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Scientific Correspondence

Nature 399, 535 (10 June 1999) | doi:10.1038/21098

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Parameters for global ecosystem models

Paul J. Crutzen1, Ray Fall2, Ian Galbally3 & Werner Lindinger4

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Tianet al.1 have used their process-based ecosystem model to estimate the net CO2exchanges, also called net ecosystem productivity, for the years 1980-94. They deduced a large interannual variability ranging between -0.2 (from land to atmosphere) and +0.7 petagrams of carbon (Pg C) per year, the variability being mostly a function of soil moisture, which in turn is largely regulated by precipitation and temperature. These values were derived by including the modelled effects of increasing atmospheric levels of CO2. The above numbers are the differences between net primary productivity and heterotrophic respiration. Over the given time period for the CO2feedback case, these values were 5.0 (plusminus0.3) and 4.8 (plusminus0.1) Pg C per year, respectively. The calculated net ecosystem productivity was thus a small fraction, between -4% and +14%, of the net primary productivity, with an average over the 15-year period of +4%.