B21M-03
The full budget of greenhouse gases in the terrestrial biosphere: From global C project to global GHG project
Tuesday, 15 December 2015: 08:30
2022-2024 (Moscone West)
Hanqin Tian1, Chaoqun Lu2, Philippe Ciais3, Anna M Michalak4, Josep Canadell5, Eri Saikawa6, Deborah N Huntzinger7, Kevin R Gurney8, Stephen Sitch9, Bowen Zhang10, Jia Yang10, Philippe Bousquet11, Lori Bruhwiler12, Guangsheng Chen13, Edward J Dlugokencky12, Pierre Friedlingstein14, Jerry M Melillo15, Shufen Pan10, Benjamin Poulter16, Ronald G Prinn17, Marielle Saunois11, Christopher Schwalm7 and Steven C Wofsy18, (1)Auburn University at Montgomery, Montgomery, AL, United States, (2)Iowa State University, Ames, IA, United States, (3)CNRS, Paris Cedex 16, France, (4)Carnegie Institution for Science Washington, Washington, DC, United States, (5)CSIRO Ocean and Atmosphere Flagship Canberra, Yarralumla, Australia, (6)Emory University, Atlanta, GA, United States, (7)Northern Arizona University, Flagstaff, AZ, United States, (8)Arizona State University, Tempe, AZ, United States, (9)University of Exeter, Exeter, United Kingdom, (10)Auburn University, International Center for Climate and Global Change Research and School of Forestry and Wildlife Sciences, Auburn, AL, United States, (11)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette Cedex, France, (12)NOAA Boulder, Boulder, CO, United States, (13)Oak Ridge National Laboratory, Oak Ridge, TN, United States, (14)University of Exeter, College of Engineering, Mathematics and Physical Sciences, Exeter, United Kingdom, (15)MBL, The Ecosystems Center, Woods Hole, MA, United States, (16)Montana State University, Bozeman, MT, United States, (17)MIT, Cambridge, MA, United States, (18)Harvard University, Cambridge, MA, United States
Abstract:
Terrestrial uptake of carbon dioxide (CO2) partially mitigates global climate change induced by anthropogenic greenhouse (GHG) emissions. However, warming from increasing biogenic emissions of methane (CH4) and nitrous oxide (N2O) resulting from human activities may negate the cooling effect of CO2 uptake by the terrestrial biosphere. Terrestrial fluxes of individual GHGs have been studied intensively, but the net balance of the three major GHGs (CO2, CH4 and N2O) remains uncertain. Here we use bottom-up (BU: e.g., inventory, statistical extrapolation of local flux measurements, process-based modeling) and top-down (TD: atmospheric inversions) approaches to quantify net terrestrial biogenic fluxes of CO2, CH4 and N2O from natural ecosystems, croplands, and other biogenic sectors. After subtracting modeled estimates of pre-industrial fluxes from contemporary biogenic fluxes, we find the biogenic CH4 and N2O emissions resulting from human activities are opposite in sign but 1.6 times in magnitude equivalent to the global land uptake of CO2 in the 2000s based on global warming potential on 100-year time horizon. Among the emissions of CH4 and N2O, those from agriculture are the most important human perturbation, offsetting 1.2 to 1.4 times the global land CO2 sink. Our results suggest that the role of the terrestrial biosphere in exacerbating climate change could be alleviated if net human-induced biogenic GHG emissions were reduced through the implementation of land-based mitigation strategies, with the largest mitigation potential being in Southern Asia, a region that includes both China and India. This study highlights the importance of simultaneously considering three major GHGs in global and regional climate assessments, mitigation options and climate policy decisions, given the likely countervailing impacts of mitigation efforts, such as enhanced N2O emissions with soil C sequestration, paddy-drying to reduce CH4 emissions, and indirect emissions from biofuels.
