Articles | Volume 12, issue 14
Biogeosciences, 12, 4385–4405, 2015
Biogeosciences, 12, 4385–4405, 2015

Research article 28 Jul 2015

Research article | 28 Jul 2015

Assessment of model estimates of land-atmosphere CO2 exchange across Northern Eurasia

M. A. Rawlins1, A. D. McGuire2, J. S. Kimball3, P. Dass1, D. Lawrence4, E. Burke5, X. Chen6, C. Delire7, C. Koven8, A. MacDougall9, S. Peng10,16, A. Rinke11,12, K. Saito13, W. Zhang14, R. Alkama7, T. J. Bohn15, P. Ciais10, B. Decharme7, I. Gouttevin16,17, T. Hajima13, D. Ji11, G. Krinner16, D. P. Lettenmaier18, P. Miller14, J. C. Moore11, B. Smith14, and T. Sueyoshi13,19 M. A. Rawlins et al.
  • 1Climate System Research Center, Department of Geosciences, University of Massachusetts, Amherst, MA, USA
  • 2US Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska, Fairbanks, Alaska 99775, USA
  • 3NTSG, University of Montana, Missoula, MT, USA
  • 4National Center for Atmospheric Research, Boulder, CO, USA
  • 5Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
  • 6Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA
  • 7CRNM-GAME, Unité mixte de recherche CNRS/Meteo-France (UMR 3589), 42 av Coriolis, 31057 Toulouse, CEDEX, France
  • 8Lawrence Berkeley National Laboratory, Berkeley, CA, USA
  • 9School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada
  • 10Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, UMR8212, 91191 Gif-sur-Yvette, France
  • 11State Key Laboratory of Earth Surface Processes and Resource Ecology, College of Global Change and Earth System Science, Beijing Normal University, Beijing, China
  • 12Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany
  • 13Department of Integrated Climate Change Projection Research, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa, Japan
  • 14Department of Physical Geography and Ecosystem Science, Lund University, Sölvegatan 12, SE 223 62 Lund, Sweden
  • 15School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
  • 16CNRS and Université Grenoble Alpes, LGGE, 38041, Grenoble, France
  • 17Irstea, UR HHLY, 5 rue de la Doua, CS 70077, 69626 Villeurbanne, CEDEX, France
  • 18Department of Geography, University of California, Los Angeles, CA, USA
  • 19National Institute of Polar Research, Tachikawa, Tokyo, Japan

Abstract. A warming climate is altering land-atmosphere exchanges of carbon, with a potential for increased vegetation productivity as well as the mobilization of permafrost soil carbon stores. Here we investigate land-atmosphere carbon dioxide (CO2) cycling through analysis of net ecosystem productivity (NEP) and its component fluxes of gross primary productivity (GPP) and ecosystem respiration (ER) and soil carbon residence time, simulated by a set of land surface models (LSMs) over a region spanning the drainage basin of Northern Eurasia. The retrospective simulations cover the period 1960–2009 at 0.5° resolution, which is a scale common among many global carbon and climate model simulations. Model performance benchmarks were drawn from comparisons against both observed CO2 fluxes derived from site-based eddy covariance measurements as well as regional-scale GPP estimates based on satellite remote-sensing data. The site-based comparisons depict a tendency for overestimates in GPP and ER for several of the models, particularly at the two sites to the south. For several models the spatial pattern in GPP explains less than half the variance in the MODIS MOD17 GPP product. Across the models NEP increases by as little as 0.01 to as much as 0.79 g C m−2 yr−2, equivalent to 3 to 340 % of the respective model means, over the analysis period. For the multimodel average the increase is 135 % of the mean from the first to last 10 years of record (1960–1969 vs. 2000–2009), with a weakening CO2 sink over the latter decades. Vegetation net primary productivity increased by 8 to 30 % from the first to last 10 years, contributing to soil carbon storage gains. The range in regional mean NEP among the group is twice the multimodel mean, indicative of the uncertainty in CO2 sink strength. The models simulate that inputs to the soil carbon pool exceeded losses, resulting in a net soil carbon gain amid a decrease in residence time. Our analysis points to improvements in model elements controlling vegetation productivity and soil respiration as being needed for reducing uncertainty in land-atmosphere CO2 exchange. These advances will require collection of new field data on vegetation and soil dynamics, the development of benchmarking data sets from measurements and remote-sensing observations, and investments in future model development and intercomparison studies.

Short summary
We used outputs from nine models to better understand land-atmosphere CO2 exchanges across Northern Eurasia over the period 1960-1990. Model estimates were assessed against independent ground and satellite measurements. We find that the models show a weakening of the CO2 sink over time; the models tend to overestimate respiration, causing an underestimate in NEP; the model range in regional NEP is twice the multimodel mean. Residence time for soil carbon decreased, amid a gain in carbon storage.
Final-revised paper