The 12,000 sperm whales in the Southern Ocean absorb roughly 400,000 tons of carbon every year — an example of marine life’s major climate benefits and something called blue carbon.
In an ideal world, a sperm whale spends 70 years swimming through oceans, regulating the food chain, and rearing its young, before finally breaking the surface for the last time and peacefully sinking to the sea floor. It’s an idyllic life for a whale, but it also has significant environmental benefits.
When they die and sink to the seabed, whales take all of the carbon they have absorbed with them. For this reason, they are an example of blue carbon, a term that refers to all of the carbon that is captured and sequestered by ocean life.
Blue carbon can refer to marine animals or plants, and it is vital in the fight against the climate crisis. But industries, including fishing, whaling, and agriculture, are some of the biggest threats to blue carbon, as well as some of the biggest impediments to ongoing efforts to protect it.
What is blue carbon?
Whales don’t just store carbon passively. They also actively drive carbon capture through what scientists call the whale pump. When whales feed at depth and surface to breathe, they release waste that is rich in iron and nitrogen — essentially fertilizing the ocean. This triggers blooms of phytoplankton, the microscopic organisms responsible for roughly half of all photosynthesis on Earth. More phytoplankton means more carbon pulled from the atmosphere. A healthy whale population, then, is a self-reinforcing climate engine.
By now, it’s common knowledge — and accepted by 99.9 percent of all scientists — that the earth is heating up. This is because the world’s biggest industries, like oil, meat, and transportation, are emitting tons of potent greenhouse gases (mostly carbon dioxide) into the atmosphere.
But there are ways to mitigate this impact and pull carbon out of the air, or in the case of blue carbon, out of the oceans. (According to the Blue Carbon Initiative, 83 percent of the global carbon cycle circulates through the world’s oceans.)
On land, rainforests provide a carbon sink. The Congo, for example, sequesters 600 million metric tonnes more carbon dioxide per year than it emits. In the oceans, seagrass and mangrove forests can do the same thing; they can sequester carbon even more effectively than trees. Seagrass can capture carbon up to 35 times faster than a tropical rainforest. And for every acre of mangrove forests, up to 220 metric tons of carbon is stored.
Salt marshes are the third pillar of coastal blue carbon, and among the most efficient carbon stores on the planet. Like mangroves, they can sequester carbon at rates that far exceed terrestrial forests — and they provide similar benefits, acting as buffers against storm surge and erosion. They are also among the most threatened habitats on earth, lost to coastal development, pollution, and rising sea levels.
When it comes to animals that help store carbon, whales aren’t alone. Bivalve mollusks are another example. One recent study found that, together with crustaceans and corals, clams were helping to store 12 million tons of carbon in the waters around the Channel Islands.
Blue carbon threats
Across the oceans, industries are threatening marine life, and in turn, their ability to sequester carbon. For example, it’s estimated that there were likely around 1.1 million sperm whales in the world’s oceans before whaling. Now, there are roughly just 300,000 left. While many countries have stopped whaling, the industry isn’t over, with Norway and Japan still active participants.
This is not only devastating for the whales and the ecosystems they support, but also for the climate. When a whale is killed and pulled from the ocean, all of the carbon stored in its body isn’t sequestered, but released into the atmosphere.
But the threats to blue carbon are bigger than just one industry. Whales are also victims of the fishing industry, as they often get accidentally caught in nets as bycatch. And bottom trawling, which refers to fishing gear that aims to catch fish near the sea floor, also destroys beds of seagrass.
Mangroves are also cut down for timber and charcoal, as well as shrimp aquaculture. Some research notes that in the last two decades, more than 238,000 hectares of mangroves have been cleared for shrimp farming.
Protecting blue carbon
The oceans and coasts are at risk, but the situation is not without hope. Humpback whales, like sperm whales, can store carbon, and are starting to increase in numbers thanks to conservation efforts. They are not without their ongoing threats (like the climate crisis itself), but it’s thought that, after they were nearly made extinct by whaling, the population of the western South Atlantic humpback whale has grown to almost pre-whaling levels of 25,000.
Many people around the world are also focusing their attention on mangrove restoration, which not only benefits blue carbon but also provides protection against storms and floods.
In Cambodia, for example, local women have been working with NGO Action Aid on a mangrove rewilding project that aims to plant more than 100,000 saplings. And in Gasi Bay, on the east coast of Kenya, where residents used to cut down mangroves for logging, a replanting project is underway.
And the government of Indonesia recently announced a new initiative called the Mangroves for Coastal Resilience Project. The project, which is supported by the World Bank, aims to rehabilitate 600,000 hectares of mangroves.
Beyond government initiatives, a market-based mechanism is beginning to take shape. Blue carbon credits — tradeable offsets tied to the protection or restoration of mangrove, seagrass, and salt marsh ecosystems — are attracting interest from both corporations and investors. The logic is straightforward: if a company can pay to preserve a mangrove forest instead of purchasing traditional carbon offsets, the climate math often works in the ocean’s favor. Critics note that the standards for measuring and verifying blue carbon sequestration are still maturing, but early frameworks from the Verified Carbon Standard and others are beginning to bring more rigor to the market.
“The success of this project will contribute significantly to achieving Indonesia’s emissions reduction target,” said Siti Nurbaya Bakar, Indonesia’s minister of environment and forestry, earlier this year.
He added: “Mangroves restoration and conservation are critical to realizing those targets and are a testament to Indonesia’s strong global commitment to adapt to and mitigate the impacts of climate change.”
Further blue carbon efforts were announced at COP27, the 2022 United Nations Climate Change conference, which took place in Egypt. One example, an initiative called the Mangrove Breakthrough, presents a new goal for the restoration and protection of mangroves by both governments and the private sector. It aims to secure $4 billion to prevent more mangrove forests from being lost, to restore half of the recent losses, and to double the protection of mangrove forests. By 2030, the aim is to restore 15 million hectares of mangroves.
A new project, a seagrass-focused plan, aims to map out all of the seagrasses in the Indian Ocean so that countries can put in place plans to protect them.
For individuals, the connection to blue carbon is more direct than it might seem. Choosing seafood that is harvested without bottom trawling, supporting organizations working on mangrove and seagrass restoration, and understanding the climate cost of industries that harm marine ecosystems are all entry points. The ocean has been doing the hard work of stabilizing the climate for millennia. The question now is whether the systems that depend on it — political, economic, and individual — can move fast enough to protect it.
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