What is blue carbon? Definition and importance

“Blue carbon” refers to the large amounts of carbon dioxide that the Earth’s oceans absorb from the atmosphere. The name first appeared in the 1990s when scientists realized the importance of marine vegetation as important carbon sinks. In addition to forests, which store ‘green carbon’, coastal ecosystems such as mangroves, salt marshes, peatlands, kelp beds and seagrass play a valuable role in the race to eliminate greenhouse gases. greenhouse that cause climate change in the air. Yet like many of our terrestrial forests, we lose these ecosystems to human encroachment, and when we do, these natural carbon sinks release huge amounts of carbon instead, exacerbating our environmental challenges. Three quarters of the world’s countries have at least one blue carbon ecosystem, and efforts are underway in many of them to protect these vital wetlands in the fight against climate change. You can also help.

What are carbon sinks?

A carbon sink is any natural system that absorbs more carbon from the atmosphere than it releases and holds it for long periods of time.

How exactly is blue carbon stored?

Through photosynthesis, marine plants and algae extract carbon dioxide from the atmosphere throughout their growth cycle. When they die, organic matter precipitates to the bottom of the ocean and becomes embedded in the soil, where it can remain intact for millennia. More than two-thirds of the carbon on Earth circulates in the ocean, and the oceans absorb about 25% of the world’s annual carbon dioxide emissions. While coastal ecosystems constitute less than 2% of the total surface of the oceans, they represent “about half of the total carbon sequestered in ocean sediments”. These environments store more carbon per area than terrestrial forests and at a rate three to five times faster – the equivalent of one billion barrels of oil per year.

Moist soils retain more carbon because they have low oxygen levels, which slows the rate of decomposition. This is also why carbon trapped in coastal soils can remain there for thousands of years. In the United States, there are some 41 million acres of coastal wetlands, mostly in the southeast. Each year, they store about eight million tonnes of carbon, or the equivalent of the emissions of 1.7 million vehicles, according to the National Oceanic and Atmospheric Administration (NOAA). Pioneering blue carbon research was conducted in the 1990s by Dr. Gail Chmura of McGill University, who studied the salt marshes of the Bay of Fundy in Canada. Since then, blue carbon has become the target of research and conservation programs of governments, universities, and coastal reserves, including the National Estuarine Research Reserve System (NERRS) in the United States. Today, blue carbon estimates have been incorporated into the greenhouse gas emissions inventory of the United States and other countries.

Why is blue carbon important?

In the 200 years since the American Revolution, more than half of the wetlands in the land area that is now the United States was lost to development, at a rate of more than 60 acres lost per hour . Since then, that rate has only accelerated: between 2004 and 2009, the United States lost an average of more than 80,000 acres of coastal wetlands per year. With every acre lost, our ability to fight climate change grows stronger. Not only are there fewer wetlands to absorb carbon, but when wetlands are destroyed, the carbon they have long sequestered is released into the atmosphere. When peatlands dry out, for example, their dead vegetation decomposes faster and releases greenhouse gases. And when mangrove forests are destroyed, at the rate of 2% per year, they release about 10% of all emissions from deforestation.

In total, the amount of carbon dioxide released into the atmosphere each year as a result of the destruction of coastal ecosystems is estimated at 1.02 billion tonnes, which is almost equal to Japan’s annual carbon dioxide emissions. This is why, despite the fact that coastal ecosystems cover such a small percentage of the ocean’s area, on a per acre basis, their protection “can provide one of the greatest climate benefits over forest or land. to other land use projects ”. If the annual loss of coastal wetlands could be halved, the equivalent of Spain’s annual emissions could be reduced.

Protecting coastal ecosystems also protects the lives and livelihoods of millions of people by improving water quality and creating jobs in fishing, tourism and recreation. Alaska’s peatlands, for example, absorb heat and produce food for endangered salmon stocks. Wetlands provide temporary habitat for birds along the Atlantic and Pacific flyways and permanent habitats for endangered species like the Florida panther and Louisiana black bear. Wetlands prevent erosion and flooding, and as sea levels rise, through accretion (accumulation) of soil, they can store even more carbon.

How to protect coastal ecosystems

Reducing greenhouse gas emissions is, of course, the main objective of reducing the threat of climate change. But even if emissions were to drop to zero, it will still be necessary to remove carbon from the atmosphere. Until recently, most nature-based carbon sequestration efforts have focused on reforestation, forest preservation, and other land-based solutions. But blue carbon is increasingly at the center of research and conservation activities, and there are many things that citizens can do too.

Conservation efforts

  • Protecting coastal ecosystems is one of the most effective (and cost effective) ways to sequester carbon. According to one estimate, carbon emissions from mangrove forests can be reduced at a cost of less than $ 10 per tonne of carbon dioxide.
  • Among other nature-based solutions, reintroducing beavers to wetlands prevents them from drying out.
  • Restoring the tidal flow reduces the amount of carbon dioxide and methane escaping from wetlands, providing “quick and lasting climate benefits” over the longer lasting benefits of reforestation efforts.
  • Preventing the amount of nitrogen runoff from agriculture and other sources into wetlands reduces the release of carbon dioxide and nitrous oxide (another potent greenhouse gas).

Restoring wetlands is key to tackling climate change. Miscellaneous photography / Getty Images.

Carbon markets

  • With the introduction of carbon markets under the Paris Agreement on climate change, wetland restoration can be profitable. By giving restoration projects the ability to sell carbon offsets, carbon markets make these projects less expensive for state and federal budgets.
  • Carbon offsets at a price of $ 10 per tonne would cover the costs of the research necessary to initiate wetland restoration projects and pay for the long-term monitoring of the program.
  • Blue Carbon is now part of the United States Greenhouse Gas Emissions Inventory, which provides authoritative data on the economic value of coastal restoration projects, allowing these projects to be credited for ’emissions.
  • While carbon credits from wetland projects are currently only part of a voluntary market, including them in a government-regulated “compliance” market would allow them to generate even more revenue by selling offsets.

What are carbon markets?

A carbon market trades carbon emission allowances. Carbon markets aim to encourage businesses and organizations to reduce their carbon emissions by allowing them to sell credits for their emission reductions. Polluters can then offset their greenhouse gas emissions by purchasing emission credits from these organizations.


  • NOAA’s National Estuarine Research Reserve System (NERRS) was established in 2010 to promote the study and monitoring of the coastal ecosystem. Twenty-nine coastal reserves in 24 states and Puerto Rico are conducting and coordinating their research on the role of wetlands as carbon sinks.
  • The Smithsonian Environmental Research Center’s Coastal Carbon Research Coordination Working Group collects data on seagrass habitats.
  • NOAA’s Coastal Change Analysis Program uses satellite imagery to inventory wetlands.
  • Researchers are developing ways to prevent frozen Alaskan peatlands from melting and releasing large amounts of carbon dioxide.


  • NERRS organizes training programs for state and local officials on the role of coastal ecosystems.
  • NERRS member organizations have organized “Roadshow Dialogues” and other public awareness programs to educate community members on the value of coastal wetlands.
  • NERRS also manages Teachers on the estuary workshops, where teachers meet local scientists to learn how to integrate coastal education into their classroom.

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