Plastics in blue carbon ecosystems: a call for global cooperation on climate change goals

Blue carbon ecosystems (BCEs; figure), comprising tidal marshes, mangrove forests, and seagrass meadows, contribute more than 50% of the total organic carbon buried in global marine sediments, despite occupying only 0·5% of the sea floor.1Duarte CM Losada IJ Hendriks IE Mazarrasa I Marbà N The role of coastal plant communities for climate change mitigation and adaptation.Nat Clim Chang. 2013; 3: 961-968Crossref Scopus (811) Google Scholar The ability of BCEs to sequester carbon dioxide into large amounts of stored sediment carbon1Duarte CM Losada IJ Hendriks IE Mazarrasa I Marbà N The role of coastal plant communities for climate change mitigation and adaptation.Nat Clim Chang. 2013; 3: 961-968Crossref Scopus (811) Google Scholar makes them important nature-based solutions for climate adaptation and mitigation.2Macreadie PI Anton A Raven JA et al.The future of Blue Carbon science.Nat Commun. 2019; 10: 1-13PubMed Google Scholar The features that make BCEs important carbon sinks (ie, their global distribution and capacity to trap and preserve a large amount of carbon dioxide at the land and ocean interface) also make them an important sink of plastic-carbon. As of 2015, about 8300 million metric tonnes of virgin plastics were produced globally,3Geyer R Jambeck JR Law KL Production, use, and fate of all plastics ever made.Sci Adv. 2017; 3e1700782Crossref PubMed Scopus (3532) Google Scholar which is equivalent to 6900 million metric tonnes of plastic-carbon. Approximately 50–80 million metric tonnes of plastic-carbon accumulate within natural systems each year due to plastic mismanagement.4Lebreton L Andrady A Future scenarios of global plastic waste generation and disposal.Palgrave Commun. 2019; 5: 1-11Crossref Scopus (370) Google Scholar By comparison, BCEs accumulate about 100 million metric tonnes of blue carbon each year.5Stubbins A Law KL Muñoz SE Bianchi TS Zhu L Plastics in the Earth system.Science. 2021; 373: 51-55Crossref PubMed Scopus (30) Google Scholar The current stocks of plastic-carbon in the global coastal systems are about 3–10 million metric tonnes,5Stubbins A Law KL Muñoz SE Bianchi TS Zhu L Plastics in the Earth system.Science. 2021; 373: 51-55Crossref PubMed Scopus (30) Google Scholar with growing reports of plastic-carbon within BCEs.6Sanchez-Vidal A Canals M de Haan WP Romero J Veny M Seagrasses provide a novel ecosystem service by trapping marine plastics.Sci Rep. 2021; 11: 1-7Crossref PubMed Scopus (16) Google Scholar, 7Martin C Baalkhuyur F Valluzzi L et al.Exponential increase of plastic burial in mangrove sediments as a major plastic sink.Sci Adv. 2020; 6eaaz5593Crossref PubMed Scopus (39) Google Scholar, 8Stead JL Cundy AB Hudson MD et al.Identification of tidal trapping of microplastics in a temperate salt marsh system using sea surface microlayer sampling.Sci Rep. 2020; 10: 1-10Crossref PubMed Scopus (8) Google Scholar If the present cubic growth trend for plastic accumulation and uncertain socioeconomic factors continue, amounts of plastic-carbon stock within the Earth system are projected to rise to 14 000 million metric tonnes by 2035, meaning that the amount of plastic-carbon will be equivalent to global blue carbon stock.5Stubbins A Law KL Muñoz SE Bianchi TS Zhu L Plastics in the Earth system.Science. 2021; 373: 51-55Crossref PubMed Scopus (30) Google Scholar The probable effects of plastics on chemical, physical, and biological processes within BCEs puts us in unchartered territory, raising questions about how plastic-carbon accumulation in BCEs might affect global blue carbon storage and sequestration capacity in future. Plastics and microplastics affect terrestrial soil ecosystems during microbial processes, plant growth, and litter decomposition, and release carbon dioxide into the atmosphere.9Rillig MC Leifheit E Lehmann J Microplastic effects on carbon cycling processes in soils.PLoS Biol. 2021; 19e3001130Crossref PubMed Google Scholar Importantly, at least 28 countries consider the conservation and restoration of BCEs, as substantial carbon dioxide sinks, as part of the nationally determined contributions (NDCs) to adapt and mitigate to climate change.10Herr D Landis E Coastal blue carbon ecosystems. Opportunities for nationally determined contributions.https://portals.iucn.org/library/sites/library/files/documents/Rep-2016-026-En.pdfDate: 2016Date accessed: October 25, 2021Google Scholar However, any disturbance of such carbon dioxide sink within BCEs in the presence of plastics could release a disproportionate amount of accumulated carbon into the atmosphere and hamper global climate goals. Despite their important global ecological, environmental, social, and economic contributions, BCEs are also considered among the most threatened ecosystems on Earth,2Macreadie PI Anton A Raven JA et al.The future of Blue Carbon science.Nat Commun. 2019; 10: 1-13PubMed Google Scholar with a global annual loss of about 340 000–980 000 hectares11Murray BC Pendleton L Jenkins WA Sifleet S Green payments for blue carbon: economic incentives for protecting threatened coastal habitats.https://nicholasinstitute.duke.edu/sites/default/files/publications/blue-carbon-report-paper.pdfDate: April 2011Date accessed: October 25, 2021Google Scholar and loss rates ranging from 0·03% to more than 1%, which is 2-times higher than those of tropical forests.1Duarte CM Losada IJ Hendriks IE Mazarrasa I Marbà N The role of coastal plant communities for climate change mitigation and adaptation.Nat Clim Chang. 2013; 3: 961-968Crossref Scopus (811) Google Scholar Therefore, the effect of multistressors (ie, habitat loss, climate change, and plastic) to BCEs can further downgrade their capacity to sequester carbon dioxide and hamper global climate targets. Plastic-carbon needs to be considered as part of the gloabl carbon cycle.12Zhu L Zhao S Bittar TB Stubbins A Li D Photochemical dissolution of buoyant microplastics to dissolved organic carbon: Rates and microbial impacts.J Hazard Mater. 2020; 383121065Crossref PubMed Scopus (75) Google Scholar Carbon dioxide and other greenhouse gases emit at every stage of the plastic lifecycle, for instance, during fossil fuel extraction and transport, plastic refining and production, and management and disposal of plastic waste; all stages of emission have consequences for our soil, atmosphere, waterways, and oceans.5Stubbins A Law KL Muñoz SE Bianchi TS Zhu L Plastics in the Earth system.Science. 2021; 373: 51-55Crossref PubMed Scopus (30) Google Scholar Despite the potential of plastic-related activities to release greenhouse gases, Earth system models or integrated assessment models do not take account of plastic-carbon emissions. A comprehensive quantification of overall greenhouse gas emissions from the plastic sector and an understanding of its effects on BCEs, global carbon budget, and climate goals are urgently needed. Developing such an estimate is a crucial next step for pinning down and communicating the relevance of plastic-related carbon dioxide emissions to decision makers in order to stop plastic use. The 26th United Nations Climate Change Conference of the Parties (COP26) held in 2021 put plastics on its agenda. We call for broader commitment from all levels to tackle the plastic problem in order to safeguard global oceans and BCEs, and quantify plastic-related greenhouse gas emissions in the global carbon budget. This year commemorates the 50th anniversary of the Convention on Wetlands (Ramsar Convention), and the UN Environment Programme will be 50 next year. Reflection on the past five decades is crucial to simultaneously control plastic pollution and protect, conserve, and restore global oceans and BCEs in future. The Kunming Declaration of the UN Biodiversity Conference of the Parties to the Convention on Biological Diversity 15th meeting (COP15, Part 1) held in 2021 emphasised the combined importance of reducing waste and pollution, enhancing the restoration of ecosystems, mitigating climate change, among others for the post-2020 global biodiversity framework. We urge further strong commitment from global leaders to acknowledge plastic-carbon in the global climate targets and also commit to scaling down and stopping the release of plastics into oceans and BCEs in the fifth session of the UN Environment Assembly (UNEA-5.2), the second part of COP15 and the UN Ocean Conference to be held in 2022. The United Nations Decade of Ocean Science for Sustainable Development and the UN Decade on Ecosystem Restoration will run until 2030, which is also the deadline for the Sustainable Development Goals. Therefore, a joint action from these global initiatives can provide a unique framework, policy interventions, and financial support to manage and restore BCEs, and stop plastics being released to marine ecosystems at the local, regional, and global scales. I declare no competing interests.