Lief Hendrikz, Aquatic Consultant at RSK Biocensus, explains the sequestering potential of ‘blue carbon’ and looks at some of the implementation challenges for the marine sector.
As the world wakes up to the harsh realities of the climate and biodiversity crises, there is much talk of action to keep global heating within the 1.5°C limit as set out by the Intergovernmental Panel on Climate Change (IPCC), which published its Sixth Assessment Report on climate change in August 2021. Reforestation, rewilding and cutting pollution were all discussed as part of the solution at COP26 in Glasgow; however, there is one potentially vital component in the battle against climate change that doesn’t seem to be as well understood, despite its impressive carbon-capturing, flood-defence and biodiversity-enhancing potential.
Blue carbon refers to the ability of wetland, marine and coastal habitats to naturally absorb and store carbon, which is absorbed by the vegetation of marine ecosystems through photosynthesis in the same way as trees and other plants on land – a process known as sequestration.
To date, the focus on carbon sequestration has been very much on terrestrial habitats such as woodland and peat marshes. However, COP26 has raised the profile of marine and coastal blue carbon habitats as carbon sinks and this focus is expected to increase as part of the UN Decade on Ecosystem Restoration and the UN Decade of Ocean Science for Sustainable Development, which both started in 2021.
What is so special about blue carbon?
Blue carbon habitats sequester carbon at a far greater rate than terrestrial habitats and can store it for millennia if undisturbed. For example, salt marshes store 218 tonnes per m2 compared to 5 tonnes per m2 in temperate forests. In the UK alone, the shelf seas cover some 500,000 km2 and are estimated to store 205 million tonnes of carbon, which is 50 million tonnes more than is held within the entire forest stock.
These habitats also offer significant non-carbon benefits, such as providing enhanced biodiversity, acting as nursery grounds for commercial and recreational fish species and offering natural storm defences, and they can be socially and culturally important to the people living around them.
Globally, these are also, unfortunately, some of the most severely degraded habitats, impacted by coastal squeeze, urbanisation, increased storm action and activities such as bottom-trawler fishing and leisure boats. This not only limits their sequestration potential, but the disruption of the carbon rich sediments also leads to the release of carbon back into the atmosphere, along with other greenhouse gas (GHG) emissions such as methane, and can contribute to ocean acidification. The protection and restoration of blue carbon habitats is therefore imperative to reduce further carbon release and enhance future capture and storage potential.
The IPCC GHG inventory guidelines already include the sequestration potential of several blue carbon habitats (saltmarsh, mangrove and seagrass). These have not been included in the UK GHG inventory to date, due to knowledge gaps in sequestration rates and uncertainty around the extent of these habitats in the UK, but estimates suggest blue carbon habitats could offset >2% of UK emissions.
In addition to seaweed habitat protection and restoration projects, seaweed aquaculture is also gaining attention as a blue carbon habitat. Currently in the UK, seaweed is grown for the nutraceutical, pharmaceutical and biofuel sectors. We are seeing huge growth in these markets and demand is high. Farming the seaweed overcomes the sustainability and degradation concerns associated with mechanical wild harvesting and there is significant global growth in seaweed farming aquaculture projects in Europe, Asia and the USA. There is also great potential for co-farming seaweed and seagrass with bivalves to provide efficiency in sequestration and food production, as well as improving water quality. But many of these combined projects are smaller in scale and evidence is still emerging on the possibility of scaling-up their benefits to meet the full scope of the carbon challenge.
Challenges in an emerging industry
As financial markets respond to growing societal pressure to decarbonise and the private sector is increasingly eager to reflect improved corporate social responsibility outcomes, the demand for a blue carbon market and offset scheme is high. There are, however, a number of challenges to the growth of a blue carbon sector that include:
- constrained private investment due to the sector’s current unregulated nature
- scientific uncertainty of carbon sequestration rates, particularly for seaweed farming, and a need for regulatory categorisation within the GHG directory
- a lack of monetisation of the wider non-carbon benefits, e.g., supporting fisheries serving as natural sea defences and providing employment opportunities
- the need to protect existing blue carbon habitats.
To address these challenges, more investment and research is needed, and quickly. The UK government is funding research into a blue carbon code to encourage private investment. Scientific research is being conducted to lessen knowledge gaps in sequestration rates and through initiatives such as the Scottish Blue Carbon Forum. Project feasibility studies are identifying new project areas and developing a salt marsh code. There is also an urgent need to protect existing blue carbon habitats through the establishment of protected areas such as Marine Protected Areas in the UK. Elsewhere in the world, community-led carbon credit and conservation blue carbon projects are proving successful, such as the Gazi Bay project in Kenya and the Cispatá Bay project, Colombia.
What happens next?
The IPCC will publish two further reports this year that will focus on the impacts of the climate crisis and the potential solutions. It will be interesting to see how fully the potential of blue carbon is reflected in these reports and how governments, policy makers and industry around the world respond. By formalising the regulation and monitoring of blue carbon projects, they can be included in the nationally determined contributions as set out in the Paris Agreement and then used as a valuable tool in the fight to address the climate challenge. Blue carbon projects have the added bonus of restoring and protecting habitats and providing economic activity. Given the scale of the climate challenge, there is not a minute to lose to ensure the potential of blue carbon habitats is protected and enhanced to enable its full contribution.
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