Global Significance of Mangrove Blue Carbon in Climate Change Mitigation

Daniel M Alongi

doi:10.3390/sci2030067

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−2a−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.

Highlights

The concept of blue carbon was introduced in 2009 in an assessment report to a special collaboration of the United Nations Environmental Programme (UNEP), Food and Agriculture Organization of the United Nations (FAO) and the Intergovernmental Oceanographic Commission of the United NationsEducational, Scientific and Cultural Organization (IOC/UNESCO) [1] with the idea that the role of coastal ecosystems such as salt marshes, mangroves and seagrass meadows in absorbing carbon (C) to reduce emissions is of global significance and they should be protected and, if necessary, restored in order to maintain and expand their ability as critical C sinks
A detailed assessment was commissioned by the International Union for Conservation of Nature (IUCN) [2] to document the C management potential of salt marshes, mangrove forests, seagrass meadows, kelp forests and coral reefs
Sci 2020, 2, 67 inventories from these habitats to properly assess their role in absorbing C emissions; (3) anthropogenic greenhouse gas emissions are being underestimated because such emissions from these coastal habitats are not being accounted for in national and international inventories, meaning their C savings from sequestration do not count towards meeting climate change commitments; and (4) these habitats continue to be destroyed and need to be protected and restored

Summary

Introduction

The concept of blue carbon was introduced in 2009 in an assessment report to a special collaboration of the United Nations Environmental Programme (UNEP), Food and Agriculture Organization of the United Nations (FAO) and the Intergovernmental Oceanographic Commission of the United Nations. Educational, Scientific and Cultural Organization (IOC/UNESCO) [1] with the idea that the role of coastal ecosystems such as salt marshes, mangroves and seagrass meadows in absorbing carbon (C) to reduce emissions is of global significance and they should be protected and, if necessary, restored in order to maintain and expand their ability as critical C sinks. Since the publication of these seminal publications, there has been an explosion of subsequent papers on blue carbon, with over 1000 papers published since 2009 [6] This impressive growth reflects the need of NGOs and various agencies around the globe for more data, as well as a lot of enthusiasm for the idea that blue carbon storage and sequestration is of national and international significance in reducing carbon emissions. The most recent data will be used to better pinpoint the range of rates of C sequestration, C stocks and potential and actual losses from deforestation

Carbon Stocks

Tg equates

Carbon Losses

Method for Estimating

Findings

Assessment of Global Significance