In this study we investigate the impact of greening on the Earth in terms of gross primary production (GPP) on the natural atmospheric CO₂ level. The total mass of CO₂ in the atmosphere is equal to the yearly amount of CO₂ that leaves the atmosphere (down flux), multiplied by the average time CO₂ remains in the atmosphere (residence time). The biological processes of photosynthesis and respiration are by far the most important components of the fluxes to and from the atmosphere. Since the preindustrial period the down flux has increased by 29% and the residence time by 16%. Together they fully explain the recent CO₂ rise, without assuming different behaviors for human-generated CO₂ compared to natural CO₂ and without the need for an ad-hoc model with multiple residence times. Based on the changes in the biosphere under the influence of higher temperatures, the present CO₂ level can be regarded as a natural level, so much larger than the assumed 280 ppmv. The current total GPP is probably not extraordinary, which makes it unlikely that the ice core records of Antarctica provide an accurate representation of the historical levels.
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