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Global air pollution and climatic change


  • Wilfrid Bach


This report reviews the findings on pollutant emissions, removal processes, and pollutant concentrations, as well as some aspects of climatic change. It is shown that emissions from agricultural burning in the tropics exceed significantly U.S. annual emission rates. The direct anthropogenic global particle production amounts to about 7% of that naturally produced. More than 70% of the man-made particles are in the form of gaseous precursors. The anthropogenic contribution to the total global particle production is about 15%. Natural emissions of particulates and CO, CO2, CH4, H2S, NO2, and NH3 exceed man-made emissions by orders of magnitude. Only SO2 is produced predominantly by human activities. Emission estimates, especially those of CO, CO2, CH4, NH3, and N2O, differ greatly among the different investigators. The major removal processes of particulate and gaseous pollutants in the troposphere and stratosphere are reviewed. Trends and current levels of particulate and gaseous pollutants for urban and background stations are discussed. The tropospheric and stratospheric global monitoring programs are outlined. The discussion of changes in the upper atmosphere centers around stratospheric aerosols CO2, CO, CH4, H2O, and O3. The relative effects of nuclear tests, SST flights, and propellants and refrigerants are discussed. Recent hypotheses of ozone destruction by chlorofluoromethanes and bromines are presented. Next evidence of climatic change is given. Natural and man-made external causes of climatic change, including fluctuations in solar emission, orbital changes, changes in CO2, dust, and land use, and internal causes of climatic change, which include Antarctic ice surges, decreases in ocean salinity, and almost intransitivity, are discussed. All these factors are interrelated via complicated feedback mechanisms. Hypotheses concerning the physical causes, the time scales, and the initial stages of ice ages are reviewed. It appears that major ice ages seem to occur every 100,000 yr and that after an interglacial interlude we are on the brink of a period of colder climate. It has been estimated that the mean temperature of the planetary atmosphere in its surface layers has decreased by about 0.3°C since the 1940's despite an 11% increase of CO2 above the nineteenth century preindustrial level of 290 ppm. It appears that the natural climatic cooling trend is roughly 3 times more powerful than the present influence of CO2. However, in the near future, far-reaching adverse climatic and ecological consequences can be expected because the CO2 increase is too rapid for the regulatory mechanisms of the oceans. The impact of an increasing aerosol loading cannot be assessed reliably yet. The net effect will probably be small or one of warming. Presently, the heat release of the order of 15–20 TW from global energy production is still relatively small. But with the continuation of the present energy growth rate, within one generation, waste heat production may reach 100–300 TW, an amount found sufficient in natural processes to cause climatic changes. Some problems related to land use changes are also discussed, especially overgrazing, which may lead to desertification, and tropical deforestation, which may alter the atmospheric circulation.