The full greenhouse gases budget of Africa: synthesis, uncertainties and vulnerabilities

Abstract

Abstract. This paper, developed under the framework of the RECCAP initiative, aims at providing improved estimates of the carbon and GHG (CO2, CH4 and N2O) balance of continental Africa. The various components and processes of the African carbon and GHG budget were considered, and new and available data derived by different methodologies (based on inventories, ecosystem fluxes, models, and atmospheric inversions) were integrated. The related uncertainties were quantified and current gaps and weakness in knowledge and in the monitoring systems were also considered in order to provide indications on the future requirements. The vast majority of the results seem to agree that Africa is probably a small sink of carbon on an annual scale, with an average value of −0.61 ± 0.58 Pg C yr−1. Nevertheless the emissions of CH4 and N2O may turn Africa into a source in terms of CO2 equivalents. At sub-regional level there is a significant spatial variability in both sources and sinks, mainly due to the biome's differences and the different anthropic impacts, with southern Africa as the main source and central Africa, with its evergreen tropical forests, as the main sink. Emissions from land use change in Africa are significant (around 0.32 ± 0.05 Pg C yr−1) and even higher than the fossil fuel ones; this is a unique feature among all the continents. In addition there can be significant carbon losses from land even without changes in the land use (forest), as results from the impact of selective logging. Fires also play a significant role, with 1.03 ± 0.22 Pg C yr−1 of carbon emissions, mainly (90%) originated by savanna and woodland burning. But whether fire carbon emissions are compensated by CO2 uptake during the growing season, or are a non-reversible loss of CO2, remains unclear. Most of these figures are subjected to a significant interannual variability, on the order of ± 0.5 Pg C yr−1 in standard deviation, accounting for around 25% of the year-to-year variation in the global carbon budget. These results, even if still highly uncertain, show the important role that Africa plays in the carbon cycle at global level, both in terms of absolute values and variability.