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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L09703, doi:10.1029/2006GL029019, 2007

Impact of terrestrial biosphere carbon exchanges on the anomalous CO2 increase in 2002–2003

W. Knorr

Quantifying and Understanding the Earth System Research (QUEST), Department of Earth Sciences, University of Bristol, Bristol, UK


N. Gobron

Institute for Environment and Sustainability, European Commission Joint Research Centre, Ispra, Italy


M. Scholze

Quantifying and Understanding the Earth System Research (QUEST), Department of Earth Sciences, University of Bristol, Bristol, UK


T. Kaminski

FastOpt, Hamburg, Germany


R. Schnur

Max-Planck-Institute for Meteorology, Hamburg, Germany


B. Pinty

Institute for Environment and Sustainability, European Commission Joint Research Centre, Ispra, Italy


Abstract

Understanding the carbon dynamics of the terrestrial biosphere during climate fluctuations is a prerequisite for any reliable modeling of the climate-carbon cycle feedback. We drive a terrestrial vegetation model with observed climate data to show that most of the fluctuations in atmospheric CO2 are consistent with the modeled shift in the balance between carbon uptake by terrestrial plants and carbon loss through soil and plant respiration. Simulated anomalies of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) during the last two El Niño events also agree well with satellite observations. Our model results suggest that changes in net primary productivity (NPP) are mainly responsible for the observed anomalies in the atmospheric CO2 growth rate. Changes in heterotrophic respiration (Rh) mostly happen in the same direction, but with smaller amplitude. We attribute the unusual acceleration of the atmospheric CO2 growth rate during 2002–2003 to a coincidence of moderate El Niño conditions in the tropics with a strong NPP decrease at northern mid latitudes, only partially compensated by decreased Rh.

Received 6 December 2006; accepted 3 April 2007; published 5 May 2007.

Keywords: carbon cycle; climate change; terrestrial biosphere.

Index Terms: 1615 Global Change: Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3360 Atmospheric Processes: Remote sensing.

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Citation: Knorr, W., N. Gobron, M. Scholze, T. Kaminski, R. Schnur, and B. Pinty (2007), Impact of terrestrial biosphere carbon exchanges on the anomalous CO2 increase in 2002–2003, Geophys. Res. Lett., 34, L09703, doi:10.1029/2006GL029019.