Editor’s note: From “eDNA” to “ecosystem services,” environmental jargon is everywhere. Conservation International looks to make sense of it in an explainer series called “What on Earth?"
In this installment, we explore blue carbon, a secret weapon in the fight against climate change, buried beneath the waves for millennia.
I've been pretending to know what blue carbon is, and now I'm too embarrassed to ask.
No worries. It's one of those terms that, once you unpack it, ends up being about pretty much everything — life, death, the planet itself.
Let’s start with “carbon.” We hear about it a lot in the age of climate change. But here's what it actually is: it's you. Your bones, your blood, every cell in your body. It's the tree outside your window. The soil beneath your feet. Carbon is the basic building block of everything alive on Earth. It is both life and death — a ceaseless cycle that returns what was once living to the soil, the sea, the air, to feed new life.
Woah. So, what makes it blue?
Because it's in the water. That's it. Scientists just use the word “blue” to tell you where the carbon is stored — underwater.
So why is everyone all worked up about this watery carbon?
Well, it isn’t in the water, it’s below it — stored in the roots and soils of coastal ecosystems. We’re talking about trees that cling to the edge of coasts — like mangroves — and tidal estuaries, meadows of seagrasses and salt flats.
Something special happens to carbon in these ecosystems — something really important to preventing climate change.
Ok, I’m here for it.
We all should be. Right now, the world has something of a carbon problem. Through the burning of fossil fuels (former living things, by the way) we are putting far more carbon into the atmosphere than nature can absorb. It's cooking the planet.
These coastal ecosystems — mangroves, seagrasses, salt marshes — are some of the most powerful natural tools we have to slow that down. That’s because their soils are waterlogged and oxygen-starved. This makes decomposition slow almost to a stop. So, the carbon that would otherwise escape gets trapped, buried, locked away for thousands of years.
These ecosystems are, in a very real sense, carbon vaults.
Amazing. But are they actually making a dent?
More than a dent. Coastal wetlands cover a tiny fraction of the Earth's surface — but they store and sequester carbon at a higher rate than tropical rainforests. A single square mile of mangrove forest holds as much carbon as the annual emissions of 90,000 cars.
But here's the kicker: we’re destroying blue carbon ecosystems at a massive rate. And when that happens, all that stored carbon doesn't stay buried. It goes straight back into the atmosphere.
What’s driving their destruction?
Coastal development is one of the biggest culprits. Shorelines are prime real estate, and ports, hotels and urban expansion routinely displace mangrove forests and coastal wetlands. Aquaculture — particularly shrimp farming — clears vast stretches of these habitats, often permanently. Logging for timber and fuelwood compounds the loss.
Pollution adds another layer of damage. Agricultural runoff carries fertilizers and chemicals into coastal waters, disrupting the delicate nutrient balances these ecosystems depend on. And then there’s climate change. Rising sea levels, stronger and more frequent storms and shifting salinity levels can all destabilize blue carbon ecosystems faster than they can adapt.
How quickly are we losing them?
Blue carbon ecosystems are some of the most threatened ecosystems on Earth, roughly 340,000 to 980,000 hectares (840,000 to 2.4 million acres) are destroyed each year. Just looking at mangroves, the world has lost roughly 1 million hectares (2.5 million acres) since 1996, an area about the size of Jamaica.
At the current rate, 30 to 40 percent of tidal marshes and seagrasses and nearly all the world’s unprotected mangroves could be lost in the next century.
And destroying these ecosystems isn’t just about carbon.
What do you mean?
Take mangroves as an example. Their dense, twisted roots stabilize soil and buffer waves, shielding shoreline communities from flooding and erosion. They also absorb excess rainfall and slow water flow — reducing flood risk even between storms.
The benefits don't stop there. Mangroves filter pollutants and sediment, improving water quality for nearby communities. And because they serve as breeding grounds and nurseries for commercially important fish species — and shelter crabs, clams and other species often harvested locally — they're a direct economic lifeline for the people who live alongside them.
Can we just replant what we’ve lost?
Unfortunately, it’s more complicated than that. Once mangroves are lost, they're extremely hard to restore. Without the root systems that once anchored the sediment, new seedlings are highly vulnerable to being swept away by waves and erosion before they can establish.
Restoration isn’t impossible — with careful planning and the help and knowledge of local communities, restoration efforts can be successful.
- Further reading: To save a dying forest, this town dug in
What is Conservation International doing to help?
I’ll give you a couple of examples.
In Australia, we’re partnering with an Indigenous-led startup to restore the planet's largest known organism: a vast seagrass meadow devastated by a marine heat wave. Their secret weapon? Sea cucumbers, which naturally enrich the seafloor and give transplanted seagrass a better chance of survival.
And in Mexico, a road cut off the water flow a mangrove forest needed to survive. The fix isn't high-tech — local community members are digging channels by hand to restore that flow and bring the ecosystem back to life.
The science matters. The funding matters. But at the heart of every restoration effort is a community who knows their coastlines and refuses to give them up.
Tell me more about the communities driving this work.
Blue carbon ecosystems have been woven into the fabric of coastal communities for millennia. Indigenous peoples and traditional fishing communities have long understood mangroves, seagrass meadows and tidal wetlands not as resources to be extracted, but as living partners in survival — timing harvests to tidal rhythms or relying on coastal wetlands as nurseries for the fish that fed their families. That knowledge, passed down through oral tradition and practice, shapes coastlines in ways that often go unseen — and that lab-based conservation science is only beginning to appreciate.
And too often, that knowledge has been sidelined. This is especially true for women. These can be deeply gendered spaces — for example, the mangrove shorelines where women harvest shellfish and crabs is not just sustenance, but a meaningful contribution to family and community life.
Recognizing these relationships is the key to designing better blue carbon projects — ones more resilient, more effective and genuinely aligned with how coastal communities function, so these ecosystems endure for generations to come.
This blog originally published on November 1, 2016.
