“We now know we have this peat carbon store, which we previously didn’t know existed,” said Greta Dargie, a researcher at the University College London and lead author of the study published Wednesday in Nature.

Tropical peatlands — wetlands filled with partially decomposed organic matter, or peat — are known for being some of the world’s most carbon-rich ecosystems. When healthy and intact, they can store billions of tons of carbon that would otherwise end up in the atmosphere. As a result, preventing them from being dried out or otherwise destroyed is widely recognized as an important strategy when it comes to fighting climate change.

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The importance of protecting the world’s peatlands has come to international attention in recent years, thanks to several immense wildfires in Indonesia largely caused by agricultural expansion and other human activities in the nation’s vast, peat-filled wetlands. In 2015 alone, researchers estimated that these wildfires emitted about 1.5 billion tons of carbon dioxide equivalents into the atmosphere. Recognizing the concern these wildfires pose to the climate, the Indonesian government recently announced a moratorium on any activities that could damage the country’s peatlands.

Until now, the central Congo Basin has been largely overlooked as a potential home for tropical peat deposits. “A few gray literature sources since the 1950s briefly mention peat occurring in the central Congo Basin, but geolocations or other details were not reported,” the new study’s authors noted in their paper. “Recently published estimates of tropical peatland area and carbon storage still rely on this scant, unverifiable information.”

But the researchers had a hunch that the region might have some secrets yet to be discovered. They were especially interested in an area called the Cuvette Centrale, a shallow depression in the Congo Basin characterized by wetlands and swamp forests.

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“With what was going on with in Southeast Asia, with the degradation of peatlands there, generally there’s an interest to find other areas of peatland across the tropics,” said Dargie, who completed the research while finishing a PhD at the University of Leeds. “People were already well aware of these peatlands in Southeast Asia, and there had been recent discoveries of peatlands in western Amazonia. So then given the size of the Congo Basin and [the literature] occasionally mentioning that there could be peatlands there, we thought we’d have a look.”

The team, composed of researchers from Britain and Congo Republic, used satellite data and an elevation model to scour the landscape and identify areas they considered likely to contain peat deposits. Then they went out into the field and sampled some of the locations to be sure. They discovered peat deposits up to nearly 20 feet in thickness, some more than 10,000 years old according to radiocarbon dating.

The researchers noted that peat was consistently present in places where specific types of forests were growing — particularly forests dominated by certain species of hardwood trees and palms. Armed with this information, they used satellite maps of the region’s forest cover to estimate where peat was likely to be found throughout the Cuvette Centrale.

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Their estimates suggested a peatland area covering approximately 145,500 square kilometers, or 56,000 square miles — about 40 percent of the entire Cuvette Centrale. This is an area five times greater than the maximum possible amount of peatland previous estimates have suggested for the region.

Using their field samples, and accounting for the estimated depth, density and carbon concentration of the total peatland area, the researchers suggest that the Cuvette Centrale peatlands are storing anywhere from 6.3 billion to 46.8 billion tons of carbon. The wide estimated range stems mostly from uncertainties about the depth of the peat deposits in any given location, Dargie explained. When taking samples in the field, the researchers found that peat thickness ranged from about 30 centimeters to nearly 6 meters.

“The only way really to reduce that [uncertainty] would be to take more depth measurements, which would be something we’d be looking to do in the future,” she said.

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The researchers’ median estimate is around 30.6 billion tons, which is the amount of carbon emitted by the United States through the burning of fossil fuels in 20 years — or the amount emitted by the entire world in three years. It’s also approximately the amount of carbon stored in the aboveground forests covering the entire Congo Basin.

Using this 30.6 billion ton estimate, the researchers suggested that the entire African continent probably stores about 34.4 billion tons of carbon in peatlands. This brings total peat carbon stocks throughout the tropics up to an estimated 104.7 billion tons.

Indonesia remains the nation with the greatest peatland area — but the new study brings Congo and Congo Republic up to second and third, respectively. And collectively, the entire Cuvette Centrale region (which stretches across both nations) probably contains the greatest expanse of tropical peatlands in the world.

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Unlike Indonesia, the Congo Basin peatlands have remained relatively undisturbed until now, the researchers noted — thanks largely to being so remote. But that doesn’t mean they’ll be safe in the future. The potential for agricultural expansion, the cause of many of the recent Indonesian wildfires, could pose a threat in the future, the authors suggest. And future climate change could also be a problem. If central Africa becomes warmer and drier in the future, the wetlands could suffer. This means protecting the Cuvette Centrale should be a new climate priority, the authors suggest.

According to Emma Stokes, director of the Wildlife Conservation Society’s Central Africa program, the government of Congo Republic has been considering an expansion to a local protected area — the Lac Télé Community Reserve, which covers an area of 1,700 square miles. The move “could safeguard an additional 5,000 square kilometres [1,900 square miles] of swamp forest — much of it overlying peat — from future disturbance,” Stokes, who was not involved with the new study, said in a statement. “We strongly support this move and commend the [Republic of the Congo] government for this initiative.”

Because the peatlands were previously undetected, the region’s potentially vast carbon stocks have largely flown under the radar until now. The new study brings to light a globally important ecosystem, which could have dire consequences for the climate should it ever be destroyed.