Global significance of mangrove blue carbon in climate change mitigation

Abstract

Mangrove forests store and sequester large area-specific quantities of blue carbon (Corg). Except for tundra and peatlands, mangroves store more Corg per unit area than any other ecosystem. Mean mangrove Corg stock is 738.9 Mg Corg ha−1 and mean global stock is 6.17 Pg Corg, which equates to only 0.4–7% of terrestrial ecosystem Corg stocks but 17% of total tropical marine Corg stocks. Per unit area, mangroves sequester 179.6 g Corg m−2·a−1 and globally about 15 Tg Corg a−1. Mangroves sequester only 4% (range 1.3–8%) of Corg 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.