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Blue Carbon – what it is, and why you (and the rest of humanity) should care

The carbon in our seas is emerging as a vital frontier for climate action. Historically the role of our ocean and its management has been largely overlooked in climate planning. Did COP26 finally change this? We take a deeper look at the implications of COP26 for the marine environment and whether ‘blue carbon’ is finally being treated within the urgency it deserves.

In the early summer of 2021, the seas around Arran in the Firth of Clyde turned a spectacular turquoise hue, the result of a phytoplankton bloom visible from space. These tiny organisms, called coccolithophores, contain the photosynthetic pigment chlorophyll, and use the sun’s energy to form calcium carbonate platelets, which are white in colour. In their millions, the coccolithophores refracted sunlight from just below the water’s surface, creating the turquoise colour – a wonderfully literal demonstration of “blue carbon” in action.

Blue carbon is, simply put, carbon stored in our marine and coastal ecosystems. This can be in the living tissue of organisms like the coccolithophores, the gas cycling between the atmosphere and our ocean water, or the stored molecules that become part of the seafloor sediment as organisms defecate and die. 83% of the global carbon cycle is circulated through the ocean via these processes (IUCN). This makes our seas potent carbon stores. For example, Scotland’s blue carbon stores sequester three times as much carbon as its forestry does annually! However, the carbon cycle depends on living animals and balanced, biodiverse ecosystems, from the tiny coccolithophores, to living reefs, to large fish and whales – and without proper protection, these ecosystems can become unbalanced.

It is serendipitous that Arran provides such an illustrative example of blue carbon in action, given that COAST (Community of Arran Seabed Trust), have helped establish management that can greatly increase the ability of our seabed to sequester and cycle carbon. The Lamlash bay No Take Zone, and wider south arran MPA is one of the most highly protected marine areas in the whole of Scotland (and the wider United Kingdom), and shows that with an end to destructive fishing practices, biodiversity can bounce back, with a 50% increase in biodiversity reported within the NTZ. Biodiversity and biomass are the drivers of ocean ecosystems’ ability to sequester carbon, locking it away on the seabed instead of releasing it into the atmosphere where it can function as a greenhouse gas.

So is blue carbon a big deal?

In the race against time to meet ‘net zero’, this matters. However, blue carbon is a relatively new concept, which gained some prominence after a groundbreaking report on the role of oceans in climate change back in 2009, but remains unfamiliar to many. In this article, we will explain why blue carbon is vitally important to the climate change debate, examine whether COP26 has changed anything in the way regulation and management of fisheries responds, and ask what role Scotland could take in becoming a blue carbon champion.

Carbon, and the accounting of carbon emissions, has never been a bigger talking point in Scotland. The historic COP 26 summit in Glasgow put all things carbon centre stage.

The function of the Glasgow COP was to reach international agreements on how the 2015 Paris Agreement can be delivered – i.e. how the parties can limit global carbon emissions in a way that caps warming at two degrees Celsius, or ideally at 1.5°C. Progress towards this goal is measured through the use of NDC’s, or Nationally Determined Contributions. These are personalised action plans for the signatory nations that outline how they will approach the goals. That includes climate targets, both in terms of reducing emissions, and significantly, keeping carbon that is already locked up (sequestered) from being released into the atmosphere.

The UK Greenhouse Gas Inventory is part of the way we calculate progress toward our NDC and is critical to our climate change plan. It is, as the name suggests, a register of greenhouse gases we, as a nation, emit. Page 16 of The UK’s NDC does include some detail on ocean and marine environment, with a vision for “clean, healthy, safe, productive and biologically diverse ocean and seas” and a National Adaptation Plan outlining how “the UK will address marine climate risks by introducing a Sustainable Fisheries policy, giving consideration to climate change in marine planning, building ecological resilience at sea and protecting natural carbon stores through the UK’s network of Marine Protected Areas”. However, these statements of intent are not being effectively delivered and indeed we are failing many of our sustainability targets. In the meantime, the GHG inventory focuses on industrial and terrestrial emissions, does not account for the potential carbon sequestration potential of seabed ecosystems. This is a big problem, because it means we are not effectively monitoring and managing our marine carbon stores.

Has COP26 made a difference?

There has been some modest progress from the summit in considering the role of our oceans in climate change, notably in paragraph 61 of the text of the Glasgow Climate Pact which:

“invites the Chair of the Subsidiary Body for Scientific and Technological Advice to hold an annual dialogue, starting at the fifty-sixth session of the Subsidiary Body for Scientific and Technological Advice (June 2022), to strengthen ocean-based action and to prepare an informal summary report thereon and make it available to the Conference of the Parties at its subsequent session”.

This means that, going forward, there will be a yearly discussion around strengthening ocean based action. It remains to be seen what the findings and recommendations of such a dialogue will be, but it is a positive step towards recognising and respecting the fundamental role our oceans can play in mitigating the effects of climate change.

The Scottish Government was already taking the path of developing a better understanding of blue carbon issues, having launched the Scottish Blue Carbon forum in 2018. This partnership between government and academia “focuses on understanding the ability of various marine and intertidal habitats to trap and store carbon alongside building an evidence base on the effects that human activities may have on these habitats. The Forum provides a platform both for researchers to provide scientific advice directly to policy makers, and for Government to engage directly with researchers.”

Towards the end of COP26, the Scottish Blue Carbon Forum hosted it’s conference “Blue Carbon: Beyond the Inventory”, which looked at emerging science in the field and underlined the importance of evidence-based policy. Cabinet Secretary for Rural Affairs and Islands Mairi Gougeon made opening remarks at the conference, and announced the Blue Carbon International Policy Challenge, which “seeks to bring together private, public and third sector organisations from across the globe to increase our knowledge of blue carbon and identify how to move from research to action”.

The climate impacts of trawling

However, in the meantime marine carbon remains “a dangerous blindspot” in the actions being implemented by the UK and Scottish governments – the carbon sequestered by and stored in our marine and coastal ecosystems is still not accounted for in the UK’s greenhouse gas inventory

This is an important oversight, as while there may be debate around figures, and how we measure them, overwhelmingly, scientific evidence suggests that altering ocean ecosystems will have a climate impact. If we do not measure this and account for it, any plan to get to net zero remains unstrategic (and non-comprehensive), without a clear view of all elements at play. As part of the Glasgow Climate Pact, all countries agreed to revisit and strengthen their current emissions targets – better management of our marine ecosystems is key to achieving this.


Unfortunately blue carbon is currently under threat from a range of pressures The impact of climate change itself is altering ecosystems. Warming waters are acidifying our seas and disrupting the life-cycles of shell-forming organisms and reef-forming habitats such as maerl. However, perhaps the most significant pressure where management action can directly impact climate change, is fishing and specifically bottom-trawling which now has a widespread footprint across the seabed globally – and the situation is no different in Scotland.

Scotland, and the wider UK, has a large bottom-trawling fishing fleet, as well as a large scallop dredging sector. A recent study in Nature has been at the center of some controversy after it suggested that bottom trawling, which disturbs seafloor sediments, may be responsible for releasing carbon into the marine environment. The paper has been widely cited as stating trawling is responsible for emissions on par with those of the global aviation industry. These fishing methods cause resuspension of geological seafloor and sea loch sediments, which are estimated to store as much as 99.84% of Scotland’s blue carbon. However, whilst the debate about the actual figures is still ongoing, the fact that trawling re-suspends carbon into the water column appears to be robust.

The debate centres largely on the extent to which the carbon released by trawling is released into the atmosphere, contributing to atmospheric CO2 and the greenhouse effect. The science of these processes is complex and not yet fully understood, but caution is surely advisable, as the concurrent and interlinked effects of warming, acidification, and deoxygenation in our oceans are potentially catastrophic. We must also recognise the clear biodiversity drivers for better spatial management of bottom-trawl fishing gear. While there may be debate about the fate of re-suspended sediment, including the carbon it contains, the fact that trawling reduces biodiversity and destroys ecosystems has long been substantiated.

If this was on land…

It is striking how differently the narrative of what is happening in our oceans is treated compared to similar processes taking place on land. In recent years, discussion of forests and deforestation has increasingly turned to their role in climate change – why then, do we not also view our impact on the seas this way, especially when the role they play in carbon sequestration outstrips terrestrial systems? The Glasgow Climate Pact includes a welcome pledge to stop deforestation by 2030. No such commitment is made to the oceans. We live on a blue planet, but all too often our attention is focused on the land we inhabit, and not the vast oceans that surround us. 70% of our planet is ocean, and a stunning 99% of earth’s habitable space (biosphere) is in our oceans! Just one example of a blue carbon ecosystem, seagrass meadows, have declined by up to 92% in the UK due to disease, physical damage, and pollution of coastal waters. This is comparable to the loss of great swathes of forest, as seagrass sequesters carbon at 2-4 times the rate of mature tropical forest, but gets a fraction of the press coverage. This habitat loss needs to be discussed more when we consider the role of our seas as a source of food production.

Those tasked with marketing seafood often like to portray the fishing industry as a ‘low carbon’ food supplier, and in some cases this may be true, when the lens is one of comparison to land-based, industrial animal agriculture. However, not all target species, and not all fishing methods are equal. Bottom trawling and dredging are two of the most damaging to biodiversity, and their low carbon credentials are looking increasingly uncertain. Some fisheries have higher fuel demands and are considered to have a higher impact – some research even concludes that trawling for scampi has a higher climate impact than beef production. (See our previous blog on climate change for more)

The ‘blue recovery’

Thankfully, the increasing understanding of blue carbon presents opportunities as well as threats. There are obvious, and relatively straightforward mitigations we can employ to limit damage. Protecting and restoring salt marshes and seagrass meadows, responding to growing consumer demand for sustainable seafood, and establishing highly protected marine protected areas (MPAs) are some examples. We can also shift our focus away from species which are harvested using high carbon, extractive and destructive to those which can be produced via some of the more sustainable forms of aquaculture, like rope-grown mussels or farmed oysters. If we innovate, we can create circular systems where little food is wasted, and by-products feed back into production: collecting and using spent oyster shells as ‘cultch’ for native oyster regeneration, as the billion oyster project in New York is doing, for example; the DEEP project in Tain at the Dornoch firth is restoring native oyster bed to help filter the final 5% of waste produced by the distillery; while Seawilding at Loch Craignish is working to restore a mix of seagrass and native oysters, habitats that can function as nurseries for our wild fisheries. Seawater solutions work in Scotland and internationally, growing salt-tolerant plants in seawater ecosystems, working with the coast rather than against it.


Until the next COP dialogue summit starts agreeing more precise measures to “strengthen ocean-based action”, the work of the Scottish Blue Carbon Forum remains vital, as does the policy implementation of the current SNP-Green Scottish Government and consequent legislative work of the Scottish Parliament. The Government has promised to set out its ‘Future Catching Policy’ and deliver spatial management of inshore fisheries by 2024. A policy of restricting trawling within the inshore zone (sign the Our Seas petition here) would provide broader, overarching protection for marine ecosystems and could do much to deliver action on climate, whether it is counted in the GHG inventory or not.

By allowing carbon to stay locked up in sediment and not disturbing a natural equilibrium, we can minimise risk to ourselves and our coastal ecosystems. This is why we are calling for the role of blue carbon-storing ecosystems like salt marshes, seagrass meadows, kelp forests, and seafloor sediments to be recognised urgently within the UK’s greenhouse gas inventory. It is crucial if we are to accurately account for our carbon footprint.

Members of:

Scottish Rewilding Alliance
Our Seas coalition
Slow Food Scotland
Scottish Food Coalition
UKELA Scotland
Stop Climate Chaos Scotland