Blue and green carbon both encompass ways that carbon is stored by natural processes, but the locations and methods are different. Both are critical to climate action as they capture carbon dioxide from the air and sequester it for decades, mitigating global warming. Blue carbon originates from life in coastal and marine environments, whereas green carbon is from land-based forests and vegetation. We need both to ensure carbon stewardship is robust and diversified, as each system presents different strengths and vulnerabilities.

Blue carbon refers to carbon captured in our ocean and coastal zones such as mangroves, salt marshes, and seagrass beds. These locations sequester carbon in plant roots and deep soils for centuries or millennia. For instance, salt marshes and mangroves can retain carbon-rich stratified soil that remains stable until the land is disturbed. Blue carbon systems are silent, but mighty. Mangroves, in particular, are potent carbon sinks. They can absorb carbon much faster than most land forests, on a per-area basis. Blue carbon ecosystems are disappearing rapidly. We’ve lost around 62% of mangroves since 2000 and it’s still not stopping from threats such as aquaculture, land use change, and land reclamation. Salt marshes have declined approximately 25% of their global extent since the 1800s. When these systems are lost, that carbon escapes back into the air, compounding the climate challenge. Studies indicate that ocean warming and acidification could decelerate the speed at which carbon sinks to the seafloor by 10-15% by century’s end, resulting in lesser carbon being sequestered in deep ocean reservoirs.

Green carbon is the carbon sequestered in terrestrial forests and vegetation. That spans, from tropical rainforests to temperate woodlands — as well as rapid-growing coastal plants such as kelp. Kelp, for instance, can grow up to 28 centimeters a day, absorbing abundant carbon dioxide in its growth. Land forests are climate action superstars — trees and earth beneath soak up and store massive amounts of carbon. Unlike blue carbon, green carbon storage can often rely more heavily on the trees’ life span and soil health. If forests are cut down or burned, that carbon is promptly returned to the atmosphere.

Combining blue and green carbon approaches can assist nations, cities and communities in making carbon management more effective. For instance, Indonesia’s blue carbon efforts prevented 13 million metric tons of carbon from entering the atmosphere between 2000 and 2010, generating $540 million in social welfare. Blue and green carbon solutions require robust science to confirm carbon remains stored for 25 to 100 years or longer.

1. Blue carbon systems — mangroves, salt marshes, seagrasses — have stored carbon in underwater soils for centuries or even millennia, but are highly sensitive to coastal development and climate change.
2. Green carbon systems (think: forests, kelp) capture carbon in trees, plants and soils, with growth rates and storage intrinsically tied to land health, forest cover, and plant species.
3. Blue carbon loss results in rapid carbon release and may be irreversible, while green carbon loss is associated with deforestation, fire, or land degradation.
4. Blue carbon systems can provide additional benefits such as flood protection and fishery sustainment, whereas green carbon systems can contribute to air quality, shade, and terrestrial biodiversity.
5. Both require sustained stewardship and conservation, but are threatened by distinct anthropogenic and climate impacts.

Comparing forests and aquatic ecosystems for carbon sequestration

Forests and aquatic systems are both crucial for capturing carbon, though they achieve this in diverse manners and locations. Forests store carbon primarily in their wood and leaves, with roots and soil as a reserve. Aquatic systems—mangroves, seagrasses, salt marshes, and even open oceans—sequester the majority of carbon deep in soil, mud, or sediment. A lot of people assume forests would be the premier carbon sinks. Many marine ecosystems can actually sequester more carbon per hectare — as much as 5-10x more than their terrestrial counterparts. Take mangroves and seagrasses, which trap carbon for millennia in nutrient-rich, rain-dampened soil, far from the clutches of the atmosphere.

Bigger isn’t always better for carbon. Coastal ecosystems span far less area than forests, but they tend to sequester carbon more rapidly and in greater quantities. A hectare of seagrass or mangrove can absorb more carbon than most tropical forests per year, research reveals. Coastal systems might be small on the map, but their carbon ‘catch’ is massive. Take the Mediterranean Sea, for example — it alone absorbs close to 18 million tons of CO2 annually, demonstrating the immense magnitude of aquatic carbon sinks. Roughly 70% of the ocean’s organic carbon is in deep water, where it remains sequestered for millennia, so it doesn’t escape back to the atmosphere anytime soon.

Whether forests or blue carbon are lost, it damages the planet’s carbon budget. When you cut the forest down or drain the wetland, the carbon that was sequestered for years can be released in minutes. Each year, the degradation of coastal mangroves and seagrasses releases between 0.15 and 1.02 billion tons of CO2 back into the atmosphere. Even 1% annual loss of mangroves or seagrass can release up to one billion metric tons of CO2. While forest loss, particularly in the tropics, compounds this since trees there remain among the world’s most effective carbon sinks. Both impact other GHGs — for instance, seagrass’s halving can reduce global N2O emissions by 0.012 teragrams annually, while mangrove losses can decrease them by 0.017 teragrams.

To capitalize on both forests and aquatic carbon sinks, it aids to examine the advantages of each territory. Some locations are good for retaining or restoring forests, and some have rare coastal wetlands or vast seagrass beds. Safeguarding both is what keeps more carbon in the ground and out of the air. Not to mention that each ecosystem contributes its own unique arsenal to the trade–when combined, they perform more effectively than solo.

Unique features of blue carbon habitats

Blue carbon habitats comprise a tiny fraction of the world’s coastal and ocean areas, yet they store a disproportionate amount of organic carbon in their sediments. Mangroves, tidal marshes and seagrass meadows contain at least 30% of seabed organic carbon despite occupying less than 2% of the ocean floor. These habitats lay along shorelines everywhere. Mangroves thrive in tropical and subtropical tidal zones. Tidal marshes are distributed in temperate and some tropical regions. Seagrass meadows extend from the tropics to cold temperate seas. Their broad scope implies they fuel local and global cycles, with impacts that extend far beyond their diminutive scale.

Blue carbon habitats are more than simply carbon sinks, they offer a plethora of services essential to coastal communities and ecosystems. They decelerate wave energy and mitigate the impact of storm surges, reducing coastal erosion and land loss. The gnarly roots and thick leaves of mangroves and marshes stabilize shorelines, while seagrass beds capture sediment. These habitats act as nurseries for numerous fish, crab and shrimp species, providing shelter and nourishment for juvenile marine creatures. This incentive increases fish populations and aids small and commercial fisheries. They filter water by trapping pollutants and excess nutrients, keeping coastal waters clear and healthy.

It is the nature of their soils and waters that fuels blue carbon habitats’ ability to trap and store carbon. Waterlogged, low-oxygen soil inhibits the decay of the plant material. This locks carbon in the soil for centuries or more. Saltwater prevents many of the microbes that would digest plant material. Consequently, these areas sequester more carbon per square meter than most terrestrial forests. If left undisturbed, they can store this carbon for centuries, some of the most stable carbon sinks on the planet.

Main ecosystem services provided by blue carbon habitats:

• Protection from coastal flooding and storm surges
• Nursery and breeding grounds for fish, crustaceans, and other sea life
• Water quality improvement by filtering runoff and trapping sediments
• Habitat for birds and wildlife, including some rare or threatened types
• Support for livelihoods through fisheries, tourism, and natural products
• Assist in climate regulation by locking away huge quantities of carbon 

Each blue carbon habitat has unique advantages. Mangroves act as powerful buffers to waves and storm surges. Marshes play a critical role in nutrient cycling. Seagrass meadows rank highest in trapping sediment and promoting water clarity. It is these features that make blue carbon habitats invaluable to people and nature alike.

Measuring and optimizing carbon capture efficiency

Precisely quantifying and optimizing carbon capture in forests and bodies of water is essential to combating climate change. Blue carbon habitats, such as mangroves, seagrasses, and salt marshes, sequester carbon at rates 10 times faster than forests. There remains no standardized method to gauge the extent or rate of carbon storage by these systems. Every ecosystem is unique and methodologies may vary from one study to the next. For both blue and green carbon, accounting for how much carbon is being sequestered, stored in soils, and maintained in biomass is complicated. Some use soil samples or satellite data or direct gas measurements, but without standards, results can differ. Without standards, it’s difficult to standardize numbers or determine if the advancement is genuine.

Blue carbon ecosystems contain an estimated 12 billion metric tons of carbon globally and contribute 81 million metric tons annually to their soils. Seagrasses, for instance, account for less than 0.2% of the ocean floor but bury approximately 10% of its carbon annually. These little patches count, yet their efficiency is contingent on the vitality of the entire system. Because food webs matter—a healthy mix of species helps keep nutrient cycles and carbon flows robust. Pollution, such as excess fertilizer or plastic waste, can fracture these cycles and damage the system’s carbon storage capacity. By keeping food webs intact and reducing pollution, it allows these ecosystems to do their job more effectively.

Restoration is an additional method for enhancing carbon capture. Too many blue carbon zones had been wrecked or destroyed, allowing stored carbon to escape. Fixing this begins with stuff like replanting mangroves and seagrasses or pulling dikes to allow salt marshes to flood naturally once more. Research finds restoring 43 to 103 million acres of coastal habitats could make a significant impact. If implemented properly, it might capture an equivalent quantity of carbon as 2.5% of global fossil fuel emissions, or approximately 841 million metric tons of CO2 annually. For forests, replanting native trees and halting wildfires is critical, but for blue carbon, releasing water and regenerating plant life is equally important.

A practical checklist can help guide efforts to strengthen carbon capture across blue and green carbon systems:

• Measure and optimize carbon capture efficiency
• Repair what’s been lost—plant mangroves and seagrasses, reconnect rivers and wetlands, remove dikes to let water flow.
• Minimize pollution sources—restrict farm, factory, and city runoff and reduce the use of toxic chemicals.
• Maintain intact food webs—back a complete spectrum of species, from small shellfish to big predators, to keep nutrient cycles in equilibrium.
• Track your impact — employ periodic monitoring of soil carbon, vegetation health, and biodiversity to identify patterns and fine-tune your efforts accordingly.
• Publicize it — tell stories and studies, such as seagrass meadows rebounding in certain bays, to generate public interest and attract investors.

Threats to carbon-rich ecosystems and their resilience

Forests and aquatic ecosystems — often referred to as green and blue carbon areas — are essential for carbon storage and mitigating climate change. However, the dwindling extent of blue carbon habitats—such as mangroves, tidal marshes and seagrass beds—reduces their carbon sink immediately. They span roughly 126 million acres of coastlines and exist across the globe, excluding Antarctica. When these habitats are lost, they are not able to absorb as much carbon from the atmosphere. This is a genuine problem as the world experiences annual decreases of approximately 1 to 2 percent in these ecosystems, with the loss rate recently accelerating to 7 percent annually.

Human activity is a primary cause of these losses. Cutting forests to farm, erect cities, and mine coastlines all fracture these carbon-rich ecosystems. Take mangroves, for instance, which have disappeared between 0.16–0.39% annually since the early 2000s — some 1.67 million acres in the past two decades alone. Tidal marshes at 1–2% per year. As these habitats shrink, they release as much as 1 billion tonnes of CO2 into the air annually. Despite mangroves composing a mere 0.7% of land, their loss contributes to as much as 10% of global deforestation carbon emissions.

Climate change piles on even more stress. Hotter temperatures, rising sea levels, and storms all make it tough for both forests and aquatic ecosystems to continue doing their job. Shifting weather can kill vegetation, alter soil, and displace wildlife. When stressed, these systems store less carbon and can even begin emitting additional greenhouse gases.

Threat Type	Examples	Potential Impacts
Land conversion	Urban sprawl, agriculture	Habitat loss, less carbon stored, soil degradation
Pollution	Chemical runoff, plastics, nutrients	Poor water quality, loss of plant/animal life
Overexploitation	Logging, overfishing	Fewer trees/fish, weaker ecosystem
Climate change	Sea level rise, extreme weather	Flooding, erosion, death of key species
Invasive species	Non-native plants/animals	Displacement of native species, less biodiversity

We still don’t know a lot about how resilient these carbon-rich systems will be. While most attention is on CO2, gases such as methane and nitrous oxide are emitted from wetlands and flooded forests. These gases could warm the planet even more than CO2. The role of shell-building animals, called calcifiers, is poorly known. They can potentially alter the amount of carbon stored by the system, but more research is required.

Conservation and restoration hold the key to keeping these places strong. Protecting what remains and restoring what was lost enables these areas to sequester carbon for decades to come. If we can slow loss and give these systems a chance to recover, we can keep them as working tools against climate change.

Co-benefits for biodiversity, economies, and communities

Protecting and restoring forests and aquatic ecosystems, or green and blue carbon sinks, delivers numerous co-benefits that extend well past their primary function of storing carbon. These systems serve as natural refuges for flora and fauna, generate employment, fortify food webs, and assist human communities in climate adaptation. The connecting link of forests to aquatic zones is crucial — for both biodiversity and the communities whose lives depend on both land and water.

Forests and blue carbon habitats such as mangroves, salt marshes and seagrass meadows provide refuge for numerous species. These habitats serve as nurseries for fish, birds and other wildlife. Mangroves, for instance, fuel a vast web of life and maintain local fish stocks. Fish catch is as much as 70% greater in adjacent spots near mangroves than in nearby locations without them. That’s because young fish and other sea life have a place to hide and grow in the tangled roots before heading out to open waters. Seagrass beds, for instance, occupy only 0.5% of the seafloor but contain half of all the carbon in marine mud. If these were lost, it could trigger more than $200 billion in climate damages from the release of trapped carbon. This underscores the significance of these sites not only for climate but for biodiversity.

The economic value of blue and green carbon systems is evident when we consider the services they provide. Mangroves covering over 56,000 square miles—nearly the size of Nepal—protect coasts and prevent over $65 billion in property damage annually through flood avoidance. These forests mean 15 million fewer people are at risk of flooding each year. Healthy wetlands and forests attract visitors, drive tourism, and provide reliable livelihoods through fishing and harvesting. Blue carbon ecosystems border approximately 126 million acres of coasts across all continents except Antarctica, providing countless communities with essential resources for their livelihoods.

Local communities rely on these systems for sustenance and employment. Coastal and forest ecosystems help secure food supplies through fish stocks and farming. Many folks close to these communities depend on wild fish, shellfish and other items for livelihoods and meals. As long as these ecosystems remain healthy, they continue to provide these benefits. Loss is swift. Over the last century, human activities have resulted in approximately 1–2% loss per year, with rates increasing to 7% in recent years for some blue carbon ecosystems. That rate is two times faster than what’s observed in land forests, underscoring the critical imperative to intervene.

Direct and indirect benefits of blue and green carbon ecosystems:

• Home and safe ground for many plants and animals
• Jobs in fishing, tourism, and farming
• Help for food security and stable incomes
• Flood control and storm protection for coastal towns
• Plus, co-benefits for biodiversity, economies, and communities.
• Cleaner water and better soil health
• Support for cultural and recreational activities

Policy, funding, and integrated conservation strategies

Blue and green carbon both capture carbon and decelerate climate change, yet they frequently lack sufficient backing in terms of policy, funding, and integrated conservation approaches across land and water. As a policy, funding and integrated conservation strategy, strong rules and support can help these systems work for climate, people and wildlife.

Policies that recognize both blue carbon — like mangroves and seagrasses — and green carbon — like forests — are rare, but necessary. Most countries have national climate plans, but only a handful connect forests and water sites in an integrated strategy. Without that, some carbon sinks slip through the cracks. Take mangroves, which are good for at least US$1.6 billion a year in ecosystem services, yet numerous locations don’t have laws preventing their removal or incentivising maintenance. Seagrasses, spanning nearly 140 million hectares, are rapidly disappearing, declining at a rate of approximately 1.5% annually—roughly 30% have already been lost. Blue carbon loss can contribute up to 1bn tonnes of CO2 to the atmosphere annually. This is why policies that safeguard land and water carbon sinks are critical, not only for climate but for food, clean water and livelihoods.

Funding for these initiatives is not meeting the demand. Huge efforts to restore or expand forests, mangroves, or seagrass beds can be expensive, but reward in the long term for capturing carbon and benefiting people. The blue carbon sites breakdown itself—that is, the emission of CO2 on an annual basis—is approximately 0.45 petagrams globally. South Asia’s Sundarbans, which covers 10,200 square km, is the world’s biggest mangrove forest and a haven for rare species and millions of people, but is underfunded and unchecked. Public and private investment should flow to places such as this, particularly in areas of high loss. When projects incorporate local communities, they are more sustainable and more rewarding.

Collaboration across land and sea remains absent nearly everywhere. Forest and aquatic managers often don’t collaborate, even though upstream events might alter downstream ones. Deforestation, for instance, can wash increased soil into rivers and strangle seagrasses and mangroves. Integrated plans, where communities steward forests, watersheds and shorelines in concert, are more effective. That might involve setting joint objectives, relying on common maps, or coordinating funding. Where this is practiced, as in parts of Australia and Southeast Asia, carbon storage and fish stocks have increased.

Transparent benchmarks and mechanisms to monitor advancement complete impactful approaches. Today, no worldwide standards exist for accounting blue and green carbon increases or decreases. This makes it difficult to demonstrate impact or fund results-based. Methane (CH4) emissions from mangroves, for example, can reduce their carbon storage by 20% as methane traps more heat than CO2. Losing 50% of the world’s seagrass or mangroves can alter global nitrous oxide (N2O) emissions—by 0.012 and 0.017 teragrams of N2O-N per year, respectively. When tracking is good, projects can address issues quickly and build trust and attract new supporters.