The global carbon cycle and possible disturbances due to man's interventions

Abstract

Global atmospheric CO 2 concentration has increased since the beginning of reliable monitoring in 1958 at a mean rate of about 0.9 ppm CO 2/yr. Now, atmospheric CO 2 concentration is at 330 ppm. From about 1860 up to 1974, man's intervention in the global carbon cycle caused a likely increase of 76.6 × 10 15 gC, corresponding to 36 ppm CO 2 in the atmosphere, if a preindustrial content of 294 ppm CO 2 or 625.3 × 10 15 g C is adopted to be valid. A further rise of atmospheric CO 2 seems to be inevitable and probably will be responsible for a climatic warming in the next several decades; therefore, a global examination of carbon reservoirs and carbon fluxes has been undertaken to determine their storage capacity for excess carbon which orginated mainly from burning fossil fuels and from land clearing. During 1860–1974 about 136 × 10 15 g C have ben emitted into the atmosphere by fossil fuel combustion and cement production. At present, the emission rate is about 5 × 10 15 g C/yr. The worldwide examination of carbon release, primarily by deforestation and soil cultivation since 1860, is estimated to be about 120 × 10 15 g C. The net transfer of carbon to the atmosphere owing to man's interference with the biosphere is now believed to be about 2.4 × 10 15 g C/yr. An oceanic uptake of roughly 179 × 10 15 g C since 1860 is open to discussion. According to the chemical buffering of sea surface water only about 35.5 × 10 15 g C could have been absorbed. It is argued, however, that oceanic circulations might have been more effective in removing atmospheric excess carbon of anthropogenic origin.