Ambition Disparity Reveals Unlocked Mitigation Potential for Blue Carbon in the Paris Agreement

Ambition Disparity Reveals Unlocked Mitigation Potential for Blue Carbon in the Paris Agreement | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Ambition Disparity Reveals Unlocked Mitigation Potential for Blue Carbon in the Paris Agreement Radhika Bhargava Gajre, Anabel Kadri, Fernanda Adame, Stacy Baez, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8942230/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Blue carbon ecosystems, despite their significant climate change mitigation potential, remain underrepresented in the Paris Agreement. Only 20% of the blue carbon-holding countries have incorporated them into National Inventory Reports (NIRs), and 46% have included them as mitigation targets in Nationally Determined Contributions (NDCs), with Non-Annex I countries accounting for the majority of these inclusions. Full protection and restoration of blue carbon ecosystems could sequester up to 122.3 GtCO₂e (95% CI: 84.03 – 160.57 GtCO₂e) by 2050—effectively offsetting 10 years of the world's current land cover change carbon footprint. However, only 25.52 GtCO₂e (95% CI: 17.52 – 33.48 GtCO2e), i.e., 30%, of their mitigation potential is currently pledged. Non-Annex I countries have committed twice (37%) the potential of Annex I countries (16.4%), highlighting both the opportunity and the disparity in policy uptake relative to mitigation potential. We demonstrate that NDCs can be utilised to incrementally integrate blue carbon, transforming disparity into strategic entry points, catalysing more ambitious climate targets while safeguarding coastal resilience. Earth and environmental sciences/Environmental social sciences/Climate-change mitigation Earth and environmental sciences/Environmental social sciences/Climate-change policy Climate change mitigation mangrove seagrass tidal marsh tidal flats Nationally Determined Contributions National Inventory Reports Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Natural Climate Solutions (NCS), such as forest protection, management and restoration 1 , can provide one-third of the climate change mitigation needed to achieve the 2°C target stated in the Paris Agreement 2 . Up to 25% of tropical countries could potentially mitigate more than half of their national emissions through cost-effective NCS 3,4 . Blue carbon ecosystems – including mangroves, seagrasses, tidal marshes, and tidal mudflats – are emerging contributors to natural climate change mitigation 5 , as they have higher rates of productivity than terrestrial ecosystems, and two to five times more carbon storage capacity per equivalent unit area 5 . Global cooperation could collectively sequester up to 2.94 million tons of carbon annually and generate $136 million from carbon storage and sequestration from blue carbon ecosystems, compared to a business-as-usual scenario 6 . These emission reductions can be significant for countries with moderate fossil fuel emissions and extensive coastlines, such as Bangladesh or Colombia 4 , as well as for small island states 7 . Blue carbon can also generate significant blue carbon wealth (US$22.8 ± 3.8 billion annually, and the largest globally) in large economies like Australia through climate change mitigation services 6 . Blue carbon holds significant potential to complement emissions reductions from other sectors and meet national climate action goals 8,9 , while simultaneously supporting adaptation 10 , biodiversity 11 , and coastal resilience 12 . This is achieved by generating accountable emission reductions within the Land Use, Land-use Change and Forestry (LULUCF) sector, which directly supports the mitigation targets specified in countries' Nationally Determined Contributions (NDCs) and is tracked in their National Inventory Reports (NIRs). Yet, the use of blue carbon and other NCS for national emission reductions is still limited, leaving potential mitigation underutilised in the Paris Agreement 13 . Moreover, despite global participation in achieving climate action through the Paris Agreement 14 , the ambition deficit persists in both Annex I (industrialised nations and economies in transition) and Non-Annex I (developing) countries 15 . Only 104 of 168 countries—predominantly Non-Annex I—have formally incorporated NCS into their NDCs, with merely 48 countries referencing coastal ecosystems 16 . Ideally, Annex I countries would take immediate action while simultaneously supporting capacity-building in Non-Annex I countries to pursue low-carbon development, adaptation and mitigation pathways 17 . In practice, however, many Annex I countries have demonstrated limited integration and specificity of nature-based mitigation, including blue carbon, in their submissions 15,18 . The global potential for blue carbon is well established 8,19 ; however, a significant yet unquantified challenge is the fundamental misalignment between national climate policy ambitions and the underlying mitigation potential of coastal countries, driven in many cases by constraints related to data availability, technical capacity, and inventory readiness, rather than a lack of policy intent 20,21 . Our study addresses this critical gap and how it is hindering opportunities for high-impact climate action. By mapping current policy commitments against national biophysical potential and identifying barriers and enabling conditions, we uncover a substantial, quantifiable mitigation gap between committed and achievable blue carbon emissions reductions, as well as future potential for enhancement. Financial barriers 22 , limited specificity in pledges, and persistent gaps between commitments and accounting readiness 20 put the success of the Paris Agreement's climate change mitigation targets at risk 13 . We demonstrate how nations can bridge ambition disparity by utilising the NDC mechanism to incrementally integrate blue carbon ecosystems – transforming national constraints into strategic entry points. By framing these habitats as strategic targets rather than omitting them due to national circumstances or barriers, nations can leverage the Paris Agreement’s inherent flexibility to bridge the ambition disparity and create the enabling conditions for more robust, holistic climate commitments. Ambition Disparity: Non-Annex I Countries Drive the Global Blue Carbon Commitment Baseline We reviewed the NIRs of 156 Paris Agreement signatories with at least one blue carbon ecosystem to identify the tier of inclusion of blue carbon ecosystems since 2015. The IPCC Tier system is a three-level accounting framework, with localisation of data (and therefore accuracy) increasing from the simple Tier 1 (which utilises globally averaged estimates of emission factors) to the highly detailed, country-specific data used in Tier 3 23 . We found that national blue carbon reporting is fundamentally fragmented. Most coastal nations either omit these ecosystems entirely or rely on lower-tier estimates that fail to capture the full scope of ecosystem potential for climate action (Fig. 1A, 1B). Blue carbon ecosystems were included in the NIRs of 20% of all blue carbon countries, of which 67% were Non-Annex 1 (Supplementary Figure 1A). However, most countries only included blue carbon ecosystems at Tier 1, relying on globally averaged emissions factors, and only the US, Australia, Croatia, Japan and New Zealand included more than one blue carbon ecosystem (Supplementary Figure 1B). Next, we examined how mitigation targets from blue carbon ecosystems were incorporated into the NDCs since 2015. The inclusion of blue carbon ecosystems as a mitigation target was uneven, with contributions disproportionately higher from Non-Annex I countries (Supplementary Figure 1C). Specifically, 46% of the countries with at least one blue carbon ecosystem included it as a mitigation target in their NDC submissions since 2015; of these, 93% were Non-Annex I countries. The limited inclusion from Annex I countries aligns with similarly low uptake of other NCS, adaptation 24 and renewable energy targets 15,25,26 . However, the NDC 3.0 submitted in 2025 showed a higher inclusion of multiple blue carbon ecosystems from Non-Annex I countries (Supplementary Figure 1C). Despite fewer financial resources, Non-Annex I countries also set quantitative blue carbon targets and committed to meeting them unconditionally. Since 2015, one-fifth of countries (21%) included at least one unconditional target, 19% included only quantitative targets (for example, hectares of carbon sequestration achieved), and 14% included both, with the majority of these being Non-Annex I countries (Supplementary Figure 2). African countries reported the highest number of quantitative and unconditional targets (18%), although regional disparities within these countries exist 27 . In Southeast Asia, blue carbon follows a clear trajectory of increasing ambition since NDCs were first submitted, echoing the regional shift toward more robust, unconditional NDC targets 24 . Non-Annex I countries frequently state ambitions in NDCs but exclude or fail to account for blue carbon ecosystems based on the IPCC Wetlands Supplement in NIRs, signalling insufficient monitoring capacity, potentially impacted by jurisdictional ambiguity 28 and staff limitations 29 . Conversely, nine countries reported mangroves in NIRs without NDC targets, highlighting gaps related to political prioritisation, data availability or other national circumstances. To understand how countries include blue carbon as a mitigation target, we conducted a thematic classification of blue carbon-based mitigation targets included in NDCs since 2015. This captured both the types of themes and the scope of blue carbon inclusion in NDCs, despite differences in national circumstances between Annex I and Non-Annex I countries. Across both groups, the key mitigation targets based on blue carbon ecosystems were similar – improved management (92%), utilisation of carbon sequestration services (72%), and restoration (66%). However, 47% of the countries also identified improving data as a key target. The NDCs also consistently incorporated supportive targets—such as closing data gaps, addressing policy requirements, ensuring community inclusion, and refining accounting—that facilitate, rather than directly execute, emission reductions (Fig. 1). While mangroves management emerged as the primary blue carbon target, a lack of specificity persisted, with many countries grouping diverse and general mitigation actions under broad, non-specific 'blue carbon' labels. Figure 1 | Integration of coastal blue carbon ecosystems into national climate mitigation targets (2015–2025). Sankey diagram illustrating the flow from geopolitical groupings and regions to coastal ecosystems and their mitigation-oriented policy themes, as extracted from NDC reports submitted between 2015 and 2025. Node widths are proportional to the frequency of countries under those mitigation targets. The visualisation reveals a predominant focus on mangrove ecosystems within Non-Annex I regions, with 'Management' and 'Carbon Sequestration' emerging as the primary thematic drivers for emission reduction commitments. Conversely, seagrass and tidal marsh ecosystems exhibit lower levels of integration into formal mitigation pathways. Themes with low frequency are not shown; see Supplementary Figure 3 for the full list. We performed a multinomial logistic regression to test whether the patterns of inclusion of blue carbon-based mitigation targets could be explained by key national characteristics: the extent of blue carbon cover, intertidal area loss (including blue carbon ecosystems), protected area, and restoration potential. We found that the inclusion of blue carbon ecosystems was associated with opportunity rather than threat (Supplementary Figure 4). For example, intertidal loss was universally yet negatively associated with adoption of blue carbon mitigation targets (p-value < 0.001 and odds ratio < 1) across all ecosystems. Countries experiencing the highest rates of intertidal loss were significantly less likely to include blue carbon-based mitigation targets, indicating a gap in the translation of observed loss into mitigation targeting. Conversely, restoration potential showed a strong positive association with management and restoration targets, particularly in mangrove (p-value = 0.008; odds ratio = 1) and seagrass habitats (p-value < 0.001; odds ratio = 1.001). Meanwhile, the extent of blue carbon habitats and protected area status associated with inclusion as a management target in regions such as Australia and Mexico suggests a resource-led policy approach, where abundance facilitated inclusion (Fig. 2). Figure 2 |Influence of current conditions of blue carbon ecosystems as the primary mitigation approach highlighted in the NDCs Map showing the relationship between the current condition of blue carbon ecosystems and their inclusion in national climate policies based on a multinomial logistic regression. Geospatial distribution of primary policy motivations, distinguishing regions where target inclusion is associated with habitat loss versus habitat extent and restoration potential. Annex 1 countries are outlined in yellow. Please refer to Supplementary Table 1 for the multinomial logistic regression coefficients and statistics. Our statistical tests revealed that while ecological baseline data and restoration potential can inform national ambition, the decision to formalise blue carbon targets remains a strategic policy choice (e.g., national circumstances driven decarbonisation interests, or focus on adaptation, resilience and livelihoods over mitigation) rather than a direct reflection of ecosystem extent or local environmental threat. For instance, the Asia Pacific region hosts the largest extent of mangroves, seagrass, and tidal flats, while Europe and the US combined have the largest extent of tidal marshes (Supplementary Figure 4C) 30–32 . Yet the geographical distribution of blue carbon ecosystems and their inclusion in NDCs were misaligned, consistent with a historical focus on mangroves in science and policy until recently. Blue carbon mitigation targets were also included by countries with minimal blue carbon area (e.g., Guyana, Kiribati), signalling recognised future mitigation potential or co-benefits. Moreover, out of 30 countries experiencing high mangrove deforestation 33 , 12 included mangrove targets, primarily for restoration rather than halting deforestation. Our results suggest great potential for improved national data to guide policy towards strategies that respond to national circumstances, such as targets for avoided conversion in countries experiencing high rates of blue carbon ecosystem loss. A country's focus on blue carbon could also be driven by the proportion of its blue carbon extent and removal potential relative to its national scale 7 . National Circumstances Guide Pathways for Strengthening Blue Carbon Ambition Through successive NDC submissions, the Paris Agreement encourages growth in mitigation ambition 18 . We thematically analysed each subsequent NDC submission for blue carbon mitigation targets since 2015 to identify opportunities and enabling conditions for strengthening NDC ambition through quantitative, mitigation-specific targets for blue carbon. Ambition evolved from management as the primary target to quantitative, mitigation-specific targets since 2015 (Fig. 3B). We observed that opportunities for blue carbon as mitigation targets were driven by national circumstances. Only 25 Non-Annex I countries submitted ambitious blue carbon mitigation targets. Focal entry points varied across countries, reflecting differing national circumstances. Enhanced management or increased protection were the most common entry points for the countries that submitted ambitious targets in later NDCs (15 countries) (Fig. 3B). Setting ambitious targets in subsequent NDCs depended on enabling conditions, progress since previous submissions, and external support. For instance, Angola, Mexico, and Sri Lanka first included blue carbon ecosystems as a carbon sequestration targets, while many others included intermediate targets on measurement, protection, and restoration before committing to specific projects. In the NDC 3.0, ambitious targets included establishing mechanisms for long-term monitoring, forming alliances, enhancing inclusion in NIRs, and designing quantitative projects. Overall, blue carbon inclusion has progressed from data generation to actionable projects over the past decade. Figure 3 | Progression, thematic density, and the incremental integration of blue carbon in climate policy. (A) Scenarios of incremental inclusion of blue carbon mitigation targets with policy and assessment and monitoring (data generation) acting as enabling conditions to overcome national-level barriers. (B) A Sankey diagram illustrating the evolution of blue carbon themes through successive NDC submissions for those countries that subsequently submitted ambitious NDC targets. The flow tracks the themes from initial entry (Entrance) through developmental stages (Middle) to their integration into Current Status. Blue nodes represent Policy Gates, identifying key transition points where specific policy frameworks enable the incremental scaling of technical themes—such as Carbon Capture, Conservation, and NIR Inclusion—from strategic intent to quantified targets. Green nodes represent data generation-based targets. Finally, our thematic analysis of targets from subsequent NDC submissions demonstrates that countries utilised the NDCs to create enabling conditions to address gaps and enhance the inclusion of blue carbon. The use of the NDC framework to create enabling conditions was national-circumstance-dependent – 13 countries included quantitative, mitigation-specific targets blue carbon targets without the need for enabling conditions, while 12 incrementally increased their ambition by overcoming barriers (Fig. 3). The two key enabling conditions that paved the way for ambitious targets were data generation and policy enhancement, although these do not necessarily imply actions in the field (Fig. 3A). Prioritising data needs highlights critical pre-existing data deficiencies and points to the systemic issues inherent in collecting robust, verifiable and standardised data required for high-integrity mitigation targets 34 . Inadequate data were addressed by setting targets to enhance the national capacity to generate the data required for blue carbon accounting since 2015. Countries are overcoming data scarcity by prioritising enhancements to blue carbon databases within their climate goals. Key data requirements included mapping land cover change (73%), quantifying local carbon biomass (73%), and monitoring restoration (66%). By stipulating these needs in NDCs, nations are formalising the transition from measurement gaps to actionable accounting pathways 35 . Filling data gaps in earlier NDCs enabled 18 out of 25 countries with subsequent NDC submissions to include blue carbon ecosystems in their NIRs, thereby bridging the gap between NDC ambition and capacity. Next, our thematic analysis highlighted that establishing enabling policy conditions was a key target for integrating blue carbon into a country’s NDC. This involved the inclusion of targets to develop policy frameworks that support the monitoring, mapping, protection, and restoration of these ecosystems (Fig. 3B). For instance, Liberia and the Bahamas amended their previous national policies to include restoration and carbon sequestration in national forest management plans. Policy framework development served as an essential precursor to actionable blue carbon targets for 13 of the 25 countries with subsequent ambitious submissions (Fig. 3). In addition, policy enhancements were shown to support land tenure, management, assessment of area extent, carbon sink enhancement, the establishment of task forces, and the development of national blue carbon strategies. Integrating blue carbon ecosystems into national legal frameworks strengthens mitigation and net-zero targets, hence providing a critical pathway for fulfilling the Paris Agreement 36 . The policies could accommodate new phases of transition (for example, blue carbon inclusion), be transferable (for example, integrating REDD+ and the Global Biodiversity Framework into NDCs), and be adaptive to feedback 37 . Despite the wide coverage of themes, the current inclusion of blue carbon lacked clarity on implementation, financial, and capacity needs. Technical support from international organisations aimed at filling scientific and policy gaps is an essential pathway to addressing financial, technical, and capacity needs 38 , 39 . Capacity-building, crucial for NDC implementation and covering finance and technology transfer 40 , remains narrowly focused on general GHG emissions reporting 41 . While examining the support countries received in writing and in developing their NDC 3.0 in 2025, 15 out of 40 countries sought essential support to fill scientific and policy gaps, as well as financial, technical, and capacity-building assistance from UN-based organisations, international organisations, or regional coalitions. Quantifying Unlocked Mitigation Potential: Future Scenarios for Closing the Global Blue Carbon Commitment Shortfall We quantified the mitigation potential of blue carbon currently included in NDCs to understand their contributions to global climate change mitigation commitments and the existing mitigation gaps to be filled. The current and future mitigation potential was estimated by calculating the mitigation potential (avoided emissions and carbon removal) under current inclusion and future protection, restoration, and sequestration in 2050. Global blue carbon integration reveals a mitigation ambition gap between Annex I and Non-Annex I countries, with a total of 25.5 GtCO 2 e (95% CI: 17.52 – 33.48 GtCO 2 e) currently committed in NDCs (Fig. 4). Non-Annex I countries are the primary drivers of this mitigation, contributing 21 GtCO 2 e (95% CI: 14.43 – 27.57 GtCO 2 e) and harnessing 37% of their available potential, largely through combined protection and restoration strategies. Annex I countries have left 84% of their potential uncommitted - a substantial shortfall in committed mitigation relative to their capacity. This disparity highlights inequitable global contributions 42 , particularly as Annex I countries have historically exceeded their carbon budgets 18,43 . High-inclusion hotspots are concentrated in the Indo-Pacific and Caribbean regions, where blue carbon is an important climate strategy for land-scarce and ocean-dependent countries. Conversely, many Annex I countries with extensive coastlines exhibit a low proportion of integration, suggesting that blue carbon is often recognised qualitatively in text but remains unquantified as a core component of total mitigation commitments (Fig. 4), with other strategies taking priority. At the ecosystem level, seagrasses currently provide a higher quantified mitigation benefit because of their larger distribution area than mangroves, despite mangroves being more commonly included in NIRs and NDCs. Despite this, substantial methodological, mapping, and accounting challenges constrain short-term advances with seagrass ecosystems 42 . While mangroves exhibit the largest future gaps, substantial unutilized potential also remains in Non-Annex I’s tidal marshes and Annex I’s seagrass meadows (Fig. 4 A, B). Non-Annex I countries—particularly Small Island Developing States and Southeast Asian countries—maintain a more holistic representation of ecosystems within their NDC mitigation potential (Fig. 4C). Closing these commitment gaps is essential to prevent the degradation of vast, non-committed carbon pools and to fully leverage coastal ecosystems as a scalable climate solution. Figure 4 | Inclusion of blue carbon mitigation in NDCs as a proportion of total opportunity and total climate mitigation commitments. A) Bar graph illustrating the total current blue carbon mitigation potential (GtCO2e) across mangroves, seagrasses, tidal marshes, and tidal mudflats. The mitigation potential of NDC commitments is defined as the carbon storage achieved through the protection or restoration of blue carbon ecosystems that are specifically included as mitigation targets in NDCs. The “Other Commitments” category encompasses policy, finance, community, and collaboration-based targets, for which potential is calculated by estimating the stored carbon in the blue carbon extent of countries with these targets as the primary focus. “Not Committed” refers to the carbon stored in the blue carbon ecosystems of countries that have not included blue carbon ecosystems in their national commitments as a mitigation target. The inclusion is estimated by the area of the total blue carbon per ecosystem type included by a country in its NDC. (B) Heatmap comparing the committed mitigation b y blue carbon ecosystem and strategy for Annex I and Non-Annex I countries. (C) Global map depicting the percentage of blue carbon targets relative to total national mitigation included in NDCs. Next, we modelled three future inclusion scenarios projected to 2050: (S1) maintenance of currently protected areas; (S2) protection of all extant blue carbon ecosystems; and (S3) full protection coupled with future restoration potential. Our estimates indicate that the widespread adoption of S3 within the current NDC cycle would result in the sequestration and storage of 122.3 GtCO₂e (95% CI: 84.03 – 160.57 GtCO₂e) by 2050. Seagrass protection and restoration offer the highest individual contribution to global mitigation potential, followed by integrated mangrove protection and restoration (Fig. 5A). Regionally, the most significant future gains are concentrated in Non-Annex I countries, where seagrass and mangrove protection and restoration represent substantial untapped carbon sinks (Fig. 5A). Spatially, the global distribution of this 2050 potential remains robust across most coastal regions. Except for some areas in Europe, South America, and Africa, blue carbon inclusion offers a high mitigation potential, ranging from 0.68 to 18 Gt CO 2 eq globally (Fig. 5B). These findings highlight a clear geographic and thematic roadmap for closing the current ambition gap through quantified, ecosystem-specific targets. Figure 5 | Global blue carbon future mitigation potential and policy inclusion scenarios . (A) Heatmap distribution of committed blue carbon (GtCO 2 e) across four coastal ecosystems—tidal marshes, tidal flats, seagrasses, and mangroves—under three scenarios of increased ambition in Nationally Determined Contributions (NDCs). Scenarios are compared against a baseline to show the impact of increasing protection and restoration efforts, disaggregated by Annex 1 and Non-Annex 1 country status. Darker colours indicate higher levels of carbon commitment. (B) Global map illustrating the spatial distribution of future blue carbon mitigation potential at the national level. Colours represent the total potential (GtCO 2 e), with green shades identifying Non-Annex 1 countries and purple shades identifying Annex 1 countries. Scaling indicates that the highest mitigation potential is concentrated within tropical regions and specific Annex 1 territories. Closing the ambition disparity through systematic, incremental and holistic inclusion For countries looking to include blue carbon ecosystems for mitigation or enhance current ambitions, the NDC mechanism could resolve challenges related to national circumstances—such as data deficits, lacking policy frameworks, and capacity needs 43 . This necessitates incorporating targets incrementally to establish enabling conditions now, creating future opportunities to integrate quantitative mitigation-based targets and accounting in NIRs. Blue carbon inventories present unique challenges due to tidal inundation, seasonality and the need to integrate non-land-based categories 35,44,45 . While ease of classification benefited mangroves, data gaps encompassed all ecosystems across both country groups. Non-Annex I and Annex I countries emphasised improving understanding, measurement, and mapping of all ecosystems. Acknowledging the flexibility inherent in the Paris Agreement, higher inclusion in national accounting is achievable by leveraging IPCC defaults for Tier 1 inclusion 23 . Moving beyond Tier 1 requires dedicated capacity, supported by global coordination and resource sharing, such as Indonesia's development of national emission factors for mangroves 46 . Additionally, establishing blue carbon-specific strata within national forest or wetland inventories, and/or REDD+ reference levels, will systematically aid in NIR integration 47 . The identified mitigation potential of 122.3 GtCO₂e (95% CI: 84.03 – 160.57 GtCO₂e) represents a substantial opportunity for the UN Global Stocktake to move beyond terrestrial-focused mitigation and address the significant "commitment gap" in national climate targets. Our findings suggest that current NDCs underutilise blue carbon, particularly in Annex I countries, while Non-Annex I countries also have significant work ahead to utilise the Paris Agreement to create enabling conditions for the future integration of quantitative targets. To align with a 1.5 °C pathway, future policy cycles need to transition from broad conservation rhetoric to quantified, ecosystem-specific targets and field implementation that include seagrasses and tidal marshes—the largest non-committed carbon pools. By integrating these high-density sinks into formal reporting frameworks (e.g., NIR Inclusion), countries can provide the transparent, science-based accounting necessary for the second Global Stocktake to reflect the true mitigation capacity of global coastal ecosystems. Blue carbon, although globally small in extent, contributes substantially as a low-cost 48 and profitable 49 NCS at the national scale 5 . We demonstrate that with full protection and restoration, blue carbon ecosystems can mitigate 2.5 years of global greenhouse gas emissions and 10 times current annual AFOLU emissions. Including blue carbon ecosystems in NDCs is a multifaceted strategy- advancing climate mitigation, conservation, and co-benefits while generating financial and technical support. Such inclusion enhances protection, attracts restoration investment 50 , informs conservation-oriented policy, and raises public awareness 51 . The Paris Agreement’s flexibility 52,53 and equity 54 mechanics can enable countries to overcome nation-specific barriers and create enabling conditions for future integration, leading to NIR inclusion for systematic monitoring. To achieve this, blue carbon ecosystems should be identified and included in NDCs and eventually in NIRs by all relevant countries. Blue carbon efforts through the Paris Agreement must transcend siloed mitigation approaches to capture the full spectrum of adaptation, social and ecological value 43 . The effectiveness of these ecosystems’ hinges on their co-benefits, requiring NDCs to link carbon sequestration targets directly with adaptation and biodiversity conservation through international agreements to enhance global synergies. Methods Thematic analysis of UNFCCC Reports Using global extent datasets (Table 1), a list of coastal countries with blue carbon ecosystems—mangroves, seagrasses, tidal marshes, and tidal flats—was created. Countries were categorised as Annex-1 and Non-Annex 1 using the UNFCCC classification. Each Annex I country submitted an NDC and NIR every 5 and 1 year, respectively. We reviewed all reports submitted by coastal countries with blue carbon ecosystems under the UNFCCC from 2015 to June 2025 via the UNFCCC party-authored reports portal (https://unfccc.int/reports). First, we searched the content of the reports for “mangrove”, “seagrass”, “tidal marsh”, “tidal flat”, “coastal wetland”, and “blue carbon”. For each report that mentioned these terms, text covering targets for biodiversity, adaptation, mitigation, and carbon sequestration was extracted and categorised as conditional/unconditional and quantitative/qualitative. A total of 331 NDCs, 446 NIRs, and 824 NCs on mitigation and carbon sequestration-based targets to identify key themes, temporally changing themes, and sub-themes (Supplementary Table 1). Inter-code validation was performed by two researchers, each of whom first coded a 30% subset of the dataset. Themes were finalised when agreement exceeded 90%, and a second round of thematic analysis was performed on 100% of the data to assign final codes and themes. A list of themes and codes is given in (Supplementary Table 1). Using the initial sets of themes, we re-coded the data to identify countries which submitted multiple NDCs with enhanced blue carbon targets. This analysis was repeated for each category of target – all targets, unconditional, quantitative, and any notes supplemented by countries related to mitigation targets. To identify countries that have included blue carbon ecosystems in their GHG inventories, blue carbon ecosystems (mangroves, seagrass, tidal marshes and tidal mudflats) were searched for in inventory reports or any other supplementary documents submitted with the NIRs. Next, we examined the methods section of these reports for the included blue carbon ecosystem to ensure that the ecosystem of interest was classified separately rather than merged into a broader category. For example, we selected only countries that included mangroves using the 2013 and 2019 IPCC Wetlands Supplement methods, rather than terrestrial forest methods. For countries that did not provide details on methods and inclusion types, we excluded them from our analysis. Thus, there might be countries that included blue carbon ecosystems in their inventory, but if they did not include the details in the methods submitted in the report, we did not include those countries. Multiple logistic regression analysis To assess the influence of the current national status of blue carbon ecosystems on the inclusion of corresponding ecosystems within national policy documents, we employed multinomial logistic regression. We constructed separate models for each of the four blue carbon ecosystems, with the dependent variable being the NDC Target (e.g., Restoration, Management, Management and Restoration, or Other Themes). The baseline for all models was the 'not included' (NI) target. We characterised the current status of blue carbon ecosystems using four independent variables that help describe trends in blue carbon ecosystem conservation: extent 31,32,55,56 , restoration potential 3,57 , protected area 58 , and intertidal loss 31 . The models yielded odds ratios and associated P-values for each policy outcome relative to the no-target baseline. NDC mitigation potential and scenario analysis The current NDC mitigation potential refers to the total carbon dioxide equivalent from all blue carbon ecosystems currently committed under the NDCs, whereas the future NDC mitigation potential represents the total avoided deforestation (from additional protection and improved management of current protected areas) and carbon removal (restoration). Since many countries included an improved management target, we assumed that improving management would reduce deforestation within protected areas. The year 2025 was used as the baseline for these calculations. Carbon biomass values for different blue carbon pools were estimated from global geospatial datasets or global averages (Supplementary Table 2). For restoration, global prediction maps were used, except for tidal flats, for which no such maps are available. Using the same datasets, three scenarios were developed to assess whether blue carbon ecosystems are included in NDCs and the potential for carbon storage in 2050, with 2025 as the baseline year. The three scenarios included the current protected area extent for blue carbon ecosystems, encompassing all blue carbon ecosystems' extent as protected areas, as well as all extent designated as protected areas, including potentially restorable areas. To estimate deforestation rates, we used global estimates for all blue carbon ecosystems 59–62 . We calculated carbon stocks for mangroves using Simard et al 63 and Sanderman et al’s 64 global mangrove aboveground and soil carbon stocks using country-level aggregation. Next, we used global carbon stock averages for aboveground and soil carbon from tidal marshes and tidal flats, as reported by Howard et al. 19 . Seagrass estimates were adopted from marine ecoregional averages presented in Krauss et al. 42 . Mangrove restoration per country was aggregated from Worthington et al. 57 , while seagrass and tidal marsh restoration values were from Griscom et al. 65 . We estimated stock growth in 2050 based on carbon sequestration between 2025 and 2050. To estimate total carbon stocks in 2050, we used carbon sequestration rates for all ecosystems from Howard et al. 19 . For mangroves, seagrass, and tidal marshes, where we had restoration area values, we assumed that the baseline carbon stock is zero and estimated a linear increase in stock due to new restorations in 2025, projected for the year 2050. Since we used secondary datasets for all our analyses, the accuracy of our estimations depends on the accuracy and uncertainty of the base datasets, as detailed in Supplementary Table 2. References Ellis, P. W. et al. The principles of natural climate solutions. Nat Commun 15 , 547 (2024). Meinshausen, M. et al. Realization of Paris Agreement pledges may limit warming just below 2 °C. 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Nat Commun 12 , 1271 (2021). Sidik, F., Lawrence, A., Wagey, T., Zamzani, F. & Lovelock, C. E. Blue carbon: A new paradigm of mangrove conservation and management in Indonesia. Marine Policy 147 , 105388 (2023). Hermwille, L., Siemons ,Anne, Förster ,Hannah & and Jeffery, L. Catalyzing mitigation ambition under the Paris Agreement: elements for an effective Global Stocktake. Climate Policy 19 , 988–1001 (2019). Kuramochi, T., Deneault, A., Chan, S., Smit, S. & Pelekh, N. Supporting the Paris Agreement through international cooperation: potential contributions, institutional robustness, and progress of Glasgow climate initiatives. npj Clim. Action 3 , 31 (2024). Sattar, U. Climate action in a “common but differentiated” framework. Humanit Soc Sci Commun 11 , 1367 (2024). Bunting, P. et al. The Global Mangrove Watch—A New 2010 Global Baseline of Mangrove Extent. Remote Sensing 10 , 1669 (2018). Worthington, T. A. et al. The distribution of global tidal marshes from Earth observation data. Global Ecology and Biogeography 33 , e13852 (2024). Worthington, T. & Spalding, M. Mangrove Restoration Potential: A global map highlighting a critical opportunity. https://doi.org/10.17863/CAM.39153 (2018) doi:10.17863/CAM.39153. IUCN & UNEP-WCMC. The World Database on Protected Areas (WDPA) and Other Effective area-based Conservation Measures (OECM). (2024). The State of the World’s Mangroves 2024 . https://repository.si.edu/handle/10088/119867 (2024) doi:10.5479/10088/119867. Convention on Wetlands et al. Global Wetland Outlook 2025: Valuing, Conserving, Restoring and Financing Wetlands . https://www.global-wetland-outlook.ramsar.org/ (2025) doi:10.69556/GWO-2025-eng. Brook, T., Millington-Drake, M., McGarrigle, A., Garbutt, A. & Rodriguez, K. State of the World’s Saltmarshes 2025. STATE OF THE WORLD (2025). UN Environmental Programme. World Seagrass Day 2025. https://www.unep.org/events/un-day/world-seagrass-day-2025 (2025). Simard, M. et al. Mangrove canopy height globally related to precipitation, temperature and cyclone frequency. Nature Geosci 12 , 40–45 (2019). Sanderman, J. et al. A global map of mangrove forest soil carbon at 30 m spatial resolution. Environ. Res. Lett. 13 , 055002 (2018). Griscom, B. W. et al. Natural climate solutions. Proceedings of the National Academy of Sciences 114 , 11645–11650 (2017). Tables Tables 1 is not available with this version. Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryFigures.docx Supplementary Information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8942230","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":602837839,"identity":"3b78c409-e14d-4a47-95bb-2fde921fc836","order_by":0,"name":"Radhika Bhargava Gajre","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYHACM4aEAwwJ/BAOMwlaJBtI0sIA1GJwgFgt5u2Htz14cMYuz/h2j/EHhgrrxAb+4xfwapE5k1ZukHAjudjszhkzCYYz6YkNEjkFeLVIMOSYSSR8YE7cdiPHjIGx7TBQC08Cfi38b0Ba6hM3z8gx/sD4D6iF/wwBLRIgW24cTtwgkWMgwdgA1MKQfoCAlmdlEglnjhdL3EgDMo6lG7dJ5ODVAXRY8jbJH8eq8/hnJG/+8KHGWraf//gD/HpQAMgTbAw8BiRogQB2UmwZBaNgFIyCEQAABdZJtBoXLuoAAAAASUVORK5CYII=","orcid":"","institution":"National University of Singapore","correspondingAuthor":true,"prefix":"","firstName":"Radhika","middleName":"Bhargava","lastName":"Gajre","suffix":""},{"id":602837840,"identity":"6a387f90-c79f-4547-948f-0ee992135435","order_by":1,"name":"Anabel Kadri","email":"","orcid":"","institution":"Tulane University","correspondingAuthor":false,"prefix":"","firstName":"Anabel","middleName":"","lastName":"Kadri","suffix":""},{"id":602837841,"identity":"ecedf8df-215c-47f2-856d-160b613824f9","order_by":2,"name":"Fernanda Adame","email":"","orcid":"https://orcid.org/0000-0001-9620-9252","institution":"Griffith University","correspondingAuthor":false,"prefix":"","firstName":"Fernanda","middleName":"","lastName":"Adame","suffix":""},{"id":602837842,"identity":"6bee4df0-0aac-497e-8fca-d9f843dc7b61","order_by":3,"name":"Stacy Baez","email":"","orcid":"","institution":"Pew Trusts","correspondingAuthor":false,"prefix":"","firstName":"Stacy","middleName":"","lastName":"Baez","suffix":""},{"id":602837843,"identity":"b03009e2-5f1b-44c4-a098-15f807d47074","order_by":4,"name":"Natasha Bhatia","email":"","orcid":"","institution":"Nanyang Technological University","correspondingAuthor":false,"prefix":"","firstName":"Natasha","middleName":"","lastName":"Bhatia","suffix":""},{"id":602837844,"identity":"9967c7f8-2b36-4678-a11b-4bb6db4476e0","order_by":5,"name":"Jacob Bukoski","email":"","orcid":"https://orcid.org/0000-0002-2334-5023","institution":"Oregon State University","correspondingAuthor":false,"prefix":"","firstName":"Jacob","middleName":"","lastName":"Bukoski","suffix":""},{"id":602837845,"identity":"ad872556-9893-45f7-8e95-59ac47f9690c","order_by":6,"name":"Miguel Cifuentes-Jara","email":"","orcid":"https://orcid.org/0000-0002-6560-947X","institution":"Smithsonian Environmental Research Center","correspondingAuthor":false,"prefix":"","firstName":"Miguel","middleName":"","lastName":"Cifuentes-Jara","suffix":""},{"id":602837846,"identity":"2edecb46-a7de-4eba-9a2c-63a056526ed0","order_by":7,"name":"Peter Macreadie","email":"","orcid":"https://orcid.org/0000-0001-7362-0882","institution":"RMIT University - Centre for Nature Positive Solutions","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"","lastName":"Macreadie","suffix":""},{"id":602837847,"identity":"641739e6-6911-48a7-b44f-37df2c4a2313","order_by":8,"name":"Sai Qu","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Sai","middleName":"","lastName":"Qu","suffix":""},{"id":602837848,"identity":"1aad363f-025b-414c-90dd-d4c19b896ccd","order_by":9,"name":"Michiel van Bruegel","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Michiel","middleName":"van","lastName":"Bruegel","suffix":""},{"id":602837849,"identity":"15d0ddb7-d756-428e-9e96-5f7bbfd868c1","order_by":10,"name":"Hao Tang","email":"","orcid":"","institution":"National University of Singapore","correspondingAuthor":false,"prefix":"","firstName":"Hao","middleName":"","lastName":"Tang","suffix":""},{"id":602837850,"identity":"7c496751-0557-4e02-aa98-4fc5a82aaa61","order_by":11,"name":"Daniel Friess","email":"","orcid":"","institution":"Tulane University","correspondingAuthor":false,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Friess","suffix":""}],"badges":[],"createdAt":"2026-02-23 02:20:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8942230/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8942230/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104779747,"identity":"f98f1624-4f62-4e79-a0b1-1a9ddaad9da4","added_by":"auto","created_at":"2026-03-17 07:45:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":182987,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eIntegration of coastal blue carbon ecosystems into national climate mitigation targets (2015–2025).\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Sankey diagram illustrating the flow from geopolitical groupings and regions to coastal ecosystems and their mitigation-oriented policy themes, as extracted from NDC reports submitted between 2015 and 2025. Node widths are proportional to the frequency of countries under those mitigation targets. The visualisation reveals a predominant focus on mangrove ecosystems within Non-Annex I regions, with 'Management' and 'Carbon Sequestration' emerging as the primary thematic drivers for emission reduction commitments. Conversely, seagrass and tidal marsh ecosystems exhibit lower levels of integration into formal mitigation pathways. Themes with low frequency are not shown; see Supplementary Figure 3 for the full list.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/36f10bb9b742581c969c81b0.jpg"},{"id":104294385,"identity":"18a332d6-2db8-417b-b7c1-aa9b0f1b2fd7","added_by":"auto","created_at":"2026-03-10 07:34:59","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":48306,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eInfluence of current conditions of blue carbon ecosystems as the primary mitigation approach highlighted in the NDCs \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eMap showing the relationship between the current condition of blue carbon ecosystems and their inclusion in national climate policies based on a multinomial logistic regression. Geospatial distribution of primary policy motivations, distinguishing regions where target inclusion is associated with habitat loss versus habitat extent and restoration potential. Annex 1 countries are outlined in yellow. Please refer to Supplementary Table 1 for the multinomial logistic regression coefficients and statistics.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/92f3ec66612314e5b83bdb30.jpg"},{"id":104405328,"identity":"d015b63e-e58c-4be3-8f5a-5a57f105aa1b","added_by":"auto","created_at":"2026-03-11 12:22:35","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":94320,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eProgression, thematic density, and the incremental integration of blue carbon in climate policy. \u003c/strong\u003e\u003c/em\u003e\u003cem\u003e(A) Scenarios of incremental inclusion of blue carbon mitigation targets with policy and assessment and monitoring (data generation) acting as enabling conditions to overcome national-level barriers. (B) A Sankey diagram illustrating the evolution of blue carbon themes through successive NDC submissions for those countries that subsequently submitted ambitious NDC targets. The flow tracks the themes from initial entry (Entrance) through developmental stages (Middle) to their integration into Current Status. Blue nodes represent Policy Gates, identifying key transition points where specific policy frameworks enable the incremental scaling of technical themes—such as Carbon Capture, Conservation, and NIR Inclusion—from strategic intent to quantified targets. Green nodes represent data generation-based targets.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/6c91a441cce916a76aee8d71.jpg"},{"id":104294380,"identity":"8ad14a62-2ff7-450d-9430-438caa2854c8","added_by":"auto","created_at":"2026-03-10 07:34:59","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":87076,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eInclusion of blue carbon mitigation in NDCs as a proportion of total opportunity and total climate mitigation commitments.\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e A) Bar graph illustrating the total current blue carbon mitigation potential (GtCO2e) across mangroves, seagrasses, tidal marshes, and tidal mudflats. The mitigation potential of NDC commitments is defined as the carbon storage achieved through the protection or restoration of blue carbon ecosystems that are specifically included as mitigation targets in NDCs. The “Other Commitments” category encompasses policy, finance, community, and collaboration-based targets, for which potential is calculated by estimating the stored carbon in the blue carbon extent of countries with these targets as the primary focus. “Not Committed” refers to the carbon stored in the blue carbon ecosystems of countries that have not included blue carbon ecosystems in their national commitments as a mitigation target. The inclusion is estimated by the area of the total blue carbon per ecosystem type included by a country in its NDC. (B) Heatmap comparing the committed mitigation \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/em\u003e\u003cem\u003ey blue carbon ecosystem and strategy for Annex I and Non-Annex I countries. (C) Global map depicting the percentage of blue carbon targets relative to total national mitigation included in NDCs.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/494e25142bcbde5f47dbaba6.jpg"},{"id":104294383,"identity":"0b98d76e-c76f-464a-9c52-859ef7a02a28","added_by":"auto","created_at":"2026-03-10 07:34:59","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":61216,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eGlobal blue carbon future mitigation potential and policy inclusion scenarios\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e. (A) Heatmap distribution of committed blue carbon (GtCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003ee) across four coastal ecosystems—tidal marshes, tidal flats, seagrasses, and mangroves—under three scenarios of increased ambition in Nationally Determined Contributions (NDCs). Scenarios are compared against a baseline to show the impact of increasing protection and restoration efforts, disaggregated by Annex 1 and Non-Annex 1 country status. Darker colours indicate higher levels of carbon commitment. (B) Global map illustrating the spatial distribution of future blue carbon mitigation potential at the national level. Colours represent the total potential (GtCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003ee), with green shades identifying Non-Annex 1 countries and purple shades identifying Annex 1 countries. Scaling indicates that the highest mitigation potential is concentrated within tropical regions and specific Annex 1 territories\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/6ea8999f09273c1c2e131d00.jpg"},{"id":104808344,"identity":"a41db95f-96c6-4eb7-80d1-8adf9621cfc0","added_by":"auto","created_at":"2026-03-17 12:36:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1643869,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/3931ba8d-b6c5-4b86-a0d7-faa34f028ca1.pdf"},{"id":104294382,"identity":"352a3824-30fb-40aa-87d2-feb5cbdc82b1","added_by":"auto","created_at":"2026-03-10 07:34:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":938917,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryFigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-8942230/v1/1fc6683936bfb6242992278b.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ambition Disparity Reveals Unlocked Mitigation Potential for Blue Carbon in the Paris Agreement","fulltext":[{"header":"Main","content":"\u003cp\u003eNatural Climate Solutions (NCS), such as forest protection, management and restoration\u003csup\u003e1\u003c/sup\u003e, can provide one-third of the climate change mitigation needed to achieve the 2\u0026deg;C target stated in the Paris Agreement\u003csup\u003e2\u003c/sup\u003e. Up to 25% of tropical countries could potentially\u0026nbsp;mitigate more than half of their national emissions through cost-effective NCS\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003csup\u003e3,4\u003c/sup\u003e. Blue carbon ecosystems \u0026ndash; including mangroves, seagrasses, tidal marshes, and tidal mudflats \u0026ndash; are\u0026nbsp;emerging contributors to natural climate change mitigation\u0026nbsp;\u003csup\u003e5\u003c/sup\u003e, as they have higher rates of productivity than terrestrial ecosystems, and two to five times more carbon storage capacity per equivalent unit area\u003csup\u003e5\u003c/sup\u003e. Global cooperation could collectively sequester up to 2.94 million tons of carbon annually and generate $136 million from carbon storage and sequestration from blue carbon ecosystems, compared to a business-as-usual scenario\u003csup\u003e6\u003c/sup\u003e. These emission reductions can be significant for countries with moderate fossil fuel emissions and extensive coastlines, such as Bangladesh or Colombia\u003csup\u003e4\u003c/sup\u003e, as well as for small island states\u003csup\u003e7\u003c/sup\u003e. Blue carbon can also generate significant blue carbon wealth (US$22.8 \u0026plusmn; 3.8 billion annually, and the largest globally) in large economies like Australia through climate change mitigation services\u003csup\u003e6\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eBlue carbon holds significant potential to complement emissions reductions from other sectors and meet national climate action goals\u003csup\u003e8,9\u003c/sup\u003e, while simultaneously supporting adaptation\u003csup\u003e10\u003c/sup\u003e, biodiversity\u003csup\u003e11\u003c/sup\u003e, and coastal resilience\u003csup\u003e12\u003c/sup\u003e. This is achieved by generating accountable emission reductions within the Land Use, Land-use Change and Forestry (LULUCF) sector, which directly supports the mitigation targets specified in countries\u0026apos; Nationally Determined Contributions (NDCs) and is tracked in their National Inventory Reports (NIRs). Yet, the use of blue carbon and other NCS for national emission reductions is still limited, leaving potential mitigation underutilised in the Paris Agreement\u003csup\u003e13\u003c/sup\u003e. Moreover, despite global participation in achieving climate action through the Paris Agreement\u003csup\u003e14\u003c/sup\u003e, the ambition deficit persists in both Annex I (industrialised nations and economies in transition) and Non-Annex I (developing) countries\u003csup\u003e15\u003c/sup\u003e. Only 104 of 168 countries\u0026mdash;predominantly Non-Annex I\u0026mdash;have formally incorporated NCS into their NDCs, with merely 48 countries referencing coastal ecosystems\u003csup\u003e16\u003c/sup\u003e. Ideally, Annex I countries would take immediate action while simultaneously supporting capacity-building in Non-Annex I countries to pursue low-carbon development, adaptation and mitigation pathways\u003csup\u003e17\u003c/sup\u003e. In practice, however, many Annex I countries have demonstrated limited integration and specificity of nature-based mitigation, including blue carbon, in their submissions\u003csup\u003e15,18\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe global potential for blue carbon is well established\u003csup\u003e8,19\u003c/sup\u003e; however, a significant yet unquantified challenge is the fundamental misalignment between national climate policy ambitions and the underlying mitigation potential of coastal countries, driven in many cases by constraints related to data availability, technical capacity, and inventory readiness, rather than a lack of policy intent\u003csup\u003e20,21\u003c/sup\u003e. Our study addresses this critical gap and how it is hindering opportunities for high-impact climate action. By mapping current policy commitments against national biophysical potential and identifying barriers and enabling conditions, we uncover a substantial, quantifiable mitigation gap between committed and achievable blue carbon emissions reductions, as well as future potential for enhancement. Financial barriers\u003csup\u003e22\u003c/sup\u003e, limited specificity in pledges, and persistent gaps between commitments and accounting readiness\u003csup\u003e20\u003c/sup\u003e put the success of the Paris Agreement\u0026apos;s climate change mitigation targets at risk\u003csup\u003e13\u003c/sup\u003e. We demonstrate how nations can bridge ambition disparity by utilising the NDC mechanism to incrementally integrate blue carbon ecosystems \u0026ndash; transforming national constraints into strategic entry points. By framing these habitats as strategic targets rather than omitting them due to national circumstances or barriers, nations can leverage the Paris Agreement\u0026rsquo;s inherent flexibility to bridge the ambition disparity and create the enabling conditions for more robust, holistic climate commitments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAmbition Disparity:\u003c/strong\u003e \u003cstrong\u003eNon-Annex I Countries Drive the Global Blue Carbon Commitment Baseline\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe reviewed the NIRs of 156 Paris Agreement signatories with at least one blue carbon ecosystem\u0026nbsp;to identify the tier of inclusion of blue carbon ecosystems since 2015. The IPCC Tier system is a three-level accounting framework, with localisation of data (and therefore accuracy) increasing from the simple Tier 1 (which utilises globally averaged estimates of emission factors) to the highly detailed, country-specific data used in Tier 3\u003csup\u003e23\u003c/sup\u003e. We found that national blue carbon reporting is fundamentally fragmented. Most coastal nations either omit these ecosystems entirely or rely on lower-tier estimates that fail to capture the full scope of ecosystem potential for climate action (Fig. 1A, 1B). Blue carbon ecosystems were included in the NIRs of 20% of all blue carbon countries, of which 67% were Non-Annex 1 (Supplementary Figure 1A). However, most countries only included blue carbon ecosystems at Tier 1, relying on globally averaged emissions factors, and only the US, Australia, Croatia, Japan and New Zealand included \u0026nbsp;more than one blue carbon ecosystem (Supplementary Figure 1B).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNext, we examined how mitigation targets from blue carbon ecosystems were incorporated into the NDCs since 2015. The inclusion of blue carbon ecosystems as a mitigation target was uneven, with contributions disproportionately higher from Non-Annex I countries (Supplementary Figure 1C). Specifically, 46% of the countries with at least one blue carbon ecosystem included it as a mitigation target in their NDC submissions since 2015; of these, 93% were Non-Annex I countries. The limited inclusion from Annex I countries aligns with similarly low uptake of other NCS, adaptation\u003csup\u003e24\u003c/sup\u003e and renewable energy targets\u003csup\u003e15,25,26\u003c/sup\u003e. However, the NDC 3.0 submitted in 2025 showed a higher inclusion of multiple blue carbon ecosystems from Non-Annex I countries (Supplementary Figure 1C).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDespite fewer financial resources, Non-Annex I countries also set quantitative blue carbon targets and committed to meeting them unconditionally. Since 2015, one-fifth of countries (21%) included at least one unconditional target, 19% included only quantitative targets (for example, hectares of carbon sequestration achieved), and 14% included both, with the majority of these being Non-Annex I countries (Supplementary Figure 2). African countries reported the highest number of quantitative and unconditional targets (18%), although regional disparities within these countries exist\u003csup\u003e27\u003c/sup\u003e. In Southeast Asia, blue carbon follows a clear trajectory of increasing ambition since NDCs were first submitted, echoing the regional shift toward more robust, unconditional NDC targets\u003csup\u003e24\u003c/sup\u003e.\u0026nbsp;Non-Annex I countries frequently state ambitions in NDCs but exclude or fail to account for blue carbon ecosystems based on the IPCC Wetlands Supplement in NIRs, signalling insufficient monitoring capacity, potentially impacted by jurisdictional ambiguity\u003csup\u003e28\u003c/sup\u003e and staff limitations\u003csup\u003e29\u003c/sup\u003e. Conversely, nine countries reported mangroves in NIRs without NDC targets, highlighting gaps related to political prioritisation, data availability or other national circumstances.\u003c/p\u003e\n\u003cp\u003eTo understand how countries include blue carbon as a mitigation target, we conducted a thematic classification of blue carbon-based mitigation targets included in NDCs since 2015. This captured both the types of themes and the scope of blue carbon inclusion in NDCs, despite differences in national circumstances between Annex I and Non-Annex I countries. Across both groups, the key mitigation targets based on blue carbon ecosystems were similar \u0026ndash; improved management (92%), utilisation of carbon sequestration services (72%), and restoration (66%). However, 47% of the countries also identified improving data as a key target. The NDCs also consistently incorporated supportive targets\u0026mdash;such as closing data gaps, addressing policy requirements, ensuring community inclusion, and refining accounting\u0026mdash;that facilitate, rather than directly execute, emission reductions (Fig. 1). While mangroves management emerged as the primary blue carbon target, a lack of specificity persisted, with many countries grouping diverse and general mitigation actions under broad, non-specific \u0026apos;blue carbon\u0026apos; labels.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 1 | Integration of coastal blue carbon ecosystems into national climate mitigation targets (2015\u0026ndash;2025).\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;Sankey diagram illustrating the flow from geopolitical groupings and regions to coastal ecosystems and their mitigation-oriented policy themes, as extracted from NDC reports submitted between 2015 and 2025. Node widths are proportional to the frequency of countries under those mitigation targets. The visualisation reveals a predominant focus on mangrove ecosystems within Non-Annex I regions, with \u0026apos;Management\u0026apos; and \u0026apos;Carbon Sequestration\u0026apos; emerging as the primary thematic drivers for emission reduction commitments. Conversely, seagrass and tidal marsh ecosystems exhibit lower levels of integration into formal mitigation pathways. Themes with low frequency are not shown; see Supplementary Figure 3 for the full list.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eWe performed a multinomial logistic regression to test whether the patterns of inclusion of blue carbon-based mitigation targets could be explained by key national characteristics: the extent of blue carbon cover, intertidal area loss (including blue carbon ecosystems), protected area, and restoration potential. We found that the inclusion of blue carbon ecosystems was associated with opportunity rather than threat (Supplementary Figure 4). For example, intertidal loss was universally yet negatively associated with adoption of blue carbon mitigation targets (p-value \u0026lt; 0.001 and odds ratio \u0026lt; 1) across all ecosystems. Countries experiencing the highest rates of intertidal loss were significantly less likely to include blue carbon-based mitigation targets, indicating a gap in the translation of observed loss into mitigation targeting. Conversely, restoration potential showed a strong positive association with management and restoration targets, particularly in mangrove (p-value = 0.008; odds ratio = 1) and seagrass habitats (p-value \u0026lt; 0.001; odds ratio = 1.001). Meanwhile, the extent of blue carbon habitats and protected area status associated with inclusion as a management target in regions such as Australia and Mexico suggests a resource-led policy approach, where abundance facilitated inclusion (Fig. 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 2 |Influence of current conditions of blue carbon ecosystems as the primary mitigation approach highlighted in the NDCs\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003eMap showing the relationship between the current condition of blue carbon ecosystems and their inclusion in national climate policies based on a multinomial logistic regression. Geospatial distribution of primary policy motivations, distinguishing regions where target inclusion is associated with habitat loss versus habitat extent and restoration potential. Annex 1 countries are outlined in yellow. Please refer to Supplementary Table 1 for the multinomial logistic regression coefficients and statistics.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOur statistical tests revealed that while ecological baseline data and restoration potential can inform national ambition, the decision to formalise blue carbon targets remains a strategic policy choice (e.g., national circumstances driven decarbonisation interests, or focus on adaptation, resilience and livelihoods over mitigation) rather than a direct reflection of ecosystem extent or local environmental threat. For instance, the Asia Pacific region hosts the largest extent of mangroves, seagrass, and tidal flats, while Europe and the US combined have the largest extent of tidal marshes (Supplementary Figure 4C)\u0026nbsp;\u003csup\u003e30\u0026ndash;32\u003c/sup\u003e. Yet the geographical distribution of blue carbon ecosystems and their inclusion in NDCs were misaligned, consistent with a historical focus on mangroves in science and policy until recently. Blue carbon mitigation targets were also included by countries with minimal blue carbon area (e.g., Guyana, Kiribati), signalling recognised future mitigation potential or co-benefits.\u0026nbsp;Moreover, out of 30 countries experiencing high mangrove deforestation\u003csup\u003e33\u003c/sup\u003e, 12 included mangrove targets, primarily for restoration rather than halting deforestation. Our results suggest great potential for improved national data to guide policy towards strategies that respond to national circumstances, such as targets for avoided conversion in countries experiencing high rates of blue carbon ecosystem loss.\u0026nbsp;A country\u0026apos;s focus on blue carbon could also be driven by the proportion of its blue carbon extent and removal potential relative to its national scale\u003csup\u003e7\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNational Circumstances Guide Pathways for Strengthening Blue Carbon Ambition\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThrough successive NDC submissions, the Paris Agreement encourages growth in mitigation ambition\u003csup\u003e18\u003c/sup\u003e. We thematically analysed each subsequent NDC submission for blue carbon mitigation targets since 2015 to identify opportunities and enabling conditions for strengthening NDC ambition through quantitative, mitigation-specific targets for blue carbon. Ambition evolved from management as the primary target to quantitative, mitigation-specific targets since 2015 (Fig. 3B). We observed that opportunities for blue carbon as mitigation targets were driven by national circumstances. Only 25 Non-Annex I countries submitted ambitious blue carbon mitigation targets. Focal entry points varied across countries, reflecting differing national circumstances. Enhanced management or increased protection were the most common entry points for the countries that submitted ambitious targets in later NDCs (15 countries) (Fig. 3B). Setting ambitious targets in subsequent NDCs depended on enabling conditions, progress since previous submissions, and external support. For instance, Angola, Mexico, and Sri Lanka first included blue carbon ecosystems as a carbon sequestration targets, while many others included intermediate targets on measurement, protection, and restoration before committing to specific projects. In the NDC 3.0, ambitious targets included establishing mechanisms for long-term monitoring, forming alliances, enhancing inclusion in NIRs, and designing quantitative projects. Overall, blue carbon inclusion has progressed from data generation to actionable projects over the past decade.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 3 | Progression, thematic density, and the incremental integration of blue carbon in climate policy.\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e(A) Scenarios of incremental inclusion of blue carbon mitigation targets with policy and assessment and monitoring (data generation) acting as enabling conditions to overcome national-level barriers. (B) A Sankey diagram illustrating the evolution of blue carbon themes through successive NDC submissions for those countries that subsequently submitted ambitious NDC targets. The flow tracks the themes from initial entry (Entrance) through developmental stages (Middle) to their integration into Current Status. Blue nodes represent Policy Gates, identifying key transition points where specific policy frameworks enable the incremental scaling of technical themes\u0026mdash;such as Carbon Capture, Conservation, and NIR Inclusion\u0026mdash;from strategic intent to quantified targets. Green nodes represent data generation-based targets.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFinally, our thematic analysis of targets from subsequent NDC submissions demonstrates that countries utilised the NDCs to create enabling conditions to address gaps and enhance the inclusion of blue carbon. The use of the NDC framework to create enabling conditions was national-circumstance-dependent \u0026ndash; 13 countries included quantitative, mitigation-specific targets blue carbon targets without the need for enabling conditions, while 12 incrementally increased their ambition by overcoming barriers (Fig. 3). The two key enabling conditions that paved the way for ambitious targets were data generation and policy enhancement, although these do not necessarily imply actions in the field (Fig. 3A). Prioritising data needs highlights critical pre-existing data deficiencies and points to the systemic issues inherent in collecting robust, verifiable and standardised data required for high-integrity mitigation targets\u003csup\u003e34\u003c/sup\u003e. Inadequate data were addressed by setting targets to enhance the national capacity to generate the data required for blue carbon accounting since 2015. Countries are overcoming data scarcity by prioritising enhancements to blue carbon databases within their climate goals. Key data requirements included mapping land cover change (73%), quantifying local carbon biomass (73%), and monitoring restoration (66%). By stipulating these needs in NDCs, nations are formalising the transition from measurement gaps to actionable accounting pathways\u003csup\u003e35\u003c/sup\u003e. Filling data gaps in earlier NDCs enabled 18 out of 25 countries with subsequent NDC submissions to include blue carbon ecosystems in their NIRs, thereby bridging the gap between NDC ambition and capacity.\u003c/p\u003e\n\u003cp\u003eNext, our thematic analysis highlighted that establishing enabling policy conditions was a key target for integrating blue carbon into a country\u0026rsquo;s NDC. This involved the inclusion of targets to develop policy frameworks that support the monitoring, mapping, protection, and restoration of these ecosystems (Fig. 3B). For instance, Liberia and the Bahamas amended their previous national policies to include restoration and carbon sequestration in national forest management plans. Policy framework development served as an essential precursor to actionable blue carbon targets for 13 of the 25 countries with subsequent ambitious submissions (Fig. 3). In addition, policy enhancements were shown to support land tenure, management, assessment of area extent, carbon sink enhancement, the establishment of task forces, and the development of national blue carbon strategies. Integrating blue carbon ecosystems into national legal frameworks strengthens mitigation and net-zero targets, hence providing a critical pathway for fulfilling the Paris Agreement\u003csup\u003e36\u003c/sup\u003e. The policies could accommodate new phases of transition (for example, blue carbon inclusion), be transferable (for example, integrating REDD+ and the Global Biodiversity Framework into NDCs), and be adaptive to feedback\u003csup\u003e37\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDespite the wide coverage of themes, the current inclusion of blue carbon lacked clarity on implementation, financial, and capacity needs. Technical support from international organisations aimed at filling scientific and policy gaps is an essential pathway to addressing financial, technical, and capacity needs\u003csup\u003e38\u003c/sup\u003e,\u003csup\u003e39\u003c/sup\u003e. Capacity-building, crucial for NDC implementation and covering finance and technology transfer\u003csup\u003e40\u003c/sup\u003e, remains narrowly focused on general GHG emissions reporting\u003csup\u003e41\u003c/sup\u003e. While examining the support countries received in writing and in developing their NDC 3.0 in 2025, 15 out of 40 countries sought essential support to fill scientific and policy gaps, as well as financial, technical, and capacity-building assistance from UN-based organisations, international organisations, or regional coalitions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eQuantifying Unlocked Mitigation Potential: Future Scenarios for Closing the Global Blue Carbon Commitment Shortfall\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe quantified the mitigation potential of blue carbon currently included in NDCs to understand their contributions to global climate change mitigation commitments and the existing mitigation gaps to be filled. The current and future mitigation potential was estimated by calculating the mitigation potential (avoided emissions and carbon removal) under current inclusion and future protection, restoration, and sequestration in 2050.\u0026nbsp;Global blue carbon integration reveals a mitigation ambition gap between Annex I and Non-Annex I countries, with a total of 25.5 GtCO\u003csub\u003e2\u003c/sub\u003ee (95% CI: 17.52 \u0026ndash; 33.48 GtCO\u003csub\u003e2\u003c/sub\u003ee) currently committed in NDCs (Fig. 4). Non-Annex I countries are the primary drivers of this mitigation, contributing 21 GtCO\u003csub\u003e2\u003c/sub\u003ee (95% CI: 14.43 \u0026ndash; 27.57 GtCO\u003csub\u003e2\u003c/sub\u003ee) and harnessing 37% of their available potential, largely through combined protection and restoration strategies. Annex I countries have left 84% of their potential uncommitted - a substantial shortfall in committed mitigation relative to their capacity. This disparity highlights inequitable global contributions\u003csup\u003e42\u003c/sup\u003e, particularly as Annex I countries have historically exceeded their carbon budgets\u003csup\u003e18,43\u003c/sup\u003e. High-inclusion hotspots are concentrated in the Indo-Pacific and Caribbean regions, where blue carbon is an important climate strategy for land-scarce and ocean-dependent countries. Conversely, many Annex I countries with extensive coastlines exhibit a low proportion of integration, suggesting that blue carbon is often recognised qualitatively in text but remains unquantified as a core component of total mitigation commitments (Fig. 4), with other strategies taking priority.\u003c/p\u003e\n\u003cp\u003eAt the ecosystem level, seagrasses currently provide a higher quantified mitigation benefit\u0026nbsp;because of their larger distribution area than mangroves, despite mangroves being more\u0026nbsp;commonly\u0026nbsp;included\u0026nbsp;in NIRs and NDCs.\u0026nbsp;Despite this, substantial methodological, mapping, and accounting\u0026nbsp;challenges constrain\u0026nbsp;short-term advances with seagrass ecosystems\u003csup\u003e42\u003c/sup\u003e. While mangroves exhibit the largest future gaps, substantial unutilized potential also remains in Non-Annex I\u0026rsquo;s tidal marshes and Annex I\u0026rsquo;s seagrass meadows (Fig. 4 A, B). Non-Annex I countries\u0026mdash;particularly Small Island Developing States and Southeast Asian countries\u0026mdash;maintain a more holistic representation of ecosystems within their NDC mitigation potential (Fig. 4C). Closing these commitment gaps is essential to prevent the degradation of vast, non-committed carbon pools and to fully leverage coastal ecosystems as a scalable climate solution.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 4 | Inclusion of blue carbon mitigation in NDCs as a proportion of total opportunity and total climate mitigation commitments.\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;A) Bar graph illustrating the total current blue carbon mitigation potential (GtCO2e) across mangroves, seagrasses, tidal marshes, and tidal mudflats. The mitigation potential of NDC commitments is defined as the carbon storage achieved through the protection or restoration of blue carbon ecosystems that are specifically included as mitigation targets in NDCs. The \u0026ldquo;Other Commitments\u0026rdquo; category encompasses policy, finance, community, and collaboration-based targets, for which potential is calculated by estimating the stored carbon in the blue carbon extent of countries with these targets as the primary focus. \u0026ldquo;Not Committed\u0026rdquo; refers to the carbon stored in the blue carbon ecosystems of countries that have not included blue carbon ecosystems in their national commitments as a mitigation target. The inclusion is estimated by the area of the total blue carbon per ecosystem type included by a country in its NDC. (B) Heatmap comparing the committed mitigation \u003cstrong\u003eb\u003c/strong\u003ey blue carbon ecosystem and strategy for Annex I and Non-Annex I countries. (C) Global map depicting the percentage of blue carbon targets relative to total national mitigation included in NDCs.\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNext, we modelled three future inclusion scenarios projected to 2050: (S1) maintenance of currently protected areas; (S2) protection of all extant blue carbon ecosystems; and (S3) full protection coupled with future restoration potential. Our estimates indicate that the widespread adoption of S3 within the current NDC cycle would result in the sequestration and storage of\u0026nbsp;122.3 GtCO₂e (95% CI: 84.03 \u0026ndash; 160.57 GtCO₂e) by 2050. Seagrass protection and restoration offer the highest individual contribution to global mitigation potential, followed by integrated mangrove protection and restoration (Fig. 5A). Regionally, the most significant future gains are concentrated in Non-Annex I countries, where seagrass and mangrove protection and restoration represent substantial untapped carbon sinks (Fig. 5A). Spatially, the global distribution of this 2050 potential remains robust across most coastal regions. Except for some areas in Europe, South America, and Africa, blue carbon inclusion offers a high mitigation potential, ranging from 0.68 to 18 Gt CO\u003csub\u003e2\u003c/sub\u003e eq globally (Fig. 5B). These findings highlight a clear geographic and thematic roadmap for closing the current ambition gap through quantified, ecosystem-specific targets.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFigure 5 |\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003cstrong\u003eGlobal blue carbon future mitigation potential and policy inclusion scenarios\u003c/strong\u003e. (A) Heatmap distribution of committed blue carbon (GtCO\u003csub\u003e2\u003c/sub\u003ee) across four coastal ecosystems\u0026mdash;tidal marshes, tidal flats, seagrasses, and mangroves\u0026mdash;under three scenarios of increased ambition in Nationally Determined Contributions (NDCs). Scenarios are compared against a baseline to show the impact of increasing protection and restoration efforts, disaggregated by Annex 1 and Non-Annex 1 country status. Darker colours indicate higher levels of carbon commitment. (B) Global map illustrating the spatial distribution of future blue carbon mitigation potential at the national level. Colours represent the total potential (GtCO\u003csub\u003e2\u003c/sub\u003ee), with green shades identifying Non-Annex 1 countries and purple shades identifying Annex 1 countries. Scaling indicates that the highest mitigation potential is concentrated within tropical regions and specific Annex 1 territories.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClosing the ambition disparity through systematic, incremental and holistic inclusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor countries looking to include blue carbon ecosystems for mitigation or enhance current ambitions, the NDC mechanism could resolve challenges related to national circumstances\u0026mdash;such as data deficits, lacking policy frameworks, and capacity needs\u003csup\u003e43\u003c/sup\u003e. This necessitates incorporating targets incrementally to establish enabling conditions now, creating future opportunities to integrate quantitative mitigation-based targets and accounting in NIRs. Blue carbon inventories present unique challenges due to tidal inundation, seasonality and the need to integrate non-land-based categories\u003csup\u003e35,44,45\u003c/sup\u003e. While ease of classification benefited mangroves, data gaps encompassed all ecosystems across both country groups. Non-Annex I and Annex I countries emphasised improving understanding, measurement, and mapping of all ecosystems. Acknowledging the flexibility inherent in the Paris Agreement, higher inclusion in national accounting is achievable by leveraging IPCC defaults for Tier 1 inclusion\u003csup\u003e23\u003c/sup\u003e. Moving beyond Tier 1 requires dedicated capacity, supported by global coordination and resource sharing, such as Indonesia\u0026apos;s development of national emission factors for mangroves\u003csup\u003e46\u003c/sup\u003e. Additionally, establishing blue carbon-specific strata within national forest or wetland inventories, and/or REDD+ reference levels, will systematically aid in NIR integration\u003csup\u003e47\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe identified mitigation potential of\u0026nbsp;122.3 GtCO₂e (95% CI: 84.03 \u0026ndash; 160.57 GtCO₂e) represents a substantial opportunity for the UN Global Stocktake to move beyond terrestrial-focused mitigation and address the significant \u0026quot;commitment gap\u0026quot; in national climate targets. Our findings suggest that current NDCs underutilise blue carbon, particularly in Annex I countries, while Non-Annex I countries also have significant work ahead to utilise the Paris Agreement to create enabling conditions for the future integration of quantitative targets. To align with a 1.5 \u0026deg;C pathway, future policy cycles need to transition from broad conservation rhetoric to quantified, ecosystem-specific targets and field implementation that include seagrasses and tidal marshes\u0026mdash;the largest non-committed carbon pools. By integrating these high-density sinks into formal reporting frameworks (e.g., NIR Inclusion), countries can provide the transparent, science-based accounting necessary for the second Global Stocktake to reflect the true mitigation capacity of global coastal ecosystems.\u003c/p\u003e\n\u003cp\u003eBlue carbon, although globally small in extent, contributes substantially as a low-cost\u003csup\u003e48\u003c/sup\u003e and profitable\u003csup\u003e49\u003c/sup\u003e NCS at the national scale\u003csup\u003e5\u003c/sup\u003e. We demonstrate that with full protection and restoration, blue carbon ecosystems can mitigate 2.5 years of global greenhouse gas emissions and 10 times current annual AFOLU emissions. Including blue carbon ecosystems in NDCs is a multifaceted strategy- advancing climate mitigation, conservation, and co-benefits while generating financial and technical support. Such inclusion enhances protection, attracts restoration investment\u003csup\u003e50\u003c/sup\u003e, informs conservation-oriented policy, and raises public awareness\u003csup\u003e51\u003c/sup\u003e. The Paris Agreement\u0026rsquo;s flexibility\u003csup\u003e52,53\u003c/sup\u003e and equity\u003csup\u003e54\u003c/sup\u003e mechanics can enable countries to overcome nation-specific barriers and create enabling conditions for future integration, leading to NIR inclusion for systematic monitoring. To achieve this, blue carbon ecosystems should be identified and included in NDCs and eventually in NIRs by all relevant countries. Blue carbon efforts through the Paris Agreement must transcend siloed mitigation approaches to capture the full spectrum of adaptation, social and ecological value\u003csup\u003e43\u003c/sup\u003e. The effectiveness of these ecosystems\u0026rsquo; hinges on their co-benefits, requiring NDCs to link carbon sequestration targets directly with adaptation and biodiversity conservation through international agreements to enhance global synergies.\u0026nbsp;\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cem\u003eThematic analysis of UNFCCC Reports\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eUsing global extent datasets (Table 1), a list of coastal countries with blue carbon ecosystems\u0026mdash;mangroves, seagrasses, tidal marshes, and tidal flats\u0026mdash;was created. Countries were categorised as Annex-1 and Non-Annex 1 using the UNFCCC classification. Each Annex I country submitted an NDC and NIR every 5 and 1 year, respectively. We reviewed all reports submitted by coastal countries with blue carbon ecosystems under the UNFCCC from 2015 to June 2025 via the UNFCCC party-authored reports portal (https://unfccc.int/reports). First, we searched the content of the reports for \u0026ldquo;mangrove\u0026rdquo;, \u0026ldquo;seagrass\u0026rdquo;, \u0026ldquo;tidal marsh\u0026rdquo;, \u0026ldquo;tidal flat\u0026rdquo;, \u0026ldquo;coastal wetland\u0026rdquo;, and \u0026ldquo;blue carbon\u0026rdquo;. For each report that mentioned these terms, text covering targets for biodiversity, adaptation, mitigation, and carbon sequestration was extracted and categorised as conditional/unconditional and quantitative/qualitative. A total of 331 NDCs, 446 NIRs, and 824 NCs on mitigation and carbon sequestration-based targets to identify key themes, temporally changing themes, and sub-themes (Supplementary Table 1). Inter-code validation was performed by two researchers, each of whom first coded a 30% subset of the dataset. Themes were finalised when agreement exceeded 90%, and a second round of thematic analysis was performed on 100% of the data to assign final codes and themes. A list of themes and codes is given in (Supplementary Table 1). Using the initial sets of themes, we re-coded the data to identify countries which submitted multiple NDCs with enhanced blue carbon targets. This analysis was repeated for each category of target \u0026ndash; all targets, unconditional, quantitative, and any notes supplemented by countries related to mitigation targets.\u003c/p\u003e\n\u003cp\u003eTo identify countries that have included blue carbon ecosystems in their GHG inventories, blue carbon ecosystems (mangroves, seagrass, tidal marshes and tidal mudflats) were searched for in inventory reports or any other supplementary documents submitted with the NIRs. Next, we examined the methods section of these reports for the included blue carbon ecosystem to ensure that the ecosystem of interest was classified separately rather than merged into a broader category. For example, we selected only countries that included mangroves using the 2013 and 2019 IPCC Wetlands Supplement methods, rather than terrestrial forest methods. For countries that did not provide details on methods and inclusion types, we excluded them from our analysis. Thus, there might be countries that included blue carbon ecosystems in their inventory, but if they did not include the details in the methods submitted in the report, we did not include those countries.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMultiple logistic regression analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTo assess the influence of the current national status of blue carbon ecosystems on the inclusion of corresponding ecosystems within national policy documents, we employed multinomial logistic regression. We constructed separate models for each of the four blue carbon ecosystems, with the dependent variable being the NDC Target (e.g., Restoration, Management, Management and Restoration, or Other Themes). The baseline for all models was the \u0026apos;not included\u0026apos; (NI) target. We characterised the current status of blue carbon ecosystems using four independent variables that help describe trends in blue carbon ecosystem conservation: extent\u003csup\u003e31,32,55,56\u003c/sup\u003e, restoration potential\u003csup\u003e3,57\u003c/sup\u003e, protected area\u003csup\u003e58\u003c/sup\u003e, and intertidal loss\u003csup\u003e31\u003c/sup\u003e. The models yielded odds ratios and associated P-values for each policy outcome relative to the no-target baseline.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eNDC mitigation potential and scenario analysis\u003c/em\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe current NDC mitigation potential refers to the total carbon dioxide equivalent from all blue carbon ecosystems currently committed under the NDCs, whereas the future NDC mitigation potential represents the total avoided deforestation (from additional protection and improved management of current protected areas) and carbon removal (restoration). Since many countries included an improved management target, we assumed that improving management would reduce deforestation within protected areas. The year 2025 was used as the baseline for these calculations. Carbon biomass values for different blue carbon pools were estimated from global geospatial datasets or global averages (Supplementary Table 2). For restoration, global prediction maps were used, except for tidal flats, for which no such maps are available. Using the same datasets, three scenarios were developed to assess whether blue carbon ecosystems are included in NDCs and the potential for carbon storage in 2050, with 2025 as the baseline year. The three scenarios included the current protected area extent for blue carbon ecosystems, encompassing all blue carbon ecosystems\u0026apos; extent as protected areas, as well as all extent designated as protected areas, including potentially restorable areas. To estimate deforestation rates, we used global estimates for all blue carbon ecosystems\u003csup\u003e59\u0026ndash;62\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eWe calculated carbon stocks for mangroves using Simard et al\u003csup\u003e63\u003c/sup\u003e and Sanderman et al\u0026rsquo;s\u003csup\u003e64\u003c/sup\u003e global mangrove aboveground and soil carbon stocks using country-level aggregation. Next, we used global carbon stock averages for aboveground and soil carbon from tidal marshes and tidal flats, as reported by Howard et al.\u003csup\u003e19\u003c/sup\u003e. Seagrass estimates were adopted from marine ecoregional averages presented in Krauss et al.\u003csup\u003e42\u003c/sup\u003e. Mangrove restoration per country was aggregated from Worthington et al.\u003csup\u003e57\u003c/sup\u003e, while seagrass and tidal marsh restoration values were from Griscom et al.\u003csup\u003e65\u003c/sup\u003e. We estimated stock growth in 2050 based on carbon sequestration between 2025 and 2050. To estimate total carbon stocks in 2050, we used carbon sequestration rates for all ecosystems from Howard et al.\u0026nbsp;\u003csup\u003e19\u003c/sup\u003e. For mangroves, seagrass, and tidal marshes, where we had restoration area values, we assumed that the baseline carbon stock is zero and estimated a linear increase in stock due to new restorations in 2025, projected for the year 2050. Since we used secondary datasets for all our analyses, the accuracy of our estimations depends on the accuracy and uncertainty of the base datasets, as detailed in Supplementary Table 2.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEllis, P. 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W. \u003cem\u003eet al.\u003c/em\u003e Natural climate solutions. \u003cem\u003eProceedings of the National Academy of Sciences\u003c/em\u003e \u003cstrong\u003e114\u003c/strong\u003e, 11645\u0026ndash;11650 (2017).\u003c/li\u003e\n\u003cli\u003e\u003cbr\u003e\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 is not available with this version.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Climate change mitigation, mangrove, seagrass, tidal marsh, tidal flats, Nationally Determined Contributions, National Inventory Reports","lastPublishedDoi":"10.21203/rs.3.rs-8942230/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8942230/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Blue carbon ecosystems, despite their significant climate change mitigation potential, remain underrepresented in the Paris Agreement. Only 20% of the blue carbon-holding countries have incorporated them into National Inventory Reports (NIRs), and 46% have included them as mitigation targets in Nationally Determined Contributions (NDCs), with Non-Annex I countries accounting for the majority of these inclusions. Full protection and restoration of blue carbon ecosystems could sequester up to 122.3 GtCO₂e (95% CI: 84.03 – 160.57 GtCO₂e) by 2050—effectively offsetting 10 years of the world's current land cover change carbon footprint. However, only 25.52 GtCO₂e (95% CI: 17.52 – 33.48 GtCO2e), i.e., 30%, of their mitigation potential is currently pledged. Non-Annex I countries have committed twice (37%) the potential of Annex I countries (16.4%), highlighting both the opportunity and the disparity in policy uptake relative to mitigation potential. We demonstrate that NDCs can be utilised to incrementally integrate blue carbon, transforming disparity into strategic entry points, catalysing more ambitious climate targets while safeguarding coastal resilience.","manuscriptTitle":"Ambition Disparity Reveals Unlocked Mitigation Potential for Blue Carbon in the Paris Agreement","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-10 07:34:53","doi":"10.21203/rs.3.rs-8942230/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-climate-change","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nclimate","sideBox":"Learn more about [Nature Climate Change](http://www.nature.com/nclimate/)","snPcode":"","submissionUrl":"","title":"Nature Climate Change","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4ca47a44-5ae8-4388-911d-8d4cc3d42997","owner":[],"postedDate":"March 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":64143493,"name":"Earth and environmental sciences/Environmental social sciences/Climate-change mitigation"},{"id":64143494,"name":"Earth and environmental sciences/Environmental social sciences/Climate-change policy"}],"tags":[],"updatedAt":"2026-04-24T03:10:41+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-10 07:34:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8942230","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8942230","identity":"rs-8942230","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}