Do Mangrove Credits Reflect Real Biomass Growth?

Mangrove carbon projects are frequently characterized by their substantial belowground carbon stocks, which are typically up to four times that of terrestrial forests and inherently difficult to measure with precision.¹ Quantification approaches often rely on fixed parameters, such as literature values, modeled assumptions or infrequent sampling campaigns.

Aboveground biomass (AGB) may offer a more transparent and observable indicator of carbon accumulation for market participants seeking more regular updates on quantified carbon outcomes. AGB estimates provide a clearer linkage between vegetation growth and issued volumes, particularly for afforestation-focused mangrove projects. This approach is embedded in the MSCI Carbon Markets Mangrove methodology, which assesses AGB growth in the project area against AGB-adjusted issuances.²

Observed AGB growth relative to credit issuance

Geospatial analysis reveals wide dispersion across projects between AGB-adjusted issuances and observed AGB growth. As shown in the first chart, when comparing issuance data with Chloris Geospatial’s analysis, nearly one-third of assessed projects appear to underestimate AGB relative to credit issuances, suggesting conservative accounting.³ More than 20% of projects show indications of declining aboveground carbon stocks since inception, however, raising questions about baseline assumptions or disturbance risk.

As shown in the second chart, geospatial analysis enables a clear comparison of AGB change from the project start date to the present. This can be used to track AGB growth or loss over a project’s lifetime.

For market participants, these findings reinforce the importance of pairing protocol compliance with independent geospatial validation. Where soil carbon remains less transparent, AGB trajectories may provide a practical benchmark for assessing whether issuances align with ecological outcomes and whether credits reflect durable climate impact.

1 Daniel M. Alongi, “Global Significance of Mangrove Blue Carbon in Climate Change Mitigation,” Sci 2 (3): 67, August 2020.

2 AGB-adjusted issuances refer to the estimated share of credited removals attributed to AGB, based on literature estimates or project-level data where available, and assessed relative to soil carbon components.

3 Chloris Geospatial is a cloud-based platform that directly measures AGB and related carbon stocks and changes using high-resolution satellite data, providing spatially explicit estimates for carbon monitoring and analysis.