The Congo peatlands are a huge carbon “timebomb” that could be triggered by the climate crisis, research has shown.
The peatlands flipped from storing carbon to releasing it into the atmosphere when the climate became drier 5,000 years ago, the study showed, before returning to accumulating carbon 2,000 years ago.
Scientists are now worried that human-caused global heating could tip the fragile system over the edge once more, accelerating the climate crisis.
The peatlands, which span the Democratic Republic of Congo and the Republic of Congo, are the largest in the tropics and cover 17m hectares (42m acres). They store a vast amount of carbon – the equivalent of three years of global fossil fuel emissions. They are also threatened by logging and oil and gas exploitation.
“We know today that these peatlands are very close to that tipping point where they could release billions of tonnes of carbon to the atmosphere,” said Prof Simon Lewis, from the University of Leeds, UK, and University College London, and a senior author of the study. “We don’t know exactly how close but we do know that for the last couple of decades, droughts have been getting longer in the centre of the Congo basin.
“Our study brings a brutal warning from the past. This is an important message for world leaders gathering at the Cop27 climate talks.”
Prof Corneille Ewango at the University of Kisangani, in the Democratic Republic of the Congo, who led the expeditions to collect peat samples, said: “The peatlands are more vulnerable than we thought, and everyone must play their role in protecting them. Polluting countries must cut their carbon emissions fast.”
The Republic of the Congo’s environment minister, Arlette Soudan-Nonault, said: “It is more than ever essential that rich and polluting countries commit financially to the protection of our peatlands, our biodiversity and local populations. If we want to prevent this gigantic carbon store from turning into a timebomb, our partners must understand that this invaluable planetary ecosystem service cannot remain free for ever.”
The research was published in the journal Nature and used cores taken through the peat layers to reconstruct the history of the peatlands. The ratio of hydrogen isotopes in the wax indicated how much rain was falling at the time the leaves grew. The work showed that drought caused the water table to drop, exposing peat to the air and decomposition.
“Our results indicate a positive feedback in the global carbon cycle – climate-induced drying in the central Congo basin leads to the release of further carbon from peat to the atmosphere,” the researchers concluded.
Further research is needed to determine how much carbon was released during the earlier dry period and how quickly, though it took at least decades or centuries, the researchers said. Dr Yannick Garcin, from the French National Research Institute for Sustainable Development and lead author of the study, said: “This drought led to a huge loss of peat, at least 2 metres. The drought flipped the peatland to a huge carbon source.”
Research published in September showed five dangerous tipping points may already have been passed owing to the 1.1C of global heating caused by humanity to date, including the collapse of Greenland’s ice cap and of a key current in the north Atlantic. The study considered the Congo basin as a potential tipping point but found insufficient evidence.
“The new study provides support for the Congo peatlands being vulnerable to climate drying,” said Prof Tim Lenton, at the University of Exeter and part of the team that undertook the September analysis. “For now, I would keep the Congo peatland and rainforest on the ‘uncertain’ and ‘slow’ list of potential tipping elements in the climate system, but it is clearly a vital carbon store and ecosystem that we should all seek to preserve.” Fires burning the peat could cause much more rapid carbon emissions, he added.
Vanessa Nakate, a prominent climate justice activist from Uganda, said: “We are on the edge of [climate] disaster. The Congo basin is one of the most underappreciated resources the planet has. It is a hive for biodiversity and a huge carbon sink. We need to protect it.”
