What are mangroves? How do carbon projects involving mangroves work? And how can you tell a credible mangrove carbon project from an untrustworthy one?
With many different types of carbon projects out there, we know it can be overwhelming to understand what they do and evaluate which your company should buy carbon credits from.
To make the process a little easier, we’re publishing a series of explainers on the different project types. So far, we’ve explored afforestation, enhanced weathering, ocean carbon removal, and Direct Air Capture.
Next up: mangroves – featuring Delta Blue Carbon as an example project.
In this article we cover:
Mangroves are a type of tree or shrub that live primarily in tropical, coastal wetlands where the land meets the sea, as well as along riverbanks.
They’re one of the only types of tree that can survive being regularly submerged in salt water and in very wet, loose, swamp-like soils. They grow long, dense, twisted roots which hold them upright in the shifting sediment of the wetland.
Unfortunately, mangroves are also one of the most threatened ecosystems in nature.
In the last 50 years, we’ve lost 30-50% of the world’s mangroves (Donato et al, 2011). The vast majority of that decline is due to wetlands being converted by humans for use in farming – particularly aquaculture i.e. farming of fish, shellfish, molluscs etc.
It’s vital we protect remaining mangroves.
Why? Three key reasons:
Because they’re one of the only plants that can survive in these coastal wetland environments, mangroves are incredibly biodiverse ecosystems – providing shelter for a wealth of both land and water wildlife, many of which are found nowhere else in the world.
Biodiversity (i.e. a wide range of animals and plants existing) is vital for life on earth – enabling the healthy ecosystems that provide us with air to breathe and food to eat.
And the earth’s overall biodiversity is dwindling rapidly – so it’s important that we protect and restore areas of rich biodiversity, like mangrove forests.
Mangroves grow on coastlines and riverbanks, creating a barrier between land and water through their dense foliage and substantial root systems.
Through this, mangroves are a natural flood defence system, reducing the risk of flooding and erosion for coastal communities.
And given that coastal communities are also facing rising sea levels and increasing extreme weather due to the impacts of climate change, the coastal defence that mangroves offers will become increasingly crucial for protection.
Mangrove forests remove and store carbon dioxide as they grow and live, making them a vital tool as we work to tackle the climate crisis.
Like trees, as mangroves grow they extract CO₂ from the air and use it to produce oxygen and carbon, through photosynthesis. The carbon they then use to build their leaves, branches, roots, and the mangrove becomes a carbon store. Mangroves are very efficient at this process, absorbing and storing at least four times as much carbon as trees (Donato et al, 2011).
When leaves, branches, or whole mangroves die, they fall to the floor of the wetland. Over time this dropped organic matter accumulates, decomposes, and forms new sediment or soil, taking the carbon with it.
So, the lifecycle of a mangrove effectively buries carbon within wetland soil, where it is stored for even longer. Studies have found that mangroves store carbon in soil for over 5,000 years if left undisturbed (Costa et al, 2022).
This combination of storing carbon in plant and sediment is rare – and makes mangroves a hugely important carbon sink.
Alongside mangroves, both salt marshes and seagrass also remove and store carbon in this way. Together, the three are referred to as blue carbon – referring to carbon removed from the air and stored in biomass and sediment in coastal and marine ecosystems.
To prevent the carbon stored in mangrove forests from being released as carbon emissions (and to maintain biodiversity and coastal defences) we must protect our remaining mangroves.
And, if we can restore and grow new mangroves, they can help us to remove further existing carbon emissions from the atmosphere too.
To enable that, mangrove projects need financing.
Which is where mangrove carbon projects come in.
How do we ensure that mangroves are protected, restored, and grown? Well, we pay people to protect, restore, and grow mangroves.
But where does the money come from?
Mangrove conservation isn’t a profitable activity in its own right, so projects require external funding.
There is some public funding available for mangrove conservation, as governments come to recognise the vital importance of mangrove conservation. For instance, the Indonesian government has set a target of protecting 23 million hectares and rehabilitating 600,000 hectares of mangroves by 2024, and is working with the World Bank to enable this.
But, public funding isn’t available in all countries that have mangrove forests – and even where it is available there’s the risk that changes in leadership could lead to the funding being withdrawn at any point in the future.
In this kind of scenario, carbon finance is a great solution.
Mangrove projects can calculate the carbon benefit produced as a direct result of the project’s lifetime activities – which, for mangrove projects, could be either emissions avoided or carbon removed:
The project can then sell a number of ex-ante carbon credits equivalent to their carbon benefit to individuals or businesses who want to buy carbon credits to compensate for their own emissions (or simply to contribute to climate solutions).
And the money gained from the sale of carbon credits is then used to fund the project’s set up and/or ongoing activities to achieve their aims and protect and restore the world’s mangroves.
This is where the voluntary carbon market truly can have a huge, tangible impact – providing a vital stream of finance to projects that are crucial to tackling the climate crisis (and other interconnected issues), and that simply could not exist without this funding.
But, as we well know, this only works when the carbon project is credible and of high-quality.
Unfortunately, there are many low-quality carbon projects out there that use this mechanism of selling carbon credits for financial gain, without actually creating the carbon benefit that they promise to buyers.
So, how can you tell if a mangrove carbon project is credible?
There are a few key markers of quality when it comes to evaluating the credibility of carbon projects, and particularly important for mangrove projects are: accuracy of measurements, durability, additionality, and co-benefits beyond carbon.
When you’re evaluating which mangrove project(s) to buy carbon credits from, you need to be looking for evidence of how the project is approaching these key markers in their methodology and project documentation.
Here’s what to look for in each of these factors.
It’s vital that this calculation is as accurate as possible and that overestimation of impact is avoided – otherwise buying carbon credits from the project will not have the expected climate impact.
In nature-based projects it’s generally more difficult to be sure of the accuracy of the carbon benefit calculated – the amount of carbon that plants absorb and store can vary a lot across individual plants, and be impacted by many external factors.
For mangroves, this is exacerbated because much of the carbon is stored in soil and sediment below the mangrove and often below water – which is even more difficult to accurately measure and quantify.
To improve accuracy and mitigate risk, in high-quality mangrove projects you can expect to find:
Mangroves offer short-term carbon storage, because the carbon will eventually be released when the plant dies and/or when the sediment in the forest is disturbed. So, they are generally a less durable or permanent type of carbon project.
However, there are several ways that a mangrove project can maximise its durability to keep the carbon out of the atmosphere for as long as possible – which you’d expect to see from a high-quality project:
Proving additionality – that the carbon benefit produced is above and beyond what would have happened without the project existing – is vital in any credible carbon project.
For mangrove projects, this includes demonstrating:
It’s important that projects think holistically about the impact that they create and ensure that local people and the environment as a whole benefit from the project’s existence – removing carbon or avoiding emissions is meaningless if it leads to loss of biodiversity or damages the livelihoods of indigenous communities, for instance.
As we’ve seen, mangrove forests have huge potential to provide co-benefits for people and ecosystems, on top of the carbon benefit they provide.
High-quality, credible mangrove projects will design their methodology to maximise this potential for co-benefits, including:
To put this into context, let’s take a look at an example of a trusted, high-quality mangrove carbon project from the Lune library: Delta Blue Carbon.
The delta of the river Indus is home to over 3,500 km2 of mangrove forest – vital for removing and storing carbon, as well as providing a habitat for many wildlife species.
But, the mangroves were under huge strain due to demand for fuelwood and land conversion for animal grazing, which was leading to large-scale deforestation and degradation of the mangrove forest.
And so, the Delta Blue Carbon project was born in 2015.
The project uses funding from the sale of carbon credits to protect and restore the existing mangroves to prevent emissions being released and maximise the carbon removal and storage potential of the mangroves.
On top of this, the project is also planting new mangrove seedlings in carefully managed plant nurseries. Once the seedlings are big enough, they’re then planted out into the existing mangrove ecosystem to increase the forest’s potential.
In terms of carbon benefit, throughout the project’s lifetime 2 million tCO₂ will be removed by the protected mangrove forest every year.
So, how do we know that Delta Blue Carbon is a credible, trustworthy, high-quality mangrove carbon project?
Here’s a few of the key markers of quality in the project:
Plus, as well as the robust and rigorous approach to the carbon benefit of the project, Delta Blue Carbon is creating substantial co-benefits beyond carbon, including:
Want to support Delta Blue Carbon’s work to protect and restore mangroves in Pakistan?
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