Huge Boost in Methane Concentrations Traced Back to Africa's Wetlands

Since 2007, methane concentrations in the atmosphere have been increasing sharply and scientists do not fully understand why. Now a team of researchers has traced a third of these increases back to Africa, suggesting tropical sources such as wetlands may be responsible for a large part of the upsurge.

Methane is a greenhouse gas that is more potent than carbon dioxide in its effect of warming the Earth's atmosphere. It comes from a variety of sources, including the production and transport of gas, oil and coal, and the agricultural industry. Methane levels have been rising since the start of the industrial revolution, but in the last 10 to 15 years they have been increasing faster.

"Methane is the second most important greenhouse gas, behind carbon dioxide," Mark Lunt, an atmospheric scientist at the U.K.'s University of Edinburgh, told Newsweek. "We need to be able to understand how and why it is changing in our atmosphere to inform how we might mitigate future emissions."

Lunt is lead author of a study that uses satellite data to find out if and where methane has been coming from in Africa, which has been largely overlooked as a source because of the lack of atmospheric data available. Findings are published in the journal Atmospheric Chemistry and Physics.

"Global levels of methane in the atmosphere have been on the rise since the mid-2000s, after a period of relative stability," he said. "There are many different explanations for why this is the case but the primary suspects have been an increase in microbial sources such as wetlands and agriculture from the tropics, as well as increases in fossil fuel emissions from countries such as the U.S. and China. Alternatively the sink—the process of removal of methane in the atmosphere—could have decreased resulting in the resumption of growth we see."

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Lunt and his team looked at annual and seasonal trends of methane concentrations between the latitudes of 26 degrees North and 26 degrees South, focusing on sub-Saharan Africa. By focusing on this area, they were able to find changes in methane emissions from individual countries.

Findings showed that about a third of the global atmospheric methane increases between 2010 and 2016 came from Africa's tropics, with most of this coming from East Africa. Authors associate the methane increase to wetlands—they found evidence of a pronounced boost in methane from Sudd, one of the world's largest wetlands.

"Wetland methane is produced through a process known as methanogenesis. Essentially wetlands are anaerobic environments which are ideal for the production of methane," Lunt said. "Microorganisms break down organic matter in a process that results in the production of methane."

Wetlands are the world's biggest natural source of methane. In 2017, research published in PNAS found that these vast ecosystems are playing a bigger role in emissions than previously thought, and this may help drive climate change. Warmer temperatures will lead to wetland organisms which decompose faster, producing more methane at a faster rate. More methane will then lead to more warming—a loop known as a positive feedback.

Lunt says that understanding how much methane is coming from wetlands and other tropical sources is important as it can help scientists improve models and better understand the causes of tropical methane emissions. This will help understand how methane emissions may change in the future.

He said the research is limited in that the data only goes back to 2009, so they cannot see what was happening when the rise in methane began in the mid 2000s. "Whilst we found a large part of the increase in methane emissions from Africa to be from the Sudd wetlands in South Sudan, the cause of the rest of the increase in Africa is still a little more uncertain," he added.

The team now plans to look at more intricate satellite data to see if they can trace back methane emissions in Africa in even greater detail.