In a study that bolsters understanding of greenhouse gas sources, the team led by scientists from the University of Edinburgh identified emissions over northern tropical Africa totalling between one million and 1.5 billion tonnes of carbon a year.
The study, which scrutinised observations from two satellites over the continent, suggests the stored carbon is being released from degraded soils – ground that is subject to prolonged or repeated drought or land use change.
Scientists say further research is required to provide a definitive explanation for the emissions in western Ethiopia and western tropical Africa, but the findings to date will bolster efforts to meet the terms of the Paris Agreement, which aims to limit average global temperature rise below 2C.
Paul Palmer, professor of quantitative earth observation of the University of Edinburgh’s school of geosciences, who led the study, said: “The tropics are home to one-third of Earth’s three billion trees and their stored carbon and yet we are only scratching the surface of understanding how they are responding to changes in climate.
“We anticipate that satellite data will continue to improve that situation.”
The carbon source might have gone undiscovered with land-based surveys alone, according to the researchers.
They examined data gathered by two NASA satellite missions – Japanese Greenhouse Gases Observing Satellite (GOSAT) and the Orbiting Carbon Observatory (OCO-2) – between 2009 and 2017.
They compared readings with three atmospheric models showing changes in vegetation and a host of other measurements of ground water, fire and levels of photosynthesis.
The study is the result of a decade of work, involving hundreds of dedicated engineers and scientists, and billions of dollars of investment by space agencies.
The study, published in Nature Communications, was funded by the Natural Environment Research Council’s National Centre for Earth Observation.
It also involved researchers from the University of Leicester, Laboratoire des Sciences du Climat et de l’Environnement in France, and Colorado State University in the US.
According to the United Nations, Africa is the continent most vulnerable to the impacts of climate change.
It is already experiencing temperature increases of approximately 0.7C over much of the continent, with predictions that temperatures will rise further.
The continent accounts for only 2 to 3 per cent of the world’s carbon dioxide emissions from energy and industrial sources.