Why Blue Carbon?

sea spaghetti seaweed underwater in cornwall

Half way through last year we switched from planting trees to over-offset what remained of our carbon footprint (after extensive minimisation, as ever), to planting mangroves. As always, we planted many more than our carbon accounting required to ensure that we overshoot on our climate commitments.  But, what are mangroves, and why do we think that mangroves and blue carbon are a better bet in the fight against climate change?

What Is Blue Carbon And Why Is It Important?

Blue carbon is the carbon captured and stored in marine and coastal ecosystems.  Coastal ecosystems such as salt marshes and coastal wetlands, sea grass meadows and mangrove forests are of particular importance, drawing down and storing away significantly more carbon compared to terrestrial ecosystems.  In addition to this direct action to mitigate climate change, these ecosystems also play key roles in adapting to the impacts of climate change, protecting coasts and coastal communities from storms and sea level rise, regulating water quality and creating valuable habitats that also provide food security and support commercially important fisheries.


The role of plants in sequestering and storing carbon from the atmosphere, and mitigating some of the impacts of climate change, should be well known by now.  Mangroves are small salt-tolerant trees and shrubs that grow in sheltered coastal waters in the tropics and sub-tropics, but when found growing together the term mangroves also refers to the mangrove forest biome or mangrove swamp created.  Stilt-like roots that make them stand up out of the water at low tide characterize these trees and shrubs, and it is these extensive root systems that are the key to their blue carbon credentials.

Mangroves As Carbon Sinks

Mangroves are the most carbon-rich forests in the tropics and are contain the highest carbon density of all terrestrial ecosystems, locking away carbon at a rate 2-4 higher than the same unit area of mature tropical forest.  In mangroves this carbon is stored in the biomass of the extensive root systems as well as in the deep carbon-rich soils of the seabed.  In fact, recent studies have estimated that the mean carbon storage capacity for a single hectare of mangroves (the soils, as well as the biomass of the plants) is 1,494mg of CO2 equivalent.   

Why We Planted Mangroves in 2020

Every year we work tirelessly to minimise Leap’s carbon footprint, but there is always some impact left that we must account for.  After calculating Leap’s total remaining carbon footprint (across all three scopes), we offset to ensure that we are acting to remove more carbon dioxide (and equivalent greenhouse gasses) from the atmosphere than we are responsible for.  We do this in several ways, one of which has traditionally been investing in tree planting with Eden Reforestation Projects.  Eden believe mangroves to be one of “the most effective and economic methods of offsetting carbon emissions”, with each mangrove tree planted removing over 380kg of CO2 from the atmosphere over its lifetime (so bout 12.3kg per year).  With the data about the increased benefits of blue carbon being so compelling, the decision to switch from investing in terrestrial forests to mangroves was an easy, almost instant one.

The Threats Faced By Blue Carbon Environments

The soils and sediments of coastal environments can be up to 6 meters deep, and stores between 50 and 99% of blue carbon.  The International Union for the Conservation of Nature (IUCN) estimates that 83% of the carbon in the global carbon cycle circulates through the ocean, and whilst coastal environments cover only 2% of the total ocean area they account for 50% of the carbon stored in sediments by the ocean.  These coastal blue carbon environments are therefore of critical importance, not only because of the opportunity to draw down and lock away more carbon but also because of the amount of carbon that they already store.  If these ecosystems are damaged, degraded, or lost, however, we not only lose the opportunity to sequester more CO2 but the carbon stored in those sediments in released back into the atmosphere or ocean, accelerating and worsening the climate crisis.  Just as the amount of carbon sequestered by blue carbon ecosystems is proportionately higher than terrestrial forests, so is the net release of carbon emissions from deforestation, making their protection of even greater importance.

According to the Blue Carbon Initiative, “Recent analysis suggests that the annual loss of the three blue carbon ecosystems is resulting in emissions similar to the annual fossil fuel CO2 emissions of the United Kingdom (the world’s 9th ranked country by emissions).”

Think Globally, Act Locally

We are committed to protecting, conserving, enhancing and growing blue carbon ecosystems.  As a business based in a coastal county of an island nation, we are close to the coast and many members of the team here have based their lives around the sea.  Many of our clients and the causes that we get behind are involved in the protection of the marine environment.  Therefore, as we move forward we plan to become more involved in the protection of blue carbon ecosystems closer to home.  The mangroves that we invested in to offset our carbon footprint are incredibly important, but they are half a world away in the tropics; there are also plenty of blue carbon projects in Cornwall that we can get behind, be that through volunteering (each member of the leap team is offered the opportunity to take paid time off to volunteer for an environmental charity, project or cause each year) or investment.  Seagrass meadows can absorb carbon 35 times faster than the amazon rainforest, and there are several sea grass habitats and conservation areas close to us on the south coast of Cornwall.  Likewise, the blue carbon potential of large seaweeds such as kelp that grow at incredible rates (giant kelp can grow up to 60cm per day in ideal conditions, reaching a height of 45 meters) is enormous.  Kelp and other seaweeds sequester carbon dioxide through photosynthesis and store it as biomass until it dies and much of the stored carbon can be sequestered in the deep sea once it sinks below 1000m deep (90%), and seabed (10%).  Whilst other blue carbon ecosystems such as eel grass meadows, salt marshes and mangroves store carbon in the sediment below them in a way that can be measured, the effectiveness of kelp and macroalgaes is more difficult to measure.  The deep sea acts as a reservoir, storing carbon for several decades as opposed to locking it up for much longer periods or even indefinitely in sediments.  However carbon stored offshore is less likely to be disturbed and released early by storm activity.  Furthermore, the capacity of kelp and macroalgaes is enormous.

“When we talk about ways oceans can sequester carbon, the conversation typically revolves around mangroves, salt marshes, and seagrass meadows. But the magnitude of carbon sequestered by algal forests is comparable to that of all those three habitats together,” – Professor Carlos Duarte, King Abdullah University of Science and Technology in Saudi Arabia.

Kelp’s rapid growth rate, around 30x that of trees and plants on land, means that its potential for rapid carbon sequestration and storage is enormous.  One study has suggested that if 9% of the ocean’s surface were given over to “Ocean Macroalgal Afforestation” (kelp farms), an area roughly four and a half times the size of Australia, 53 billion tonnes of CO2 would be removed from the atmosphere offsetting all of humanity’s current emissions.

We are excited to explore the opportunities available to us locally to get behind blue carbon projects on the coast of Cornwall.  If you are involved with or know of any blue carbon initiatives in Cornwall (such as sea grass meadow protection or kelp habitat restoration) that could benefit from our design for change expertise through our Grant For Good programme, then please get in touch.

Mangrove images by Eden Reforestation Projects