What Is Blue Carbon? Definition and Importance

Protected ecological carbon capture mangrove in Everglade City, Florida.
Mangroves store carbon dioxide in greater quantities than any other types of forests. Marie Hickman/Getty Images.

“Blue carbon” refers to the vast amounts of carbon dioxide that Earth's oceans absorb from the atmosphere. The name emerged in the 1990s when scientists realized the importance of marine vegetation as important carbon sinks. Along with forests, which store “green carbon,” coastal ecosystems such as mangrove swamps, salt marshes, peatlands, kelp beds, and sea grasses play a valuable role in the race to remove the greenhouse gases that cause climate change from the air. Yet like many of our land-based forests, we are losing these ecosystems to human encroachment, and when we do, these natural carbon sinks instead release enormous amounts of carbon, compounding our environmental challenges. Three-quarters of the countries of the world have at least one blue carbon ecosystem, and efforts are underway in many of them to protect these vital wetlands in the battle against climate change. You can help, too.

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, the organic material precipitates to the ocean floor and gets embedded in soils, where it can remain undisturbed for millennia. More than two-thirds of the carbon on Earth circulates in the ocean, and oceans take up about 25% of the world's annual carbon dioxide emissions. While coastal ecosystems constitute less than 2% of the total ocean area, they account for “approximately half of the total carbon sequestered in ocean sediments.” These environments store more carbon per area than land-based forests and at a rate three to five times faster—the equivalent of one billion barrels of oil per year.

Wet soils retain more carbon because they have low oxygen levels, which slows down the rate of decomposition. That is also why the 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 an estimated eight million tons of carbon, the equivalent of the emissions of 1.7 million vehicles, according to the National Oceanic and Atmospheric Administration (NOAA). Pioneering research into blue carbon was conducted in the 1990s by Dr. Gail Chmura of McGill University, who studied the salt marshes in Canada's Bay of Fundy. Since then, blue carbon has become the target of research and conservation programs by governments, universities, and coastal reserves, including the National Estuarine Research Reserve System (NERRS) in the United States. Today, blue carbon estimates have been integrated 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 has been lost to development, at a rate of over 60 acres lost per hour. Since then, that rate has only sped up: between 2004 and 2009, the United States lost an average of over 80,000 acres of coastal wetlands per year. With each acre lost, our ability to combat climate change grows harder. Not only are there fewer wetlands to absorb carbon, but when wetlands are destroyed, the carbon that they have long sequestered is released into the atmosphere. When peatlands dry out, for example, their dead vegetation decomposes more quickly and releases greenhouse gases. And when mangrove forests are destroyed, at a rate of 2% a year, they release roughly 10% of all emissions from deforestation.

In total, the amount of carbon dioxide released annually into the atmosphere from the destruction of coastal ecosystems is an estimated 1.02 billion tons, nearly equal to the annual carbon dioxide emissions of Japan. This is why, despite the fact that coastal ecosystems cover such a small percentage of the ocean's surface area, on a per-acre basis, protecting them “can provide among the greatest climate benefits compared to forest or other land use projects." If the annual loss of coastal wetlands could be cut in half, the equivalent of the annual emissions of Spain could be reduced.

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

How to Protect Coastal Ecosystems

Cutting greenhouse gas emissions is, of course, the primary target in reducing the threat of climate change. But even if emissions dropped to zero, removing carbon from the atmosphere will still be necessary. Until recently, most nature-based carbon sequestration efforts have focused on reforestation, forest preservation, and other land-based solutions. But blue carbon has increasingly become the focus of research and conservation activity, and there is much that individual citizens can do as well.

Conservation Efforts

  • Protecting coastal ecosystems is one of the most effective (and cost-effective) means of sequestering carbon. One estimate projects that carbon emissions from mangrove forests can be abated at a cost of less than $10 per ton of carbon dioxide.
  • Among other nature-based solutions, reintroducing beavers to wetlands prevents them from drying out.
  • Restoring tidal flow reduces the amount of carbon dioxide and methane escaping from wetlands, providing “quick and sustained climate benefits” compared to the longer duration 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).
Restoration sign in the wetlands in Alviso Marsh, Don Edwards wildlife refuge, south San Francisco bay, California
Wetlands restoration is key to combating climate change. Sundry Photography/Getty Images.

Carbon Markets

  • With the introduction of carbon markets as part of the Paris Agreement on Climate Change, wetland restoration can be profitable. By giving restoration projects the ability to sell carbon offsets, carbon markets make those projects less burdensome on state and federal budgets.
  • Carbon offsets priced at $10 per ton would cover the costs of the research needed to launch wetlands restoration projects and pay for long-term monitoring of the program.
  • Blue carbon is now part of the United States' greenhouse gas emissions inventory, which gives authoritative data about the economic value of coastal restoration projects, allowing those projects to be awarded emissions credits.
  • While the 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 income from selling offsets.

What Are Carbon Markets?

A carbon market trades in carbon emissions allowances. Carbon markets aim to encourage companies 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 emissions credits from those organizations.


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


  • NERRS runs training programs for state and local officials about the role of coastal ecosystems.
  • Member organizations of NERRS have run “Roadshow Dialogues” and other public outreach programs to educate community members about the value of coastal wetlands.
  • NERRS also runs Teachers on the Estuary workshops, where teachers meet with local scientists in order to learn how to integrate coastal education into their classroom.
View Article Sources
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