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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Dec 2019

Submitted as: research article | 09 Dec 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Carbon-concentration and carbon-climate feedbacks in CMIP6 models, and their comparison to CMIP5 models

Vivek K. Arora1, Anna Katavouta2, Richard G. Williams2, Chris D. Jones3, Victor Brovkin4, Pierre Friedlingstein5, Jörg Schwinger6, Laurent Bopp7, Olivier Boucher7, Patricia Cadule7, Matthew A. Chamberlain8, James R. Christian1, Christine Delire9, Rosie A. Fisher10, Tomohiro Hajima11, Tatiana Ilyina4, Emilie Joetzjer9, Michio Kawamiya11, Charles Koven12, John Krasting13, Rachel M. Law14, David M. Lawrence15, Andrew Lenton8, Keith Lindsay15, Julia Pongratz4,16, Thomas Raddatz4, Roland Séférian9, Kaoru Tachiiri11, Jerry F. Tjiputra6, Andy Wiltshire3, Tongwen Wu17, and Tilo Ziehn14 Vivek K. Arora et al.
  • 1Canadian Centre for Climate Modelling and Analysis, Environment Canada, University of Victoria, Victoria, B.C., V8W 2Y2, Canada
  • 2School of Environmental Sciences, Liverpool University, Liverpool, UK
  • 3Met Office Hadley Centre, Exeter, UK
  • 4Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany
  • 5College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK
  • 6NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway
  • 7IPSL, CNRS, Sorbonne Université, Paris, France
  • 8CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
  • 9CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 10National Center for Atmospheric Research, Boulder, CO, USA and Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique, (CERFACS). Toulouse, France
  • 11Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan
  • 12Climate and Ecosystem Sciences Division, Lawrence Berkeley National Lab, Berkeley California, USA
  • 13NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, United States of America
  • 14CSIRO Oceans and Atmosphere, Aspendale, Victoria, Australia
  • 15Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 16Ludwig-Maximilians University, Munich
  • 17Beijing Climate Center, China Meteorological Administration, 46 Zongguancun Nandajie, Haidian District, Beijing, China

Abstract. Results from the fully-, biogeochemically-, and radiatively-coupled simulations in which CO2 increases at a rate of 1 % per year (1pctCO2) from its pre-industrial value are analyzed to quantify the magnitude of two feedback parameters which characterize the coupled carbon-climate system. These feedback parameters quantify the response of ocean and terrestrial carbon pools to changes in atmospheric CO2 concentration and the resulting change in global climate. The results are based on eight comprehensive Earth system models from the fifth Coupled Model Intercomparison Project (CMIP5) and eleven models from the sixth CMIP (CMIP6). The comparison of model results from two CMIP phases shows that, for both land and ocean, the model mean values of the feedback parameters and their multi-model spread has not changed significantly across the two CMIP phases. The absolute values of feedback parameters are lower for land with models that include a representation of nitrogen cycle. The sensitivity of feedback parameters to the three different ways in which they may be calculated is shown and, consistent with existing studies, the most relevant definition is that calculated using results from the fully- and biogeochemically-coupled configurations. Based on these two simulations simplified expressions for the feedback parameters are obtained when the small temperature change in the biogeochemically-coupled simulation is ignored. Decomposition of the terms of these simplified expressions for the feedback parameters allows identification of the reasons for differing responses among ocean and land carbon cycle models.

Vivek K. Arora et al.
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Short summary
Since the pre-industrial period, land and ocean have taken up about half of the carbon emitted into the atmosphere by humans. Comparison of different earth system models with carbon cycle allows to assess how carbon uptake by land and ocean differs among models. This yields an estimate of uncertainty of our understanding of how land and ocean respond to increasing atmospheric CO2. This manuscript summarizes results from two such model intercomparisons projects.
Since the pre-industrial period, land and ocean have taken up about half of the carbon emitted...