Climate Change

Sea-level rise: 6 states in US may lose 83% coastal marshes

The coastal area will stop being a carbon sink and start releasing more carbon into the atmosphere  

By Susan Chacko
Published: Tuesday 28 June 2022

A 1.2 metre rise in sea level by 2104 will result in the loss of 83 per cent of the existing coastal marshes and 26 per cent of the existing seagrasses in six mid-Atlantic states of the United States, a new study projected.

In addition, some 270,000 hectares of forest and forested wetlands in low-lying coastal areas will get converted to coastal marshes, the report by researchers from Duke niversity and National Oceanic and Atmospheric Administration stated.

Such habitat changes driven by sea-level rise (SLR) can cause the study area (New York, New Jersey, Delaware, Maryland, Virginia and North Carolina) to shift from being a carbon sink to a source, the report published in PLOS Climate said.

Net carbon sequestration in these six places may decline by 57-99 per cent, it added. 

The study identified areas where coastal marshes can be created or restored by hydrologically connecting or reconnecting open water and freshwater wetlands to tidal flows. This would expand future salt marshes and reduce methane emissions associated with freshwater habitats.

Significance of mitigation measures

Coastal ecosystems provide essential ecosystem services: Protection from storms and erosion, enhancing water quality and nursery grounds for fish. They sequester and store blue carbon (carbon captured by the world's ocean and coastal ecosystems).  Thus, they are an essential piece of the solution to global climate change.

Carbon fluxes in coastal habitats and habitat changes due to sea-level rise 


The International Blue Carbon Initiative focuses on mitigating climate change through conservation and restoration of coastal and marine ecosystems.

Coastal wetlands in the conterminous US removed 4.8 million tonnes of carbon dioxide equivalent from the atmosphere in 2019, according to the US Environmental Protection Agency report Inventory of US greenhouse gas emissions and sinks, 1990-2019.

Restoring tidal wetland is the largest wetland natural climate solution. Around 27 per cent of US salt marshes are disconnected from the ocean and subject to freshwater inundation, the report noted. This results in a large increase in methane emissions from these 'freshened' salt marshes. 

Reconnecting salt marshes with the ocean through culverts under roads or other barriers, can avoid these methane emissions by 12 metric tonnes CO2e / year, a November 2018 report in Science Advances found.

Conserving and increasing blue carbon in coastal habitats is an important carbon mitigation strategy. 

The spatially explicit modeling of coastal change and coastal carbon can be used to inform a selection of coastal areas for future research and monitoring, and to prioritise areas for conservation and restoration projects.  

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