CAN CLIMATE VARIABILITY CONTRIBUTE TO THE MISSING CO2 SINK

The contemporary carbon budget for the atmosphere requires a large ''m issing'' carbon sink to balance anthropogenic carbon inputs. We invest igated climatic effects on carbon exchanges between the atmosphere and the undisturbed biosphere and assessed the possible contribution of c limate variability to the carbon sink. Empirical models and global tem perature and precipitation data sets were used in the study. It was fo und that climate perturbations during 1940-1988 caused considerable va riations in plant productivity and soil respiration. The different sen sitivities of the fluxes to climate perturbations led to a significant carbon accumulation in the biosphere. The cumulative carbon sink for the period 1950-1984 (approximately 20+/-5 GtC or 10(12) kg C) was pre dominantly located in mid-latitudes in the northern hemisphere (30-deg rees-60-degrees-N) and could amount to half of the missing CO2 sink as derived from deconvolution analyses. Our results indicate that climat e variations have unequal impacts on biospheric carbon fluxes from dif ferent ecosystems and imply that caution must be exercised in generali zing in situ observations to the globe.