Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

Background

Mangrove forests sequester proportionately greater amounts of carbon than most terrestrial environments. However, natural greenhouse gas (GHG) fluxes from these ecosystems and the carbon released when they are degraded counteract their carbon sequestration potential. Therefore, it is necessary to examine carbon stocks, rates of carbon sequestration, and carbon losses from these environments to clarify the global and regional potential of mangrove forests to mitigate climate change.

Goals and Methods

To synthesize the global and regional estimates of mangrove carbon sequestration potential, the authors compiled published data to compare carbon stock estimates, carbon sequestration rates, and carbon loss from disturbances (e.g., natural erosion, tree mortality, tropical storm damage, deforestation, conversion to aquaculture or agriculture). This dataset includes mangrove forests from different countries and at different maturities, in addition to carbon stock measurements from other carbon-sequestering environments (e.g., salt marshes, seagrass meadows, coral reefs, the tropical coastal ocean, and terrestrial environments).

Conclusions and Takeaways

The global average mangrove ecosystem organic carbon (C_org) stock is 711 to 766.8 megagrams of C_org per hectare, and the average rate of carbon sequestration is 179.6 grams of C_org per square meter per year. Releases of methane and dissolved inorganic carbon (DIC) offset the carbon storage potential of mangroves, especially in deforested areas from tropical storms (54.6 to 75.8 megagrams of carbon dioxide equivalent per hectare per year) and conversion to aquaculture or agriculture (1802.2 megagrams of carbon dioxide equivalent per hectare per year). Mangrove forest carbon stocks and fluxes are significant at the tropical coastal ocean scale (17% of tropical marine carbon stock), but they only play a minor role at a global scale compared to other carbon-sequestering environments. This suggests that blue carbon projects for climate change mitigation could be more effective at the national scale, especially for countries experiencing high levels of mangrove loss from tropical storms or deforestation.