The blue carbon wealth of nations

The study addresses how much economic value coastal blue carbon ecosystems (mangroves, salt marshes, and seagrass meadows) generate via carbon sequestration and storage, and how that value is distributed among nations. Although blue carbon ecosystems are recognized as major carbon sinks, reliable quantitative national-level valuations have been lacking. The authors develop a framework grounded in inclusive wealth and shadow pricing to value sequestration using the social cost of carbon, with a focus on country-specific social costs of carbon (CSCC). The research quantifies both countries’ contributions to global blue carbon wealth and the redistribution of that wealth across borders, providing information relevant for national decision-making, conservation, and restoration strategies.

Prior work established the role of vegetated coastal habitats as significant carbon sinks and introduced the ‘blue carbon’ concept. Inclusive wealth approaches and the social cost of carbon (SCC) have been used to assess sustainability and comprehensive investment at aggregate levels, but without resolving contributions of specific ecosystem sinks spatially by country. Previous global valuations of coastal ecosystems often aggregate all ecosystem services (e.g., multi-trillion-dollar estimates) rather than isolating carbon sequestration services, or focus on regional case studies (e.g., Mediterranean). Existing studies typically use global SCC averages and thus do not reflect heterogeneity in country impacts and valuations, which this paper addresses by using CSCC to identify donor and recipient nations of blue carbon wealth.

• Spatial assessment of ecosystem areas: The authors compile global spatial datasets for mangroves (Giri et al.), salt marshes (McOwen et al.), and seagrass meadows (UNEP-WCMC; Green and Short). Areas are allocated to countries by intersecting with land and Exclusive Economic Zones (EEZs) using the Flanders Marine Institute’s union shapefile of country boundaries and EEZs. Overlapping polygons are dissolved to avoid double counting; areas are computed in an equal-area Mollweide projection. Areas outside national jurisdictions are excluded, which is negligible given these ecosystems occur on land, intertidal, or nearshore waters.
• Ecosystem coverage totals: 317,828 km² seagrass, 54,662 km² salt marsh, and 137,682 km² mangroves globally. Of 245 countries, 165 have at least one BCE type; 45 overseas territories are assigned to sovereign states.
• Sequestration rates: Mean ± s.e. rates used are 174 ± 23 (mangroves), 245 ± 26 (salt marsh), and 138 ± 38 t C yr⁻¹ km⁻² (seagrass). For each country i and ecosystem type j, absolute annual sequestration potential S_ij is computed as area A_ij times rate s_j; national totals sum over j.
• Computation of blue carbon wealth: The contribution to global blue carbon wealth equals national carbon sequestration (converted via CO₂ with SCC) valued by the global SCC, defined as the sum of all CSCCs. CSCCs are drawn from Ricke et al. across all combinations of SSPs (1–5), RCPs (4.5, 6.0, 8.5), discounting, and impact functions. The authors apply a resampling weighted bootstrap to derive CSCC distributions, weighting climate impact function variants to equalize probabilities across functions.
• Wealth redistribution accounting: For each country i, outbound blue carbon wealth is the value of sequestration within i for all other countries (national sequestration times the sum of other countries’ CSCCs). Inbound wealth is the value to i of sequestration occurring in all other countries (country i’s CSCC times all foreign sequestration). Net redistribution equals outbound minus inbound; surplus indicates donor status, deficit indicates recipient status. Countries with negative CSCCs can experience net wealth losses from sequestration. Countries without CSCC have their outbound contribution included but lack inbound/domestic valuation.
• Treatment of uncertainties and territories: Uncertainties in sequestration rates are propagated using standard errors; CSCC uncertainty arises from bootstrapping across scenarios. Overseas territories’ BCE areas and sequestration are attributed to France, United States, United Kingdom, Australia, and the Netherlands as applicable.

• Global totals: Coastal BCEs generate US$190.7 ± 29.5 bn yr⁻¹ in blue carbon wealth using a global mean SCC of US$640.3 ± 4.93 tCO₂⁻¹ (s.d. US$188.45 tCO₂⁻¹).
• Global sequestration potentials: Mean ± s.e.m. cumulative sequestration is 24.0 ± 3.2 MtC yr⁻¹ (mangroves), 13.4 ± 1.4 MtC yr⁻¹ (salt marshes), and 43.9 ± 12.1 MtC yr⁻¹ (seagrass), totaling 81.2 ± 12.6 MtC yr⁻¹.
• Countries with largest annual sequestration potentials: Australia 10.6 ± 1.6 MtC yr⁻¹, United States 7.5 ± 0.8 MtC yr⁻¹, Indonesia 7.2 ± 0.9 MtC yr⁻¹. Countries with smallest include Mauritania 2.4 ± 0.3 tC yr⁻¹, Bulgaria 77.3 ± 8.2 tC yr⁻¹, and Saint Vincent and the Grenadines 81.3 ± 10.7 tC yr⁻¹.
• Largest contributors to global blue carbon wealth (by sequestration): Australia contributes US$25.0 ± 3.8 bn yr⁻¹, with full national lists in Supplementary Data.
• Net blue carbon wealth redistribution: Largest donor countries are Australia, Indonesia, Cuba (also Russia and Guinea-Bissau among top donors). Largest recipient countries are India, China, United States, Pakistan, and Japan.
• Major recipients’ net inbound benefits: India US$26.4 ± 5.0 bn yr⁻¹, China US$16.6 ± 3.4 bn yr⁻¹, United States US$14.7 ± 4.9 bn yr⁻¹, reflecting their large CSCC shares (United States 17.0% of SCC, India 15.4%, China 11.7%).
• Continental redistribution: 53% of Asia’s contribution remains in Asia; 99% of Oceania’s contribution is realized abroad.
• Accounting for fossil and industrial CO₂ emissions would leave only a small set of countries (e.g., Guinea-Bissau, Belize, Vanuatu, Sierra Leone, Solomon Islands, Guinea, Comoros, Samoa, Madagascar, Papua New Guinea) with positive net outbound blue wealth when including emissions.
• Some countries with negative CSCC (e.g., Russia) can experience wealth loss from inbound sequestration (example: Russia outbound ~US$4.3 ± 0.4 bn yr⁻¹; inbound −US$1.8 ± 0.4 bn yr⁻¹).

By valuing carbon sequestration through country-specific social costs of carbon, the study reveals that the economic benefits of coastal BCE carbon sequestration are unevenly distributed internationally. Nations with large sequestration but low or negative CSCCs (e.g., Australia) are predominant donors, while countries with high CSCCs (e.g., India, China, United States) are major recipients even when their own sequestration potentials are substantial. This approach addresses the policy-relevant question of who benefits from conservation and restoration of coastal BCEs and by how much, enabling national cost–benefit analyses and informing international support or compensation mechanisms. Embedding blue carbon sequestration into an inclusive wealth framework highlights both its monetary and potential non-monetary value, supporting strong sustainability principles that call for maintaining natural capital above critical thresholds.

The paper provides a spatially explicit, country-level valuation of blue carbon sequestration and a novel accounting of cross-border blue carbon wealth redistribution based on CSCCs. It identifies key donor (Australia, Indonesia, Cuba) and recipient (India, China, United States) countries and quantifies the magnitude of wealth flows, demonstrating the global significance of coastal BCEs for climate damage avoidance. Future research should: (1) improve spatial data quality and completeness for BCE extents; (2) incorporate region-specific and context-dependent sequestration rates and account for disturbances; (3) refine SCC/CSCC estimates, including impacts on natural capital; and (4) extend the wealth redistribution framework to include all carbon sinks and emissions for a comprehensive assessment of carbon-related wealth dynamics.

• Spatial data limitations: Global BCE coverage datasets are compiled from heterogeneous sources with geographic and historical biases; some regions (e.g., northern Russia, South America for tidal marshes; seagrass globally) are under-sampled. This likely makes estimates conservative and uneven across regions.
• Sequestration rates: Global average rates are used; site-specific conditions, disturbances, and regional variability are not explicitly modeled, and only partially captured via standard errors from primary studies.
• Temporal dynamics: Recent and historical losses of BCEs are not fully reflected; changes over time (e.g., declining mangrove loss rates) are not dynamically modeled.
• SCC/CSCC uncertainty: Large uncertainties exist across models, scenarios, discount rates, and damage functions. Results depend on the Ricke et al. CSCC framework; alternative SCC estimates (e.g., Tol) would change valuation magnitudes.
• Scope restriction: Analysis values sequestration only, excluding other ecosystem services and other carbon sinks/sources (e.g., forests, emissions). Some countries with negative CSCC may experience net wealth losses from sequestration.
• Countries without CSCC: For 31 countries lacking CSCC estimates, inbound and domestic valuations are unavailable (though outbound contributions are included).