Climate sciences: Tropics are an unexpected source of CO2 emissions

Carbon dioxide (CO2) emissions from tropical northern Africa are much larger than previously thought, according to a study using satellite observations in Nature Communications. The results turn the tropics as a whole into an unexpected net source of this greenhouse gas.

Terrestrial ecosystems in the tropics store vast reservoirs of carbon in plants and soil. The fate of this carbon - whether it will stay trapped in the biosphere or be released into the atmosphere as CO2 - has been difficult to predict because of sparse measurements across this region.

Paul Palmer and colleagues used observations from multiple satellites to map seasonal trends in CO2 emissions across the tropics from 2009 - 2017. Although tropical Asia, Australia, and South America are sinks that absorb and store CO2, tropical Africa is emitting approximately 1,250 billion kilograms of carbon per year - a level much higher than previously estimated. The authors suggest that the release of CO2 from soils due to sustained land degradation could have a substantial role in this observation.

These results highlight how climate change mitigation strategies, like the Paris Agreement, will need to be re-focused following the identification of previously unknown areas of high emissions. These strategies largely rely on the continued functioning of natural CO2 sinks to meet their goals. However, unexpected tropical CO2 spikes highlight how human induced changes could hamper efforts to meet these goals.