Africa’s tropical land released close to 6bn tonnes of CO2 in 2016, according to data taken by satellites.
This means that, if Africa’s tropical regions were a country, it would be the second largest emitter of CO2 in the world – ahead of the US, which currently emits 5.3bn tonnes of CO2 a year.
The region’s 2016 emissions were “unexpectedly large”, the authors write in Nature Communications. This is because the land surface is covered by tropical forests and peatlands, environments which typically absorb large amounts of CO2 from the atmosphere.
The high rate of CO2 loss in 2016 could be associated with a “strong” El Niño, scientists tell Carbon Brief. El Niño is a natural phenomenon that periodically affects weather in many parts of the world. In the African tropics, it can cause unusually high temperatures and drought.
Other causes of CO2 emissions could include “substantial land-use change”, including deforestation and fires associated with agriculture, the study says.
Africa is home to one third of the world’s tropical rainforests. Tropical forests are capable of storing large amounts of CO2. This is because trees absorb carbon from the atmosphere during photosynthesis and then use it to grow new leaves, shoots and roots.
The continent is also home to around 3% of the world’s peatlands, including the world’s most extensive tropical peatland. Peatlands are water-logged environments that can hold huge stores of soil carbon.
Though the African tropics are a globally important carbon store, there have been few studies looking into the extent of year-to-year CO2 emissions from the land in this region.
The new study analyses data taken by two satellites that recorded CO2 emissions stemming from the Africa’s tropical land from 2014-17. These satellites include Japan’s greenhouse gases observing satellite (GOSAT) and NASA’s orbiting carbon observatory (OCO-2).
Data taken from both satellites shows that some parts of tropical Africa’s land are now releasing more CO2 into the atmosphere than they are able to absorb through their trees and soils, says study lead author Prof Paul Palmer, a researcher of geosciences from the University of Edinburgh. He tells Carbon Brief:
- “This is a new perspective. Other satellites have reported widespread land degradation over this region but our study is the first to link surface processes to changes in CO2. What the data suggests is that the land is degrading in certain parts of tropical Africa to a point where it is beginning to release carbon.”
The results show that net CO2 emissions from Africa’s tropical land totalled 5.4bn tonnes and 6bn tonnes in 2015 and 2016, respectively. (This figure considers the difference between the amount of CO2 absorbed and emitted by the land.)
Across the tropics as a whole, net CO2 emissions reached 3.8bn tonnes and 5.9bn tonnes in 2015 and 2016, respectively.
This is because the CO2 emissions from tropical Africa were offset by other tropical regions, such as parts of South America, which acted as net removers of CO2 (“carbon sinks”) between 2015 and 2016.
The maps below, taken from the paper’s supplementary information, show the extent of CO2 emissions from tropical land in 2015 and 2016. On the map, dark blue shows regions that acted as carbon sinks while yellow shows regions that were net emitters of CO2.