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

[摘要] This paper, developed under the framework of the RECCAP initiative, aims atproviding improved estimates of the carbon and GHG (CO₂, CH₄ andN₂O) balance of continental Africa. The various components and processesof the African carbon and GHG budget are considered, existing data reviewed,and new data from different methodologies (inventories, ecosystem fluxmeasurements, models, and atmospheric inversions) presented. Uncertaintiesare quantified and current gaps and weaknesses in knowledge and monitoringsystems described in order to guide future requirements. The majority ofresults agree that Africa is a small sink of carbon on an annual scale, withan average value of −0.61 ± 0.58 Pg C yr⁻¹. Nevertheless, theemissions of CH₄ and N₂O may turn Africa into a net source ofradiative forcing in CO₂ equivalent terms. At sub-regional level, thereis significant spatial variability in both sources and sinks, due to thediversity of biomes represented and differences in the degree of anthropicimpacts. Southern Africa is the main source region; while central Africa,with its evergreen tropical forests, is the main sink. Emissions from land-use change in Africa are significant (around0.32 ± 0.05 Pg C yr⁻¹), even higher than the fossil fuelemissions: this is a unique feature among all the continents. There could besignificant carbon losses from forest land even without deforestation,resulting from the impact of selective logging. Fires play a significant rolein the African carbon cycle, with 1.03 ± 0.22 Pg C yr⁻¹ ofcarbon emissions, and 90% originating in savannas and dry woodlands. Alarge portion of the wild fire emissions are compensated by CO₂ uptakeduring the growing season, but an uncertain fraction of the emission fromwood harvested for domestic use is not. Most of these fluxes have largeinterannual variability, on the order of ±0.5 Pg C yr⁻¹ instandard deviation, accounting for around 25% of the year-to-yearvariation in the global carbon budget.

Despite the high uncertainty, the estimates provided in this paper show theimportant role that Africa plays in the global carbon cycle, both in termsof absolute contribution, and as a key source of interannual variability.

[学科分类] 地球化学与岩石