Carbon offsetting in the aquatic environment

29th July 2022

Chris Smith

The worlds ecosystems are experiencing significant and observable impacts from climate change and our vast ocean is the ecosystem most affected! 

In the last 200 years, the oceans have absorbed a third of the CO2 produced by human activities and 90% of the extra heat trapped by the rising concentration of greenhouse gases.

But even though the challenge of addressing climate change seems immense, solutions are possible to secure a living ocean for a healthy global climate.

What is blue carbon?

Blue carbon is the term for carbon captured by the word’s ocean and coastal ecosystems. These ecosystems are carbon storage powerhouses, storing up to 10 time as much carbon as forests! Blue carbon ecosystems include seagrass meadows, tidal marshes, and mangroves. They are among the most intensive carbon sinks in the biosphere and play a central role in climate mitigation.

Seagrass is a naturally growing, photosynthesising frond like grass growing up to 2 metres long in clear water where sunlight passes through. They once covered most sand and mudflats in the UK and other shallow coastal waters.

In the UK and globally, the natural and highly effective marine carbon sink is vanishing. The UK has lost more than 90% of the seagrass meadows that once surrounded the nation, research has found.

With the pressure on countries and companies to reach net zero, blue carbon is gaining international attention. Projects, mainly involving mangroves, are using “blue carbon credits” to fund their work.

Why it is important?

Undisturbed meadows and their soils can persist for millennia, permanently storing carbon at 35 times the rate of tropical rainforests as well as harbour up to 40 times more marine life than bare seabed’s.

The 50 marine sites on UNESCO's World Heritage List comprise at least 21% of the global area of blue carbon ecosystems and 15% of global blue carbon assets - carbon stores that are equivalent to about 10% of global greenhouse gas emissions in 2018.

The challenges

Restoring seagrass meadows through planting is a highly manual process, it can take 5-7 years to create viable seagrass growth and resilience between new and old growth. Seagrass covers about 0.1% of the ocean globally but provides 10-15% of its carbon storage. A 2020 UN report however, said 7% of this key marine habitat was being lost worldwide each year, equivalent to a football field of seagrass vanishing every 30 minutes.

The Seagrass Ocean Rescue project are taking opportunities to build it back and is already planting millions of seeds on the shallow seabed in Dale Bay, Pembrokeshire.

Peter Jones, of University College London(UCL), said: “The next decade is a crucial window of opportunity to address the inter-related crises of biodiversity loss and climate change. The restoration of seagrass meadows would be an important contribution to this. This will involve restrictions such as reduced boat anchor damage, restricting damaging fishing methods and reducing coastal pollution.”

Blue carbon credits

Blue carbon credits are created by the growth and conservation of carbon-absorbing plants, such as mangrove forests and their associated marine habitat.

Cispatá Bay’s mangrove forests off the Caribbean coast of Colombia are now a flourishing coastal marine park of 11,000 protected hectares (27,000 acres) of mangroves and a major biodiversity hotspot.

This Cispatá conservation project, is a collaboration between Colombia’s Marine and Coastal Research Institute (Invemar), Conservation International (CI) and Apple, has also attracted the attention of marine scientists, researchers, and corporations, as it is among the first to measure and sell the new type of credit to fund conservation: “blue carbon”.

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