Blue carbon

Blue carbon is used in more than one sense. In a broad ocean-carbon context, it includes carbon absorbed by the ocean, much of which dissolves in seawater. In conservation and climate-policy discussions, the term commonly refers more narrowly to carbon captured and stored in coastal ecosystems, particularly mangroves, salt marshes and seagrass meadows. Distinguishing the broad ocean carbon reservoir from the coastal ecosystem concept helps avoid treating all ocean carbon as a single, easily managed climate solution.

Plants in coastal wetlands and seagrass beds take up carbon dioxide through photosynthesis. Carbon enters sediments through roots, leaves and other organic matter. Because saturated soils often have little oxygen, decomposition can be slower than in well-aerated soils; some organic carbon may consequently remain buried for centuries or longer. Storage differs among places and depends on ecological conditions, sediment processes and how the habitat is managed.

When coastal habitats are disturbed, drained or converted, the capacity to take up additional carbon can decline, and carbon already held in soils may be exposed to decomposition. Protecting or restoring these ecosystems can therefore support climate mitigation while also benefiting wildlife, fisheries and coastal resilience. Those co-benefits do not mean every project produces a guaranteed or permanent quantity of carbon removal: results depend on the site, baseline, duration and measurement methods.

Estimating blue-carbon gains requires accounting for carbon stocks and changes over time, including below-ground soil carbon, emissions and the possibility that stored carbon may later be released. IPCC guidance published in 2013 provides methods for countries to account for coastal wetlands in national greenhouse-gas inventories. Scientific assessment and monitoring remain important because ecosystems and carbon pathways vary, and restoration outcomes cannot be assumed from area alone.