Part 2: Our incredible ocean carbon sink is disappearing-the only way to replace it is expensive, labor-intensive and takes years. Experts say it's worth

Part 1: Hidden carbon dioxide sinks that can save the planet

Last modified on Wednesday, November 10, 2021, 13.31 EST

I was in a wooden boathouse on the shore of Lake Craignesh, with a lot of leaves sitting in two 1,000-liter water tanks. The leaves are seaweed, and they are full of seeds. Next to the water tank is a Heath Robinson style pump series. The laboratory may be low-tech, but it is the headquarters of a groundbreaking, community-led climate experiment.

The goal is to restore the seagrass meadows where the lake once thrived. Danny Renton, founder of the Craignish Ocean and Coastal Habitat Restoration Organization (Cromach) and Seawilding, said: “We are trying to bring about earth-shaking changes to the health of this sea lake. This charity is based in Afghanistan. People in the villages around Gael support Hebit, about three hours’ drive from the Cop26 summit in Glasgow.

“Seagrass sequesters carbon 35 times faster than rainforest. This is an amazing carbon sink,” Renton said. "As part of photosynthesis, it absorbs carbon dioxide from water and traps it in mud."

The UK has almost no tropical rainforest that can absorb carbon dioxide emissions, but it does have approximately 11,000 miles (17,700 kilometers) of coastline dotted with salt marshes and seagrass. Together with tropical mangroves, these two habitats are the most well-known reservoirs of "blue carbon", the carbon contained in marine ecosystems (as opposed to the "green carbon" of terrestrial habitats).

These blue carbon ecosystems can absorb up to 2% of the UK's carbon emissions each year, mainly in the soil, and can be stored for thousands of years if they are not disturbed. In Scotland, the blue carbon pool can absorb 28.4 MtCO2e (tons of carbon dioxide equivalent) per year, which is about three times the total amount of forests in Scotland.

However, although tropical rainforests, peatlands, and other terrestrial habitats are known for their importance in the climate crisis, coastal wetlands are still neglected. The Intergovernmental Panel on Climate Change (IPCC) includes them in the national greenhouse gas inventory, but they are also one of the most threatened ecosystems on the planet. A study earlier this year concluded that 92% of the UK’s seagrass has disappeared in the past two centuries, compared to 39% due to pollution caused by industry, mining and agriculture, as well as dredging, bottom trawling and coastal development. The seagrass has disappeared since the 1980s. Several pieces of seagrass remaining in Lake Craignesh have been fragmented.

"Lake Craignish is very typical," Renton said, checking the map of the remaining 10 grasslands. "Most lakes have caused damage to the seabed due to bottom trawl fishing and aquaculture, and pollution such as nitrate enters the water."

The lake used to have huge beds of native oysters and scallops. Its seagrass meadows provide nurseries for herring and cod. Now, most of it has passed.

In fact, according to a United Nations report in 2020, seagrass covers about 0.1% of the world’s oceans, but provides 18% of carbon storage, reducing it by 7% every year-equivalent to the disappearance of a football field every 30 minutes.

Renton's goal is to increase the grassland by half a hectare this year. It is part of a wider wildlife restoration project that has reintroduced 220,000 oysters into the lake, providing habitat for wildlife and acting as a water filter, allowing seagrass to photosynthesize better. In addition to climate sinks, wetlands also protect the coast from storm surges and increase biodiversity. For example, underwater seagrass meadows can hold 40 times more marine life than bare seabeds.

But restoring seaweed, even half a hectare, is labor-intensive and complicated. In August, 40 volunteers in wetsuits and snorkels swam across the remaining grassland, collecting leaves full of seeds, which are now mature in the water tank. After maturity, hundreds of thousands of seeds are filtered through a pump, and then put into linen bags, 50 seeds per bag, and planted on the lake bed at intervals of one meter. Bags that are weighted with sand to make them sink help protect the seeds from predators.

Since the survival rate of seagrass seeds is about 10%, it may take five to seven years for new seagrass growth to connect with old growth to form a meadow. "That's why it's so complicated," Renton said.

As countries and companies face pressure to achieve net zero emissions, blue carbon is receiving international attention. Projects that mainly involve mangroves are using "blue carbon credits" to fund their work. Companies keen to fund the Loch Craignish project in exchange for carbon credits have approached Renton.

But he said that it is too early to consider quantifying how remediation work affects carbon storage, let alone verification. "We have no verifiable indicators to offset carbon emissions," he said. "We know that carbon storage can be very effective, but we don't know much."

It is only a question of how much carbon can be absorbed by seagrass restoration. According to recent research, labor-intensive seaweed restoration is expensive and has a lower success rate than mangroves and salt marshes.

Although Project Seagrass, the marine conservation charity that established the Lake Craigney Lake Laboratory, aims to mechanize more labor-intensive aspects, including seed collection, a report in Nature concludes that seagrass meadows are restored on a large scale It is "feasible" but "still challenging."

Richard Unsworth, director and associate professor of the Seagrass Program at Swansea University, admitted that the science behind blue carbon is still developing. But he said: "This is an important part of the complex puzzle of tackling climate change."

In July, more than 7,000 marine and climate scientists, human rights experts, and others urged world leaders to include legally binding blue carbon targets in their emission reduction plans.

Unsworth said that there is no time to waste. "Until a few years ago, no one wanted to pay attention to the carbon content in ocean sediments. There was not much data in Europe, let alone the United Kingdom," he said. "Their maps are poor, they are poorly understood, and they are not protected."

Currently, he is doing what he can. A consortium including Project Seagrass, World Wide Fund for Nature and Swansea University has planted more than 750,000 seagrass seeds in Dale Bay, Pembrokeshire, with the goal of eventually recovering 3,000 hectares (12 square miles) in the UK by 2030 Grass. Seagrass can absorb emissions from 3,000 small cars, create habitats for billions of small animals, support 4,700 more fish than exposed sediment, and increase sediment intensity tenfold to prevent erosion.

"This is a win-win situation," Unsworth said. "It must be part of the vision to improve the whole of nature."

Tomorrow – Part 3: The Future of Blue Carbon

This article was revised on November 7, 2021. Earlier versions incorrectly stated that there are no tropical rain forests in the UK.