This Danish island became carbon-negative in under a decade. Now locals are building a reef to bring back marine life

Towering evergreens absorb all sound beyond the trees, amplifying the gentle susurrations and chirrups of insects and birds. The pale blue of an early spring sky peeks through the leaves.

Samsø, about an hour’s ferry ride from Aarhus on the Danish mainland, is home to the Guinness-certified largest tree-maze in the world. Covering 15 acres (60,000 square meters), it’s not only a fun attraction, but its 50,000 trees absorb roughly 1,000 to 1,250 metric tons of CO2 annually—about as much as 1,000 round trip economy flights between New York and London.

Opened in 2000, The Labyrinten used trees from an abandoned Christmas tree plantation. It’s just one example of how the island’s 4,000-strong population innovated together after winning a national contest in 1997 to demonstrate how carbon emissions could be reduced.

While Samsø wasn’t given financial support for its projects, the Danish government did stump up for a salary. It went to Søren Hermansen, a Samsø-born-and-bred farmer who was later celebrated as an environmental hero by Time Magazine.

Expecting resistance from residents, many from generations-old farming families, community buy-in was key to Hermansen’s persuasive plan. Eventually, 21 wind turbines—10 offshore and 11 on land—were financed by the Samsø Municipality, local residents and cooperatives. The island is also now home to around 50 photovoltaic plants, converting sunlight into electricity, plus biomass heating plants powered by straw, bought directly from Samsø’s farmers.

“When I was a child, we could fish straight from the beach. As I grew older, I realized that this was no longer possible because marine habitats had been depleted by stone-fishing.”

- Michael Kristensen, Samsø native and resident

Today, Samsø is effectively carbon-negative, which means it produces more energy than it consumes; the surplus is sent to the mainland, generating income for invested Samsø residents. On a wider scale, it’s now recognized as the world’s first renewable energy island—and one from which other countries and communities can learn.

Such environmental wins are often discussed in scholarly articles; less acknowledged are the ways these changes have affected the very fabric and psyche of the island. A previously ageing population has been invigorated by younger residents remaining or returning, with people from elsewhere attracted by research and work opportunities at places such as the Energy Academy, the island’s environmental education and global outreach center. Meanwhile, long-term residents have approached Samsø life with fresh eyes.

The Labyrinten is just one example of using what’s on the island to create something new. Over lunch at nearby Smagen af Øen (‘taste of the island’) in Nordby, I learn that when this café and grocery store opened in 2008, the owners aimed to stock solely locally made products. There were only four; simple jams and vinegars. Now, the shelves groan under the weight of onion marmalade, berry preserves, rapeseed oils and apple juices.

Samsø is known as ‘The Pantry of Denmark’ (a selection of its first potato crop is always earmarked for the Royal Family), so there’s plenty of bounty to choose from—even ants, which Mads Nielsen uses for the citrus notes in his Sams Island gin. Vegans may not approve, but there’s no escaping the lack of food mile-generated CO2 involved.

Local farmer Aage Madsen pivoted from traditional farming to making his own jams and juices from island-grown fruits: you can stock up at his Samsø Bær farm shop before hiking the nearby Besser Rev. This rocky, three-mile (five-kilometer) ‘overground reef’, is a natural spit formed of glacial marine deposits, replete with cormorants, oystercatchers and Arctic terns.

But it’s the establishment of an underwater reef, just off Samsø’s southeastern coast, that’s piqued my interest on this visit. A keen diver, I’ve participated in coral reef restoration on Australia’s Great Barrier Reef and in the Maldives. Stone reef restoration, however, is a new concept to me.

The practice stems from recognizing that harvesting underwater rocks for construction depletes marine habitats. Between 1900 and 2000, around 9.15 million tons (8.3 million cubic meters) of stone was ‘fished’ from Danish sea beds—roughly eight Empire State Buildings—before legislation banned it in 2010.

Such efforts perhaps aren’t so surprising in a country with an ambitious, and legally binding, commitment to carbon neutrality by 2050—that’s to say, it plans to actively absorb more carbon than it emits. Other stone reefs have been established around the country’s frilled, frayed coastline, rebuilding cavernous structures where algae and fish can flourish.

The plight of coral reefs has had a great deal of airtime in recent years, but it’s far less recognised that rocky structures can also provide safe havens for marine life.

But here, in the first territory in the world to have made the transition from reliance on fossil fuels to 100 percent renewable energy, the creation of BARREEF, as it’s been named, seems even more compelling.

I meet with Morten Westergaard, climate expert head of Samsø’s Energy Academy, where long, sleek lines give the buildings the appearance of Viking longhouses. He begins by telling me that BARREEF’s origins sound something like a fairytale by Danish storyteller H. C Andersen: “Once upon a time, there was a little boy who loved to fish … but then one day, he realized that all of the fish were gone …”

That boy was Michael Kristensen, a Samsø native. “When I was child, we could fish straight from the beach,” he says, when he joins us. “As I grew older, I realized that this was no longer possible because marine habitats had been depleted by stone-fishing.”

The plight of coral reefs has had a great deal of airtime in recent years, but it’s far less recognised that rocky structures can also provide safe havens for marine life. As Cæcilie Erichsen Kudsk, a marine biologist from DTU Aqua, National Institute of Aquatic Resources tells me, however, almost any submerged hard structure can play such a role. As wind turbines cartwheel lazily overhead, their bases are surfaces on which marine organisms can grow.

As well as creating marine habitats, rock reefs can play a role in carbon sequestration—the process of capturing and storing carbon in solid structures. By sucking bicarbonate ions from the water and combining them with calcium, skeletal structures, similar to coral, are formed, locking the carbon away.

It all seems like a lot to expect of ‘replacing rocks on the seabed’, something that, I’m told, is simple enough (I wonder if it would make a fun summer solstice community activity, a heavier-weight version of skimming stones?) but, where nature is accommodating, the administrative hoops proved, initially at least, much trickier. As with Samsø’s move to energy self-sufficiency, community buy-in and government funding were required.

Then there was the question of where on Samsø’s 75 miles (120 kilometers) of coastline the reef should be located. “There’s a stretch of gravel road on Samsø’s east side, which often suffered damage from storm winds and waves,” says Kristensen. “Our investigations became three-pronged: Could a stone reef help to prevent coastal erosion; could it reinstate marine habitats and, thirdly, could the area between the reef and the shoreline support the growth of equally vital sea grasses?”

Using 6,000 tonnes of granite waste purchased from Norwegian quarries, BARREEF was eventually established near this road, close to the lively harbor village of Ballen. Watery dimples over submerged rocks hint at its presence; otherwise, buoys marking the area are the only clue to a world coming back to life. Because yes, it’s early days, but the project looks successful. According to Kudsk, underwater cameras have shown algae growth, as well as the presence of fish species, including goby and wrasse.

Unlike the Labyrinten, the purpose of BARREEF was not to establish an attraction—sailing is prohibited in its environs. But benefits to Samsø and its marine life seem likely. In the future, paddleboarders, swimmers, snorkelers and divers may well have good reason to take to the waters—and I absolutely intend to be one of them.

On my first visit to Samsø, I’d failed to escape the Labyrinten; this second time, I was more successful, but swimming in May’s eight-degree Celsius (46°F) waters saw my head remaining resolutely above water. Next time, I tell Morten and Michael, I’ll be at depth—and face-to-face with side-eyeing fish that have, almost as in an Andersen fairytale, been summoned back to Samsø’s waters.

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