Blue carbon is the carbon stored in ocean and coastal habitats such as mangrove forests, seagrass meadows, saltwater marshes, kelp, and even the biomass of marine animals. These habitats are complex and dynamic, providing a range of ecosystem services beyond carbon storage, such as climate regulation, water filtration, food and medicine, and storm protection.

Blue carbon ecosystems are unique because they are incredibly biodiverse, can store more carbon than terrestrial forests, and are critical for many indigenous and local communities that rely on them for their livelihoods and subsistence.

While the trade of green carbon offsets is relatively established on the VCM, blue carbon is a new and rapidly evolving market with few accredited projects. For a snapshot of blue carbon on the VCM, see Fair Carbon’s Blue Carbon Project Map.

Blue Carbon Ecosystems

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Seagrass: Seagrass is a grass-like plant that grows in shallow seawater, often forming extensive underwater meadows. Seagrass is found anywhere except the poles; however, the global extent of seagrass has not been accurately mapped. There is one accepted methodology (Verra VCS VM0033) for generating carbon offsets from seagrass, and a project in the Chesapeake Bay between Virginia and Maryland is the first trial underway with the Verra Verified Carbon Standard (VCS). 


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Salt marshes: A salt marsh or tidal marsh is a coastal wetland habitat occasionally inundated or influenced by the ocean’s tides. Verra published a carbon methodology for saltmarsh projects (Verra VCS VM0033), and NGOs such as The Nature Conservancy have begun feasibility studies of trial sites. Currently, there are no registered tidal marsh offset projects on the voluntary market, nor are there any in an advanced stage of development.



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Kelp (and other macroalgae): Kelp and other seaweeds are large ocean algae that form underwater forests in coastal areas worldwide. There is no accepted methodology for generating offsets from kelp and other seaweeds. Less than 1% of natural kelp forests store carbon, and measuring carbon storage in kelp forests is technically challenging. The kelp must be harvested and stored somewhere to ensure the carbon captured by growing kelp is not re-released. While sinking kelp in the deep ocean is one proposed option, there is no consensus on how best to store kelp carbon permanently. Currently, no methodology for kelp carbon projects is accepted by any ICROA-endorsed standard.


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Ocean Biomass: Fish, whales, and other creatures hold carbon in the physical mass of their bodies, called biomass. As these creatures grow throughout their lifetime, they release faeces to the seafloor that either provides nutrients for other organisms or is sequestered in the sediment. Large organisms, such as whales, accumulate significant amounts of carbon within their tissue. Some sink to the ocean floor at the end of their lives, where their biomass may provide nutrients for other organisms and become stored in the sediment. This natural carbon cycle is disturbed by destructive human activities, such as bottom trawling or deep seabed mining that unsettle the ocean floor.

Quantifying how human activities affect the carbon cycle is essential to mitigating our impact on the ocean. However, carbon credits for ocean biomass are unlikely to be feasible soon, since it is unknown how much carbon is stored and is mainly consumed by scavengers rather than being buried in the ocean floor.

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Mangroves: Mangrove forests are trees and shrubs that evolved to tolerate exposure to saltwater and grow in the intertidal zone in the tropics. Mangroves store carbon in their tree biomass, and capture carbon-rich sediments and organic matter in their root systems for hundreds of years. For more information, see our article on Mangrove Ecosystems.

The science and methodologies behind mangrove carbon projects are relatively well-established. The first project was certified in 2012 under the Plan Vivo Standard. However, due to the time and high project development cost, there are only a handful of fully accredited mangrove projects globally.

Fair Carbon's first modular guide presents current best practices for designing, implementing, and managing mangrove carbon projects. Guides to accreditation in other blue carbon ecosystems will be developed and added as new methodologies are published, and data from successful trial sites become available.

The Colours of Carbon

Carbon offset can be categorised using a colour-coded classification system based on how the carbon was captured. Typically, industrial offsets are referred to as brown or red, and nature-based offsets are blue, teal, and green.

  • Red carbon projects use innovative technologies such as wind, solar, and geothermal energy and new alternative fuel sources to reduce emissions.
  • Brown carbon projects improve efficiency in industrial practices such as through energy efficiency, landfill carbon capture, and fuel switching to reduce emissions.
  • Green carbon projects protect, restore, or enhance terrestrial ecosystems and vegetation to sequester carbon through the growth of new biomass (e.g., tree planting), or avoid the destruction of forests or other habitats.
  • Teal carbon projects protect, restore or enhance freshwater ecosystems such as peat swamps, but the term is rarely used. Instead, projects in freshwater ecosystems are generally included under the umbrella of green carbon projects. 
  • Blue carbon projects protect, restore, or enhance coastal or marine habitats to sequester carbon in mangrove trees, seaweeds, seagrasses and sediments or avoid marine or coastal habitat destruction.


Industrial Offsets

Red Carbon:

Using innovative technologies such as wind, solar, and geothermal energy, and new alternative fuel sources to reduce emissions.


Brown Carbon:

Improving efficiency in industrial practices, such as through energy efficiency, landfill carbon capture, and fuel switching to reduce emissions.


Nature-Based Offsets

Green Carbon:

Protecting, restoring, or enhancing terrestrial ecosystems to sequester carbon or avoid emissions from terrestrial habitat destruction.


Teal Carbon:

Protecting, restoring, or enhancing freshwater ecosystems such as peat swamps to sequester carbon.


Blue Carbon:

Protecting, restoring, or enhancing coastal or marine habitats to sequester carbon in mangrove trees, seaweeds, seagrasses, salt marshes and sediments, or avoid marine or coastal habitat destruction.



Nature-Based Solutions

Nature-based solutions to climate change aim to reduce or remove GHG emissions by protecting, conserving, and sustainably managing or restoring natural ecosystems while benefiting human-wellbeing, coastal resilience and biodiversity.

Nature-based solutions include blue, green and teal carbon projects.

For example, a nature-based solution could enhance and protect natural carbon sinks to mitigate climate change. Carbon “sinks” are areas that capture more carbon than they emit, such as mangroves.

Nature-based solutions are often more cost-effective than other climate mitigation strategies and provide additional valuable services. They can protect human communities from storms or sea level rise, provide biodiversity habitats, or supply local communities with food, medicine, and other resources. These additional benefits that go above and beyond emissions reductions or removals are called co-benefits.

Monetising natural carbon storage through carbon projects can provide communities with economic incentives to protect local ecosystems. Nature-based carbon projects may offer long-term income to supplement or replace traditional philanthropic or government funding to protect ecosystems, and/or replace the income they would gain from extractive or destructive practices, such as deforestation.

Co-Benefits and the Price of Credits

Credit buyers may be willing to pay more for nature-based carbon projects if they demonstrate co-benefits. However, blue and green carbon projects produce different co-benefits or may not produce any co-benefits at all.

For example, a mangrove restoration project that plants only one tree species (called a monoculture plantation)  may remove CO2 from the atmosphere. However, monoculture mangrove plantations may not survive in the long-term, or support as much biodiversity as a multi-species planting. Similarly, a project that does not engage with local communities will not have the same impact as a project that employs community members, incorporates their feedback into project design, and provides financial benefits to that community.

It is often up to the credit buyer to determine whether a project has significant co-benefits, whether the asking price for the credits is justified, and whether investing in the project poses a reputational risk (e.g., if the project is not legitimate). Some buyers undertake a due diligence process to evaluate the integrity of a project’s claims. Each buyer has their own due diligence process that may look at project quality indicators, such as community and biodiversity reporting or certifications.