%) x carbon dioxide equilibrated (%) = Carbon dioxide removed (kilograms)

Combining these processes results in the CDR values that are needed to generate a kelp carbon credit.

Creating a Carbon Market

The Voluntary Carbon Market

Within the voluntary carbon market, companies seeking to offset their carbon emissions can finance projects that protect or restore habitats that remove CO2 from the atmosphere. In return, they receive certificates acknowledging their contribution to emission reduction. This market operates outside of legal mandates, driven by corporate responsibility and public perception of environmental stewardship.

Considerations for Carbon Markets

Several key considerations underpin the effectiveness of carbon markets. These include engaging local beneficiaries in the projects, ensuring credible issuance and verification of credits, and establishing transparent mechanisms for buyers to connect with projects. Furthermore, the standards and methodologies governing these projects need to be rigorous and consistently applied, often developed by specialized entities that understand the complexities involved.

Carbon Methodologies for Coastal Habitats

While CDR methodologies have been established for habitats like mangroves, tidal wetlands, and seagrass meadows10, kelp forest methodologies are still in development. The confidence that kelp contributes to CDR is high, but the challenge lies in measuring CDR accurately and determining the research and development costs required.

Challenges in Creating a Methodology

Creating a methodology for kelp forest conservation involves addressing complex issues such as defining project boundaries, establishing baseline scenarios for carbon capture, and developing robust monitoring protocols.

Projects must also consider leakage—unintended increases in greenhouse gases outside the project's scope—and the risks associated with non-permanence of removed carbon.

A conservative buffer built into the emission reduction calculations can account for these uncertainties.

Future Directions in Kelp Forest Conservation Finance

Looking ahead, the field must embrace methodologies that accommodate various conservation activities, including farming, protection, and restoration. These methodologies will initially be based on incomplete science and will require refinement as knowledge advances. Early projects will likely incur higher costs due to their role in pioneering these methods. Additionally, there's a need to consider carbon transport at the seascape level, acknowledging the interconnectedness of marine ecosystems. Innovative financial strategies, such as integrating carbon credits with biodiversity credits, mitigation strategies, or blue bonds, will also be essential to advance kelp forest conservation efforts.

Creating Biodiversity Credits

Ecological and Economic Importance of Kelp Forests

Kelp forests, characterized by their incredible primary production, form foundational habitats across a substantial portion of the world's coastlines, supporting over 1500 documented fish and invertebrates. The biodiversity benefit that accompanies carbon removal efforts in kelp forests is not merely incidental but an intrinsic co-benefit. These ecosystems are not only crucial for marine life but also support human well-being through fisheries, nutrient cycling, eco-tourism, and various local industries, while holding immense cultural value. The potential economic valuation of these benefits is estimated at 500 billion USD annually, illustrating the vast ecological wealth kelp forests provide beyond their role as carbon sinks3.

Biodiversity Credits: A New Conservation Currency

Biodiversity credits are an emerging market-based mechanism designed to incentivize organisations to benefit nature. Analogous to carbon credits, these credits can be created and potentially traded by organizations aiming to contribute positively to nature or offset their environmental footprint. Unlike mandated biodiversity offsets, which are project-specific, biodiversity credits in the voluntary market could potentially become more standardized, and transferable. Future legislation could then transition the voluntary market into a mandatory one11.

Defining Biodiversity and Its Market Potential

The term 'biodiversity credits' encompasses various facets of ecological health, from ecosystems to specific species, specific habitats, or vegetation conditions. In a voluntary setting, the definition of these credits can be flexible, with the buyer's satisfaction ultimately determining their adequacy.

However, regulated credits would necessitate adherence to stringent standards with explicit conservation goals. Currently, credits can be categorized as:

  1. Ecosystem: A ‘basket- of-metrics’ across all aspects of the relevant ecosystem type (primary producers, animals, biophysical conditions).
  2. Habitat supporting: A set of biodiversity metrics across critical aspects of a habitat for a specific animal species.
  3. “Vegetation”: A set of biodiversity metrics relevant to foundation species (plant or algae) condition as a proxy for the overall condition of terrestrial or marine ecosystems.

The Rise of Interest and Frameworks in Biodiversity Credits

Recent years have seen a surge in interest regarding biodiversity credits, with several working groups and task forces focused on establishing measurement standards for companies' impacts on nature and developing frameworks for credit systems. These efforts span across measuring, standard-setting, and assessing applications on regional and national levels, indicating a growing consensus on the importance of biodiversity conservation.

Core groups include:

Taskforce for Nature Based Disclosures

World Economic Forum Biodiversity Credits Working Group

Biodiversity Credits Alliance

IUCN Global Standard for Nature Based Solutions

Accounting for Nature

Creating a Biodiversity Credit: The Process

Developing a biodiversity credit requires the below steps:

  1. Desire and demand from organizations to go nature positive or offset their environmental impact.
  2. Identifying eligible remedial actions that qualify for credit creation.
  3. Implementing these actions.
  4. Quantifying their lasting impact.
  5. Independent third-party verification (market dependent).
  6. Issuing a credit that can then be purchased.

Eligible Actions and Market Dynamics

Projects that protect, restore, or steward biodiversity are eligible to generate credits. Protecting biodiversity involves preventing harmful activities, while restoration activities aim to rejuvenate areas lacking in biodiversity. Stewardship maintains ecosystem health to prevent decline.

The supply of biodiversity credits must consider:

  • Equivalency: That the species or ecosystem lost is the same as the one restored.

  • Counterfactual: That that outcome would only have happened with the accredited intervention.

  • Equity: Ensuring that local communities are consulted, engaged, and renumerated for activities that generate credits.

  • Longevity: That any biodiversity gains are persistent for a defined period. There is not currently an agreed upon period of permanence for biodiversity credits.

Applying Biodiversity Credits to Kelp Forests

In kelp forests, several activities would qualify for credits, reflecting the diverse approaches to conservation12 .


  • Eliminating or reducing kelp harvesting
  • Eliminating or reducing water pollution
  • Eliminating or reducing habitat destruction

Protection or stewardship

  • Creating and maintaining marine protected areas
  • Protecting or restoring natural predator populations which benefit kelp forests problematic species control
  • Removing problematic competitors
  • Managing the populations of competitors such as turf algae or coralline algae


  • Seeding
  • Transplanting
  • Supplementing natural habitat

Market Landscape and Future Considerations

Biodiversity credit markets are currently led by a mix of for-profit and non-profit entities, with several countries hosting markets that include kelp forests, notably the UK and Australia. However, no market currently holds a kelp biodiversity credit.

Key considerations for the demand side include the price and perceived value of the credits, the legal landscape, and the robustness of credit development. The overall desire for companies to enhance their nature-positive actions is high, underscoring the need for credible and transparent biodiversity credit markets.


Unit of Measure

Ton of CO2e – Carbon dioxide equivalent


The set of rules, procedures, and guidelines used to quantify, monitor, and verify GHG reductions or removals. Methodologies outline how to calculate emissions reductions from specific project activities and are crucial for ensuring the credibility and integrity of carbon credits.


The defined area of a carbon removal project, in which the action of carbon removal is measured against a baseline.


A scenario used as a reference point to measure the impact of a carbon project. It represents the estimated amount of GHG emissions that would have occurred in the absence of the project. The difference between the baseline emissions and the project’s actual emissions represents the emissions reductions or removals achieved.


The enduring nature of the GHG reductions or removals achieved by a carbon project. It's a measure of how long the carbon will be kept out of the atmosphere. Ensuring permanence is crucial, as temporary removals may not effectively mitigate climate change in the long term.


Occurs when actions taken to reduce emissions in one area inadvertently cause an increase in emissions elsewhere. Accounting for and minimizing leakage is important in ensuring the overall effectiveness of carbon projects.


The emissions reductions or removals would not have occurred without the carbon project. It ensures that carbon credits represent genuine, extra reductions in emissions, and not reductions that would have happened anyway due to other factors.


A system for issuing, tracking, and retiring carbon credits. It ensures transparency and accountability in the carbon market by maintaining records of the creation, ownership, and use of carbon credits. Registries help prevent double counting and provide a platform for the trading of credits.


The year in which a particular carbon credit was generated. Carbon credits have a "year of creation," which can be important for buyers who may prefer credits from certain years due to various reasons such as methodological rigor or relevance to their sustainability goals.


A credit that is taken out of circulation and can no longer be traded or sold. This is done to ensure that each ton of CO2e reduction is only counted once toward offsetting emissions. Once retired, the credit is used to claim the environmental benefit of the emissions reduction or removal it represents.

DOC (Dissolved Organic Carbon)

DOC refers to organic carbon molecules dissolved in water, making them a part of the water column's chemical composition. These molecules can range from simple compounds like sugars to more complex molecules like fulvic and humic acids.

POC (Particulate Organic Carbon)

POC consists of larger particles of organic carbon that are not dissolved but suspended in the water column. These particles can include detritus, dead and decaying organic matter, and living organisms like phytoplankton and zooplankton. POC is visible to the naked eye and can settle to the bottom of a body of water, potentially becoming part of the sediment.

Refractory DOC

Refractory DOC is a subset of dissolved organic carbon that is resistant to microbial breakdown and decomposition. It remains in the water column for extended periods, potentially on the scale of thousands of years, and can be considered a more permanent form of carbon storage when transported to the deep ocean.

Suggested Citation:

Kelp Forest Alliance, 2023. The Role of Kelp Forests in Carbon Dioxide Removal and Climate Mitigation. Contributing Authors, Pessarrodona, A., Hurd, C., Ward, M., Eger, A. M. Sydney, Australia.


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10 Vera

11 Waterford, FitzSimons, Back. (2023). State of Voluntary Biodiversity Credit Markets: A Global Review of Biodiversity Credit Schemes. Pollination, Sydney, Australia.

12 IUCN Typology on Kelp Forest Conservation. Kelp Forest Challenge Typology.

  • Key point that human actions are requisite for any carbon credit.