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Net carbon dioxide losses of northern ecosystems in response to autumn warming


The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring1,2,3,4, with spring and autumn temperatures over northern latitudes having risen by about 1.1 °C and 0.8 °C, respectively, over the past two decades5. A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity6,7. These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future8. Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC °C-1, offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested9,10.

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Figure 1: Atmospheric CO 2 concentration data analysis from long-term records of the global NOAA-ERSL air-sampling network.
Figure 2: Eddy-covariance flux data analysis from boreal sites in North America and Eurasia.
Figure 3: A model view of the spatial distribution of the effects of autumn (September to November) temperature warming on gross and net carbon fluxes, obtained with the ORCHIDEE model.


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We thank all the people and their respective funding agencies who worked to provide data for this study, and specifically B. Amiro, M. A. Arain, T. A. Black, C. Bourque, L. Flanagan, J. H. McCaughey and S. Wofsy for providing some of the flux data from the Canadian sites, and M.-A. Giasson and C. Coursolle for their help in compiling the data. We also thank A. Friend, P. Rayner and N. Viovy for helpful comments and discussions. This study was supported by European Community-funded projects ENSEMBLES and CARBOEUROPE IP, and by the National Natural Science Foundation of China as well as by Fluxnet-Canada, which was supported by CFCAS, NSERC, BIOCAP, MSC and NRCan. The computer time was provided by CEA. We thank the NOAA-ERSL global air sampling program for collecting and analysing the long-term CO2 flask data, and K. Masarie at NOAA-ERSL for generating each year the GLOBALVIEW-CO2 collaborative data product, which formed the basis of our atmospheric data analysis. The ongoing exchange of ideas, data and model results in the international research community on the carbon cycle is facilitated by the Global Carbon Project.

Author Contributions P.C., S.P., P.F. and P.P. designed the research. S.P., P.C. and P.F. performed ORCHIDEE modelling analysis. P.P. and S.P. performed transport analysis. S.P., S.L., M.R., H.M. and P.C. performed eddy-covariance data analysis. S.P., P.C. and J.F. performed satellite data analysis. All authors contributed to the interpretation and writing.

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Correspondence to Shilong Piao or Philippe Ciais.

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Piao, S., Ciais, P., Friedlingstein, P. et al. Net carbon dioxide losses of northern ecosystems in response to autumn warming. Nature 451, 49–52 (2008).

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