BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-11-3547-2014 Current systematic carbon-cycle observations and the need for implementing a policy-relevant carbon observing system Ciais P. 1 Dolman A. J. https://orcid.org/0000-0003-0099-0457 2 Bombelli A. 3 Duren R. 4 Peregon A. 1 Rayner P. J. https://orcid.org/0000-0001-7707-6298 5 Miller C. 4 Gobron N. 6 Kinderman G. 7 Marland G. 8 Gruber N. https://orcid.org/0000-0002-2085-2310 9 Chevallier F. https://orcid.org/0000-0002-4327-3813 1 Andres R. J. 10 Balsamo G. https://orcid.org/0000-0002-1745-3634 11 Bopp L. 1 Bréon F.-M. https://orcid.org/0000-0003-2128-739X 1 Broquet G. 1 Dargaville R. 5 Battin T. J. 12 Borges A. https://orcid.org/0000-0002-5434-2247 13 Bovensmann H. https://orcid.org/0000-0001-8882-4108 14 Buchwitz M. https://orcid.org/0000-0001-7616-1837 14 Butler J. 15 Canadell J. G. 16 Cook R. B. 10 DeFries R. 17 Engelen R. https://orcid.org/0000-0003-1577-5143 11 Gurney K. R. 18 Heinze C. https://orcid.org/0000-0003-4074-8390 21 20 19 Heimann M. https://orcid.org/0000-0001-6296-5113 22 Held A. 23 Henry M. 24 Law B. https://orcid.org/0000-0002-1605-1203 25 Luyssaert S. https://orcid.org/0000-0003-1121-1869 1 Miller J. https://orcid.org/0000-0001-8630-1610 26 15 Moriyama T. 27 Moulin C. 1 Myneni R. B. 28 Nussli C. 29 Obersteiner M. 7 Ojima D. 30 Pan Y. 31 Paris J.-D. 1 Piao S. L. 32 Poulter B. https://orcid.org/0000-0002-9493-8600 1 Plummer S. https://orcid.org/0000-0002-7033-9865 33 Quegan S. 34 Raymond P. https://orcid.org/0000-0002-8564-7860 35 Reichstein M. 22 Rivier L. 1 Sabine C. 36 Schimel D. https://orcid.org/0000-0003-3473-8065 37 Tarasova O. 38 Valentini R. https://orcid.org/0000-0002-6756-5634 3 Wang R. 1 van der Werf G. 2 Wickland D. 39 Williams M. 40 Zehner C. 41 Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, UMR8212, 91191, Gif sur Yvette Cedex, France VU University Amsterdam, Amsterdam, the Netherlands Euro-Mediterranean Center for Climate Change, CMCC, Division Climate Change Impacts on Agriculture, Forests and Natural Ecosystems; via Augusto Imperatore 16, 73100 Lecce, Italy Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109, USA School of Earth Sciences, University of Melbourne, Australia Global Environmental Monitoring Unit, Institute for Environment and Sustainability, European Commission Joint Research Center, Ispra, Italy International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, Laxenburg, Austria Research Institute for Environment, Energy, and Economics, Appalachian State University, Boone, NC 28608, USA Institute of Biogeochemistry and Pollutant Dynamics and Center for Climate Systems Modeling, ETH Zürich, Zürich, Switzerland Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6290, USA European Centre for Medium-Range Weather Forecast (ECMWF), Shinfield Park, Reading, RG2 9AX, UK Department of Limnology, University of Vienna, A-1090 Vienna, Austria Chemical Oceanography Unit, University of Liège, Institute de Physique (B5), 4000 Liège, Belgium Institute of Environmental Physics (IUP), University of Bremen, Bremen, Germany NOAA Earth System Research Laboratory (ESRL), 325, Broadway, Boulder, CO 80305-3337, USA CSIRO Marine and Atmospheric Research, Canberra, ACT 2601, Australia Department of Geography and Environment, Boston University, Boston, MA 02115, USA School of Life Sciences, School of Sustainability, Arizona State University, Tempe, AZ 85287, USA Geophysical Institute, University of Bergen, Allégaten 70, 5007 Bergen, Norway Bjerknes Centre for Climate Research, Bergen, Norway Uni Bjerknes Centre, Uni Research, Bergen, Norway Max-Planck-Institute for Biogeochemistry, Jena, Germany AusCover Facility, Terrestrial Ecosystem Research Network – TERN, CSIRO, GPO Box 3023, Canberra ACT 2601, Australia Forestry Department, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00153 Rome, Italy Department of Forest Ecosystems and Society, 321 Richardson Hall, Oregon State University, Corvallis, OR 97331, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA Japan Aerospace Exploration Agency (JAXA), Tokyo Department of Earth and Environment, Boston University, Boston, MA 02215, USA Thales Alenia Space, Toulouse, France Natural Resource Ecology Laboratory, Campus Mail 1499, Fort Collins, CO 80523-1499, USA US Department of Agriculture Forest Service, Newtown Square, PA 19073, USA Department of Ecology, Peking University, Beijing 100871, China ESA Climate Office, European Space Agency – Harwell, Didcot, Oxfordshire OX11 0QX, UK Centre for Terrestrial Carbon Dynamics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK Yale School of Forestry and Environmental Studies, 195 Prospect Street, New Haven, CT 06511, USA Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA 98115, USA National Ecological Observatory Network, Boulder, CO 80301, USA World Meteorological Organization, 7bis Avenue de la Paix, 1211 Geneva, Switzerland National Aeronautics and Space Administration, Suite 3B74, 300 E Street SW, Washington, DC 20546, USA School of GeoSciences, University of Edinburgh, Edinburgh, EH9 3JN, UK ESA/ESRIN, Earth Observation Applications Engineer, Via Galileo Galilei CP, 64, Frascati Italy 03 07 2014 11 13 3547 3602 Copyright: © 2014 P. Ciais et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/11/3547/2014/bg-11-3547-2014.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/11/3547/2014/bg-11-3547-2014.pdf

A globally integrated carbon observation and analysis system is needed to improve the fundamental understanding of the global carbon cycle, to improve our ability to project future changes, and to verify the effectiveness of policies aiming to reduce greenhouse gas emissions and increase carbon sequestration. Building an integrated carbon observation system requires transformational advances from the existing sparse, exploratory framework towards a dense, robust, and sustained system in all components: anthropogenic emissions, the atmosphere, the ocean, and the terrestrial biosphere. The paper is addressed to scientists, policymakers, and funding agencies who need to have a global picture of the current state of the (diverse) carbon observations. We identify the current state of carbon observations, and the needs and notional requirements for a global integrated carbon observation system that can be built in the next decade. A key conclusion is the substantial expansion of the ground-based observation networks required to reach the high spatial resolution for CO<sub>2</sub> and CH<sub>4</sub> fluxes, and for carbon stocks for addressing policy-relevant objectives, and attributing flux changes to underlying processes in each region. In order to establish flux and stock diagnostics over areas such as the southern oceans, tropical forests, and the Arctic, in situ observations will have to be complemented with remote-sensing measurements. Remote sensing offers the advantage of dense spatial coverage and frequent revisit. A key challenge is to bring remote-sensing measurements to a level of long-term consistency and accuracy so that they can be efficiently combined in models to reduce uncertainties, in synergy with ground-based data. Bringing tight observational constraints on fossil fuel and land use change emissions will be the biggest challenge for deployment of a policy-relevant integrated carbon observation system. This will require in situ and remotely sensed data at much higher resolution and density than currently achieved for natural fluxes, although over a small land area (cities, industrial sites, power plants), as well as the inclusion of fossil fuel CO<sub>2</sub> proxy measurements such as radiocarbon in CO<sub>2</sub> and carbon-fuel combustion tracers. Additionally, a policy-relevant carbon monitoring system should also provide mechanisms for reconciling regional top-down (atmosphere-based) and bottom-up (surface-based) flux estimates across the range of spatial and temporal scales relevant to mitigation policies. In addition, uncertainties for each observation data-stream should be assessed. The success of the system will rely on long-term commitments to monitoring, on improved international collaboration to fill gaps in the current observations, on sustained efforts to improve access to the different data streams and make databases interoperable, and on the calibration of each component of the system to agreed-upon international scales.

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