The study, in which the ICM-CSIC has participated, focuses on ecosystems such as mangroves, salt marshes and seagrass beds, the destruction of which can release vast quantities of carbon that have been stored for centuries.
Mangroves, salt marshes, seagrass meadows, and in some cases kelp forests—collectively known as blue carbon ecosystems—are increasingly being positioned at the center of global climate strategies. These ecosystems store large amounts of carbon in their biomass and sediments while also supporting biodiversity, protecting coastlines, and sustaining livelihoods.
A new global scientific review co-authored by researchers from the Institut de Ciències del Mar (ICM-CSIC) and an international team of colleagues examines how these ecosystems are being integrated into the carbon market—and warns that scientific and market development must progress together to ensure credible climate outcomes.
The study, published in the journal Annual Review of Environment and Resources, estimates that restoring blue carbon ecosystems could remove around 109 (subject to uncertainty and assumptions) million tonnes (Mt) of organic carbon per year, while preventing continued habitat loss could avoid up to 63 Mt of CO₂ equivalent emissions annually. These findings confirm the significant climate mitigation potential of coastal ecosystems—but also highlight the need for robust frameworks to translate that potential into measurable, verifiable outcomes.
Voluntary carbon markets
The voluntary carbon market (VCM) has emerged as an important—but still evolving and constrained—mechanism to channel private finance into blue carbon conservation and restoration. By enabling developers to generate carbon credits from emissions reductions and removals, the VCM offers a way to fund large-scale ecosystem recovery efforts.
Yet the study finds that current blue carbon market activity is highly uneven. Around 89% of projects are concentrated in mangrove ecosystems, where methodologies, datasets, and implementation experience are more established. Other ecosystems—particularly seagrass meadows, salt marshes, and kelp forests—are far less represented. This imbalance reflects significant scientific and technical barriers that limit their inclusion in carbon markets, despite their potentially large climate benefits.
Scientific alignment
The study highlights that the rapid expansion of carbon markets must be matched by equally robust scientific understanding. If not, there is a risk that the VCM could move ahead of the science needed to ensure that carbon credits represent real, durable climate benefits.
Blue carbon ecosystems are complex, dynamic systems. Carbon flows not only vertically into sediments but also laterally across interconnected coastal environments through tides, currents, and biological processes. These dynamics make it difficult to define project boundaries and accurately quantify carbon storage and removals. In addition, key elements of carbon accounting—such as baseline scenarios, emissions factors, and long-term permanence—often rely on limited data, particularly outside well-studied mangrove systems.
Without sufficient scientific rigor, there is a risk of misrepresenting carbon benefits, underestimating risks, or issuing credits that do not reflect real climate mitigation. The authors emphasize that while carbon markets can accelerate action, they must be grounded in conservative, science-based approaches to maintain credibility and avoid undermining climate goals.
Project barriers
The review identifies several key challenges that currently limit the growth of high-integrity blue carbon projects in the VCM. These primary hurdles consist of high monitoring, reporting, and verification (MRV) costs, limited mapping and spatial data especially for seagrass and seaweed ecosystems, gaps in emissions factors and empirical data, and complex carbon accounting due to uncertainties in lateral carbon transport and ecosystem connectivity.
These barriers increase costs and uncertainty, making many projects difficult to implement—particularly for ecosystems beyond mangroves. At the same time, restoration benefits take time: carbon sequestration in restored ecosystems may require years to decades to reach levels comparable to intact habitats, delaying returns and increasing project risk.
Balancing integrity
To scale blue carbon solutions effectively, the study highlights the need to balance cost reduction with scientific integrity. Emerging approaches—such as improved models, emissions factors, and remote sensing—offer opportunities to lower costs and expand market participation. However, these tools must be carefully validated and applied conservatively to ensure accuracy.
The authors also stress the importance of transparent and conservative accounting, particularly where uncertainty remains, to maintain trust in carbon markets and avoid reputational risks.
Strategic pathways
To ensure that the voluntary carbon market can support blue carbon ecosystems at scale, the study identifies several priority areas. Action must center around improved mapping and monitoring of coastal ecosystems, achieving a better understanding of carbon transport across connected seascapes, the development of robust emissions factors, and the inclusion of additional carbon pathways, such as dissolved and inorganic carbon processes. Advancing these areas will be essential to expanding the scope of ecosystems included in the VCM while maintaining scientific credibility.
All in all, blue carbon ecosystems represent a major opportunity to deliver climate mitigation while supporting biodiversity and coastal resilience. The voluntary carbon market has a key role to play in unlocking the finance needed to realize this potential.
However, the study makes clear that speed must not come at the expense of accuracy. Ensuring that carbon markets are grounded in strong science will be essential to delivering real, lasting climate benefits. As demand for nature-based solutions grows, aligning scientific rigor with market development will be critical to ensuring that blue carbon fulfills its promise as a credible and effective climate solution.