When the ambitious plan to allow sea water to flood over the Steart peninsula in Somerset was completed in 2014, critics called it a waste of money. Floods had recently blighted the nearby area, and some local people argued the GBP20m spent on creating a new 250-hectare (617-acre) salt marsh would have been better spent on other flood-prevention projects.
Seven years ago, the concept of “blue carbon” – how marine ecosystems store carbon – was in its infancy. Some research had looked at how mangrove forests absorb carbon, but little was known about how effective seagrass and salt marshes also were at absorbing greenhouse gas emissions.
The two groups behind the salt marsh – the Environment Agency and the Wildfowl & Wetlands Trust (WWT) – barely mentioned the climate. They said the purpose of the marsh was to protect the coast from erosion and create a new valuable habitat for birdlife. Ian Liddell-Grainger, MP for Bridgwater and West Somerset, called the marsh an “extravagant, ridiculous scheme” that put birds ahead of humans.
Less than eight years later, however, everything has changed. Blue carbon is at the forefront of the fight against the climate crisis – and as world leaders gather at Cop26, evidence has emerged that the Steart marsh could be a more powerful carbon sink than anybody imagined.
Scientists at Manchester Metropolitan University found that Steart marshes absorbed 19 tonnes of organic carbon a hectare every year, or 18,000 tonnes in four years – the equivalent of eliminating the greenhouse gas emissions of 32,900 cars. Their work is part of a growing body of research suggesting blue carbon is an order of magnitude more efficient than its terrestrial equivalent.
“The carbon storage at Steart is phenomenal,” says Tim McGrath, head of project development at WWT, which manages the salt marsh. “These exceptional findings could indicate that the carbon storage potential of restoring salt marsh around the UK coast has been underestimated.”
It would take 100 years for a woodland to sequester and store as much carbon as Steart can store in six years, McGrath says. “Trees and peat can take us so far, but blue carbon ecosystems, such as salt marshes, can take us further. It’s time governments seized this opportunity.”
But as world leaders at Cop26 earlier pledge to end deforestation by 2030, campaigners and marine conservationists say the powerful carbon sinks in the ocean are being overlooked. Only 43 out of 113 countries to submit greenhouse gas inventories, or nationally determined contributions (NDCs), have included blue carbon ecosystems as part of their mitigation measures. The UK, despite being a coastal nation with vast reserves of potential blue carbon, is one of those to failing to do so.
“If we are not protecting and counting the blue carbon in our seas, this leaves a dangerous blindspot” for UK policy, says Ailsa McLellan, coordinator for Our Seas, a coalition of Scottish businesses, communities and environmental groups. “It’s time we counted blue carbon, reinstated a limit on damaging methods of fishing, and put future generations first.”
One study suggests bottom trawling could release as much carbon as global aviation emissions. Our Seas is calling on Kwasi Kwarteng, the business secretary, to establish an accounting system for blue carbon, so that marine and coastal ecosystems, including salt marshes, can be protected as part of the UK’s efforts to meet its climate goals.
“Blue carbon habitats are some of the most effective carbon sequestration habitats, area for area, on the planet,” says Bill Austin, professor in ocean science at St Andrews University and chair of the Scottish government’s blue carbon forum. He is working on a government-funded “salt marsh code” that could allow companies to invest in restoration schemes.
For now, blue carbon remains a bit of an outlier when it comes to carbon credits. Out of the big three coastal wetlands, says Austin, mangroves are the best studied, followed by salt marshes and then seagrass. “There is definitely scope for us to raise our ambition” by including blue carbon in the UK’s NDCs, he says.
The Department for Environment, Food and Rural Affairs says the UK recognises the important role blue carbon habitats can play in carbon sequestration, as well as preventing biodiversity loss and building resilience to climate crises: “The ocean plays a vital role in climate mitigation, and we continue to build the evidence base on blue carbon habitats as we strive towards net zero.”
That is a coded way of saying that the science of blue carbon is relatively young. The term was coined in 2009. Recent research estimates that conserving and restoring blue carbon ecosystems could remove the equivalent of 3% of annual global greenhouse emissions.
But the future is another country – and one leading expert predicts that, over time, the ocean’s contribution towards mitigating climate emissions could soar.
Carlos Duarte, a professor of marine science at King Abdullah University of Science and Technology in Saudi Arabia and one of the paper’s authors, says 3% was a “conservative estimate” because the scope for restoration of some ecosystems could be larger than previously believed.
“It is very well understood for mangroves, not well understood for salt marshes and very poorly understood for seagrass,” says Duarte. “We have huge gaps in our knowledge of the amount of seagrass in the ocean. The scope for restoring seagrass could be as much as five or 10 times larger than what we thought.”
The contribution of blue carbon to mitigating climate emissions could be as high as 10% to 15%, he predicts, if “all blue carbon strategies are activated”, including as yet unexplored possibilities such as more seaweed farming, avoiding disturbing sediments on continental shelves, restoring kelp forests and protecting whales.
Other scientists caution that uncertainty in some areas, such as seaweed farms and kelp – neither of which are included in the Intergovernmental Panel on Climate Change’s greenhouse gas emission inventory – makes accurate predictions difficult.
That’s why Duarte wants to study these areas. He is working with Oceans 2050, an organisation run by Alexandra Cousteau, the granddaughter of the oceanographer Jacques, to sample sediments from seaweed farms in 12 countries to find out how much carbon they really soak up.
“I would be hard-pressed to find a climate-mitigation solution that has been proven to be as effective as blue carbon,” says Duarte. “Some people worry that 3% is too little to worry about. To these people in search of solutions that are going to magically deliver many betagrammes of emission, I tell them there are no low-hanging betagrammes.”
There is no time to waste arguing over exactly how much blue carbon can help us cut emissions; all options must be pursued, Duarte says. Blue carbon ecosystems do not just reduce emissions: they help fight the other crisis, such as biodiversity loss and preventing natural disasters.
Blue carbon, he says, has been overlooked for too long. “By the time we find these solutions that can deliver 5% of the job, we will be in 2050 – and we will be burning.”