Mangroves and climate

Mangroves occupy a narrow strip of coastline -- intertidal zones in tropical and subtropical regions where land and sea meet daily. For much of the 20th century they were treated as unproductive wasteland, cleared without consequence for aquaculture, development, and agriculture. The science of the past two decades tells a very different story.

Carbon storage: biomass and sediment

Mangroves store carbon in two very different ways. Above ground, their woody trunks, branches, and dense root systems hold substantial amounts of biomass carbon -- comparable to or exceeding that of many tropical forest types. Below ground, the more significant store lies in sediments that have accumulated over centuries in the anaerobic, waterlogged conditions of intertidal zones.¹

It is the sediment carbon that makes mangroves so climatically important. In terrestrial forests, carbon stored in wood and leaf litter is vulnerable to decomposition and fire -- it cycles back to the atmosphere within years to decades. In mangrove soils, the absence of oxygen prevents the microbial activity that drives decomposition, allowing carbon to remain stable for hundreds to thousands of years. Some mangrove sediment cores in Southeast Asia contain carbon laid down over more than 5,000 years of continuous accumulation.²

Biodiversity strengthens carbon storage

New research has added important nuance to how we understand mangrove carbon. It is not simply a property of the ecosystem type -- it depends significantly on the diversity within it. Studies examining functional distinctiveness in mangrove communities have found that forests with species performing different ecological roles store measurably more carbon than lower-diversity stands.³

This creates a direct link between biodiversity conservation and climate mitigation that is more concrete than is often acknowledged. Protecting mangrove biodiversity -- the full range of species, root morphologies, and ecological functions within a forest -- is not separate from maximizing its carbon storage capacity. The two are the same goal.

Coastal protection as climate adaptation

Carbon storage is mitigation -- reducing how much warming occurs. Coastal protection is adaptation -- reducing the harm from warming that is already locked in. Mangroves deliver both.

Their interlocking root systems dissipate wave energy before it reaches the shore, reducing the destructive force of storm surges. Studies in the Philippines following Typhoon Hainan, and in Sri Lanka following the 2004 Indian Ocean tsunami, found that coastal communities behind intact mangrove forests suffered substantially less damage than those in comparable locations where mangroves had been cleared.⁴ Economic modeling has estimated the value of this protection service at billions of dollars annually in reduced flood damage and infrastructure losses.

As sea levels rise and tropical storm intensity increases under climate change, this adaptation value will grow. The economics of mangrove conservation become more compelling every decade -- not less.

Fisheries and community livelihoods

Mangrove forests are nursery habitat for a large proportion of the fish species that support tropical and subtropical fisheries -- both commercial and subsistence. Juvenile fish, shrimp, and crustaceans use the root systems for shelter and feeding during the stages of their life cycle when they are most vulnerable to predation. Estimates suggest that a significant share of the global seafood catch -- including many species traded internationally -- spends part of its juvenile life in mangrove habitat.⁵

The irony of mangrove-to-aquaculture conversion is therefore acute. Clearing mangroves to build shrimp ponds destroys the nursery habitat on which wild shrimp populations depend. Many coastal communities that converted mangroves to aquaculture in the 1980s and 1990s saw their wild catch collapse within a decade.

Mangroves in carbon markets and policy

The climate value of mangroves is now sufficiently well-established that it is reshaping both carbon markets and coastal policy. Verified carbon methodologies for mangrove restoration projects now exist under major voluntary market frameworks, allowing landowners and governments to generate carbon credits from protection and restoration activities.⁶

Countries with major mangrove resources -- Indonesia, Australia, Brazil, Mexico, India -- are incorporating their coastal ecosystems into national climate accounting and into Nationally Determined Contributions under the Paris Agreement. For Indonesia, which holds more mangrove area than any other country, this is not a marginal climate strategy. It is central to national decarbonization planning.⁷