United Nations Environment Programme (UNEP)
Global  Environment Outlook-1 - The Web version

Chapter 4: Looking to the Future

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Climate Change and Acidification

This section focuses on climate change, acidification of the environment, and the interaction of these two problems. The results illustrate the importance of studying linkages between environmental problems.

Past and Present Trends

Since its establishment in 1988 by UNEP and the World Meteorological Organization, the Intergovernmental Panel on Climate Change (IPCC) has published a series of assessment reports, the latest of which concluded that "the balance of evidence suggests a discernible human influence on global climate." The detection of the resulting impacts on ecosystems remains difficult, however (IPCC, 1996).

Acidification of the environment occurs when two key conditions exist. First, a region has a high level of economic activity with extensive use of fossil fuels leading to large atmospheric emissions of acidifying pollutants that are transported both locally and for long distances. Second, soil, forest, and aquatic ecosystems in a region are susceptible to these acidifying pollutants. Up to now, most developing countries have not experienced acidification because only the second condition exists, whereas acidification has been well established in North America and Europe for at least the last two decades (see also Tolba et al., 1992). Now, however, certain regions in Asia that have rapidly expanding economies (see, for example, Khemani et al., 1989; Shindo et al.,1994; Zhao and Seip, 1991) also fulfil the first condition for being at risk of acidification.

Rodhe et al.(1988) identified schematically areas in which acidification might represent a serious threat in the future on the basis of expected emissions, population density, and soil sensitivity. Areas at potential risk at that time included the northern and south-western parts of South America, the south-eastern part of Brazil and the La Plata region, and the southern part of West Africa (Kuylenstierna et al.,1995).

Recent assessments have identified the northern and central part of Europe (Hettelingh et al.,1995a), the eastern part of China, and southern parts of Asia (Hettelingh et al., 1995b and 1995c) as being the regions at the greatest risk of damage.

Climate change and acidification are recognized as current or potential problems in both industrial and developing countries. Recently, a better understanding of how these two problems overlap and interact has emerged (see, for example, Houghton et al., 1995).

First, greater combustion of fossil fuels increases the emissions of many acidifying pollutants as well as greenhouse gases. Second, changes in weather patterns stimulated by climate change will alter the intensity and distribution of acid deposition. Third and perhaps most important, because it complicates projections of climate change emissions of acidifying pollutants, especially sulphur dioxide, lead to the accumulation in the upper atmosphere of aerosols that partly mask the effects of greenhouse gases (IPCC, 1996).

The two important global issues addressed here climate change and acidification have the same underlying cause: a high level of economic activity that results in the emission of huge amounts of polluting substances into the atmosphere. Industrial activities particularly energy production from the burning of fossil fuels and raw material use release into the atmosphere acidifying gases, sulphur dioxide, and nitrogen oxides, and greenhouse gases, nitrous oxide, carbon dioxide, halocarbons, and other unwelcome by-products. They are, therefore, important sources of both acidifying gases and the greenhouse gases that are closely associated with climate change. In 1990, the burning of fossil fuels accounted for more than 80 per cent of the global emissions of carbon dioxide, the main greenhouse gas (IPCC, 1992), and about 94 per cent of the emissions of sulphur dioxide in Europe, the main cause of the acidification of the environment in that region (EEA, 1995).

Energy consumption in industrial regions has increased almost exponentially with the growth of population and economies. As Figure 4.5 illustrates, the cause of this environmental pressure has not been distributed equally world-wide.

Only in the last 10-20 years have there been signs of a decoupling between economic activity and the use of energy and materials in industrial countries. This is associated with their transition into service-based, less resource-intensive economies, as well as efficiency improvements. Concerns about human health and more recently about the natural environment have induced governments of industrial countries to develop and enforce environmental regulations to curb the level of atmospheric emissions. Initially, this involved lowering concentration levels by dilution and dispersion (through high chimneys, for example); later, it entailed so-called end-of-pipe technologies, preventing pollutants from entering the environment, and an increased use of cleaner and more efficient production technologies; recently, improved efficiency has been obvious in some parts of the world.

Figure 4.6 shows that as a consequence of these measures, global emissions of sulphur compounds have lately decreased, the emissions of nitrogen oxides have more or less stabilized, but carbon dioxide emissions continue to grow.  These global trends, however, mask important regional differences: emissions are decreasing in Europe, but significantly increasing in Asia.

The growth in the number of motor vehicles world-wide is among the factors responsible for continuing high levels of nitrogen oxides emissions despite technological advances in the design of car engines. Agricultural activity is another important source of emissions. Expansion of this sector often leads to forest clearance and the burning of trees and the shrub layer; together, these release large amounts of carbon dioxide and other greenhouse gases into the atmosphere. Other agricultural sources of greenhouse gases are methane emitted by livestock and released from wet rice fields, and nitrogen oxides from crop fertilizers. As a result of the growth of energy use, deposits of acidifying substances have more than quadrupled compared to pre-industrial levels.

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