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Coastal Blue Carbon

Why saving our coastlines is crucial to saving the ocean—and the planet

October 6, 2022 By: Ariana Sutton-Grier Read time:

In this Issue:

  • Winter 2022
  • A New Generation's Ocean Literacy
  • Coastal Blue Carbon
  • How to Reverse the Ocean-Climate Crisis
  • How We Can Avoid the 'Danger Zone' of Climate Change
  • How We Can Help Marine Protected Areas Save Our Ocean
  • Indigenous Knowledge Is Essential for the Future of the Ocean
  • The Ocean Is in Trouble
  • Our Ocean Is Choking on Plastic
  • The Global Ocean
  • When Too Many Boats Chase Too Few Fish
  • View All Other Issues
Coastal Blue Carbon

The effects of climate change are now evident, threatening our lands and seas. And where the water meets the land offers some of the greatest opportunity for mitigating the rising temperatures that are warming the world.

Not only are our coastlines natural buffers to rising seas, but they are home to important seagrasses, mangroves, and other vegetation that are some of nature’s best storehouses of the carbon in the atmosphere that must be absorbed to keep Earth’s climate healthy. The popular name for this is blue carbon. In this case, blue is all about good. But, in fact, blue carbon is actually brown.

It might help to start with a brief, basic science lesson.

All living things are made of carbon, and all living things—you, me, animals—eat food that our bodies break down and extract energy from using oxygen through the process of respiration. A byproduct of this process is carbon dioxide. Of course, the burning of fossil fuels also releases carbon dioxide in especially large doses into the atmosphere and, to continue our color analogy, this is called black carbon.

Plants are different from other living things because they make their own food through photosynthesis. They take carbon dioxide from the atmosphere, along with water and sunlight, and make sugar that sustains them—but a small portion of that carbon also gets stored away in leaves, stems, roots, and tree trunks and is used to grow more of the plant (this carbon is called organic carbon because the carbon is now part of a living organism). So, plants make organic carbon (food for other living things) while other organisms, including people, break down this food to use for energy: A lovely transaction.

This transaction has served the world well for millennia. In fact, the current atmosphere of the modern human world has lower levels of carbon dioxide than when dinosaurs roamed the planet. That’s because, over the course of history, large amounts of carbon were stored away for a long time, buried deep in the Earth. But that is changing now: The oil we extract to power our daily lives comes from those dead plants that lived millions of years ago. The burning of fossil fuels means that we are bringing back into the atmosphere more carbon than the world has seen in hundreds of thousands of years.

So we need to place special importance on the Earth’s ecosystems that can continue to safely keep carbon out of the atmosphere—places known as natural carbon sinks.

Forests are usually the prime example of a natural carbon sink. We see grand towering trees and know that their trunks and branches are storing carbon—and that there is more stored underground in their roots.

Less visible but equally important is another critical carbon sink: the planet’s coastal grasslands and wetlands.

Much is correctly made about the fact that the ocean is a great carbon storehouse. But where the ocean meets the land is especially important. Coastal blue carbon accounts for about 50% of all the carbon stored in the ocean even though coastal wetlands cover less than 1% of the ocean’s area.

Mangroves, tidal marshes, and seagrasses are some of the most productive ecosystems on the planet, meaning that they take up a lot of carbon dioxide per unit area. Some of this carbon gets buried underground in the wet, tidally inundated soils. These wet soils are largely devoid of oxygen, which means that decomposition of the organic carbon slows way down, making them the perfect place for carbon to accumulate and turning them deep—by now you’ve got it, right?—brown, not blue. Some coastal wetland soils are many meters thick and are storing thousands of years’ worth of carbon. The amount of carbon buried in coastal wetlands over time is 10 times greater than that stored in other forest soils.

When we disturb or destroy these coastal wetlands for agriculture or development, we lose their continued sequestration ability, and when we drain them, we introduce oxygen into the soils, changing their anaerobic decomposition of carbon to the faster oxygenated process. Losing just 1 acre of coastland has the equivalent impact on carbon emissions of losing 10 to 40 acres of native forest. This is why protecting existing coastal wetlands and restoring them where they have been degraded are excellent climate mitigation strategies.

The challenge is that we have already lost more than half of the coastal wetlands around the world over the past century. These are some of the most threatened ecosystems on the planet, and today they are continuing to lose up to 3% of their global area per year. In the state of Louisiana alone, 2,000 square miles of coastal wetlands have disappeared since the 1930s. The reasons why are disheartening because they were caused by us: Natural sediment was lost when the Mississippi River was diverted to reduce flooding, the ground has subsided from oil and water extraction, and still more wetlands disappeared from the construction of pipelines and shipping lanes. And now rising sea levels due to climate change mean that even more coastal wetlands are being lost.

We lose so much coastal wetland area around the world each year that the carbon emitted from those disruptions is equivalent to the annual carbon emissions of the United Kingdom. In effect, these incredible natural carbon sinks have become additional human sources of greenhouse gases.

With new studies showing the Earth warming faster than previously believed, we need action that can make a difference quickly in reducing greenhouse gases in the atmosphere. That makes protecting coastal wetlands an even more attractive and necessary strategy, not just from a scientific point of view, but from the vantage of policymakers. Not only are coastal wetlands immensely effective carbon sinks, but they are within national boundaries, allowing every coastal nation to act in its own interest and protect them—without the extensive negotiation among nations that strategies involving international waters would.

It is essential to limit development in wetlands— history has shown that is obvious. Less obvious but just as meaningful are strategies to promote and protect wetlands, including new approaches to aquaculture. For example, one promising strategy is guaranteeing higher market prices for sustainably farmed shrimp when shrimp growers retain or plant at least 50% mangrove cover over their aquaculture areas. This practice leads to larger shrimp and smaller environmental impacts and has been successfully implemented in the Mekong Delta in Vietnam.

Carbon financing can also support coastal wetland restoration. An innovative tool that places a financial value on carbon emissions, carbon financing allows companies to offset their emissions by purchasing carbon credits from sustainable projects. One successful example is the Mikoko Pamoja project in Kenya, in which the sale of mangrove carbon credits has helped the local community restore its mangrove forests and bring clean water and school supplies to villagers. The project also provides alternate livelihood options, particularly for women in the community who have been active in growing, planting, and monitoring the restored mangroves. This approach offers wins for the community, the climate, and biodiversity conservation—and could be duplicated elsewhere.

For places in the world where coastal wetland tidal flow has been affected by development, restoration is essential. Many temperate coastal salt marshes, including 27% of the coastal wetlands along the U.S. Atlantic coast, have been altered by development, including roads, bridges, or railroad tracks, which run through or directly behind these wetlands and have cut off their natural tidal cycles. These saltwater wetlands have “freshened” and now produce far more methane, a potent greenhouse gas, than they would in their natural salty state. In these areas, we can widen inlets and culverts to remove barriers and open up tidal flushing that restores the salt marshes, allowing them to play their key role in reducing greenhouse gas emissions.

The multitude of benefits from preserving and restoring the world’s coastal wetlands has become increasingly clear and must be encouraged. Of course, these coastal regions alone cannot cure climate change—that will require a range of strategies, beginning with reducing carbon emissions throughout the world. But blue carbon has shown its essential and even decisive role in protecting the planet. Every coastal nation can act to protect and nurture its wetlands—and make the future blue.

The Takeaway

Coastal wetlands hold half of all the carbon stored in the ocean, making them essential to mitigating climate change.

Ariana Sutton-Grier is an ecosystem ecologist who is a visiting associate research professor at the University of Maryland in the Earth System Science Interdisciplinary Center.


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