The world’s oceans are some of the harshest victims of climate change, including acidification, coral bleaching and sea-level rises – but scientists say that they could also be part of the solution to global warming.
Researchers are keen to increase quantities of “blue carbon”, which is carbon stored in marine environments such as mangrove forests, seagrass meadows and salt marshes.
Globally, blue carbon ecosystems are thought to store more than 30 billion tonnes of carbon and restoring them could cancel out about three per cent of the world’s emissions each year, a study in Nature calculated.
“Unlike other carbon stores – plants and trees – they actually store the carbon in the sediments,” Maitha Al Hameli, section head of marine assessment and conservation, terrestrial and marine biodiversity at the Environment Agency – Abu Dhabi (EAD), said.
“That’s why we refer to them as carbon sinks because they do exactly that – they remove them from the air and sink them in the oil and store them.
“They have an amazing ability to capture and store the carbon dioxide … As long as the area is not disturbed, this carbon is stored for years and years.”
Going beyond for solutions
Their importance extends beyond carbon storage: mangrove forests and other natural coastal environments are credited with improving biodiversity, keeping waters clean, protecting coastlines and much else.
“Because they are natural, they do have this multi-benefit that you won’t find in solutions that are created by humans to tackle a certain issue,” Ms Al Hameli, who is also a fellow of the National Experts community of Emirati experts, said.
While blue carbon habitats can play an important part in climate change mitigation, they are under threat, with the International Union for Conservation of Nature having estimated a decade ago that the area covered by seagrass, for example, shrinks by seven per cent a year.
Coastal development, ocean acidification, rising temperatures, physical disturbance from anchoring boats and pollution threaten these habitats.
Putting efforts into conserving resources
Prof William Austin, of the University of St Andrews in Scotland, said that the past decade or so had, however, seen a growth in awareness of the importance of conserving the natural environment around coasts and losses had slowed. Efforts should be focused, he said, on conserving what remains.
“Where we are losing them, say, for the development of a port, [which is] perhaps important to the economy of a country, increasingly we’ll see compensatory schemes where we do a restoration project elsewhere so that the net loss is balanced,” said Prof Austin, who chairs the Scottish Blue Carbon Forum, which brings together experts from a wide variety of institutions and advises government.
Aside from protecting and rehabilitating seagrass beds, mangrove forests and salt marshes, other approaches to increasing blue carbon storage are being looked at.
These carbon dioxide removal (CDR) strategies include, for example, nutrient fertilisation, which aims to increase the rate at which the seas take up and store carbon dioxide, a key greenhouse gas.
Adding nutrients such as iron, phosphorus or nitrogen to the sea surface aims to increase the rate at which tiny phytoplankton photosynthesise and draw CO2 out of the water.
The hope is that this newly formed organic carbon ultimately ends up in the deep sea, where it could be stored for hundreds of years.
“I’m somewhat concerned about the ecological impacts of some of these proposed CDR methods. They’re largely untested but in theory they offer a scalable solution that could make more of an impact,” Prof Austin said.
“Personally I think blue carbon and the restoration of natural ecosystems is a much safer option. It’s a much more immediate option that is known to be delivering a whole range of benefits.”
He sees fewer concerns with efforts to promote macroalgae or seaweed habitats, which store carbon and have other beneficial effects.
“With macroalgae they provide important nursery grounds for commercial fisheries,” Prof Austin said. “Where we can restore these habitats they can provide a whole range of benefits beyond the blue carbon impact.”
Mangroves on the rise
While the UAE has lost natural habitats because of coastal development, industrial activity and pollution, among other factors, Abu Dhabi has in recent years been increasing its area of mangrove forests, which show great resilience to the region’s extreme temperatures.
“We have a number of mangrove restoration projects that have been running for the past 10 years and are still running,” Ms Al Hameli said.
“We’ve also worked closely with private companies and tech companies to look at more effective ways to plant mangroves.”
One pilot project that investigated using drones to plant mangroves was a success, leading to a wider roll-out of this approach.
The UAE’s waters also boast about 3,000 square kilometres of seagrass beds, providing vital food for dugongs. The country has the world’s second-largest population of these mammals after Australia.
“We have a very healthy seagrass area in Abu Dhabi and it extends from Ghantoot all the way to the border with Saudi. They’re healthy, lush seagrass meadows that are doing really well,” Ms Al Hameli said.
Healthy coastal environments also provide great benefits to people who enjoy them for leisure activities, such as birdwatching.
Kayaking and stand-up paddleboarding are popular around Abu Dhabi’s mangrove forests, which reach up to the city itself.
“You drive down the eastern mangrove road and it’s an amazing sight to see these lush green forests in the middle of the city.” Ms Al Hameli said.
The way that mangrove forests and other natural coastal habitats protect coastlines is expected to become increasingly important as sea levels rise because of climate change.
Mangroves are even credited with reducing the impact of tsunamis, as they act as a first line of defence to absorb energy.
Sea-level rises will, however, also pose difficulties in the conservation of blue carbon habitats, as ideally these environments would be allowed to migrate inland as water levels rise.
“We’re going to have to create space inland for these habitats to naturally migrate, which they will do and we know that they’ve done this in the recent past when sea levels have naturally fluctuated,” Prof Austin said.
“In some regions you can’t do that – there might be infrastructure inland – a road, a railway – so we tend to build coastal defences.”
As a result, in certain areas these habitats face the problem of “coastal squeeze”, where they are trapped between a fixed coastline and rising sea levels.
“This makes it even more important to create areas for … managed realignment of the coastline, where you let the sea naturally flood inland,” Prof Austin said.
“There are places where it would be appropriate and useful to do that … We want to future-proof some of these solutions we’re implementing for climate and biodiversity.”
