Journal of Health Science, 55(1) 125–127 (2009) 125 Population Is a Critical Factor for Global Carbon Dioxide Increase Kikuo Onozaki∗ Department of Molecular Health Sciences, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuho-ku, Tanabe-dori 3–1, 467–8603, Japan (Received August 25, 2008; Accepted October 31, 2008; Published online November 10, 2008) Based on Intergovernmental Panel on Climate Change (IPCC) assessment report at 2007, it is likely that there has been a substantial anthropogenic con- tribution to global warming. Carbon dioxide (CO2) is a major anthropogenic greenhouse gas and its in- crease is thought to give rise to the recent global warming. Although studies suggested the impact of population growth on carbon dioxide increase, much attention has not been paid. In this study population was plotted as compared to the atmospheric CO2 con- centration. A quite linear relationship was observed between population and CO2 concentration at both before and after 1970, after which the global temper- ature rapidly increased. In addition, direct and indi- rect human-derived CO2 emission appeared to con- tribute much to the total amount of CO2 emission in developing countries and as the economy grow fossil- fuel-derived CO2 emission increased more as com- pared to human-derived emission. These findings in- dicate that population growth especially in develop- ing countries is a critical factor for manipulation of global CO2 increase. Key words —— population, carbon dioxide, global warming INTRODUCTION Global warming is a serious issue for human be- ings. The 4th Intergovernmental Panel on Climate Change (IPCC) assessment report at 2007 indicated that carbon dioxide (CO2) has increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values, and the amount of ∗To whom correspondent should be addressed: Department of Molecular Health Sciences, Graduate School of Pharmaceuti- cal Sciences, Nagoya City University, Mizuho-ku, Tanabe-dori 3–1, 467–8603, Japan. Tel. & Fax: +81-52-836-3419; E-mail: konozaki@phar.nagoya-cu.ac.jp CO2 in the atmosphere in 2005 (379 ppm) exceeds by far the natural range of the last 650000 years (180–300 ppm).1) CO2 is a major anthropogenic green house gas, which is believed to contribute to the global warming. Human activities require energy for essentials of life such as clothing, food, housing and so on, which require CO2 emission. The human activities increase as the growth of population. Studies sug- gested that population growth is one of the major factors for CO2 emission in both developed and de- veloping countries.2–5) It has been also suggested that rising income levels have been associated with the increased CO2 emission. 5) However, still much attention has not been paid for the population. In this study the impact of population on CO2 increase in atmosphere was determined. The study indicates that population growth is closely associated with the increase of CO2 in atmosphere, and suggests that population growth in developing countries is a crit- ical factor for manipulation of global CO2 increase. MATERIALS AND METHODS Population is based on United Nations (UN) world population prospect: The 2006 revision. Global temperature (5-year mean) is based on National Aeronautics and Space Administration/ Earth System Research Laboratory (NASA/ESRL). The atmosphere CO2 concentration is based on NASA/ESRL and Carbon Dioxide Information Analysis Center (CDIAC). The amount of CO2 emission of is based on CDIAC. RESULTS AND DISCUSSION Population was plotted as compared to the at- mospheric CO2 concentration and global atmo- spheric temperature (Fig. 1). The temperature in- dicates 5-year mean surface temperature anomaly relative to 1950–1980 mean. Almost all the plots were closely associated with CO2 concentration. In- terestingly these associations were observed at both before and after 1970. Before 1970, CO2 concen- tration does not fit with the global temperature, but after 1970 the temperature rapidly increased with concurrent increase of CO2. A quite linear rela- tionship was observed between population and CO2 concentration (Fig. 2). It is of note, however, that af- ter 1960, whose population was 3 billion, the slope 126 Vol. 55 (2009) Fig. 1. Comparison between Population, Global Temperature and Atmospheric CO2 Concentration Fig. 2. Relationship between Population and Atmospheric CO2 Concentration Fig. 3. Comparison of the Amount of CO2 Emission from Human (Direct and Indirect) and Fossil-Fuel among Developing and Devel- oped Countries Human-derived CO2 was estimated by the report of Prairie and Duarte. 6) was steep as compared to 1960s from 1940, whose population was 2 billion. This difference could be due to social events like wars, energy crisis, saving energy, economical growth and so forth. These find- ings strongly support the notion that natural factors, such as volcanic activity, do not much contribute to the CO2 increase. IPCC indicated that most of the anthropogenic CO2 is derived from fossil fuel use and changes in land use.1) However, it is reported that direct and indirect metabolic CO2 release by No. 1 127 humanity much contributes to the CO2 emission. Direct metabolic CO2 is comprised of respiration of humans, and indirect CO2 is composed of the de- composition of their resulting wastes, and respira- tion and resulting decomposition from a large live- stock population to feed themselves as well as a large number of domestic animals. The direct and indirect metabolic CO2 release from humans (3.1 Giga ton Carbon (GtC)) assessed at 2003 reaches up to 43% of the total CO2 emission (7.2 GtC) from fossil fuel consumption and changes in land use at 2000–2005.6) This amount cannot be overlooked. Next, the amount of CO2 emission from human (di- rect and indirect) and fossil-fuel was compared be- tween developing (China and India) and developed countries (America and Japan, Fig. 3). In China, be- fore 1980 human-derived emission was larger than fossil-fuel-derived emission. After 1990 fossil-fuel- derived emission exceeded human derived emission and it rapidly increased as compared to that of hu- man derived emission. In India, up to 2005 human- derived emission was larger than that of fossil- fuel-derived emission although the latter rapidly in- creased. In both America and Japan, human-derived emission was quite small as compared to that of fossil-fuel-derived emission, and total amount of emission reached almost plateau. These results indi- cate that human-derived CO2 emission contributes much to the total amount of CO2 emission in de- veloping countries and that as the economy grow fossil-fuel-derived CO2 emission increases more as compared to human-derived emission. When the fossil-fuel-derived emission per capita was com- pared among these countries at 2005, those of China (1.16 metric tons of carbon per capita), India (0.35) were smaller than those of America (5.32) and Japan (2.63). In addition, rising income levels have been associated with the increased CO2 emission. 5) Currently a large number of people are living in de- veloping countries and their numbers are increas- ing, consequently as the economy grow, in other words as the CO2 emission per capita increases, more and more CO2 will be emitted. If we want American and Japanese like life-style at 2005 by limiting CO2 emission at the level of 1960, where global temperature was not steeply increased, the population should be 0.534 and 1.21 billion, respec- tively. Therefore, more attention should be paid for the population growth to reduce the atmosphere CO2 increase. REFERENCES 1) Le Treut, H., Somerville, R., Cubasch, U., Ding, Y., Mauritzen, C., Mokssit, A., Peterson, T and Prather, M. (2007) Historical Overview of Climate Change. In: Climate Change 2007: The Physical Science Ba- sis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K. B., Tignor, M. and Miller, H. L. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 2) Birdsall, N. (1992) Another Look at Population and Global Warming. Policy Research Working Papers, No. 1020, Washington D.C., The World Bank. 3) Engleman, R. (1994) Stabilizing the Atmosphere: Population, Consumption, and Greenhouse Gases, Washington, D.C., Population Action International. 4) Royal Society of London and U.S. National Academy of Sciences (1992) Population Growth, Resource Consumption and a Sustainable World, Washington, D.C., U.S. National Academy of Sci- ences. 5) Anqing, S. (2001) Population Growth and Global Carbon Dioxide Emissions. http://www.iussp.org/ Brazil2001/s00/S09 04 Shi.pdf 6) Prairie, Y. T. and Duarte, C. M. 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