According to new research, the world's largest tropical peatland shifted from being a major carbon store to a source of harmful carbon dioxide emissions thousands of years ago as a result of climate change.
The climate of central Congo began to dry around the time Stonehenge was built, causing the peatlands to emit carbon dioxide.
According to a major international study, peatlands only stopped releasing carbon and reverted to taking carbon out of the atmosphere when the climate became wetter again in the last 2,000 years.
Scientists involved in the study are warning that if modern-day global warming causes droughts in the Congo region, history could repeat itself, dangerously accelerating climate change.
Climate change could trigger the Congo peatlands to release billions of tons of carbon
The study's researchers warn that if modern-day global warming causes droughts in the Congo region, history could repeat itself, dangerously accelerating climate change, as per ScienceDaily.
If this occurs, up to 30 billion tonnes of carbon dioxide, a potent greenhouse gas could be released from the peatlands into the atmosphere. This is the same as the global emissions from fossil fuel combustion over three years.
"Our study brings a brutal warning from the past," said Professor Simon Lewis of the University of Leeds and University College London, a senior author of the study.
"If the peatlands dry beyond a certain threshold, they will release colossal quantities of carbon to the atmosphere, further accelerating climate change."
The Congo peatlands, located in central Africa, are the world's largest tropical peatlands complex, covering an area larger than England and Wales combined.
Congolese and European scientists collected peat samples from central Congo's remote swamp forests. The researchers were able to create a record of the vegetation and rainfall in the central Congo basin over the last 17,500 years by analyzing plant remains.
Waxes from plant leave preserved in peat were used to calculate rainfall levels during the plant's life.
The findings, titled "Hydroclimatic vulnerability of peat carbon in the central Congo Basin," paint a picture of a drier climate developing in central Africa around 5,000 years ago.
During the most severe drought, rainfall was reduced by at least 800 mm per year.
This caused the Congo peatlands' water table to drop, exposing older layers of peat to the air and causing oxidation and carbon dioxide release.
The peat layers either decomposed or never accumulated between 7,500 and 2,000 years ago.
The researchers dubbed this the "ghost interval," and it was discovered in peat samples from hundreds of kilometers away in the Democratic Republic of the Congo (DRC), indicating that it occurred throughout the entire peatland region.
The study's lead author, Dr. Yannick Garcin of France's National Research Institute for Sustainable Development, stated, "The peat samples show that there was a period of around 5,000 years when there was almost no build-up of peat, less than 0.1 mm per year."
The samples also reveal information about the rainfall and vegetation that existed at the time the peat was formed.
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Peatlands are 'vulnerable'
Rainfall was reduced by at least 800 mm per year during the worst of the drought, as per Earth.com.
This caused the Congo peatlands' water table to drop, exposing older layers of peat to the air, resulting in decomposition and the release of carbon dioxide.
According to the study's findings, peatlands only stopped releasing carbon and reverted to taking carbon out of the atmosphere when the climate became wetter again in the last 2,000 years.
According to Dr. Garcin, the drought caused a 2-meter loss of peat. As the peat decomposed due to the drought, it became a massive carbon source.
This decomposition ceased only when the drought ended, allowing peat to begin accumulating again.
The scientists warn that, while the peatlands are currently mostly intact and sustainably managed by locals, they are vulnerable.
If current global warming causes drying in the Congo region, history may repeat itself, with 30 billion tons of carbon from decomposing peat ending up in the atmosphere.
This is the equivalent of all global emissions from fossil fuel combustion over a three-year period, and the impact on climate change could be disastrous.
The expeditions to collect peat samples in the Democratic Republic of the Congo were led by Professor Corneille Ewango of the University of Kisangani in the DRC.
This is yet another astounding discovery about peatlands. They are more vulnerable than we thought, and everyone must work together to protect them, according to Professor Ewango.
Polluting countries must reduce carbon emissions as soon as possible to avoid droughts pushing peatlands over the edge.
The DRC will also need to strengthen peatland protection. One of the most diverse and carbon-rich ecosystems on the planet is at stake.
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