Compensatory water effects link yearly global land CO2 sink changes to temperature.
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Large interannual variations in the measured growth rate of atmospheric carbon dioxide (CO2) originate primarily from fluctuations in carbon uptake by land ecosystems. It remains uncertain, however, to what extent temperature and water availability control the carbon balance of land ecosystems across spatial and temporal scales. Here we use empirical models based on eddy covariance data and process-based models to investigate the effect of changes in temperature and water availability on gross primary productivity (GPP), terrestrial ecosystem respiration (TER) and net ecosystem exchange (NEE) at local and global scales. We find that water availability is the dominant driver of the local interannual variability in GPP and TER. To a lesser extent this is true also for NEE at the local scale, but when integrated globally, temporal NEE variability is mostly driven by temperature fluctuations. We suggest that this apparent paradox can be explained by two compensatory water effects. Temporal water-driven GPP and TER variations compensate locally, dampening water-driven NEE variability. Spatial water availability anomalies also compensate, leaving a dominant temperature signal in the year-to-year fluctuations of the land carbon sink. These findings help to reconcile seemingly contradictory reports regarding the importance of temperature and water in controlling the interannual variability of the terrestrial carbon balance. Our study indicates that spatial climate covariation drives the global carbon cycle response.
We thank P. Peylin for providing RECCAP inversion results. We also thank P. Bodesheim for help with the mathematical notations, J. Nelson for proofreading the Supplementary Information, S. Schott for help with artwork, and G. Boenisch, L. Maack and P. Koch for help archiving the FLUXCOM data. M.J., M.R. and D.P. acknowledge funding from the European Union (EU) FP7 project GEOCARBON (grant number 283080) and the EU H2020 BACI project (grant number 640176). F.G. and M.R. acknowledge the European Space Agency for funding the ‘Coupled Biosphere–Atmosphere virtual LABoratory’ (CAB-LAB). S.Z. acknowledges support from the European Research Council (ERC) under the EU’s Horizon 2020 research and innovation programme (QUINCY; grant number 647204). A. Arneth acknowledges support from the EU FP7 project LUC4C (grant number 603542). C.R.S. was supported by National Aeronautics and Space Administration (NASA) grants NNX12AK12G, NNX12AP74G, NNX10AG01A and NNX11AO08A. P.C. acknowledges support from the ERC Synergy grant ERC-2013-SyG-610028 IMBALANCE-P. K.I. acknowledges support from the Environment Research and Technology Development Funds (2-1401) from the Ministry of the Environment of Japan. S.S. acknowledges the support of the Natural Environment Research Council (NERC) South AMerican Biomass Burning Analysis (SAMBBA) project (grant code NE/J010057/1). C.H. is grateful for support from the NERC CEH National Capability fund. A. Ahlström acknowledges support from The Royal Physiographic Society in Lund (Birgit and Hellmuth Hertz’ Foundation) and the Swedish Research Council (637-2014-6895). G.C.-V. was supported by the EU under ERC consolidator grant SEDAL-647423.
This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.
Vol. 541, pp. 516 - 520
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