2.3.1 Increase of Atmospheric CO2 Over 97% of the energy demand of the industrial world is being met through the combustion of conventional fossil fuels.50 The major by-product of this fossil fuel combustion is carbon dioxide, which is injected directly into the atmosphere. Although the production of cement and the flaring of natural gas are sources of CO2 emission into the atmosphere, fossil fuel combustion releases the largest amount of CO2. Carbon dioxide is the only combustion product for which a global increase has been documented.5 in particular, the increase in atmospheric CO2 levels in the last few decades has been significant and has corresponded to a similar increase in fossil fuel use. The base concentration of CO2 in the atmosphere in the pre-industrial, late 19th century is generally accepted to have been around 290 ppm. Currently (in 1978), global CO2 concentrations are approximately 335 ppm, which represents close to a 15% increase over the past 100 years.51 This averages out to an increase of about 0.4 ppm/yr; however, the most recent trends indicate that the increase has accelerated beyond 1.0 ppm/yr.^0 Figure 2.3 shows global carbon dioxide production from 1880 to 1975. Since 1958, the concentration of CO2 in the atmosphere has been measured at two remote stations: Mauna Loa Observatory in Hawaii and the South Pole.52 a plot of the data from Mauna Loa (Figure 2.4) shows the steady rise of CO2 levels as well as seasonal variations. The seasonal cycle is due to the uptake of CO2 during photosynthesis and its eventual release to the atmosphere when organic matter rots or otherwise oxidizes. 2.3.2 Global Carbon Budget The CO2 present in the earth-atmosphere system is located in the atmosphere, the oceans, and in the living and decaying biomass. There is continuous exchange between the reservoirs, as well as an input of CO2 from the combustion of fossil fuels. Figure 2.5 summarizes the reservoirs for CO2 and the exchanges between them. The important issue from the standpoint of climate change is to determine the reason for the observed rise in the global concentration of CO2.
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