Blue carbon ecosystems, encompassing mangroves, salt marshes, and seagrasses, are crucial for climate change mitigation due to their high carbon sequestration efficiency. These ecosystems, despite covering only 0.2% of the ocean, contribute to approximately 50% of carbon burial in marine sediments. Growing global recognition of their importance has led to initiatives like the Blue Carbon Initiative. While previous research has focused on carbon storage and socio-economic aspects, a comprehensive assessment of global blue carbon sustainable development, integrating ecological and socio-economic factors, is lacking. This study addresses this gap by developing a novel index to assess the long-term sustainable development of blue carbon in coastal countries and proposing a cooperation model to quantify potential economic and ecological benefits through international collaboration. The study aims to provide insights into the spatial and temporal dynamics of blue carbon sustainability and guide policymaking for enhanced conservation and restoration efforts.

Existing literature extensively documents the role of blue carbon ecosystems in carbon sequestration, surpassing that of terrestrial forests. Studies have estimated the global carbon stock in coastal wetlands, highlighting their significance as nature-based climate change solutions. Research also explores the diverse ecological services provided by blue carbon ecosystems, including pollution purification, coastal protection, and habitat provision. However, the literature lacks a holistic assessment of the sustainable development level of blue carbon ecosystems globally, and the interrelationships between blue carbon, climate change mitigation drivers, and socioeconomic development capacity remain unclear. This research aims to fill this knowledge gap by providing a comprehensive analysis of the long-term sustainable development of blue carbon on a global scale and proposing strategies for global cooperation to enhance both ecological and economic benefits.

This study developed a Blue Carbon Development Index (BCDI) to assess the sustainable development level of blue carbon in 136 coastal countries over a 24-year period (1996-2019). The BCDI framework comprises three interconnected subsystems: driving force, resource endowment, and development capacity. Each subsystem incorporates multiple indicators (detailed in Supplementary Information Table S1), reflecting various aspects of blue carbon sustainability. Principal Component Analysis (PCA) was used to determine the weights for each indicator within the subsystems, ensuring objectivity and minimizing collinearity. The BCDI score for each country was calculated as a weighted average of the three subsystem scores. Data were standardized to a 0-100 scale for comparability across indicators, years, and regions. To understand the relationship between blue carbon ecosystem area and the three subsystems, linear mixed models were employed. For future projections, three scenarios were considered: Business-as-Usual (BAU), Global Cooperation (GC), and Global Deep Cooperation (GDC). The BAU scenario used Holt's linear trend model for predictions. The GC and GDC scenarios incorporated a cooperation model, allocating carbon sequestration benefits based on the Separable Cost Remaining Benefit (SCRB) method. The economic benefits and costs of cooperation were assessed using a country-level social cost of carbon (CSCC) framework. Data sources included various global datasets on carbon emissions, energy, climate risk, population, GDP, scientific publications, corruption perception, marine protected areas, mangrove, salt marsh, and seagrass distributions, and ecosystem health. Proximity interpolation was used to handle missing data.

The BCDI scores showed a significant upward trend (60.69% increase) from 1996 to 2019, driven primarily by improvements in the development capacity subsystem. However, the resource endowment subsystem showed a slight decline, primarily due to reduced ecosystem area and health. Regional variations in BCDI scores were observed, with Europe and North America generally performing better than other regions. The analysis revealed a positive correlation between development capacity and resource endowment. Scenario simulations using the global cooperation model demonstrated substantial benefits under the GDC scenario compared to the BAU scenario. Specifically, under the GDC scenario, a global average BCDI score increase, an additional 2.96 Mt of annual carbon sequestration, and $136.34 million in economic benefits in 2030 were projected. The United States, Indonesia, and Malaysia showed the most substantial increase in carbon sequestration under the GDC scenario. Although developed countries showed less absolute increase in carbon sequestration, their relative benefit from cooperation was substantial (23.60% increase compared to the GC scenario). The study highlighted that countries in Asia, Latin America and the Caribbean, and Sub-Saharan Africa could significantly benefit from cooperation with developed countries to improve their blue carbon development capacity and contribute to global climate change mitigation efforts.

The findings demonstrate the effectiveness of socioeconomic interventions in enhancing blue carbon sustainable development. The positive correlation between development capacity and resource endowment suggests that investments in governance, technology, and marine protection are crucial for protecting and restoring blue carbon ecosystems. The proposed global cooperation model provides a feasible pathway for enhancing carbon sequestration and generating economic benefits. The regional variations highlight the need for tailored strategies that address specific challenges in different regions. The significant improvement projected under the GDC scenario underscores the potential of international collaboration to achieve both ecological and economic gains. The study's results support the integration of blue carbon into national climate change mitigation strategies and international agreements.

This study provides a comprehensive assessment of global blue carbon sustainable development using a novel BCDI framework and a global cooperation model. The findings demonstrate an upward trend in BCDI scores driven by improved development capacity, alongside regional variations. The proposed cooperation model showcases the significant potential for enhancing carbon sequestration and generating economic benefits through international collaboration. Future research should focus on refining the BCDI at local scales, incorporating additional ecosystem services, and further developing the cooperation model to ensure equitable benefit sharing. The findings highlight the urgent need for increased investments in blue carbon conservation and restoration efforts, strengthened international cooperation, and the integration of blue carbon into national and global climate strategies.

The study acknowledges uncertainties associated with data availability and the use of various global datasets. Proximity interpolation was used to address missing data, which might affect the accuracy of the results. The study focused primarily on the carbon sequestration function of blue carbon ecosystems, neglecting other important ecosystem services due to data limitations at the national level. Future research could incorporate these additional services for a more comprehensive assessment. The cooperation model relies on specific assumptions regarding the allocation of benefits, and the actual outcomes may vary depending on the specific mechanisms implemented.