Ancient Carbon Venting From Lakes in the Congo Basin Peatlands Spells Trouble for Climate Targets.

The swamps in the center of Central Africa were long regarded as a sort of geological savings account. Carbon entered and remained there. The material became older the deeper you dug into the Cuvette Centrale’s peat, and it was assumed that anything that had been buried there for three millennia would respectfully stay buried. Now, that assumption is beginning to seem dubious.

Two sizable lakes in the Democratic Republic of the Congo, Mai Ndombe and Tumba, may be releasing truly ancient carbon, according to research recently published in Nature Geoscience by a team led by Travis Drake at ETH Zurich. Long before the rise of most modern empires, the researchers report that up to 40% of the carbon dioxide drifting off these dark, humic-stained surfaces was sealed inside nearby peatlands. It’s the kind of discovery that, instead of providing an answer, modifies a question.

The geography of this story has an almost cinematic quality. As you stand at the meeting point of the Fimi and Kasaï rivers, you can witness the collision of two distinct worlds on the water itself: the near-black flow draining out of Mai Ndombe and the rust-red current of the Kasaï. Savanna sediment is the source of the iron-tinted red, while leaves and soils provide the darkness. It’s an oddly lovely place to discover that something is wrong.

The mechanism—or rather, the absence of one—is problematic. Although scientists are able to date the peat upstream and measure the radiocarbon signature of the gas escaping the lakes, the precise route linking the two is still somewhat mysterious. According to co-author Matti Barthel, there is a leak in the reservoir. That metaphor is working hard, but probably not hard enough. A leak suggests that you are aware of the location of the hole.

It’s difficult to ignore how this adds complexity to the larger climate accounting. Every significant carbon budget has identified tropical peatlands as a reasonably reliable sink, and policymakers have relied on this stability when outlining net-zero pathways. Some of those figures were subtly counting the same molecules in the wrong column if a significant portion of the CO2 exiting Congo’s blackwater lakes turns out to be millennia-old peat carbon rather than recently fallen leaves.

The factors that humans can control and those that they cannot determine whether this trend gets worse. Deforestation, cropland conversion, and drought all push the basin closer to releasing its stored resources. For years, Amazon has had to deal with its own version of this discussion. The peat fires in Southeast Asia presented an even more direct argument. Due in part to the fact that the central basin is actually difficult to access, Africa has contributed less to the conversation. The primary research instruments are still patience and pirogues.

Reading the study gives us the impression that we should have looked at this earlier. Only around ten years ago was the Cuvette Centrale properly mapped. We are still in the early stages of comprehending how this region, which contains one-third of the carbon in tropical peatlands worldwide, breathes. In the grand scheme of things, the leak might be minor. It might not be, too.

For the time being, the lakes continue to exhale slow, ancient breath into a warming sky, as they seem to have been doing for a while. Somehow, that breath will need to be accommodated in the climate targets written in air-conditioned conference rooms in Geneva and New York. Unconcerned, the peat continues to release what it once held.