the atmosphere corresponds to only a 5% to 8% increase in photosynthesis. This is because plant growth in many parts of the world is not limited by CO2, but rather by temperature, light, water, and soil nutrients. Furthermore, the major sinks for carbon storage on land occur in forests covering much of Canada, the Soviet Union, and the tropics. Due to increases in population and per capita consumption of natural resources, much of these forests may be exploited for wood products or cleared for agricultural use. It is currently unknown whether the global land biomass has increased during this century, in response to increased CO2 levels, or has decreased due to deforestation.53 Some investigators claim that the destruction of the biosphere is a source of atmospheric CO2 that is of a magnitude comparable to man’s fossil fuel input.54,55 The carbon content of ocean waters, to a depth of 100 m, is approximately equal to that of the atmosphere.56 The partial pressure of the CO2 in equilibrium with the sea water is determined by the alkalinity, the total dissolved inorganic carbon, and the temperature of the sea water. A 10% increase in the partial pressure of CO2 in equilibrium with sea water leads to a 1% increase in the total inorganic carbon content of the water. If the inorganic carbon content of the water is constant, the partial pressure of CO2 in equilibrium with the water rises 4% per 1°C rise in water temperature. The average sea-surface temperature of the North Atlantic decreased by 0.6°C over the period 1951-1972,57 which would indicate an increase in the ability of the oceans to act as a sink for atmospheric CO2 over this period. However, a warming of the sea-surface, caused by global warming due to CO2, would presumably reverse this trend. The ability of the oceans to act as a buffer for atmospheric CO2 changes is limited. Only the well-mixed surface layer of the ocean can exchange CO2 with the atmosphere and remain in equilibrium with it in the course of a few years. The deep waters below 1 km contain 60 times as much CO2 as the atmosphere, but the time needed to exchange this water with surface water is probably 500 to 1000 years or more. Thus, the ocean has a limited ability to take up additional CO2 in a short time. Records of observed increases in atmospheric CO2 and the release of fossil fuel CO2 to the atmosphere verify that the biosphere and oceans are limited sinks for atmospheric CO2. Table 2.7 summarizes the atmospheric
RkJQdWJsaXNoZXIy MTU5NjU0Mg==