title: Carbon cycle. The dominant role of semi-arid ecosystems in the trend and variability of the land CO₂ sink.
abstract: The growth rate of atmospheric carbon dioxide (CO2) concentrations since industrialization is characterized by large interannual variability, mostly resulting from variability in CO2 uptake by terrestrial ecosystems (typically termed carbon sink). However, the contributions of regional ecosystems to that variability are not well known. Using an ensemble of ecosystem and land-surface models and an empirical observation-based product of global gross primary production, we show that the mean sink, trend, and interannual variability in CO2 uptake by terrestrial ecosystems are dominated by distinct biogeographic regions. Whereas the mean sink is dominated by highly productive lands (mainly tropical forests), the trend and interannual variability of the sink are dominated by semi-arid ecosystems whose carbon balance is strongly associated with circulation-driven variations in both precipitation and temperature.
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, 223 62 Lund, Sweden. Department of Earth System Science, School of Earth, Energy and Environmental Sciences, Stanford University, Stanford, CA 94305, USA. anders.ahlstrom@nateko.lu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlström
authors.affiliation: Climate Change Institute, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Raupach
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, 1350 Copenhagen, Denmark.
authors.forename: Guy
authors.initials: G
authors.lastname: Schurgers
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, 223 62 Lund, Sweden.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Smith
authors.affiliation: Institute for Meteorology and Climate Research-Atmospheric Environmental Research, Karlsruhe Institute for Technology, 82476 Garmisch-Partenkirchen, Germany.
authors.forename: Almut
authors.initials: A
authors.lastname: Arneth
authors.affiliation: Biogeochemical Intergration Department, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Jung
authors.affiliation: Biogeochemical Intergration Department, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Reichstein
authors.affiliation: Global Carbon Project, CSIRO Oceans and Atmospheric Flagship, Canberra, ACT, Australia.
authors.forename: Josep G
authors.initials: JG
authors.lastname: Canadell
authors.affiliation: College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK.
authors.forename: Pierre
authors.initials: P
authors.lastname: Friedlingstein
authors.affiliation: Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Atul K
authors.initials: AK
authors.lastname: Jain
authors.affiliation: Institute of Applied Energy, 105-0003 Tokyo, Japan.
authors.forename: Etsushi
authors.initials: E
authors.lastname: Kato
authors.affiliation: Institute on Ecosystems and the Department of Ecology, Montana State University, Bozeman, MT 59717, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Poulter
authors.affiliation: College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Sitch
authors.affiliation: Department of Life Sciences, Imperial College, Ascot SL5 7PY, UK. Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Stocker
authors.affiliation: Laboratoire des sciences du climat et de l'environnement, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Viovy
authors.affiliation: CSIRO Ocean and Atmosphere Flagship, PMB 1, Aspendale, Victoria 3195, Australia.
authors.forename: Ying Ping
authors.initials: YP
authors.lastname: Wang
authors.affiliation: Met Office Hadley Centre, Fitzroy Road, Exeter EX1 3PB, UK.
authors.forename: Andy
authors.initials: A
authors.lastname: Wiltshire
authors.affiliation: Biogeochemical Intergration Department, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany.
authors.forename: Sönke
authors.initials: S
authors.lastname: Zaehle
authors.affiliation: Department of Atmospheric and Oceanic Science and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zeng
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000032:analysis*; D065928:Forests; D065948:Grassland
chemical_list: D002245:Carbon Dioxide