It is of interest to examine potential sources of atmospheric C02 by analysis of the global distribution of carbon in all its forms. The data presented in Table 1.8 show that atmospheric carbon, which can be assumed to be essentially all in the form of C02 (i. e., 700 Gt carbon equals 2570 Gt of COz) comprises

only about 1.6% of total global carbon, excluding lithospheric carbon. Obvious sources of direct or indirect additions of C02 to the atmosphere are therefore fossil fuel deposits, since portions of them are combusted each year as fuels, and terrestrial biomass. Biomass, the photosynthetic sink for removal of C02 from the atmosphere, is important because any changes that modify natural biomass growth can affect ambient C02 concentration. Reducing the size of the photosynthetic sink by such practices as slash-and-bum agriculture, large — scale wood burning, and rain-forest destruction causes an overall reduction in the amount of natural photosynthesis.

To develop more quantitative information regarding atmospheric C02, the emissions on combustion of coal, oil, and natural gas per energy input unit (Appendix C) were used to calculate the C02 generated from fossil fuel combus­tion for the world’s regions and each of the top 10 energy-consuming countries (Table 1.9). Oil is the largest C02 source, followed by coal and natural gas. It is obvious that the largest energy-consuming regions of the world generate relatively more fossil-based C02, and that the world’s 10 top energy-consuming

countries generate almost two-thirds of the world’s total C02 emitted on combustion of fossil fuels. This kind of information has led to several national plans and international agreements to attempt to lower or at least maintain atmospheric C02 by reducing fossil fuel consumption through such mecha­nisms as fossil carbon consumption taxes and higher-efficiency hardware. A

variety of technologies for removal of C02 from the environment have also been proposed.

Although the position has been supported with limited and sometimes questionable data, it has come to be accepted as fact by manv if not most climate change specialists that fossil fuel consumption is the major cause of atmospheric C02 buildup. The C02 in the atmosphere is estimated to have a mass of about 2640 Gt (Table 1.7). Uncertainty is a factor because it is only by inference that the mass is calculated. But many direct analyses of atmo­spheric C02 have been made at different locations throughout the world. Analysis of air trapped in ancient ice cores shows that about 160,000 years ago, atmospheric C02 concentration was about 200 ppm and then peaked at about 300 ppm 130,000 and 10,000 years ago. The concentration then began to increase from an apparent equilibrium value of about 280 ppm in the eighteenth century to its present level of about 360 ppm, the highest concentra­tion in the past 160,000 years. Atmospheric C02 concentration has increased at least 50 ppm since 1860 and is currently increasing at an annual rate of about 1.5 ppm according to analyses carried out continuously over the last several decades. Presuming the atmospheric mass of 2640 Gt is correct, this corresponds to an annual increase of about 11.3 Gt/year.

Compared to other carbon flows, C02 emissions from fossil fuel consump­tion by country are perhaps the most accurate, large-scale carbon flux calcu­lations that can be performed. The reason for this is that detailed data on fos­sil fuel production and consumption are compiled and reported worldwide. Since the mid-1800s, fossil fuel usage has increased significantly, notably since World War II as discussed earlier, to over 300 EJ/year (Fig. 1.6). Global C02 emissions from fossil fuel combustion have been calculated and reported to four significant figures for many years; the annual average from 1978 to 1987 was 18.91 Gt/year (Klass, 1993) and is in the 22-Gt/year range in the 1990s (Table 1.9). So fossil fuel emissions are about twice the annual atmospheric C02 buildup. This type of “factual data” comprises the essence of the argument that fossil fuel consumption is the primary cause of C02 buildup in the atmo­sphere, and sic climate change. Much of the additional evidence is qualitative and uncertain because the study of global C02 buildup is inextricably related to global carbon cycles and reservoirs and the myriad of processes that take place over time on a living planet. The problem from an investigative standpoint is extremely difficult to elaborate. Few direct measurements can be made with precision and then be reproduced. Broad use is made of modeling, and real- world confirmation of the conclusions is often anecdotal. As will be shown later (Chapter 2), biomass has a very important role in atmospheric C02 fluxes and may affect ambient concentrations much more than fossil fuel consumption alone. Because of the environmental trends today, it appears that international agreements to limit fossil fuel consumption will be implemented sometime in the twenty-first century. This will require much greater usage of alternative fuels, especially renewable biomass energy and biofuels manufactured from biomass.

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