ABSTRACT
Natural green plant photosynthesis is the most important chemical reaction on the Earth — and the basis of all life processes. Most of the Earth’s carbon, 10*^ tons, is deposited as carbonates, while about 10 "^^ tons are estimated to be the total amount of carbon dioxide in the atmosphere and the oceans and thus available for photosynthesis.^ From this, about 2 x 10^ ^ tons of biomass are produced yearly by natural plant photosynthesis.^ One of the largest carbon reservoirs on the Earth’s surface is oceanic dissolved organic carbon (DOC). This is composed mainly of compounds such as humic substances, which are resistant to biological degradation, but which are photochemically degraded by sunlight to biologically labile compounds. Since the future depletion of atmospheric ozone will increase the solar UV flux, this photochemical degradation is likely to enhance the recycling of biologically refractory DOC.^ On the other hand, the rate of growth of forests and of other biomass increases with the partial pressure of carbon dioxide. At present, the fertilization effect of increased carbon dioxide is considered to out weigh the effects of forest clearance. Thus, the biota provides a large enough sink of atmospheric carbon dioxide to enable a balance of the global carbon budget." ^One of the uncertainties is the amount of interhemispheric transport of carbon dioxide provided by ocean circulation.^ The total uptake of anthropogenic CO2 by the Earth’s oceans has been estimated to be about 1 gigatons carbon (2 X 10^ tons) per year.^
Among the components of air, carbon dioxide comprises only about 0.034% by volume. This carbon dioxide content is responsible for the acidity (pH 5.7) of precipitations from the troposphere, the natural acid rainJ
The ever-increasing consumption of fossil fuel since the industrial revolution some 150 years ago — together with specific industries such as cement production and, possibly, also the rapid deforestation of the Earth’s tropical rain forests®’^ — have caused a very marked increase in the global concentration of carbon dioxide, which now amounts to 7 x 10^ tons/year. The annual increase (%) of the important greenhouse gases is presented in Figure 1.
