Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

Mangrove forests store and sequester large area-specific quantities of blue carbon (C_org). Except for tundra and peatlands, mangroves store more C_org per unit area than any other ecosystem. Mean mangrove C_org stock is 738.9 Mg C_org ha⁻¹ and mean global stock is 6.17 Pg C_org, which equates to only 0.4–7% of terrestrial ecosystem C_org stocks but 17% of total tropical marine C_org stocks. Per unit area, mangroves sequester 179.6 g C_org m⁻²a⁻¹ and globally about 15 Tg C_org a⁻¹. Mangroves sequester only 4% (range 1.3–8%) of C_org sequestered by terrestrial ecosystems, indicating that mangroves are a minor contributor to global C storage and sequestration. CO₂ emissions from mangrove losses equate to 0.036 Pg CO₂-equivalents a⁻¹ based on rates of C sequestration but 0.088 Pg CO₂-equivalents a⁻¹ based on complete destruction for conversion to aquaculture and agriculture. Mangrove CO₂ emissions account for only 0.2% of total global CO₂ emissions but 18% of CO₂ emissions from the tropical coastal ocean. Despite significant data limitations, the role of mangrove ecosystems in climate change mitigation is small at the global scale but more significant in the tropical coastal ocean and effective at the national and regional scale, especially in areas with high rates of deforestation and destruction.