Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 653-679, 2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
02 Feb 2015
Recent trends and drivers of regional sources and sinks of carbon dioxide
S. Sitch1, P. Friedlingstein1, N. Gruber2, S. D. Jones3, G. Murray-Tortarolo1, A. Ahlström4, S. C. Doney5, H. Graven6, C. Heinze7,8,9, C. Huntingford10, S. Levis11, P. E. Levy12, M. Lomas13, B. Poulter14, N. Viovy15, S. Zaehle16, N. Zeng17, A. Arneth18, G. Bonan11, L. Bopp15, J. G. Canadell19, F. Chevallier15, P. Ciais15, R. Ellis10, M. Gloor20, P. Peylin15, S. L. Piao21, C. Le Quéré3, B. Smith4, Z. Zhu22,23, and R. Myneni24 1University of Exeter, Exeter EX4 4QF, UK
2Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland
3Tyndall Centre for Climate Change Research, University of East Anglia, Norwich NR4 7TJ, UK
4Lund University, Department of Physical Geography and Ecosystem Science, Sölvegatan 12, 223 62 Lund, Sweden
5Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA
6Department of Physics and Grantham Institute for Climate Change, Imperial College London, London SW7 2AZ, UK
7Geophysical Institute, University of Bergen, Bergen, Norway
8Bjerknes Centre for Climate Research, Bergen, Norway
9Uni Climate, Uni Research AS, Bergen, Norway
10Centre for Ecology and Hydrology, Benson Lane, Wallingford OX10 8BB, UK
11National Center for Atmospheric Research, Boulder, Colorado, USA
12Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, UK
13Department of Animal {&} Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
14Institute on Ecosystems and Department of Ecology, Montana State University, Bozeman, MT 59717, USA
15Laboratoire des Sciences du Climat et de l'Environnement, CEA CNRS UVSQ, 91191 Gif-sur-Yvette, France
16Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, P.O. Box 10 01 64, 07701 Jena, Germany
17Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20740, USA
18Karlsruhe Institute of Technology, Garmisch-Partenkirchen, Germany
19Global Carbon Project, CSIRO Oceans and Atmosphere Flagship, Canberra, Australia
20University of Leeds, School of Geography, Woodhouse Lane, Leeds LS9 2JT, UK
21College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
22State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
23Center for Applications of Spatial Information Technologies in Public Health, Beijing 100101, China
24Department of Geography and Environment, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA
Abstract. The land and ocean absorb on average just over half of the anthropogenic emissions of carbon dioxide (CO2) every year. These CO2 "sinks" are modulated by climate change and variability. Here we use a suite of nine dynamic global vegetation models (DGVMs) and four ocean biogeochemical general circulation models (OBGCMs) to estimate trends driven by global and regional climate and atmospheric CO2 in land and oceanic CO2 exchanges with the atmosphere over the period 1990–2009, to attribute these trends to underlying processes in the models, and to quantify the uncertainty and level of inter-model agreement. The models were forced with reconstructed climate fields and observed global atmospheric CO2; land use and land cover changes are not included for the DGVMs. Over the period 1990–2009, the DGVMs simulate a mean global land carbon sink of −2.4 ± 0.7 Pg C yr−1 with a small significant trend of −0.06 ± 0.03 Pg C yr−2 (increasing sink). Over the more limited period 1990–2004, the ocean models simulate a mean ocean sink of −2.2 ± 0.2 Pg C yr−1 with a trend in the net C uptake that is indistinguishable from zero (−0.01 ± 0.02 Pg C yr−2). The two ocean models that extended the simulations until 2009 suggest a slightly stronger, but still small, trend of −0.02 ± 0.01 Pg C yr−2. Trends from land and ocean models compare favourably to the land greenness trends from remote sensing, atmospheric inversion results, and the residual land sink required to close the global carbon budget. Trends in the land sink are driven by increasing net primary production (NPP), whose statistically significant trend of 0.22 ± 0.08 Pg C yr−2 exceeds a significant trend in heterotrophic respiration of 0.16 ± 0.05 Pg C yr−2 – primarily as a consequence of widespread CO2 fertilisation of plant production. Most of the land-based trend in simulated net carbon uptake originates from natural ecosystems in the tropics (−0.04 ± 0.01 Pg C yr−2), with almost no trend over the northern land region, where recent warming and reduced rainfall offsets the positive impact of elevated atmospheric CO2 and changes in growing season length on carbon storage. The small uptake trend in the ocean models emerges because climate variability and change, and in particular increasing sea surface temperatures, tend to counter\-act the trend in ocean uptake driven by the increase in atmospheric CO2. Large uncertainty remains in the magnitude and sign of modelled carbon trends in several regions, as well as regarding the influence of land use and land cover changes on regional trends.

Citation: Sitch, S., Friedlingstein, P., Gruber, N., Jones, S. D., Murray-Tortarolo, G., Ahlström, A., Doney, S. C., Graven, H., Heinze, C., Huntingford, C., Levis, S., Levy, P. E., Lomas, M., Poulter, B., Viovy, N., Zaehle, S., Zeng, N., Arneth, A., Bonan, G., Bopp, L., Canadell, J. G., Chevallier, F., Ciais, P., Ellis, R., Gloor, M., Peylin, P., Piao, S. L., Le Quéré, C., Smith, B., Zhu, Z., and Myneni, R.: Recent trends and drivers of regional sources and sinks of carbon dioxide, Biogeosciences, 12, 653-679, doi:10.5194/bg-12-653-2015, 2015.
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