title: The terrestrial biosphere as a net source of greenhouse gases to the atmosphere.
abstract: The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and therefore has an important role in regulating atmospheric composition and climate. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change. The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO2 equivalent per year) of 3.9 ± 3.8 (top down) and 5.4 ± 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Hanqin
authors.initials: H
authors.lastname: Tian
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.|Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Iowa 50011, USA.
authors.forename: Chaoqun
authors.initials: C
authors.lastname: Lu
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, 91191 Gif sur Yvette, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.affiliation: Department of Global Ecology, Carnegie Institution for Science, Stanford, California 94305, USA.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Michalak
authors.affiliation: Global Carbon Project, CSIRO Oceans and Atmosphere Research, GPO Box 3023, Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Josep G
authors.initials: JG
authors.lastname: Canadell
authors.affiliation: Department of Environmental Sciences, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: Eri
authors.initials: E
authors.lastname: Saikawa
authors.affiliation: School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA.
authors.forename: Deborah N
authors.initials: DN
authors.lastname: Huntzinger
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Gurney
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: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Bowen
authors.initials: B
authors.lastname: Zhang
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Yang
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, 91191 Gif sur Yvette, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Bousquet
authors.affiliation: NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado 80305, USA.
authors.forename: Lori
authors.initials: L
authors.lastname: Bruhwiler
authors.affiliation: Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Guangsheng
authors.initials: G
authors.lastname: Chen
authors.affiliation: NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, Colorado 80305, USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Dlugokencky
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: The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
authors.forename: Jerry
authors.initials: J
authors.lastname: Melillo
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Shufen
authors.initials: S
authors.lastname: Pan
authors.affiliation: Institute of Ecosystems and Department of Ecology, Montana State University, Bozeman, Montana 59717, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Poulter
authors.affiliation: Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Prinn
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, 91191 Gif sur Yvette, France.
authors.forename: Marielle
authors.initials: M
authors.lastname: Saunois
authors.affiliation: School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA.|Woods Hole Research Center, Falmouth, Massachusetts 02540, USA.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Schwalm
authors.affiliation: Department of Earth and Planetary Science, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Steven C
authors.initials: SC
authors.lastname: Wofsy
mesh_terms: D000383:Agriculture / Q000706:statistics & numerical data; D001208:Asia; D001272:Atmosphere / Q000737:chemistry*; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D017753:Ecosystem; D057232:Global Warming / Q000517:prevention & control / Q000706:statistics & numerical data*; D017752:Greenhouse Effect / Q000517:prevention & control / Q000706:statistics & numerical data*; D006802:Human Activities / Q000706:statistics & numerical data; D008697:Methane / Q000032:analysis / Q000378:metabolism*; D009609:Nitrous Oxide / Q000032:analysis / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D009609:Nitrous Oxide; D008697:Methane