Executive Summary
Blue carbon ecosystems – mangroves, seagrasses, saltmarshes, and macroalgae – are coastal ecosystems that sequester carbon and protect coastlines from sea level rise, storms, and erosion. In the face of climate change, it is essential to protect these ecosystems by (1) replanting coastal ecosystems, (2) including coastal ecosystems in nationally protected areas, and (3) protecting coastal ecosystems from development. All signatories of the Paris Climate Agreement with blue carbon ecosystems should include these three measures in their 2025 revised Nationally Determined Contributions.

Climate Change, Blue Carbon Ecosystems, and Coastal Protection

Sea level rise and worsening storms, which are driven by climate change, are expediting coastal erosion,  increasing flood risk, causing property damage, and decreasing the habitability of coastal areas. Billions of people are already grappling with these challenges, and with 70% of the world’s urban population expected to reside in coastal cities by 2025, this number is growing (Lecerf et. al., 2021). Fortunately, nature has already given us a solution: blue carbon ecosystems (BCEs), which are coastal ecosystems that sequester atmospheric carbon. There are four types of  BCEs: seagrasses, saltmarshes, macroalgae (seaweed), and mangroves. These marine plants capture carbon dioxide when they photosynthesise, hold it in their tissue, and ultimately bury it in marine sediment when they die. While they only occupy 0.2% of the ocean’s surface, they account for 50% of the carbon held in marine sediments. Unfortunately, current human activities are putting this vital carbon sink at risk (Duarte et. al., 2016).

Pollution, agriculture, and coastal development are destroying BCEs at an alarming rate. Mangrove coverage is decreasing by 2% annually, accounting for 10% of emissions from deforestation. Tidal marshes – already at only 50% of their historic coverage – are shrinking by 1-2% per year, and seagrasses – already at 70% of their historic coverage – are disappearing by 1.5% each year (Blue Carbon Initiative, n.d.). To put this into perspective, losing just one-third of the remaining BCE coverage is equivalent to increasing carbon dioxide emissions by 1 GtC every year, or a total of 75 GtC from when NDCs are submitted in 2025 through the end of the century (Duarte et. al., 2016). The foremost goal of the Paris Climate Agreement is to keep warming well below 2°C by 2100, and achieving this requires removing 100-1000 GtC throughout the century, an impossible target if blue carbon ecosystems are destroyed (IPCC, 2018). 

The negative impacts of decreased BCE coverage go well beyond losing a vital carbon sink. When a BCE is destroyed, such as when a mangrove is cleared for a palm oil or rice plantation, the carbon already stored in that ecosystem is released (Blue Carbon Initiative, n.d). Additionally, the other services that BCEs provide – namely coastal protection – are eliminated. All BCEs diminish the power of storms and provide a buffer between the coast and populated areas, plus the root systems of saltmarshes, mangroves, and seagrasses raise the seafloor and reduce erosion by holding sediment in place (Duarte et. al., 2016). For example, mangroves reduce the wave action, wind velocity, and storm surge of hurricanes and cyclones. A 2020 study of hurricane resilience in Central America found that coastal regions buffered by 1 km of mangroves were unaffected by category 3 hurricanes while similar areas without mangroves suffered losses of life and property (del Valle, 2020). Sea level rise, storms, and coastal erosion will continue to worsen, even if warming is kept to below 2°C, making BCEs all the more vital (Lecerf et. al., 2021). 

Essential Measures for 2025 Revised Nationally Determined Contributions

1. Replant BCEs throughout their historical range to increase the amount of carbon they sequester and to protect vulnerable coasts.
2. Include BCEs in nationally protected lands. Commit to protecting 30% of BCEs by 2030 to prevent catastrophic losses to carbon sequestration and protect coastal populations.
3. Require proposals for coastal development to include an assessment of their impact on BCEs, including BCEs directly cleared or built on and those impacted by pollution from the development activities. Additionally, develop further from the coast to preserve the buffer BCEs provide against erosion and storms.

Conclusions

Keeping warming below 2°C by 2100 will require taking all measures necessary to reduce carbon dioxide emissions and increase carbon sequestration. Coastal populations are particularly vulnerable to the consequences of climate change because of sea level rise, storms of increasing frequency and severity, and increasing rates of coastal erosion. Blue carbon ecosystems protect against these threats while simultaneously sequestering great quantities of carbon. By replanting and preserving these ecosystems, countries can safeguard coastal populations against some of the most severe consequences of climate change.

Works Cited

1. Blue Carbon Initiative (n.d.). Mitigating Climate Change Through Coastal Ecosystem Management. Retrieved March 8, 2022, from  https://www.thebluecarboninitiative.org/
2. del Valle, A., Eriksson, M., Ishizawa, O., Miranda, J., (2020). Mangroves protect coastal economic activity from hurricanes. Proceedings of the National Academy of Sciences of the United States of America 1(265-270). https://doi.org/10.1073/pnas.1911617116
3. Duarte, C., Losada, I., Hendriks, I., Mazarrasa, I., Marbà, N., (2013). The role of coastal plant communities for climate change mitigation and adaptation. Nature Climate Change 3(961-968).  https://doi.org/10.1038/nclimate1970
4. Lecerf, M., Herr D., Thomas, T., Elverum, C., Delrieu, E. and Picourt, L., (2021). Coastal and marine ecosystems as Nature-based Solutions in new or updated Nationally Determined Contributions. Ocean & Climate Platform, Conservation International, IUCN, GIZ, Rare, The Nature Conservancy, Wetlands International and WWF.
5. Intergovernmental Panel on Climate Change, 2018: Global Warming of 1.5°C.An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press.