Can climate variability contribute to the “missing” CO₂ sink?

The contemporary carbon budget for the atmosphere requires a large “missing” carbon sink to balance anthropogenic carbon inputs. We investigated climatic effects on carbon exchanges between the atmosphere and the undisturbed biosphere and assessed the possible contribution of climate variability to the carbon sink. Empirical models and global temperature and precipitation data sets were used in the study. It was found that climate perturbations during 1940‐1988 caused considerable variations in plant productivity and soil respiration. The different sensitivities of the fluxes to climate perturbations led to a significant carbon accumulation in the biosphere. The cumulative carbon sink for the period 1950‐1984 (∼20±5 GtC or 10¹² kg C) was predominantly located in mid‐latitudes in the northern hemisphere (30°–60°N) and could amount to half of the missing CO₂ sink as derived from deconvolution analyses. Our results indicate that climate variations have unequal impacts on biospheric carbon fluxes from different ecosystems and imply that caution must be exercised in generalizing in situ observations to the globe.