Uptake factor, anthropogenic

The emission of C02 from anthropogenic activities (the combustion of C-based fossil fuels, deforestation, combustion of woods) amounts to approximately 7.5 Gtc per year, or about 3.5% of the total amount cycled in the natural cycle. However, as the natural systems are unable to use such C02, this leads to its accumulation into the atmosphere. The assumption that an increase of the concentration of C02 in the atmosphere would have boosted both the photosynthesis and the dissolution into the oceans has not been proven to be true. In fact, the solubility of C02 is governed by complex equilibria, while photosynthetic fixation is limited by several factors so that, under the increase of the atmospheric concentration from 280 ppm of the preindustrial era to the present-day 380 ppm, there has not been any sensible improvement of the uptake. Therefore, under natural conditions the uptake of C02 has reached an equilibrium state, and the further increase in atmospheric concentrations may more likely cause climate changes through the greenhouse effect and destabilization of the thermal structure of the atmosphere, than improve the elimination of C02 from the atmosphere. 

We can now use the knowledge of the Revelle factor to estimate the anthropogenic GO2 uptake by the ocean at equilibrium. Presuming that after some reasonable time the ocean carbonate system comes into equilibrium or nearly so with GO2 in the atmosphere, we can calculate the fraction of the anthropogenic GO2 taken up by the ocean as a function of the depth of the layer into which... 

Consequently, an intensive uptake of sulfur occurs in hydrosphere, lithosphere, and biosphere. This is the main reason that the content of gaseous sulfur species in the atmosphere is rather small and even in polluted air does not exceed 2-3 ppmv. In unpolluted atmosphere the concentration of most S compounds is at ppbv levels, despite the intense sulfuroutgassing from the Earth s interior. The atmospheric content of the major gaseous S species, either SO2 or H2S, is highly variable and is influenced by both natural and anthropogenic factors. The role of anthropogenic sulfur emission in acid rain chemistry will be discussed in Chapter 10. The influence of natural parameters, microbiological activity in particular, is described in Box 7. 

It should be mentioned that only about the half of anthropogenic C02 remained airborne in the past decades.4 However, this does not necessarily mean that the fraction of man-made C02 stored in the atmosphere will always be the same in the future. For this reason it is essential to determine from past variations the factors governing the fate of anthropogenic carbon dioxide. It is also essential to include these factors in so-called reservoir or box models5 to calculate, on the one hand, the fraction absorbed by oceans and, on the other hand, the part of the emission used by the land biota. Since the uptake of carbon dioxide by ocean waters is governed by more or less known physical and chemical laws the response of land plants to the increase of C02 level, which is much more complicated, can be estimated by difference between total C02 input and oceanic absorption (e.g. Keeling, 1973). 

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