title: African tropical rainforest net carbon dioxide fluxes in the twentieth century.
abstract: The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO₂ fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (-0.02 kg C m⁻² yr⁻¹ or -0.04 Pg C yr⁻¹, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO₂ flux at the beginning of the century (σ1901 = 0.02 kg C m⁻² yr⁻¹), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m⁻² yr⁻¹). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO₂, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO₂ fluxes with increasing atmospheric CO₂ concentrations and extreme climatic events, as the uncertainties will only amplify in the next century.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA. jbfisher@jpl.nasa.gov
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Fisher
authors.forename: Munish
authors.initials: M
authors.lastname: Sikka
authors.forename: Stephen
authors.initials: S
authors.lastname: Sitch
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.forename: Benjamin
authors.initials: B
authors.lastname: Poulter
authors.forename: David
authors.initials: D
authors.lastname: Galbraith
authors.forename: Jung-Eun
authors.initials: JE
authors.lastname: Lee
authors.forename: Chris
authors.initials: C
authors.lastname: Huntingford
authors.forename: Nicolas
authors.initials: N
authors.lastname: Viovy
authors.forename: Ning
authors.initials: N
authors.lastname: Zeng
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlström
authors.forename: Mark R
authors.initials: MR
authors.lastname: Lomas
authors.forename: Peter E
authors.initials: PE
authors.lastname: Levy
authors.forename: Christian
authors.initials: C
authors.lastname: Frankenberg
authors.forename: Sassan
authors.initials: S
authors.lastname: Saatchi
authors.forename: Yadvinder
authors.initials: Y
authors.lastname: Malhi
mesh_terms: D000349:Africa; D002245:Carbon Dioxide / Q000378:metabolism; D057965:Carbon Sequestration; D057231:Climate Change / Q000266:history; D049673:History, 20th Century; D049674:History, 21st Century; D008954:Models, Biological; D011891:Rain; D014197:Trees / Q000378:metabolism; D014329:Tropical Climate
chemical_list: D002245:Carbon Dioxide
keywords: Africa; Congo; carbon; rainforest; tropic; uncertainty